SYSTEMThe upper respiratory system is made up of the nasal passages, throat, larynx, and trachea (see the figure Anatomy of the Head on page 232). The bronchi and lungs make up the lower respiratory tract. The breathing tubes branch into progressively smaller passages until they open into the air sacs (alveoli). The lungs are composed of the bronchi, air sacs, and blood vessels. The ribs and muscles of the chest, along with the diaphragm, function as a bellows, moving the air into and out of the lungs.
RAPID, LABORED BREATHING
A dog at rest takes about 10 to 30 breaths per minute. Breathing at a faster rate suggests fever, pain, anxiety, or a problem with the lungs or chest. Rapid breathing should be distinguished from panting. Panting is the primary way a dog lowers her body temperature; water evaporates from the mouth, tongue, and lungs, and warm air in the body is exchanged for cooler air in the atmosphere.
Rapid breathing, when accompanied by labored or difficult breathing, is a sign of distress. Dogs with congestive heart failure and/or lung disease often have rapid, labored breathing at rest or with only mild exertion. Other causes of rapid, labored breathing are shock, heat stroke, dehydration, and ketoacidosis associated with diabetes, kidney failure, and some kinds of poisoning. Dogs with rapid, labored breathing should be seen by a veterinarian.
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Noisy breathing indicates an obstruction in the nasal passages, the back of the throat, or the larynx. Snorting and snoring are typically heard with the brachycephalic syndrome discussed on page 313. If your dog normally
breathes quietly but suddenly develops noisy breathing, this is a cause for concern. She should be checked by a veterinarian. STRIDOR (CROUPY BREATHING)
Croupy breathing, or stridor, is a high-pitched raspy sound caused by air passing through a narrowed voice box. It may be heard only when the dog exercises. When the onset is sudden, the most likely cause is a foreign body in the voice box. When croupy breathing has been present for some time, laryngeal paralysis is a possible cause.
A wheeze is a whistling sound heard when the dog inhales or exhales, or both. Wheezing indicates spasm or narrowing in the trachea or bronchi. Wheezes in the lungs are best heard with a stethoscope. Some causes of wheezing are chronic bronchitis, congestive heart failure, and tumors of the larynx, trachea, and lungs. 13_067857 ch10.qxp 7/6/07 10:40 PM Page 313
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Shallow breathing is seen in dogs with broken ribs and severe bruising of the chest wall. Blood, pus, or serum in the chest cavity (called pleural effusion) restricts breathing by interfering with the range of motion of the chest and expansion of the lungs. A dog with shallow breathing compensates by breathing more rapidly. BRACHYCEPHALIC SYNDROME
Bulldogs, Pugs, Pekingese, Shih Tzu, English Toy Spaniels, Boston Terriers, Chow Chows, and other dogs with broad skulls and short muzzles frequently show some degree of airway obstruction, known as brachycephalic syndrome, manifested by mouth breathing, snorting, and snoring. These difficulties become more pronounced when the dog is exercising or is overheated, and
tend to get worse as the dog grows older.
The obstructed breathing in these dogs is caused by deformities that include collapsed nostrils, an elongated soft palate, and eversion of the laryngeal saccules. These deformities often occur together. Collapsed nostrils and elongated soft palate are congenital. Eversion of the laryngeal saccules is acquired.
Stenotic Nares (Collapsed Nostrils)
In puppies with stenotic nares, the nasal openings are small and the nasal cartilage is soft and floppy, causing the nostrils to collapse as the puppy breathes in. This produces varying degrees of airway obstruction, manifested by mouth breathing, noisy breathing, and occasionally a nasal discharge. In severe cases the chest is flattened from front to back. These pups fail to thrive and are poorly developed.
Treatment: Stenotic nares can be treated successfully by surgically enlarging the nasal openings. This is accomplished by removing a wedge of nasal skin and cartilage. Not all dogs with stenotic nares require surgery. In some dogs the cartilage firms up satisfactorily by 6 months of age. If there is no urgency in symptoms, your veterinarian may delay treatment to see if this happens.
Elongated Soft Palate
The soft palate is a flap of mucosa that closes off the nasopharynx during swallowing (see the figure Anatomy of the Head, page 232). Normally, it touches or slightly overlaps the epiglottis. In dogs with an elongated soft palate, the palate overlaps the epiglottis to a considerable degree, partially obstructing the airway during breathing. This is manifested by snorting, snoring, stridor, gurgling, and gagging. The obstruction is worse with exercise. In time, stretched ligaments in the larynx lead to labored breathing and laryngeal collapse.
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Treatment: An elongated soft palate is treated by surgically shortening the palate so that the edge opposes or slightly overlaps the epiglottis. Results are good if the operation is done before destructive changes occur in the larynx.
Eversion of the Laryngeal Saccules
Laryngeal saccules are small mucosal pouches that project into the larynx. In long-standing upper airway obstruction the saccules enlarge and turn out (eversion), narrowing the airway even further.
Treatment: Everted laryngeal saccules often accompany an elongated soft palate. If present, they should be removed. This operation is done at the same time as shortening of the palate. Your veterinarian may refer you to a surgical specialist for these surgeries.
The Larynx (Voice Box)
The larynx is an oblong box of tissue located in the throat above the windpipe (trachea). Just above the larynx is the epiglottis, a leaflike flap of cartilage that closes over the larynx and protects the airway during swallowing.
The larynx is composed of cartilage held together by ligaments. Within the larynx are the vocal cords, which is why the larynx is sometimes called the voice box. A dog’s vocal chords are thick and prominent, enabling them to 13_067857 ch10.qxp 7/6/07 10:40 PM Page 315
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bark loudly. The interior of the larynx is lined with a mucous membrane. The mucosa of the larynx, unlike the rest of the respiratory tract, does not contain cilia—hairlike structures that help move things through the passage.
Therefore, mucus tends to pool in the larynx. Exaggerated throat-clearing is required to bring up the phlegm.
The larynx is the most sensitive cough area in the respiratory tract.
Pressure over the larynx, such as that caused by a tight choke collar, can cause episodes of explosive coughing.
Diseases of the larynx cause hoarseness and progressive loss of the ability to bark. Choking, gagging, and coughing may be observed, especially while eating or drinking. Laryngeal obstructions such as those caused by laryngeal collapse, vocal cord paralysis, or a foreign body in the airway produce shortness of breath on exertion, stridor, cyanosis, and collapse.
Laryngitis is inflammation and swelling of the vocal cords and surrounding laryngeal mucosa. The signs are hoarseness and the inability to bark. The most common cause of laryngitis is voice strain caused by excessive barking or coughing. In the absence of these, suspect vocal cord paralysis. Laryngitis can accompany tonsillitis, throat infections, kennel cough, or tumors in the throat.
Treatment: Laryngitis due to excessive barking usually responds to removing the stimulus for the barking (see Excessive Barking, page 318). When voice strain is due to prolonged coughing, take your dog to the veterinarian to investigate and eliminate the cause of the coughing.
Sudden swelling of the larynx and vocal cords can result in marked narrowing or complete obstruction of the airway. Signs are stridor, rapid labored breathing, cyanosis, and collapse. Insect bites can cause an anaphylactic reaction with sudden swelling of the larynx. Another cause of laryngeal edema is excessive panting, particularly when it is associated with heat stroke. Similarly, any process that results in forced breathing across a narrowed airway (such as vocal cord paralysis) can lead to swelling that exacerbates the original disease.
Treatment: Sudden stridor and difficulty breathing is an acute emergency. Proceed as quickly as possible to the nearest veterinary clinic. Corticosteroids are given to reduce swelling and inflammation. Adrenalin is a specific antidote for an allergic reaction (see Anaphylactic Shock, page 13). Antihistamines also are beneficial. Sedatives help to relieve anxiety and panting.
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CHOKING (FOREIGN BODY IN THE LARYNX)
The sudden onset of forceful coughing, pawing at the mouth, and respiratory distress in a healthy dog suggest a foreign body caught in the larynx. This is an emergency! If the dog is conscious and able to breathe, proceed at once to the nearest veterinary clinic.
If your dog is gagging and retching but is not experiencing difficulty in breathing, assume a foreign object such as a bone splinter or rubber ball is caught in her mouth or in the back of her throat. These subjects are discussed in Foreign Body in the Throat, page 252.
Fortunately, a foreign body in the larynx is not common. Most objects are expelled by the forceful coughing that results from laryngeal stimulation.
Treatment: If the dog collapses and is unable to breathe, place her on her side with her head down. Open her mouth, pull out her tongue as far as you can, sweep your fingers from side to side, grasp the object, and remove it. Then administer artificial respiration or CPR as necessary (see CPR, page 7). If the object cannot be easily removed, do not try to get around it with your fingers. This will force it further down the throat. Instead, proceed to the Heimlich Maneuver.
The Heimlich Maneuver
1. Abdominal compressions. It may be easiest to hold the dog upside down in your lap, with her back against your chest and her head highest, but facing down. Place your arms around the dog’s waist from behind.
Make a fist and grasp it with the other hand. For a small dog, you may
have to just use two fingers. Place your fist or fingers in the dog’s upper mid-abdomen close to the breast bone at the apex of the V formed by
the rib cage.
Compress the abdomen by forcefully thrusting up and in with the fist or
fingers four times in quick succession. This maneuver pushes the
diaphragm upward and forces a burst of air through the larynx. This usually dislodges the object. Proceed to step 2. 2. Finger sweeps. Pull out the tongue and sweep the mouth. Remove the foreign body and proceed to step 5. If you are unable to dislodge the
object, proceed to step 3.
3. Artificial respiration. Give five mouth-to-nose respirations. Even a small volume of air getting past the obstruction is beneficial. Proceed to step 4.
4. Chest thumps. Deliver a sharp blow with the heel of your hand to the dog’s back between the shoulder blades. Repeat the finger sweeps. If the object is still not dislodged, repeat steps 1 through 4 until the object is dislodged.
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5. Ventilation. Once the object is dislodged, check for breathing and heart rate; administer artificial respiration and CPR if necessary. When the
dog revives, proceed to the veterinary hospital for further treatment.
LARYNGOSPASM (REVERSE SNEEZING)
This uncommon condition can be alarming because it sounds as if the dog
can’t catch her breath. During an attack, the dog produces a loud snorting noise caused by violent attempts to draw in air. This may occur several times in succession. After the attack, the dog appears completely normal.
Reverse sneezing is believed to be caused by a temporary spasm of the muscles of the larynx, possibly the result of a drop of mucus that falls on the vocal cords from the soft palate. The attack can be ended by making the dog swallow. This is accomplished by massaging the front of the neck in the region of the pharynx just beneath the jaw. Alternatively, place your hand over the dog’s nostrils for an instant.
If the attack does not stop and the dog collapses, suspect a foreign body in the larynx. Reverse sneezing is commonly seen in Corgis and Beagles. (See Choking, page 316.)
LARYNGEAL PARALYSIS (VOCAL CORD PARALYSIS)
This is an acquired disease that occurs in older dogs of the large and giant breeds, particularly Labrador Retrievers, Golden Retrievers, Irish Setters, St. Bernards, and Great Pyrenees. In Siberian Huskies, Bouviers des Flandres, Bull Terriers, and Dalmatians it occurs as a hereditary defect. In these breeds, dogs with this problem should not be bred.
Laryngeal paralysis results from damage to the nerves that control the
movement of the larynx. Trauma and age may be factors. Hypothyroidism
may also contribute to this problem.
A classic sign of laryngeal paralysis is a characteristic croupy or “roaring”
noise heard as the dog inhales. Initially it appears during or after exercise. Later it occurs at rest. Another sign is progressive weakening of the bark, which ends in a croaky whisper. In time the dog develops noisy breathing, labored breathing, reduced exercise tolerance, and fainting spells. Laryngeal edema may develop and further compromise the airway, causing respiratory collapse and even death.
The diagnosis is made by examining the vocal cords with a laryngoscope.
Paralyzed vocal cords come together in the middle instead of remaining well apart. This produces a tight air passage through the larynx.
Treatment: A number of surgical procedures have been used to enlarge the airway. The technique used most often involves removing both the vocal
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is unable to bark. Surgery may also predispose the dog to aspiration pneumonia, so usually medical therapy is tried first (keep dog calm and cool, and have sedatives and corticosteroids on hand).
Choke chain injuries, tight slip collars, or any rope around the neck can fracture the hyoid bone and/or cause compression damage to the nerves of the pharynx and larynx. Other causes of trauma to the larynx include bite wounds and sharp foreign objects such as bones and pins that penetrate the larynx. Dogs with laryngeal injuries often breathe normally at rest but show respiratory distress during exertion.
Treatment: Treatment of laryngeal trauma involves confining and resting the dog and administering anti-inflammatory medications. If the larynx is severely traumatized, a tracheostomy (an operation in which an opening is made through the skin into the trachea to establish a new airway) may be required. Choke chain injuries can be prevented by using a buckle collar, head halter, or chest harness.
This is a late stage in airway obstruction. Pressure changes in the upper airway caused by stenotic nares, an elongated soft palate, laryngeal paralysis, or everted laryngeal saccules stretch the ligaments that support the laryngeal cartilages. These cartilages gradually collapse inward and block the airway. At this stage any change in the dog’s need for air can cause acute respiratory insufficiency and cardiac arrest.
Treatment: The first step is to surgically correct predisposing factors. If symptoms persist, the dog may benefit from a permanent tracheostomy. DEBARKING AND BARKING PROBLEMS
Some dogs simply seem to enjoy barking. But constant shrill barking can lead to problems with neighbors and a dog being dropped off at the local shelter. Debarking surgery removes some of the vocal chord tissue. This can be
done through the mouth or through the throat. Lasers are sometimes used for this surgery. After debarking, dogs can still bark but it is a quieter, hoarse sound. If the dog develops scar tissue, she may recover the ability to bark normally. Too much scar tissue may interfere with breathing. Postoperative care is important, because any swelling in this area could cause acute breathing problems. You may need to search for a veterinarian experienced with this surgery.
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Before doing debarking surgery, you should try behavior training and/or
eliminate the cause of the excessive barking. Using a citronella or electronic bark collar may also work. These deliver a negative response when your dog barks, either with a spray of citronella or a mild shock.
Coughing is a reflex initiated by an irritation in the airway. Coughs are caused by respiratory infections, congestive heart failure, chronic bronchitis, respiratory tract tumors, collapsing trachea, pressure from tight collars, and inhaled irritants such as grass seeds, fumes, and food particles.
Coughs are self-perpetuating. Coughing dries out the mucous membranes
and irritates the breathing tubes—leading to further coughing.
DIAGNOSING A COUGH
The type of cough often suggests the diagnosis:
• A deep, dry, hacking cough made worse by exercise or excitement is
characteristic of kennel cough.
• A moist, bubbling cough indicates fluid or phlegm in the lungs and suggests pneumonia.
• A high, weak, gagging cough, followed by swallowing and licking the
lips, is characteristic of tonsillitis and sore throat.
• A spasm of prolonged coughing that occurs at night or while lying on
the sternum suggests heart disease.
• A “goose-honk” cough in a toy breed dog indicates a collapsing trachea. The diagnostic workup of a dog with a chronic cough includes a chest
X-ray and transtracheal washings. Washings are cells obtained by flushing the trachea with saline solution. This can be done with a sterile tube passed down the trachea while the dog is sedated, or by direct penetration of the trachea through the skin of the neck using a needle and catheter. The washings are processed for cytology and bacterial culture. The information usually leads to a specific diagnosis.
Bronchoscopy is particularly useful in the investigation of chronic coughs and coughs with the production of mucus and blood. The procedure requires sedation or general anesthesia. A rigid or flexible endoscope is passed into the trachea and bronchi. This enables the veterinarian to see the interior of the respiratory tract. Biopsies can be taken with accuracy, and washings collected for examination and culture. Bronchoscopy is also the procedure of choice for removing bronchial foreign bodies.
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TREATING A COUGH
Only minor coughs of brief duration should be treated at home. Coughs
accompanied by labored breathing, a discharge from the eyes or nose, or the production of bloody sputum should be seen and treated by a veterinarian. It is important to identify and correct any contributing factors. Eliminate any irritating atmospheric pollutants, such as cigarette smoke, aerosol insecticides, strong cleaners, house dust, and perfumes, from the home environment. Breaking the cough cycle is an important part of treating irritant coughs. A variety of children’s cough medicines are available over the counter.
Children’s Robitussin is an effective cough medicine that contains an expectorant called guaifenesin. It does not suppress the cough reflex, but does liquefy mucus secretions so that they can be brought up more easily. Robitussin is safe to use for all coughs.
Robitussin-DM and Benylin Expectorant, also available over the counter,
contain the cough suppressant dextromethorphan. (The correct dosage for all these cough preparations is given in the table Over-the-Counter Drugs for Home Veterinary Use, page 571.) When stronger cough suppressants are needed, preparations containing the narcotics hydrocodone bitartrate
(Hycodan) and butorphanol tartrate (Torbutrol, Torbugesic) are available by prescription from your veterinarian.
Cough suppressants should be used selectively and only for short periods. Although they decrease the frequency and severity of the cough, they do not treat the condition causing it. Overuse may delay diagnosis and treatment. Cough suppressants (but not expectorants) should be avoided in dogs with bacterial infections and when phlegm is being brought up or swallowed. In these cases, productive coughs are clearing unwanted material from the airway. Dogs with a dry cough can be helped by keeping them in the bathroom
while you shower and not using the fan. The added moisture may loosen
secretions. Using a humidifier can also be helpful.
Trachea and Bronchi
ACUTE TRACHEOBRONCHITIS (KENNEL COUGH COMPLEX)
The kennel cough complex is a group of highly contagious respiratory diseases in dogs. The name comes from the fact that the infection tends to spread rapidly, especially among dogs in boarding kennels or dogs who have been to places where large numbers of dogs congregate, including dog shows and dog parks. Several viruses and bacteria, alone or in combination, can cause the disease. The organisms most frequently involved are canine parainfluenza virus and the bacteria Bordetella bronchiseptica (both are discussed in chapter 3). Canine adenovirus types CAV-1 and CAV-2, as well as canine herpesvirus, canine distemper, and mycoplasma, are other causes of kennel cough.
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A harsh, dry, hacking cough is the characteristic sign of tracheobronchitis. The cough is unproductive and is often accompanied by gagging and retching. Except for the cough, the dog is bright and alert, and has a good appetite and a normal temperature. In most cases kennel cough is a mild disease. With rest and a stress-free environment, most adult dogs recover completely in 7 to 14
days. Keeping the dog quiet will speed recovery.
Kennel cough may be complicated by secondary bacterial pneumonia. This
is most likely to occur in dogs with bronchitis, collapsing trachea, or diseases that lower their resistance to infection. In puppies, kennel cough can be accompanied by nasal congestion. These puppies require frequent care to
loosen thick secretions, improve breathing, and prevent pneumonia. This is also true for toy breeds.
A severe form of tracheobronchitis that can lead to pneumonia is characterized by low-grade fluctuating fever, loss of appetite, and depression. These dogs have a moist productive cough, nasal discharge, exercise intolerance, wheezing, and rapid breathing. This form of kennel cough requires hospitalization.
Treatment: Kennel cough should be treated by a veterinarian. Isolate dogs to prevent spreading the disease. The quarters should be warm, dry, and wellventilated. Humidification is beneficial. A cool mist vaporizer offers some advantage over a heat vaporizer, because it is less likely to add excessive heat to the atmosphere. If one is not available, having the dog in the bathroom while you shower can help.
Moderate daily exercise is beneficial to the extent that it assists bronchial drainage. Strenuous exertion off leash should be avoided. If the dog drags against her collar, use a harness or head halter.
Antibiotics are routinely used to treat kennel cough. The drugs of choice are the tetracyclines and trimethoprimsulfa. Continue the antibiotics for 7 to 10 days. Excessive coughing is controlled with cough suppressants.
Dogs with severe tracheobronchitis or pneumonia must be hospitalized and treated intensively with intramuscular or intravenous antibiotics and drugs that dilate the breathing passages.
Prevention: The intranasal Bordetella vaccine is useful but may have to be given twice annually. There is also an intramuscular Bordetella vaccine. CPI and CAV-2 vaccines—incorporated into routine immunizations—will
decrease the prevalence and severity of kennel cough. Show dogs, boarded dogs, and dogs who go to grooming salons may benefit from the optional bordetella vaccination (For more information, see Vaccinations, page 92.) FOREIGN BODY IN THE LUNGS
Grass seeds and food particles are the most common foreign materials inhaled by dogs that are big enough to lodge in the smaller breathing tubes. Most of these are quickly coughed up. If the object becomes fixed in the airway, it 13_067857 ch10.qxp 7/6/07 10:40 PM Page 322
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causes intense irritation and swelling of the air passage. Mucus collects below the obstruction and forms an ideal medium for bacterial growth and infection. Objects that remain in the lungs for several weeks can cause pneumonia.
Sudden attacks of coughing that occur immediately after vomiting or after a dog has been running in tall grass and weeds suggest inhalation of a foreign body. Lungworms in the bronchi also cause severe coughing spasms.
Treatment: Unexplained coughing should be investigated by a veterinarian. Avoid cough medicines, unless prescribed by your veterinarian, since they delay treatment. Bronchoscopy is usually successful in locating and removing bronchial foreign bodies, particularly if the procedure is done within two weeks of inhalation.
This condition occurs primarily in older dogs of the toy breeds, particularly Chihuahuas, Pomeranians, and Toy Poodles, and occasionally in young dogs as a congenital defect.
Collapsing trachea occurs because the C-shaped tracheal rings do not possess normal rigidity. As a result, the involved wall of the trachea collapses as the dog inhales. Obesity is a predisposing factor, as is chronic bronchitis. The principal sign of collapsing trachea is a characteristic goose-honk
cough. The cough is made worse by stress and exertion, including pulling against a collar. Coughing may also occur when the dog eats or drinks.
Respiratory insufficiency develops as the disease progresses.
Treatment: Examination by a veterinarian is the first step. Diseases of the heart and lungs should be ruled out before making the diagnosis. Dogs with mild to moderate symptoms respond to proper nutrition and a low-stress routine that avoids situations that trigger episodes of coughing. Moderate exercise is beneficial. Using a harness or head halter instead of a collar is important.
Overweight dogs should be put on a weight-loss diet, as described for
chronic bronchitis (page 323). Eliminate cigarette smoke and other atmospheric pollutants that can trigger coughing. Collapsing tracheal cartilages lack rigidity and are drawn into the airway when the dog inhales.
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This chest X-ray shows an enlarged air column (dark shadow) in the neck, indicat- ing a normal-sized trachea, and a narrow air column in the chest, indicating a collapsing trachea.
Bronchodilator drugs such as aminophylline, theophylline, or albuterol are beneficial for many small dogs. Mild low-dose sedatives during stressful periods also are helpful. Cough suppressants and corticosteroids may be prescribed when the coughing is particularly severe. Respiratory infections require prompt treatment with antibiotics.
Surgery can be considered in severe cases. It involves suturing plastic rings around the trachea, which then keep the airway open. Complications are
This disease affects middle-aged dogs of both sexes. It is characterized by an acute inflammatory reaction of the interior of the smaller airways. Chronic bronchitis should be considered whenever a cough persists for more than two months.
In most cases the cause is unknown. Although some cases are preceded by
kennel cough, infectious agents usually do not play a role except as secondary invaders. House dust, cigarette smoke, and other atmospheric irritants contribute to bronchial inflammation. The hallmark of chronic bronchitis is a harsh, dry cough that may or may not be productive. Coughing is triggered by exercise and excitement. Episodes often end with gagging, retching, and the expectoration of foamy saliva. This can be mistaken for vomiting. The dog’s appetite and weight are well maintained. 13_067857 ch10.qxp 7/6/07 10:40 PM Page 324
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Unchecked chronic bronchitis damages the airways and leads to the accumulation of infected mucus and pus in dilated bronchi. This is called bronchiectasis. Chronic coughing can also lead to enlargement of the alveoli (lung air sacs), a condition called emphysema. These two diseases are not reversible and gradually progress to chronic lung disease and congestive heart failure.
The diagnostic workup for bronchitis is the same as that described in
Diagnosing a Cough, page 319.
Treatment: General measures include eliminating atmospheric pollutants such as dust and cigarette smoke. Minimize stress, fatigue, and excitement. Overweight dogs should be put on a weight-loss diet (see Weight Reduction, page 308). Walking on a leash is good exercise, but don’t overdo it. To avoid pressure on the larynx, switch from a collar to a chest harness or head halter. Medical management is directed toward reducing bronchial inflammation.
Your veterinarian may prescribe a course of corticosteroids for 10 to 14 days. If this is beneficial, the dog may be placed on a maintenance dose given daily or every other day. Bronchodilators such as theophylline or albuterol relax the breathing passages and reduce respiratory fatigue. They are beneficial for dogs with associated wheezing and airway spasms.
If the cough gets worse there is probably a secondary bacterial infection. Seek veterinary attention, because antibiotics will be required. Cough suppressants are beneficial for episodes of exhaustive coughing, but should be used only for short periods, as they interfere with host defenses and prevent the elimination of purulent secretions. Expectorants can be used as often as needed. The response to treatment varies. Some dogs make a near-normal recovery, while others require frequent medication adjustments.
Pneumonia can be caused by viruses, bacteria, fungi, or parasites. Bacterial and viral pneumonia are often preceded by an infection in the nasopharynx or airways.
Pneumonia is uncommon in healthy adult dogs. It tends to target the very young and the very old, and those whose immune systems have been compromised as a result of corticosteroid therapy, chemotherapy, or chronic illness. Dogs with chronic bronchitis, collapsing trachea, or foreign bodies in the lower airway frequently develop bacterial pneumonia.
Inhalation or aspiration pneumonia occurs with megaesophagus, gastroesophageal reflux, paralysis of the swallowing mechanism, and reflux of gastric contents into the lungs during general anesthesia or vomiting. Chemical
pneumonia is caused by inhaling smoke or ingesting hydrocarbons such as
gasoline or kerosene.
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Signs of pneumonia are cough, fever, depression, rapid breathing, rapid
pulse, and occasionally a nasal discharge that is thick with mucus. The cough is moist and bubbling, indicating fluid in the lungs. Dogs with severe pneumonia frequently sit with their head extended and elbows turned out to allow for greater expansion of the chest.
The diagnosis is made by chest X-ray and blood tests. Bacterial culture and sensitivity tests aid in selecting the most effective antibiotic.
Treatment: Dogs with fever and signs of respiratory infection should receive urgent veterinary care. Take the dog to the hospital immediately. Do not give cough suppressants. Coughing is beneficial because it clears the airway and facilitates breathing.
Bacterial infection responds well to antibiotics selected specifically for the bacteria causing the disease. Your veterinarian will select the most appropriate drug. The antibiotic should be continued for at least three weeks, or until the follow-up chest X-rays show clearing.
Any predisposing causes, such as gastroesophageal reflux or a bronchial foreign body, should be treated to prevent recurrence. PULMONARY INFILTRATES OF EOSINOPHILS
Pulmonary infiltrates of eosinophils (PIE) is an uncommon respiratory disease in dogs, caused by the presence of numerous eosinophils (a type of white blood cell) in the blood, respiratory secretions, and lungs. Eosinophils usually indicate a hypersensitivity reaction. Accordingly, an allergic basis for PIE has been proposed. What the dog is allergic to is usually unknown.
Before a diagnosis of PIE can be made, other causes of eosinophilia, such as heartworms, lungworms, migrating intestinal parasites, fungal infections, and lymphosarcoma, must be excluded.
The signs of PIE are fever, cough, rapid breathing, and weight loss. Listening to the chest with a stethoscope reveals dry, crackling sounds. The diagnosis is made by finding eosinophils in the blood and transtracheal washings.
Treatment: Treatment involves large doses of corticosteroids that are tapered off gradually over several weeks. Many dogs recover fully, but relapses can occur.
This respiratory virus first was isolated from racing Greyhounds in 2004. The virus appears to have mutated from the equine influenza virus. It has been found in dogs of all breeds and mixes and across North America.
Affected dogs will have a high fever, a soft, gagging cough (unlike the
goose-honk cough of kennel cough), and may have a nasal discharge. While 80 percent of dogs have a mild course of disease when exposed to this new 13_067857 ch10.qxp 7/6/07 10:40 PM Page 326
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pathogen, some will go on to develop pneumonia. Mortality is about 5 to 8
percent, with most fatalities in puppies, old dogs, and dogs with compromised immune systems. Some dogs will shed the virus either before becoming ill or chronically.
To differentiate this problem from “standard” kennel cough will require
laboratory tests. Treatment should start immediately, however.
Treatment: Isolate the dog, because this disease is contagious and is spread through the air. Supportive care is important, with antibiotics used if a secondary bacterial infection develops. Many dogs require fluids and hospitalization if they develop pneumonia. There is no vaccine at this time. PLEURAL EFFUSION
A pleural effusion is an accumulation of serum or blood in the chest. The most common cause is congestive heart failure. Other causes include liver disease, kidney failure, pancreatitis, and primary and metastatic tumors of the lungs. Bacterial pneumonia can extend to the pleural space, producing an infected pleural effusion called empyema. Blood in the pleural space (called hemothorax) occurs with chest trauma, malignant lung tumors, and spontaneous bleeding disorders. Chylothorax is a buildup of lymphatic fluid in the chest that can occur with lung torsions, tumors, and a blockage of lymphatic flow. Afghan Hounds have a breed predisposition to this, and possibly Shiba Inus.
Large pleural effusions press on the lungs and cause respiratory distress. Severely affected dogs have rapid, labored breathing and often stand or sit with elbows out, chest fully expanded, and head and neck extended.
Breathing is open-mouthed. The lips, gums, and tongue may appear blue. The least bit of effort can cause collapse.
Treatment: Urgent veterinary attention is required. The fluid in the lungs must be removed as soon as possible to facilitate breathing. This is done by inserting a needle or catheter into the pleural space and withdrawing the fluid by syringe. The dog should be hospitalized to discover and treat the cause of the problem.
Tumors of the Larynx, Trachea, and Lungs
Benign and malignant tumors occur in the larynx, trachea, bronchi, and
lungs. The diagnosis of laryngeal, tracheal, and lung tumors is based on chest X-rays, ultrasound, bronchoscopy and/or transtracheal washings and cytology (see Diagnosing a Cough, page 319). Tissue biopsy provides an accurate diagnosis and helps in planning treatment.
Laryngeal tumors are uncommon and occur in middle-aged to older dogs. Most are malignant (squamous cell carcinomas). Signs are noisy breathing, 13_067857 ch10.qxp 7/6/07 10:40 PM Page 327
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change in voice, and loss of bark. A characteristic stridor may be heard when the dog inhales. Sudden death can occur from respiratory obstruction.
Tracheal tumors are rare. In older dogs they tend to be malignant (osteosarcomas). In young dogs they are more likely to be benign (osteochondromas). The most common sign is a productive cough. Stridor on inhalation may be noted during exercise or panting. Cyanosis and collapse can occur when the tumors get very large and cause severe respiratory obstruction. Lung tumors account for about 1 percent of all neoplasms in dogs. Most arise from cells lining the bronchi. They tend to occur in older dogs of both sexes. Lung tumors in dogs may be associated with exposure to cigarette
Most primary lung tumors are malignant and will have already spread to
other parts of the body by the time they are diagnosed.
A harsh, nonproductive cough is the most common sign. Pleural effusion may occur as a late complication.
Metastatic lung tumors—that is, tumors that spread to the lungs from other parts of the body—are more common than primary lung tumors. Tumors that metastasize to the lungs include mammary gland cancers, osteosarcomas, thyroid cancers, melanomas, and squamous cell carcinomas.
Treatment: Surgical exploration and removal of small tumors offers the best chance for cure. Larger tumors usually cannot be cured, but may respond to chemotherapy. The advanced age of many dogs with respiratory tract
tumors usually makes aggressive treatment impractical.
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C h a p t e r
SYSTEMThe circulatory system comprises the heart, the blood, and the blood vessels. The heart is a pump made up of four chambers: the right atrium and right ventricle, and the left atrium and left ventricle. The two sides of the heart are separated by a muscular wall. In a dog with normal anatomy, blood cannot get from one side of the heart to the other without first going through the general or pulmonary circulation. Four heart valves keep blood flowing in one direction. When the valves are diseased, blood can leak backward, creating difficulties. In a dog with normal circulation, blood is pumped out of the left ventricle, through the aortic valve, and into the aorta. It passes through arteries of progressively smaller size until it reaches the capillary beds of the skin, muscles, brain, and internal organs. In these capillary beds, oxygen is exchanged for carbon dioxide. From the capillaries blood is carried back through veins of progressively larger diameter, finally reaching two large veins called the anterior and posterior vena cavae. From these large veins, the blood enters the right atrium. It passes from the right atrium through the tricuspid valve and into the right ventricle. As the right ventricle contracts, the pulmonary valve opens, allowing the blood to enter the main pulmonary artery. The pulmonary artery branches into smaller vessels and finally into capillaries around the air sacs of the lungs. It is here that carbon dioxide is exchanged for oxygen. The blood then returns via the pulmonary veins, passes through the mitral valve, and into the left ventricle. As the left ventricle contracts, the aortic valve opens and blood is pumped into the general circulation—thus completing the cycle.
The beating of the heart is controlled by its own internal electrical system, but also responds to outside influences. Thus, the heart beats faster when a dog exercises, becomes frightened, is overheated, or requires greater blood 329
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flow to the body. The arteries and veins can expand or contract to maintain correct blood pressure.
The Normal Heart
There are outward physical signs that help determine whether a dog’s heart and circulatory system are working normally. Familiarize yourself with what is normal so you can recognize any abnormality.
The pulse, a transmitted heartbeat, is easily detected by feeling the femoral artery, located in the groin. With your dog standing, or preferably lying on his back, feel along the inside of the thigh where the leg joins the body. Press with your fingers until you locate the pulse.
You can also feel a dog’s pulse by pressing against the rib cage over his heart. Feel the heartbeat just below and behind the elbow joint. If the heart is enlarged or diseased, you may be able to detect a buzzing or vibration over the chest wall.
The pulse rate is determined by counting the number of beats per minute. Most adult dogs at rest maintain a rate of 60 to 160 beats per minute. In large dogs the rate is somewhat slower and in toy dogs it’s somewhat faster. In young puppies the heart rate is about 220 beats per minute.
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Feel for the femoral pulse
in the thigh, where the
leg joins the body.
Another way to take the
pulse is to feel the heart-
beat behind the left
Veterinarians use a stethoscope to listen to the heart. You can listen to your dog’s heart by placing your ear against his chest. The normal heartbeat is divided into two sounds. The first is a lub, followed by a slight pause and then a dub. Put together, the sound is lub-dub, lub-dub . . . in a steady, evenly spaced rhythm. 14_067857 ch11.qxp 7/6/07 10:42 PM Page 332
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The heartbeat should be strong, steady, and regular. A slight alteration in rhythm as the dog breathes in and out is normal. An exceedingly fast pulse can indicate anxiety, fever, anemia, blood loss, dehydration, shock, infection, heat stroke, or heart (and lung) disease. A slow pulse can indicate heart disease, pressure on the brain, or an advanced morbid condition causing collapse of the circulation.
An erratic, irregular or disordered pulse indicates a cardiac arrhythmia. Many arrhythmias are associated with a sudden drop in blood pressure as the arrhythmia begins. The corresponding decrease in blood flow to the muscles and brain is accompanied by sudden weakness or collapse, often giving the impression of a fainting spell.
When the heart sounds can be heard all over the chest, the heart is probably enlarged. Heart murmurs are common. Murmurs are caused by turbulence in the flow of blood through the heart. Serious murmurs are caused by heart disease or anatomical defects.. Anemia can cause a heart murmur.
Not all murmurs are serious. Some are said to be innocent; that is, there is no disease, just a normal degree of turbulence. To determine whether a murmur is serious or innocent, your veterinarian may request diagnostic
studies such as a chest X-ray, an electrocardiogram ( ECG or EKG), and an echocardiogram.
Thrills are caused by turbulence of such a degree that you can feel a buzzing or vibration over the chest. This suggests an obstruction to the flow of blood—for example, a constricted valve or a hole in the wall between two chambers of the heart. A thrill indicates a serious heart condition.
You can determine the adequacy of your dog’s circulation and the presence or absence of anemia by examining the gums and tongue. A deep pink color is a sign of good circulation and a normal red blood cell volume. A pale color indicates anemia. A gray or bluish tinge is a sign of insufficient oxygen in the blood (called cyanosis). With severe circulatory collapse, the mucous membranes are cool and gray. However, some dogs, such as Chows Chows, have pigmented lips, gums, and even tongues. These will normally appear bluish, purple, or even black all the time. Know what is normal for your dog.
The adequacy of the circulation can be tested by noting how long it takes for the gums to “pink up” after being firmly pressed with a finger. This is called capillary refill time. The normal response is one second or less. More than two seconds suggests poor circulation. When the finger impression remains pale for three seconds or longer, the dog is in shock.
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The leading cause of heart failure in dogs is chronic valvular disease. Next is dilated cardiomyopathy, followed by congenital heart disease and heartworms. More infrequent causes include bacterial endocarditis and myocarditis. Coronary artery disease is rare in dogs. It occurs only in dogs with severe hypothyroidism accompanied by extremely high serum cholesterol levels.
CHRONIC VALVULAR DISEASE
This common heart disease of unknown cause affects 20 to 40 percent of dogs. It occurs most often in toy and small breed dogs, particularly Cavalier King Charles Spaniels, Miniature and Toy Poodles, Chihuahuas, Lhasa Apsos,
Yorkshire Terriers, Schnauzers, and Cocker Spaniels.
Chronic valvular disease is characterized by degenerative changes in the heart valves. The mitral valve is affected in nearly all cases; the tricuspid valve in about one-third of cases. The valve leaflets become thickened and distorted so that the free edges of the valves no longer make contact. The cords that attach the valve leaflets to the lining of the heart may rupture, allowing the valve to flap in the bloodstream.
These changes result in loss of valve function and a fall in cardiac output. When the ventricles contract, some blood is ejected backward into the corresponding atrium. This is called regurgitation. Regurgitation increases the 14_067857 ch11.qxp 7/6/07 10:42 PM Page 334
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blood pressure in the atrium and causes it to enlarge. Because the mitral valve is invariably involved, chronic valvular disease is also sometimes called mitral valve disease or mitral regurgitation.
The hallmark of chronic valvular disease is a loud heart murmur heard over the left side of the chest. A chest X-ray, ECG, and echocardiogram may show an enlarged left atrium, thickened valves, or a ruptured cord (muscle band). If the tricuspid valve is involved, there will be a loud heart murmur heard over the right side of the heart. It is important to exclude heartworms as a cause of a right-sided heart murmur.
Signs of congestive heart failure can be attributed to low cardiac output and lung congestion. They include a cough that occurs after exercise and/or is worse at night; lethargy and tiring easily; and fainting spells often related to cardiac arrhythmias.
Treatment: Many dogs with uncomplicated heart murmurs associated with chronic valvular disease remain asymptomatic for years. The disease, however, is chronic and progressive. Treatment should be started at the first signs of impending heart failure (coughing, easy tiring). The outlook depends on how far the disease has progressed and the general health and age of the dog. (For more information on treatment, see Congestive Heart Failure, page 339.) DILATED CARDIOMYOPATHY
Dilated cardiomyopathy is a disease in which the heart chambers enlarge and the walls of the ventricles become thin. The heart muscle weakens and begins to fail.
Dilated cardiomyopathy is the most common cause of congestive heart failure in large and giant breed dogs. It is rare in toy breeds and small dogs. A high incidence is found in Boxers, Doberman Pinschers, Springer Spaniels, and American and English Cocker Spaniels. Other breeds affected include
German Shepherd Dogs, Great Danes, Old English Sheepdogs, St. Bernards,
and Schnauzers. Most dogs are 2 to 5 years of age at the onset of symptoms. The majority are males.
In most cases the cause of dilated cardiomyopathy is unknown.
Myocarditis, an inflammation of the heart muscle, may precede dilated cardiomyopathy in some dogs. Hypothyroidism has been associated with dilated cardiomyopathy. A genetic or familial basis has been proposed for giant and large breed dogs. Cardiomyopathy related to taurine and/or carnitine deficiency is seen in American Cocker Spaniels, Boxers, and possibly Golden Retrievers, Newfoundlands, and other breeds.
The signs of dilated cardiomyopathy are the same as those of congestive
heart failure and cardiac arrhythmias. Weight loss can occur in a matter of weeks. Affected dogs are lethargic, tire easily, breathe rapidly, and cough frequently, sometimes bringing up bloody sputum. Coughing is especially
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This dog’s swollen abdomen is associated with dilated cardiomyopathy and conges- tive heart failure.
common at night. A swollen abdomen (called ascites) may be noted. Cardiac arrhythmias can cause weakness and collapse.
The diagnosis of dilated cardiomyopathy is based on ECG changes showing cardiac arrhythmias, a chest X-ray showing enlarged heart chambers, and an echocardiogram showing the characteristic pattern of a failing heart muscle.
Treatment: Treatment is directed at improving the force of the heart muscle, controlling arrhythmias, and preventing the buildup of fluid in the lungs and abdomen (see Congestive Heart Failure, page 339). Many dogs benefit from the addition of taurine and/or carnitine to their diet. The prognosis for long-term survival is guarded. With excellent medical control, some dogs may live for a year or more. Death usually occurs as the result of a sudden cardiac arrhythmia. Some dogs will drop dead without any noticeable signs beforehand.
CONGENITAL HEART DISEASE
All forms of congenital heart disease occur in dogs. The most common defects are valve malformations (called dysplasias), valve narrowing (stenosis), abnormal openings between the heart chambers (septal defects), patent ductus arteriosus, and Tetralogy of Fallot. 14_067857 ch11.qxp 7/6/07 10:42 PM Page 336
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Patent ductus arteriosus is a persistent arterial connection between the aorta and pulmonary artery that normally closes at birth or shortly thereafter. In the uterus, the ductus plays an important role in shunting blood away from the nonfunctioning lungs. Many large and small breeds are affected by patent ductus arteriosus. This murmur can often be felt through the body wall—it feels like a washing machine churning.
Tetralogy of Fallot is a congenital defect of the heart consisting of four abnormalities that result in insufficiently oxygenated blood pumped to the body.
Most dogs with severe congenital heart defects die within the first year of life. Dogs with moderate defects may survive but usually exhibit exercise intolerance, fainting episodes, and stunted growth. In these individuals, heart failure can occur suddenly and unexpectedly. Dogs with mild valvular disease or small septal defects are often asymptomatic; the only indication of a congenital heart defect is a heart murmur discovered on physical examination. The diagnosis of congenital heart defect is based on ECG, chest X-rays and echocardiogram. An ultrasound study called Doppler echocardiography measures the velocity and direction of blood flow in the heart chambers. This information makes the diagnosis of congenital heart defects extremely accurate. You may need to be referred to a specialty clinic for this test. Cardiac catheterization with angiocardiography was once the “gold standard” for diagnosing congenital heart defects, but it carries a small risk and is often available only at referral veterinary hospitals. Doppler echocardiography, being accurate and noninvasive, has largely replaced cardiac catheterization for routine diagnosis.
Treatment: Dogs with minor heart defects have a good prognosis and do not benefit from surgery. However, many dogs benefit from surgery to correct more severe defects. Many of these surgeries will require referral to a large veterinary center. Patent ductus arteriosus is an example of a defect that does benefit from surgery. Without surgery, 60 percent of affected puppies die within the first year. With surgery, the death rate is less than 10 percent.
Moderate atrial and ventricular septal defects can be repaired surgically with varying degrees of success. This requires open-heart surgery and cardiopulmonary bypass. Valve dysplasias and large septal defects have a poor prognosis, regardless of the method of treatment. Affected dogs are at risk of congestive heart failure and sudden death.
The treatment of congestive heart failure and cardiac arrhythmias is discussed later in this chapter.
Prevention: Most congenital heart defects have a hereditary basis. Breeds with a known predisposition for specific congenital heart defects are shown in the accompanying chart. This list is by no means comprehensive, and individuals of other breeds and mixed breeds may also show these defects. 14_067857 ch11.qxp 7/6/07 10:42 PM Page 337
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Breed Predispositions for Congenital Heart Defects
Atrial septal defects
Ventricular septal defects
Aortic and subaortic stenosis
Newfoundland, Golden Retriever, German
Shepherd, Rottweiler, Boxer, German Shorthaired
Labrador Retriever, Great Dane, Weimaraner,
German Shepherd Dog
Great Dane, German Shepherd Dog, Bull Terrier
Patent ductus arteriosus
Poodle, Pomeranian, Collie, Shetland Sheepdog,
German Shepherd Dog, Cocker Spaniel, English
Beagle, Labrador Retriever, Cocker Spaniel,
Schnauzer, Newfoundland, Rottweiler
Tetralogy of Fallot
Keeshond, English Bulldog, Miniature Poodle,
It is important to identify affected individuals when treatment is most
likely to be successful and before the dog is used for breeding. The best time to screen puppies for congenital heart defects is when they are 6 to 8 weeks of age, before being released to their new homes. Screening is done by carefully listening for murmurs with a stethoscope over the four valve areas. The examination is best performed by a veterinarian who is experienced in recognizing heart murmurs. Murmurs heard at this age may not be associated with disease; some will disappear as the pup matures. If the murmur is present at 16 weeks, however, the puppy should be screened using cardiac ultrasound.
OFA maintains a cardiac registry to gather data on congenital heart defects. (See appendix D for information on how to contact OFA.) Dogs are screened at 12 months of age or later by a board-certified veterinary cardiologist, and if they are found to be unaffected, they are issued a certificate and a registration number. For bloodlines with an increased incidence of congenital heart defects, it is highly desirable to seek OFA certification before selecting breeding animals.
Bacterial endocarditis is an infection of the heart valves and the lining of the heart. The disease is not common. It is caused by bacterial species that gain entrance to the circulation system through wounds and infections elsewhere in the body. In many cases the actual source of infection is unknown. Dogs on 14_067857 ch11.qxp 7/6/07 10:42 PM Page 338
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corticosteroids and immunosuppressant drugs are at increased risk, as are midsize and large dogs. As the bacteria invade the heart valves, they produce ulcerations and small wartlike bumps called vegetations. The effects on the valves are similar to those of chronic valvular disease. In addition, parts of infected vegetation can break off and spread the infection to other organs. This seeding process causes a variety of signs, including fever, shaking, chills, swollen joints, lameness, spontaneous bleeding, blindness, behavioral and personality changes, unstable gait, stupor, and seizures. These signs are nonspecific and may suggest a number of other diseases.
The presence of a heart murmur, particularly a new or changing murmur, suggests a diagnosis of bacterial endocarditis. This can be confirmed by ECG, chest X-rays, and echocardiography. Blood cultures identify the causative bacteria.
Treatment: Antibiotics must be selected based on blood culture and sensitivity tests. To eliminate vegetations, long-term antibiotic therapy (two to four months) is required. The dog should be monitored closely for signs of congestive heart failure, which may appear suddenly, and for the development of antibiotic-resistant organisms.
Dogs with less severe valve disease may recover with only mild permanent damage. The prognosis is guarded for dogs with mitral valve involvement and poor for those with aortic valve involvement.
Myocarditis is an inflammation of the heart muscle. It is an uncommon cause of heart disease in dogs. Myocarditis occurs with American trypanosomiasis, Lyme disease, viral diseases including distemper, and bacterial, fungal, and protozoan infections. Parvovirus produces a fatal form of myocarditis in neonatal puppies. It is rarely seen now because of the practice of routinely immunizing brood bitches against parvo.
One of the first signs of myocarditis is weakness and fainting caused by cardiac arrhythmias. It can also be suspected by the sudden appearance of congestive heart failure, along with abnormal findings on an ECG and echocardiogram. If necessary, the diagnosis can be confirmed by a heart muscle biopsy. This must be done at a medical center.
Treatment: Treatment and prognosis are similar to those described for dilated cardiomyopathy (page 334). If a specific cause is found, it should be treated. Arrhythmias
Arrhythmias are irregular or erratic heartbeats. Normally the heart beats at a steady, regular pace. This changes with activity or rest, but is almost always a regular rhythm. Abnormal rhythms may be slower than normal (called bradycardia) 14_067857 ch11.qxp 7/6/07 10:42 PM Page 339
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or faster than normal (called tachycardia). Sometimes the speed or rate may be normal but the heartbeats follow an abnormal path through the heart muscle. Many things may cause irregular heart rates and rhythms, including
increased potassium, hormonal influences, certain cancers such as hemangiosarcoma, and heart diseases such as cardiomyopathy. Affected dogs may show anxiety, weakness, lethargy or even faint.
To diagnose these problems, your dog will need an EKG (electrocardiogram, sometimes also called ECG) and possibly a cardiac ultrasound evaluation. Your veterinarian may decide to have your dog wear a special heart monitor for 24 hours if the abnormality is infrequent.
Treatment: This may include various drugs to regulate the heart rate or rhythm. Some dogs benefit from having a pacemaker implanted.
Congestive Heart Failure
Congestive heart failure is the inability of the heart to provide adequate circulation to meet the body’s needs. It is the end result of a weakened heart muscle. The health of the liver, kidneys, lungs, and other organs is impaired by the circulatory failure, resulting in a problem involving multiple organs. A diseased heart can compensate for many months or years without signs
of failure. When failure does occur, it may appear suddenly and unexpectedly—sometimes immediately after strenuous exercise, when the heart is unable to keep up with the body’s demands.
In toy and small-breed dogs, chronic valvular disease with mitral regurgitation is the most common cause of congestive heart failure. In large-breed dogs it is dilated cardiomyopathy.
The early signs of congestive heart failure are tiring easily, a decrease in activity level, and intermittent coughing. The coughing occurs during periods of exertion or excitation. It also tends to occur at night, usually about two hours after the dog goes to bed. Dogs may be restless—pacing instead of
quickly settling down to sleep.
These early signs are nonspecific and may even be considered normal for
the dog’s age. As heart failure progresses the dog develops other signs, such as lack of appetite, rapid breathing, abdominal swelling, and a marked loss of weight.
Because the heart no longer pumps effectively, blood backs up in the lungs, liver, legs, and other organs. Increased pressure in the veins causes fluid to leak into the lungs and peritoneal cavity. Fluid in the lungs is the cause of the coughing. A rapid accumulation of fluid in the small airways can cause the dog to cough up a bubbly red fluid, a condition called pulmonary edema.
Pulmonary edema indicates failure of the left ventricle.
With failure of the right ventricle, fluid leaks into the abdomen, giving the belly a characteristic swelling or potbellied appearance (called ascites). This
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This dog suffers from right-sided congestive heart failure with ascites and depend- ent leg edema.
may be accompanied by swelling of the legs (dependent edema). An accumulation of fluid in the chest cavity ( pleural effusion) also occurs with right-sided heart failure.
In the late stages of congestive heart failure the dog sits with his elbows spread and his head extended. Breathing is labored. The pulse is rapid,
thready, and often irregular. The mucous membranes of the gums and tongue are bluish-gray and cool. A thrill may be felt over the chest. Fainting can occur with stress or exertion.
An accurate diagnosis is established through chest X-rays, ECG, echocar- diography, and other tests (such as a heartworm antigen test) as indicated.
Treatment: It is important to correct any underlying cause whenever possible. Heartworms, bacterial endocarditis, and some forms of congenital heart disease are potentially curable if they are treated before the heart is damaged. Treatment of congestive heart failure involves feeding the dog a low-salt diet, restricting exercise, and giving appropriate medications to increase heart function and prevent cardiac arrhythmias.
Most commercial diets contain excessive amounts of salt. Your veterinarian may prescribe a low-salt prescription diet such as Hill’s h/d, Purina CV, or Royal Canin EC. In dogs with mild symptoms, salt restriction may be the only treatment required.
Exercise is beneficial, but only for dogs who are not symptomatic. If symptoms such as easy tiring, coughing, or rapid breathing appear with exercise, do not allow your dog to engage in activities that elicit these symptoms. Various drugs are available that increase the force and contraction of the heart muscle or decrease the workload. They include the digitalis glycosides, 14_067857 ch11.qxp 7/6/07 10:42 PM Page 341
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calcium channel blockers, angiotensin-converting enzyme (ACE) inhibitors, beta blockers, and anti-arrhythmics. These are the same drugs used in people. ACE inhibitors such as enalapril maleate (Enacard) and benazepril (Fortekor) may prolong the life of dogs with valvular heart disease and cardiomyopathy, and are commonly used in dogs with these diseases. Fluid accumulation in the lungs and elsewhere is managed by diuretics such as furosemide (Lasix).
Potassium supplements may be necessary when giving certain diuretics. A
diuretic that spares the potassium the body needs is spironolactone
Dogs with congestive heart failure may benefit from vitamin-B supplements and taurine or carnitine. Coenzyme Q is another supplement that may help dogs with cardiac problems.
When treating cardiac arrhythmias, it is important to search for and correct any underlying electrolyte or metabolic problems that might trigger an attack. A number of cardiac drugs, including digitalis, lidocaine, diltiazem, procainamide, atropine, and propanalol (Inderal), are used to control
arrhythmias in dogs. Dogs whose primary problem is an arrhythmia may be
able to have a pacemaker implanted to help control the heart rate.
With proper treatment, a dog with congestive heart failure can live a
longer and more comfortable life. However, heart disease requires close monitoring. You will need to return to your veterinarian regularly for checkups. Heartworms
Heartworm disease, so named because the adult worms live in the right side of the heart, continues to be a major problem for many species of animals.
Heartworms are spread by mosquitoes, and thus are found throughout the
world. In the United States the prevalence is highest along the southeastern Atlantic and Gulf Coasts, but heartworm has been found in all 50 states. The disease is less prevalent at higher elevations.
The highest infection rates (up to 45 percent) in dogs not maintained on heartworm preventive are observed within 150 miles of the Atlantic Coast from Texas to New Jersey and along the Mississippi River and its major tributaries. Other areas of the United States have lower incidence rates (5 percent or less) of canine heartworm disease, while some regions have environmental, mosquito, and dog population factors that combine for a higher incidence of heartworm infection. The infection rate in male dogs is as much as four times that of female dogs, and dogs housed outdoors are four to five times more likely to be infected than indoor dogs.
Although there are differences in frequency of infection for various groups of dogs, all dogs in endemic regions should be considered at risk and placed on prevention programs.
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HEARTWORM LIFE CYCLE
A knowledge of the life cycle of this parasite ( Dirofilaria immitis) is needed to understand how to prevent and treat it. Infection begins when L infective 3
larvae in the mouthparts of a mosquito enter the dog’s skin at the site of a bite. The larvae burrow beneath the skin and undergo two molts that eventually lead to the development of small immature worms. The first molt (L to L ) 3
occurs one to 12 days after the dog is bitten by the mosquito. The larvae remain in the L stage for 50 to 68 days, and then molt into the L stage
It is only during the brief L stage, 1 to 12 days after the larvae enter the 3
dog’s body, that they are susceptible to the killing effects of diethylcarbamazine. However, throughout the L and L stages the larvae are susceptible 3
to three other drugs: ivermectin, selamectin, and milbemycin.
Immature worms make their way into a peripheral vein and are carried to
the right ventricle and the pulmonary arteries. Approximately six months after entering the dog’s body, they mature into adults. Adults can grow to 4 to 12 inches (10 to 30 cm) long and live up to five years. As many as 250 worms may be found in a heavily infested dog.
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This model shows heart-
worms in the right atrium
and right ventricle.
Sexual reproduction occurs if worms of both sexes are present. Females
give birth to live young called microfilaria; 5,000 microfilariae can be produced in one day by a single worm. Microfilaria are able to remain alive in the dog’s circulatory system for up to three years.
Before the microfilariae can become infective to another dog, the L larvae i
must go into a secondary host, the mosquito. This occurs when the mosquito bites the dog. The L larvae in the mosquito molt to L larvae. In warm southI 3
ern climates this process takes less than 10 days; in northern climates it can take up to 17 days. The L larvae then move to the mouthparts of the mos3
quito and are ready to infect a new host.
When there are fewer than 50 adult worms in the average-size dog, the worms live primarily in the pulmonary arteries and the right ventricle of the heart. When the numbers are greater than 75, the worms usually extend into the
right atrium. With a heavier infestation, the worms may migrate into the superior and inferior vena cavae and the veins of the liver.
Worms in the lungs can migrate into the terminal branches of the pulmonary arteries, where they obstruct the flow of blood and cause the vessels to clot. This is known as pulmonary thromboembolism. Even after treatment,
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dead worms can be carried by the bloodstream into the pulmonary circulation, resulting in a similar severe and sometimes fatal reaction. Chronic pulmonary thromboembolism causes loss of lung tissue and right-sided congestive heart failure. Dogs with thromboembolism may cough up bloody
Worms entwined about the heart valves can interfere with the mechanics
of the heart and produce effects similar to those of chronic valvular disease. Worm clumps in the vena cava or hepatic veins are responsible for a condition called vena cava syndrome, which causes liver failure with jaundice, ascites, spontaneous bleeding, and anemia. Collapse and death can occur in two to three days.
The signs of heartworm disease depend on the number of worms and the size of the dog. Dogs with a light infestation involving only a few worms may remain asymptomatic.
The typical early signs of heartworm infestation are tiring easily, exercise intolerance, and a soft, deep cough. As the disease progresses these symptoms become more severe and the dog loses weight, breathes more rapidly, and may cough after exercise to the point of fainting. The ribs become prominent and the chest starts to bulge. Acute vena cava syndrome or episode of thromboembolism can lead to collapse and death. A number of blood tests are available to diagnose heartworms. The most
accurate is the heartworm antigen test, which identifies an antigen produced by the adult female heartworm. False negatives occur in dogs with early infections (before the appearance of mature worms), in light infections with fewer than five adult worms, and in infections in which only males are present. False positives are rare.
Another important heartworm test is the microfilarial concentration test, in which parasites in a sample of blood are identified under the microscope. Although a positive test definitely indicates heartworms, a negative test does not rule out the diagnosis because typically 10 to 25 percent of infected dogs do not have microfilariae circulating in the peripheral blood.
Dogs with a negative microfilarial concentration test who do have heartworms are said to be suffering from an occult infection. There are a number of explanations for occult infection. One is that the dog is receiving a heartworm preventive. Preventives kill microfilaria but not adult worms. Thus these dogs will have a positive heartworm antigen test and a negative microfilarial concentration test. Also, a dog could be infected with adult heartworms of just one sex, which means no reproduction is taking place. There is yet another type of microfilaria that can be present in dogs tested for heartworms. It is called Dipetalonema. It is a harmless worm living under 14_067857 ch11.qxp 7/6/07 10:42 PM Page 345
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the skin. Its importance lies in the fact that its microfilaria may be mistaken for those of heartworm. This can be differentiated from heartworm microfilaria by careful examination under a microscope. A chest X-ray is the best test for determining the severity of the infection. Dogs with a heavy burden of worms in the pulmonary artery have X-rays that show enlargement of the right ventricle and/or pulmonary arteries.
An ECG may show right ventricular enlargement and cardiac arrhythmias. An echocardiogram may show worms in the main pulmonary artery or the right ventricle. In dogs with vena cava syndrome, heartworms can be seen in the vena cava. Blood and urine samples are obtained to check for anemia and
assess kidney and liver function.
TREATING HEARTWORM DISEASE
When and how to treat depends on the number of heartworms, their location, any medical complications (such as congestive heart failure or liver or kidney disease), the age and condition of the dog, and the presence of circulating microfilariae. After a thorough medical examination, your veterinarian will discuss these options and recommend a treatment program based on the findings. For dogs with uncomplicated heartworm disease, the objectives are to
eliminate all adult worms, kill the microfilariae (if present), and initiate preventive measures. At the same time, it is important to avoid complications associated with drug toxicity and the passage of dead worms into the lungs. Some veterinarians may choose to reduce the microfilaria numbers first, then go after the adult worms.
If you and your veterinarian decide to eliminate the adult worms first, the first step in dealing with uncomplicated heartworm infection is to administer an agent that will poison the worms. Two drugs that are FDA-approved and commonly used are thiacetarsamide (Caparsolate) and melarsamine
(Immiticide). Both contain arsenic. Caparsolate is given intravenously twice a day for two days. Significant toxic reactions can occur, and include loss of appetite, vomiting, diarrhea, jaundice, kidney failure, and death. Caparsolate does not always kill all the worms. Immature worms, especially females, are relatively resistant. Treatment with Caparsolate must be followed by treatment for microfilaria. The drug is not safe to use on high-risk dogs with congestive heart failure, liver failure, or kidney impairment. Immiticide eliminates more than 90 percent of worms, making it more
effective than Caparsolate. It has a higher margin of safety and can be given to dogs at high risk. Immiticide is given by intramuscular injection once a day for two days. If the dog is severely debilitated by heartworms, the drug can be given in divided doses 30 days apart. Complications are similar to those of Caparsolate, but occur less often. Both drugs can cause a local reaction at the site of injection. Thromboembolism is a complication associated with the death of adult worms, and can occur with either drug.
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Approximately 10 percent of dogs are poor candidates for immediate drug
treatment because of severe pulmonary artery infestation and congestive
heart failure. These dogs will benefit from complete rest and confinement for a minimum of two to three weeks before and after drug therapy. Aspirin, a mild anticoagulant, is given to help prevent respiratory failure due to worm thromboembolism.
Elderly dogs with heartworms are at high risk of death from therapy to kill the adult worms. Some old dogs may be better off without treatment. An
acceptable alternative is to restrict exercise and administer a low dose of aspirin daily to prevent further damage to the lungs. Give the dog a monthly heartworm preventive to prevent new worms from being acquired.
Surgical removal of worms is reserved for critically ill dogs with vena cava syndrome who are not candidates for drug therapy because of the risk of liver failure or thromboembolism. To remove the worms this way, an incision is made over the jugular vein in the neck. The vein is opened and a long grasping instrument is passed down through the superior vena cava into the right atrium and the inferior vena cava. The worms are grasped one by one and
removed. The procedure requires X-ray equipment and special skills. Residual worms are eliminated with drug therapy after the dog improves.
A heartworm antigen test should be performed three to five months after
drug therapy. If all worms have been eliminated, the test will be negative. If the test is positive, consider retreatment.
The next step is to kill circulating microfilaria. This step is omitted if parasites are not found on a microfilaria concentration test. Most veterinarians wait four weeks to allow the dog to recover from the effects of killing the adult worms before beginning therapy to kill the microfilaria. Currently there are four drugs used—although none is licensed for this purpose. They are ivermectin, selamectin, moxidectin, and milbemycin. Ivermectin is considered the most effective and has the fewest complications, except in dogs with drug sensitivity (see page 349).
Currently many veterinarians choose to simply give the monthly preventive drugs to dogs with circulating microfilaria, knowing that the microfilaria will slowly die off over six to nine months. Since the dogs are heartworm carriers during that time, they should be kept indoors during times of high mosquito activity and wear bug repellant when outside. If the veterinarian decides the microfilaria must be eliminated as quickly as possible, the dog is admitted to the hospital on the morning of treatment. Ivermectin is given orally and the dog is observed for 10 to 12 hours for signs of toxicity, including vomiting, diarrhea, lethargy, weakness, and shock. Most reactions are mild and respond to intravenous fluids and corticosteroids. Shock and death have occurred in Collies, Shetland Sheepdogs, Australian
Shepherds, Old English Sheepdogs, and other herding breeds and their crosses with the genetic defect that allows these drugs to pass into the brain (see Ivermectin Sensitivity, page 349). Ivermectin should not be used in these dogs. 14_067857 ch11.qxp 7/6/07 10:42 PM Page 347
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Dramatic declines in microfilaria counts occur over the next few days.
Ninety percent of dogs are free of all microfilaria at three weeks. At this time the dog should return for a microfilaria concentration test. If positive, the protocol is repeated. If negative, begin heartworm prevention.
A positive microfilaria concentration test after two treatments strongly suggests that adult worms are still present in the dog. Confirm this with a heartworm antigen test and treat accordingly.
As the previous section on treatment illustrates, treating a heartworm infestation is difficult and dangerous. It is far easier and more effective to prevent the problem in the first place. In theory, the best way to prevent heartworms is to keep your dog from being bitten by a mosquito. Unfortunately, preventing mosquito bites can never be 100 percent effective. Dogs can be reasonably protected if they remain indoors in the late afternoon and evening, when mosquitoes are feeding.
Areas of most frequent heartworm infestation are along coastal regions,
where swamps or other brackish water provide ideal conditions for mosquitoes to breed. Since mosquitoes have a flight range of one quarter mile, spraying around the yard and kennel and removing standing water can be partially
effective, but they will never eliminate the threat.
If you live or travel with your dog in an area where heartworm is endemic, your dog should be on a heartworm prevention program. Ask your veterinarian about local prevalence and follow their recommendations for prevention. Most dogs should be on a heartworm preventive program.
A prevention program should be started at 6 to 8 weeks of age in endemic areas, or as soon thereafter as climate conditions dictate. In the Deep South, where mosquitoes are a year-round problem, dogs should be kept on preventive drugs all year long. In areas where it is not necessary to administer the drug year round, start one month before the mosquito season and continue one month beyond the first frost (generally from May or June to November or December). Heartworm prevention is important for the dog’s whole life.
Some owners may elect to give heartworm preventives year round for
zoonotic parasite protection and to reduce the risk of breakthrough heartworm disease in case they miss a monthly dose. All dogs 7 months and older should have an antigen test for heartworms before starting a prevention program. If the test is positive, a microfilaria concentration test should be performed. The antigen test should be repeated annually or as frequently as your veterinarian recommends—even if the dog is on a heartworm prevention program. Many heartworm preventives can cause illness if given to a dog with circulating microfilaria.
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There are a number of drugs currently in use as heartworm preventives. They include ivermectin (Ivomec, Heartgard), milbemycin oxime (Interceptor), and selamectin (Revolution).
Heartgard is an effective preventive that is given once a month. This drug acts on the L larvae. It has the advantage that dogs do not have to be heart4
worm-free to initiate therapy; dogs infected for as long as two months before treatment will not develop heartworms. If a monthly dose is missed, restart the drug and obtain a heartworm antigen test seven months later. Heartgard is marketed in chewable tablets of different sizes, depending on the weight of the dog. The recommended dose is generally considered to be safe to use on Collies and other herding breeds. However, with safer alternatives available, most owners avoid this for the breeds with the genetic defect that causes sensitivity to ivermectin. Heartgard Plus is a popular chewable tablet that combines ivermectin with pyrantel pamoate. This combination prevents heartworms and also controls roundworms and hookworms.
Interceptor (milbemycin oxime) is another orally administered once-amonth heartworm preventive that also acts on the L larvae. Like Heartgard, 4
this drug is marketed in different dosages based on the weight of the dog. Interceptor also controls hookworms, roundworms, and whipworms. This
drug is safer to use on Collies and Collie crosses.
The injectable form of ProHeart, called ProHeart 6, was considered to provide protection for six months. However, it has been removed from the market due to potential side effects. The FDA is still considering a final decision about this medication.
Selamectin (Revolution) is a once-a-month liquid heartworm preventive
applied to the skin of the dog’s neck between the shoulder blades. It is available from your veterinarian in premeasured doses based on the dog’s size and age. A principal advantage of selamectin is that it also controls adult fleas and prevents flea eggs from hatching for one month. In addition, it treats ear mites and the mites that cause scabies.
Diethylcarbamazine (DEC) has proven over many years to be extremely
safe and effective when given daily. It is less convenient than the drugs just described, and unlike them it does not protect if two or three days are missed. DEC is currently unavailable because so many dog owners have switched to the convenient monthly medications. If it should become available again, the following precautions must be taken.
Dogs over 6 months of age must be tested for microfilaria before starting on DEC. If microfilaria are found in the blood, the drug should not be given because anaphylactic reactions of varying severity, including death, may develop. DEC kills L infective larvae before they molt to L . Since molting can
occur in as little as 24 hours, DEC must be given daily to be effective. If more than two days of treatment are missed, stop the drug and consult your veterinarian for further instructions. 14_067857 ch11.qxp 7/6/07 10:42 PM Page 349
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Medications containing DEC have an extremely bitter taste and need to be mixed with flavoring agents to be given in chewable form.
Some breeds show an increased susceptibility to the potential toxicity of ivermectin and similar drugs. In these dogs, there is a defect of the gene MDR-1. This is a multi-drug transporter gene that influences the movement of drugs across the blood brain barrier. Dogs who are homozygous for this autosomal recessive trait will have severe, potentially fatal reactions to some drugs, including ivermectin. Dogs who are heterozygous may be able to safely take the medications, but may pass on the defective trait to their offspring. A genetic test for this defect is available through Washington State
University’s Veterinary Laboratory of Clinical Pharmacology. A cheek swab can be sent to determine if your dog has the gene. This testing is recommended for Collies, Border Collies, Shetland Sheepdogs, Australian Shepherds, Old English Sheepdogs, and longhaired Whippets. In breeds such as the Collie, more than 70 percent of the dogs tested are either homozygous for this defect or carry it.
Anemia and Clotting Disorders
Anemia is a defined as a deficiency of red blood cells ( erythrocytes) in the circulatory system. Adult dogs are anemic when the concentration of red cells in whole blood is less than 37 percent by volume. The normal range is 39 to 60 percent. Red cells are produced by the bone marrow and have an average life span of 110 to 120 days. Old red cells are trapped by the spleen and removed from the circulation. The iron they contain is recycled to make new erythrocytes. The purpose of red blood cells is to carry oxygen. Thus, the symptoms of anemia are caused by insufficient oxygen in the organs and muscles. Signs include lack of appetite, lethargy, and weakness. The mucous membranes of the gums and tongue become pale pink to white. In dogs with severe anemia, the pulse and respiratory rate are rapid and the dog may collapse with exertion. A heart murmur may be heard. Anemia can be caused by blood loss, hemolysis, or inadequate red blood
In adult dogs the most common causes of blood loss are trauma, slow gastrointestinal bleeding associated with stomach and duodenal ulcers, parasites, and tumors in the gastrointestinal tract. Chronic blood loss also occurs through the urinary system (see Blood in the Urine, page 412). Hookworms and fleas are common causes of chronic blood loss in puppies.
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Treatment: Treatment must be directed toward the cause of the anemia. Gastrointestinal bleeding can be detected by checking the stools for microscopic traces of blood. Urinalysis will pick up traces of blood in the urine that may not be visible to the naked eye. Other tests can also be used to determine the cause of the occult (microscopic) bleeding.
Hemolysis is an acceleration in the normal process of red blood cell breakdown. Red blood cells break down to form bile and hemoglobin. With severe hemolysis, these breakdown products accumulate in the body. Accordingly, in a dog experiencing an acute hemolytic crisis you would expect to see jaundice and hemoglobinuria (passing dark-brown urine that contains hemoglobin). In addition, the dog appears weak and pale and has a rapid pulse. The spleen, liver, and lymph nodes may be enlarged.
Causes of hemolysis include immune-mediated hemolytic anemia, congenital hemolytic anemia, infectious diseases (such as canine babesiosis and leptospirosis), drug reactions to medications such as acetaminophen, and poisonous snake bites. A number of bacteria produce toxins that destroy red blood cells, so hemolysis can also occur with severe infections.
Neonatal isoerythrolysis is a hemolytic disease of newborn puppies; it is discussed on page 503.
Immune-Mediated Hemolytic Anemia
This is the most common cause of hemolysis in adult dogs. Red blood cell destruction is caused by auto-antibodies that attack antigens present on the surface of the cells, or by antigens from medications or organisms attached to the red blood cell walls. The weakened cells are trapped in the spleen and destroyed.
Poodles, Old English Sheepdogs, Irish Setters, and Cocker Spaniels are
predisposed to immune-mediated hemolytic anemia, but all breeds are susceptible. Affected dogs are usually between 2 and 8 years of age; females outnumber males four to one. Most cases of immune-mediated hemolytic anemia are idiopathic. That is,
the reason why the auto-antibodies developed in that particular dog is
unknown. In some cases there is a history of recent drug therapy. An immunemediated hemolytic anemia also occurs with systemic lupus erythematosus. The diagnosis is made by microscopic examination of blood smears, looking for specific changes in the appearance of the erythrocytes and other blood elements; and by serologic blood tests.
Treatment: Treatment of idiopathic immune-mediated hemolytic anemia is directed toward preventing further red cell destruction by blocking the antigen-antibody reaction using corticosteroids and immunosuppressants.
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Severe anemia is corrected with blood transfusions. Splenectomy (removal of the spleen) may be beneficial, but only when tests prove that the spleen is contributing to the hemolytic process.
The response to treatment depends on the rate of hemolysis and whether
an underlying cause can be found and corrected. The outlook is guarded; even with appropriate medical treatment, the mortality rate is close to 40 percent.
Congenital Hemolytic Anemia
Several inherited abnormalities in the structure of red blood cells can result in their premature destruction. Phosphofructokinase deficiency is an autosomal recessive trait that occurs in English Springer Spaniels and Cocker Spaniels. A deficiency of this enzyme results in changes in the pH of red blood cells, causing the cells to periodically fragment and produce bouts of hemoglobinuria. There is no effective treatment. Pyruvate kinase deficiency is another red blood cell enzyme deficiency
caused by an autosomal recessive gene. This disease is recognized in several breeds, including Basenjis, Beagles, and West Highland White Terriers.
Puppies usually develop the hemolytic anemia at 2 to 12 months of age.
Death by age 3 is the usual outcome.
Genetic tests for phosphofructokinase and pyruvate kinase deficiency are available through the University of Pennsylvania at PennGen, and from
OptiGen and VetGen.
OFA maintains a voluntary diagnostic service and registry for dogs with phosphofructokinase deficiency, and Basenjis with pyruvate kinase deficiency, in cooperation with the respective national breed clubs (see appendix D). INADEQUATE RED BLOOD CELL PRODUCTION
When the metabolic activity of the bone marrow is depressed, new red blood cells are not manufactured as fast as old ones are destroyed. This results in an anemia due to inadequate red blood cell production. A common cause of
bone marrow depression is chronic illness, especially associated with kidney and liver disease.
Iron, trace minerals, vitamins, and fatty acids are all incorporated into red blood cells. Thus a deficiency of one or more of these nutrients could slow down or stop cell production. This is an unusual cause of anemia in dogs, because commercial dog foods contain more than adequate amounts of essential vitamins and minerals. Iron deficiency is an exception. It occurs when iron is lost from the body faster than it can be replaced through the diet. The two situations in which this is most likely to happen are chronic gastrointestinal bleeding and a heavy infestation of blood-sucking insects (such as fleas, ticks, or lice).
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Red blood cell production can be depressed by certain drugs. Estrogen is an important cause of bone marrow depression. This includes estrogens given for medical purposes as well as those produced by testicular and ovarian tumors. Other drugs that depress the bone marrow include chemotherapy agents,
chloramphenicol, butazolidin, thiacetarsamide, quinidine, and trimethoprimsulfadiazine. Primary and metastatic cancer can invade the bone marrow and crowd out
normal cells, also depressing red blood cell production.
The diagnosis of inadequate red cell production is made by bone marrow
Treatment: Treatment is directed toward eliminating the cause of the bone marrow deficiency. The dog should be screened for kidney and liver disease. Iron deficiency anemia warrants stool examination and a further medical workup. Estrogen-producing tumors of the ovary or testicle should be sought and treated. Many drug-related causes of bone marrow depression
reverse when the drug is stopped.
Erythropoietin is a substance that stimulates red blood cell production. It is normally manufactured by the kidneys and, to a much lesser extent, by the liver. Recombinant erythropoietin can be helpful in dogs if the bone marrow is capable of responding. Human erythropoietin has been used for the most part, but the dog eventually develops antibodies against it. A new canine recombinant version will be available soon.
Clotting disorders are caused by an absence of one of the coagulation factors needed to complete the clotting sequence. Severe deficiencies are associated with spontaneous bleeding. Blood in the urine or stools may be associated with a spontaneous bleeding disorder.
Von Willebrand’s Disease
Von Willebrand’s disease (vWD) is the most common inherited bleeding disorder in dogs. It has been described in more than 50 breeds. Both males and females can transmit and express the genetic trait. The disease is inherited as an autosomal dominant gene with variable expression. That is, the severity of the bleeding is related to the degree to which the gene is expressed.
The bleeding is caused by a deficiency of a plasma protein called the von Willebrand factor, which is critical for normal platelet function in the early stages of clotting.
In most cases the bleeding in vWD is mild or inapparent, and lessens with age. Severe problems include prolonged nosebleeds, bleeding beneath the
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history of bleeding from the gums following tooth eruptions, and oozing from wounds following tail docking and dewclaw removal.
Breeds at risk for vWD in which bleeding is likely to be mild include the Doberman Pinscher, Golden Retriever, Standard Poodle, Pembroke Welsh
Corgi, Manchester Terrier, Miniature Schnauzer, Akita, and others. Breeds in which bleeding is likely to be more severe include the Scottish Terrier, Shetland Sheepdog, German Shorthaired Pointer, and Chesapeake Bay Retriever.
Hypothyroidism is common in dogs with vWD, and may contribute to the
The diagnosis is made by specific blood tests, including a bleeding time. In this test, a small cut is made and the amount of time it takes for bleeding to stop on its own is measured. From a nail cut too short, two to six minutes is normal, while from a cut on the gums, two to four minutes is normal. A quantitative test for von Willebrand’s disease involves measuring the vWD antigen. Dogs with vWD antigen levels below the normal range are at risk for expressing and/or carrying the trait.
OFA maintains a vWD registry for many of the breeds mentioned here. A
DNA test to identify affected dogs and carriers is available through VetGen and is the most accurate diagnostic test.
This is a sex-linked recessive trait that occurs only in males who inherit a maternal X chromosome carrying a defective gene. Females always inherit
two X chromosomes, at least one of which usually contains a normal dominant gene. Thus females can carry the trait but do not develop the disease—
the exception being a female who inherits two recessive genes: one from a hemophiliac father and the other from a mother who is either a hemophiliac or a carrier. This is extremely rare.
Hemophilia produces bleeding into the chest and abdominal cavities, muscles, and subcutaneous tissues. Bleeding into the joints is common. Hemophilia A (the most common type) is a deficiency of coagulation factor VIII. Hemophilia B is a deficiency of factor IX. Hemophilia occurs in all breeds, with a predisposition among German Shepherd Dogs, Airedale
Terriers, and Bichons Frises.
Other coagulation deficiencies involve factors VII, X, XI, and prothrombin. These deficiencies are inherited as single-factor autosomal traits and affect males and females alike. They are less common than hemophilia.
Affected breeds include the Boxer, English and American Cocker Spaniel,
English Springer Spaniel, Beagle, and Kerry Blue Terrier.
The diagnosis of a coagulation factor deficiency is based on a number of clotting tests, plus an analysis for the specific factor that is deficient. PennGen offers genetic tests for factor VII and factor XI.
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Disseminated Intravascular Coagulation
This is an acquired bleeding disorder triggered by shock and infection, certain tumors (particularly hemangiosarcomas, osteosarcomas, and cancers of the prostate and mammary glands), and severe injuries such as crush wounds and burns. Disseminated intravascular coagulation (DIC) is characterized by
intravascular clotting throughout the entire capillary circulation, followed by spontaneous bleeding when all the clotting factors have been consumed. The bleeding associated with DIC involves the nose, mouth, gastrointestinal tract, and body cavities. Dogs with DIC are extremely ill and often die.
Another acquired bleeding disorder is caused by vitamin K deficiency. It is discussed in Rodent Poisons (page 27).
Treating Clotting Disorders
Successful treatment of spontaneous bleeding requires rapid diagnosis. Dogs with severe blood loss are given fresh, whole blood containing red cells, platelets, and active coagulation factors. Dogs with less severe blood loss who don’t require a blood transfusion are given fresh-frozen plasma or concentrates containing the missing coagulation factor. Blood banks are available in some areas to provide canine blood and clotting factors.
Treating vWD hypothyroid dogs with thyroid replacement therapy may
prevent subsequent bleeding episodes.
An important additional step in treating DIC is to control the underlying cause of the intravascular coagulation. While it may seem contradictory, these dogs may need heparin to limit the clotting taking place.
Dogs with inherited coagulation disorders, and those who may be carriers, should not be bred.
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C h a p t e r
01_067857 ffirs.qxp 7/6/07 10:28 PM Page iii
FINDING IT QUICKLY
TRIBUTE TO A DOG
THE SKIN AND COAT
SIDE VIEW OF THE EYE
THE MOUTH AND
THE URINARY SYSTEM
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