Felipedia

© Norsworthy, GD (2003) The Feline Patient. 2nd Edition. Lincott Williams & Wilkins

Of all the deep mycotic agents, Coccioides immitis has the most limited geographic distribution. Cats are infrequently infected with this organism outside the endemic area of the dry south-western United States. The ecologic lower Sonoran life zone is well suited to support growth of this organism: dry hot summers are followed by moderately wet winters, and the soil is sandy and alkaline. Although only a limited number of cases have been described in cats, it appears that the primary route of infection is by inhalation of small airborne arthrospores.

Infection by direct inoculation of the organism has also been reported. Dissemination occurs through hematogenous and lymphatic routes. A competent cell-mediated immune response must be present to contain infection. Infection with feline leukemia and feline immunodeficiency viruses does not appear to predispose cats to coccidioidomycosis. Humans are not at risk for the disease from contact with infected cats but may become infected through shared environmental exposure.

Nonspecific signs of fever, anorexia, and weight loss are common. Dermatologic abnormalities, such as draining lesions and abscesses, are the most common finding in infected cats. Ocular inflammation, bony lesions, and lower respiratory signs are less frequently reported clinical findings.


Geographical locality for endemic Coccioides infection	Coccidioidomycosis in a human femur

Coccidioides arthrospores in lung tissue

Direct microscopy of skin scrapings from a cutaneous lesion mounted in 10% KOH and Parker ink solution showing characteristic endosporulating spherules (sporangia) of Coccidioides immitis. The presence of spherules with endospores is diagnostic.	Tissue section showing typical endosporulating spherules of Coccidioides immitis Young spherules have a clear centre with peripheral cytoplasm and a prominent thick walled. Endospores (sporangiospores) are later formed within the spherule by repeated cytoplasmic cleavage. Rupture of the spherule releases endospores into the surrounding tissue where they re-initiate the cycle of spherule development.

Clinical signs are nonspecific; however, cats from the endemic area with signs of systemic disease should be suspected of being infected. Cytologic specimens may be sufficient to make a diagnosis. These may be obtained by aspiration of lung parenchyma or lymph nodes, impression smears from draining tracts, or bronchoalveolar lavage. Negative findings do not rule out the disease. The associated inflammatory response is granulomatous. Routine in-office stains sometimes fail to stain the organism. Special stains may be requested from commercial diagnostic laboratories.

As with cytological specimens, special stains may be required to identify the organism in tissue. Grocott-Gomori methanamine silver nitrate and periodic acid-Schiff stains are often useful. The laboratory should be alerted when coccidioidomycosis is a differential diagnosis.

On radiological examination, hilar lymphadenopathy, interstitial lung disease, and pleural disease may be present. Infected bone may have osteoproductive or osteolytic lesions.

Recent studies suggest that serological testing may be more useful than previously thought. Precipitin antibodies and complement-fixing antibodies were found in most cats tested in one study. False negatives may occur. At present, serology is a questionable means of detecting progression of disease and response to therapy.

The organism does not typically exfoliate in large numbers, so identification may require a careful microscopic search.

Imidazole drugs: The potential value of itraconazole in treating this disease remains to be determined, Itraconazole is safely dosed at 5 mg/kg PO bid and should be given with a meal, an acid environment in the stomach enhances absorption of the drug. Previous efforts to treat with ketoconazole have met with limited success for long-term resolution of the disease. The imidazole drugs at present are considered fungistatic, not fungicidal.