Chapter 11 Diseases of the Respiratory System

All of the cells within an animal’s body require oxygen for metabolism. When glucose is burned (in the cell) with oxygen, the by-products are energy, water, and carbon dioxide. Carbon dioxide, a waste product, must be eliminated from the body, whereas water and energy are used to maintain all the life processes. The respiratory system transports oxygen to the bloodstream and removes carbon dioxide. Malfunction of this system affects all functions in the living animal.

We can arbitrarily divide the respiratory system into the upper respiratory tract (nasal cavity, sinuses, nasopharynx, and larynx; Fig. 11-1) and the lower respiratory tract (trachea, bronchi, lungs, and pleural cavity; Fig. 11-2). The technology student is referred to an anatomy text for review of the anatomy and physiology of the respiratory system.

Figure 11-1 Cross section of the upper respiratory tract of the dog.

(From McBride DF: Learning veterinary terminology, ed 2, St Louis, 2002, Mosby, by permission.)

Figure 11-2 Lower respiratory tract, including an alveolus.

(From McBride DF: Learning veterinary terminology, ed 2, St Louis, 2002, Mosby, by permission.)

DISEASES OF THE LOWER RESPIRATORY TRACT

Diseases that involve the lower respiratory tract are of more serious clinical significance than those of the upper airways (see Color Plate 10). Examples of lower airway diseases include tracheobronchitis, tracheal collapse, feline asthma, feline viral respiratory infections, pneumonia, heartworm disease (feline), neoplasia, pulmonary edema, and hemothorax/pneumothorax.

Infectious Canine Tracheobronchitis (Kennel Cough)

Infectious canine tracheobronchitis syndrome involves a collection of agents including viruses, bacteria, mycoplasmas, fungi, and parasites. Some of the most commonly incriminated agents are canine parainfluenza virus, canine adenovirus, canine herpesvirus, reovirus, Bordetella bronchiseptica, mycoplasma, and occasionally the canine distemper virus.

CLINICAL SIGNS

• A history of exposure to other animals at a kennel, hospital, grooming facility, or show

• A dry, hacking, paroxysmal cough (except for cough, a normal, healthy-looking animal)

DIAGNOSIS

• Clinical signs and history

• Cough on tracheal palpation in an otherwise healthy dog

TREATMENT

• Administer antibiotics if any deeper respiratory involvement is found or if animal is febrile (base choice on culture and sensitivity results)

Novobiocin/tetracycline/prednisolone combination (Delta-Albaplex; Upjohn, Kalamazoo, Mich.): PO every 12 hours

• Glucocorticoids:

Trimeprazine with prednisolone (Temaril-P): every 12 hours

Prednisone, prednisolone: twice a day for 5 to 7 days, then taper dose

• Antitussives:

Hycodan (5 mg hydrocodone bitartrate): PO two to four times a day

Codeine: every 6 to 8 hours

Butorphanol tartrate (Torbutrol): every 6 to 12 hours

• Bronchial dilators:

Aminophylline: PO every 6 to 12 hours

Terbutaline (Brethine): PO every 8 to 12 hours

INFORMATION FOR CLIENTS

• Infectious canine tracheobronchitis is a self-limiting disease. It can take 2 to 3 weeks to resolve.

• Treatment is aimed at making the animal (and often the owner) more comfortable.

• Vaccination with an injectable vaccine should be obtained 2 to 3 weeks before boarding or possible exposure to the disease. Intranasal vaccine can be given closer to the time of exposure. Vaccination significantly reduces the severity of the disease.

Feline Bordetella Infection

Bordetella bronchiseptica colonize the ciliated respiratory mucosa, a tissue normally designed to eliminate foreign material from the respiratory tract. The resulting damage and loss of tracheal lining cells is thought to contribute to the clinical symptoms and spread of the disease. After colonization of the tracheal cells, the organism releases toxins that are responsible for local and systemic inflammatory damage. The disease is usually self-limiting in cats; however, severe bronchopneumonias and fatalities have been seen in young kittens.

CLINICAL SIGNS

• Fever

• Sneezing

• Nasal discharge

• Submandibular lymphadenopathy

• Coughing and rales

TECH ALERT

Many of the signs of this infection look exactly like respiratory viral infections.

DIAGNOSIS

• Culture from oropharyngeal swabs

TREATMENT

• The disease is usually self-limiting. Antibiotics may be of value:

Tetracycline PO or doxycycline PO

PREVENTION

• Eliminate stress

• Good hygiene

• Good nutrition

• Isolate sick cats

• Vaccinate cats

INFORMATION FOR CLIENTS

1. This respiratory disease looks similar to those caused by feline herpes viruses and feline caliciviruses.

2. The disease is usually self-limiting.

3. Vaccination of cats in multicat households or catteries should be considered.

4. Cats with this disease are infective to other cats.

Collapsing Trachea

The cause of collapsing trachea is not entirely known; however, a reduction in the glycoprotein and glycosaminoglycan content of the hyaline cartilage of the tracheal rings is a constant finding in dogs affected by this syndrome. This syndrome is frequently seen in middle age to old, obese toy and miniature breeds, but can also be seen in young animals (Yorkies seem to be overrepresented). The defect involves tracheal rings that lose their ability to remain firm, subsequently collapsing during respiration.

CLINICAL SIGNS

• History of paroxysmal cough (harsh, dry, “goose honk” cough)

• Cough often worse on exercise or excitement or when pulling on the collar

• Often concurrent signs of heart disease

DIAGNOSIS

• Tracheal palpation elicits a “goose honk” cough.

• All other physical examination parameters may be normal.

• Radiography on static views may or may not show an alteration in the contour of the trachea. Dorsoventral (DV) and lateral views (both inspiratory and expiratory) are necessary to see this condition.

• Bronchoscopy demonstrates the actual ring collapsing when the animal breathes.

• Ultrasound provides real-time pictures of collapse.

• Fluoroscopy shows collapse on respirations.

• Rule out all other causes of cough.

TREATMENT

Symptomatic treatment

• Treatment to slow breathing in acute cases:

Acepromazine: intravenously (IV), intramuscularly (IM), subcutaneously (SQ)

Oxygen therapy (mask) or intubation

Dexamethasone: IV

Butorphanol: IV, IM, SQ every 6 to 12 hours

• Treatment to slow breathing in chronic cases:

Antitussives:

Hycodan (5 mg hydrocodone bitartrate): PO two to three times a day

Butorphanol: PO every 12 hours

Diphenoxylate hydrochloride and atropine sulfate (Lomotil): PO every 12 hours (unproven drug for this purpose in the United States; this product contains atropine, which can cause constipation)

Glucocorticoids:

Prednisolone: PO every 12 hours; taper dose after 7 to 10 days

Bronchial dilators (bronchial dilators act to decrease intrathoracic pressures during expiration, thereby decreasing the collapse of the tracheal membrane):

Theophylline: PO every 12 hours

Terbutaline (Brethine, Ciba): PO every 8 to 12 hours

Surgical treatment

• Keep the trachea open with the insertion of external prosthetic supports.

• Surgical correction involves a number of possible complications, making the procedure unrewarding.

INFORMATION FOR CLIENTS

• Once this condition develops, it requires lifelong management.

• Treatment is aimed at reducing inflammation in the airway and making the animal more comfortable.

• Management techniques that help include the following:

Aggressive weight reduction

Decreased exposure to inhaled irritants such as cigarette smoke

Use of a harness instead of a collar for restraint

Aggressive treatment of respiratory infections

Monitoring and treatment of congestive heart failure if it develops

Feline Asthma

Feline asthma, as in human asthma, is a disease characterized by spontaneous bronchoconstriction, airway inflammation, and airway hyperreactivity. Clinical signs of feline asthma include coughing, wheezing, and labored breathing, usually of acute onset.

In affected cats, airway epithelium may hypertrophy, goblet cells and submucosal glands may produce excessive amounts of mucus, and the bronchial mucosa may become infiltrated with inflammatory cells. All of these changes result in decreased airflow. A 50% decrease in the lumen of the airway results in a sixteenfold decrease in the amount of air moving through the system.

It would seem that chronic airway inflammation plays an important role in feline asthma. Decreasing inflammation in the airways and improving airflow are the primary goals of treatment.

CLINICAL SIGNS

• Acute onset of labored breathing

• Cough (may be chronic)

• Wheeze

• Lethargy

DIAGNOSIS

• No physical examination findings are diagnostic for feline asthma.

• Clinical signs and history help establish diagnosis.

• Radiographs may show signs of diffuse prominent bronchial markings consistent with airway inflammation (often described as “doughnuts”).

TREATMENT

• Manage airway inflammation with high-dose, long-term corticosteroid therapy:

Prednisone: PO every 12 hours for 10 to 14 days, then slowly taper over 2 to 3 months

DepoMedrol: IM every 2 to 4 weeks (if unable to dose orally)

• Bronchodilators:

Terbutaline (Brethine): SQ, IM every 12 hours; or PO every 12 hours

Cyproheptadine: PO every 12 hours (used in cats not responding to the maximum doses of terbutaline and corticosteroids)

• Oxygen therapy

INFORMATION FOR CLIENTS

• The prognosis for cats with asthma is variable.

• If allergens can be determined and exposure decreased before permanent damage occurs, most cats do well.

• Most cats with asthma require periodic medication. Cats with chronic asthma may require continuous medication.

• Aggressive treatment at the veterinary hospital is needed for acute bouts of respiratory distress.

• A cure is usually not possible.

Feline Heartworm Disease

Heartworm infection in cats is less common than in dogs (about 5%-20% of canine prevalence). Clinical symptoms of the disease in cats, however, are often more severe than in the dog, although the worm burden is usually small (Table 11-1). This disease is seen in 38 of the 50 states, mostly along coastal areas and the Mississippi River Valley.

Table 11-1 Feline Heartworm Disease versus Canine Heartworm Disease

	Dog	Cat
Biology of Dilofilaria immitis
Microfilaremia	30%-80% of infected dogs	Rare, transient
Number of adult worms	>50 common	1-3 common
Ectopic migration	Rare	More common
Adult lifespan	Approximately 5 yr	Approximately 2 yr
Clinical signs of heartworm disease
No signs	Most common	Most common
Respiratory signs	Common	Common
Vomiting	Unusual	Fairly common
Exercise intolerance	Common	Rare
Ascites	Common	Rare
Sudden death	Rare	More common
Radiographic findings
Enlarged pulmonary arteries	Characteristic	Characteristic
Blunting/tortuosity	Common	Occasional
Infiltrates in lung	Possible	Possible
Right-sided heart enlargement	Occasional	Rare
Pulmonary artery “knob”	Characteristic	Not seen

Clinical signs in cats are often different from those seen in dogs. Cough and dyspnea are hallmark signs. The standard enzyme-linked immunosorbent assay antigen tests are of little value, missing as many as 50% of natural infections. Male cats (aged 4-6 years) appear to be predisposed to this condition.

CLINICAL SIGNS

• Cough

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