Respiratory Infections

Chapter 163 Respiratory Infections

The respiratory system is a common portal of entry for infectious agents of all varieties, with many of these infectious agents have been identified as respiratory pathogens (Table 163-1). The purpose of this chapter is to emphasize clinical aspects of common respiratory infections in dogs and cats. For details concerning specific infectious diseases, the reader is referred to Chapter 11 for respiratory virus and chlamydia infections of the cat, Chapter 12 for bordetellosis and viral tracheobronchitis of the dog, Chapter 13 for canine distemper, Chapter 20 for the systemic mycoses, and Chapter 21 for toxoplasmosis. Diagnostic procedures relevant for respiratory infections are summarized in Table 163-2 and are discussed in Chapters 158 and 159. Management of noninfective bronchopulmonary diseases and of chronic bronchitis in the dog and cat are described in Chapter 162. Management of pleural infections is described in Chapter 164.

It is helpful to identify the principal anatomical site(s) of infection, as many infectious agents produce a characteristic pattern of respiratory disease. This approach may help the clinician in the differential diagnosis and in directing appropriate laboratory studies. Good examples of localized respiratory disease are the viral upper respiratory infections of cats and canine infectious tracheobronchitis. Because clinicians generally speak in terms of the anatomic diagnosis—rhinitis, sinusitis, laryngitis, tracheitis, bronchitis, pneumonia, pleuritis, or mediastinitis—respiratory infections will be discussed using this classification (see Tables 163-1 and 163-2).


*This list is not comprehensive; important clinical conditions are indicated with the most commonly affected species designated as [C] = canine; [F] = feline.



Infections of the nasal cavity and paranasal sinuses are common, and clinical signs may also involve the nasopharynx. Acute rhinitis is frequently caused by viral and bacterial pathogens that directly invade the nasal mucosa. Chronic rhinitis often can be traced to another predisposing problem such as immunosuppression, foreign body, or tumor. Because the nasal cavity is not sterile, standard culture and sensitivity tests are of little value in diagnosis and management of these diseases.


Fungal infection of the nasal cavity or sinuses (see Table 163-1) can also be associated with immunosuppression; however, this immunodeficiency may be difficult to demonstrate in dogs. Aspergillus flavus, for example, is a normal inhabitant of the nasal cavity, but may invade respiratory epithelium in dogs with altered immunity or preexistent inflammation (e.g., lymphocytic-plasmacytic rhinitis, foreign body, or trauma).


The differential diagnosis of upper respiratory infections is extensive (Table 163-3), including primary infectious diseases, secondary infections, and a large number of non-infective disorders. The age, vaccination status, history, and physical examination tend to focus the diagnostic considerations in most cases. The diagnostic studies chosen depend on the presumptive diagnosis and response to initial therapy (see Table 163-2).

Infections caused by Aspergillus spp. and Penicillium spp. require histologic examination of nasal tissue, sometimes with special staining (e.g., silver stains) to detect hyphae. A positive agar gel immunodiffusion (AGID) test may also be supportive of the diagnosis. Routine culture is nonspecific because these fungi can be normal inhabitants of the nasal cavity.
Aug 27, 2016 | Posted by in SMALL ANIMAL | Comments Off on Respiratory Infections

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