Causes of fever in dogs and cats

A dog or a cat with fever should be evaluated in a systematic fashion. In general, a three-stage approach is used at the clinic. The first stage consists of a thorough history-taking and physical examination, as well as a minimum database. The second stage consists of additional non-invasive and invasive diagnostic tests. The third stage consists of a therapeutic trial, which is instituted if no diagnosis can be obtained after completion of the second stage.

When a dog or cat with fever fails to respond to antibacterial treatment, a course of action must be formulated. A thorough history should be obtained and a complete physical examination performed. The history rarely provides clues to the cause of the fever in dogs and cats; however, a history of ticks may indicate a trickettsial or hemoparasitic disorder; previous administration of tetracycline (mainly to cats) may indicate a drug-induced fever; and travel to areas where systemic mycoses are endemic should prompt further investigation consisting of cytologic or serologic studies or fungal cultures.

During a physical examination, it is important to evaluate the lymphoreticular organs, because numerous infectious and neoplastic diseases affecting these organs (e.g., ehrlichiosis, Rocky Mountain spotted fever, bartonellosis, leukemia, systemic mycoses) may cause fever in dogs and cats.

An enlarged lymph node or spleen should be evaluated cytologically using specimens obtained by fine-needle aspiration (FNA); an FNA sample can also be obtained for bacterial and fungal culture and susceptibility testing, should the cytologic studies reveal evidence of infection or inflammation. Any palpable mass or swelling should also be evaluated using specimens obtained by FNA to rule out granulomatous, pyogranulomatous, suppurative inflammation as well as neoplasia.

When suspecting fever in dogs and cats, the clinician should thoroughly inspect and palpate the oropharynx, searching for signs of pharyngitis, stomatitis, or tooth root abscesses. The bones should also be palpated, particularly in young dogs, because metabolic bone disorders, such as hypertrophic osteodystrophy, can cause fever associated with with bone pain. Palpation and passive motion of all joints is also indicated, in search of monoarthritis, oligoarthritis, or polyarthritis. A neurologic examination should be conducted to detect signs of meningitis or other central nervous system lesions. In older cats, the ventral cervical region should be palpated to detect thyroid enlargement or nodules.

The thorax should be auscultated carefully in search of a murmur, which could indicate bacterial endocarditis. An ocular examination may reveal changes suggestive of a specific cause (chorioretinitis in cats with feline infectious peritonitis or in dogs with ehrlichiosis).

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