Histoplasmosis is the second most common systemic fungal disease in cats, and is found primarily in the central United States, including the Mississippi, Missouri and Ohio river valleys. Histoplasmosis is most frequently reported in the states of Oklahoma, Texas, Virginia and Louisiana, though it has been found on every continent except Antarctica. Cats are infected by inhaling, or less commonly ingesting, infectious spores of the fungus Histoplasma capsulatum, found in soil contaminated with bat and bird feces. Though outdoor cats are more likely to encounter this type of contaminated soil, histoplasmosis is found in both indoor and outdoor cats. Possible exposure to infection for indoor cats includes potted plants and unfinished basements, and cats with Feline Leukemia Virus (FeLV) infection are slightly more likely to develop histoplasmosis than FeLV-negative cats.

Clinical signs of feline histoplasmosis are generally vague and non-specific, including lethargy, weight loss, anorexia, and fever. Respiratory signs such as cough or trouble breathing are also common, and enlarged lymph nodes, skin masses, and ocular changes can occur less frequently. The disease is usually diagnosed by visualizing fungal segments in tissues under a microscope. Some blood and urine tests are available, but these can have a high false-negative rate and can fail to differentiate histoplasmosis and other fungal infections, such as blastomycosis. Treatment for feline histoplasmosis involves oral antifungal therapy, generally with itraconazole or fluconazole, for an average of 6 months. In one study this treatment was about 66% successful, but prognosis varies based on the extent of the disease.

Last updated 2021