THE MERCK VETERINARY MANUAL
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Overview of Respiratory Diseases of Small Animals

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Respiratory diseases are common in dogs and cats. Although clinical signs such as coughing and dyspnea are commonly referable to primary problems of the respiratory tract, they may also occur secondary to disorders of other organ systems (eg, congestive heart failure).

Both young and aged animals are at increased risk of developing respiratory disease. At birth, the respiratory and immune systems are incompletely developed; this facilitates the introduction and spread of pathogens within the lungs, and alveolar flooding may occur. In aged animals, chronic degenerative changes that disrupt normal mucociliary clearance and immunologic anergy may render the lungs more vulnerable to airborne pathogens and toxic particulates.

A varying flora of indigenous commensal organisms (including Pasteurella multocida, Bordetella bronchiseptica, streptococci, staphylococci, pseudomonads, and coliform bacteria) normally reside in the canine and feline nasal passages, nasopharynx, and upper trachea, and at least intermittently in the lungs, without causing clinical signs. Opportunistic infections by these bacteria may occur when respiratory defense mechanisms are compromised by infection with a primary pathogen (eg, distemper, parainfluenza virus, or canine type 2 adenovirus in dogs, and rhinotracheitis virus or calicivirus in cats), other insults (eg, inhalation of smoke or noxious gases), or diseases such as congestive heart failure and pulmonary neoplasia. Secondary bacterial infections complicate the management of viral respiratory infections of both dogs and cats. Pathogens may continue to reside in the respiratory tract of convalescent animals. When stressed, these animals may relapse; they can also act as a source of infection for others. Poor management practices (eg, overcrowding) are often associated with poor hygienic and environmental conditions, and the resultant stress increases both the incidence and severity of infections. Conditions that favor the spread of infections often occur in catteries, kennels, pet shops, boarding facilities, and humane shelters.

Congenital abnormalities, such as stenotic nares, elongation of the soft palate, nasopharyngeal turbinates, and tracheal stenosis, can cause respiratory dysfunction. Neoplastic masses, degenerative changes of the airways, and tracheal collapse can result in dyspnea and other clinical manifestations of respiratory disease.

Tracheal collapse is most common in toy and miniature breeds of dogs and rare in cats. The cause is unknown. Affected animals have a nonproductive, honking, chronic cough and inspiratory or expiratory dyspnea. Frequently they are obese and may have concurrent cardiovascular or other pulmonary disease (especially chronic bronchitis). Weight loss (if obese) is critical in management. Other measures include exercise restriction, reduction of excitement and stress, and medical therapy, eg, antitussives, antibiotics, bronchodilators, and corticosteroids.

Last full review/revision November 2013 by Ned F. Kuehn, DVM, MS, DACVIM

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