Diseases of the Respiratory System

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.


Diseases of the upper respiratory system include rhinitis, nasal tumors, epistaxis, sinusitis, tonsillitis, and laryngitis. Although upper airway disease is not nearly as common in dogs and cats as it is in humans, it is still seen clinically and causes concern for owners.


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.

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.

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.

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.

Aug 31, 2016 | Posted by in GENERAL | Comments Off on Diseases of the Respiratory System

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