Histoplasmosis Infections in Indoor-only Cats in Non-Endemic Areas

Three clusters of feline histoplasmosis infection have been reported in indoor-only cats in the non-endemic states of Colorado, California, and Texas.

Description of cases

Colorado cluster

Three indoor-only cats living in a house near the Denver metro area became ill and died between April-May 2009. Their symptoms included anorexia and erratic behavior. Upon necropsy, a diagnosis of histoplasmosis was made based on histopathology for two of the cats, which was later confirmed by PCR conducted by the CDC Mycotic Diseases Branch laboratory. The remaining cat had a pneumonia-like pattern on X-ray. The home had no visible bird or bat infestation.

California cluster

Two indoor-only cats living in a home of 12 cats in Los Angeles County developed pulmonary symptoms in October 2009, and one of the cats died. Upon necropsy, a diagnosis of histoplasmosis was made based on histopathology. The diagnosis was confirmed by PCR conducted by the CDC. The surviving cat had a positive histoplasmosis urine antigen test. The ten other cats in the home had negative urine antigen tests. The two ill cats were the only long-haired cats in the home. The home was investigated and found to have many potential sources of mold, but no evidence of bird or bat guano. The cats' human owner had pulmonary symptoms, but her urine antigen test was negative.

Texas cluster

Three indoor-only cats living in a home of 12 cats in East Texas were found to have  histoplasmosis. The first cat became ill with pulmonary symptoms and decreased activity in 2006. Chest radiograph showed pulmonary lesions, and a needle biopsy of the lung revealed Histoplasma spp. The cat was started on antifungals and recovered within 60 days. The second cat became ill in 2007 and had an identical presentation and treatment course. The third cat developed a limp in the fall 2009, and was found to have a swelling of its carpus. Needle aspirate revealed Histoplasma spp. The third cat died despite antifungal treatment. The home was examined by a state veterinarian and found to be clean with no evidence of bird or bat infestation, and no cat-accessible indoor sources of soil.

Public health concern

While all of these cases represent feline cases, concern is raised because these indoor-only cats may be exposed to a source of histoplasmosis that could, potentially, also become a public health threat to their human owners. Public health practitioners, physicians and veterinarians who identify suspected or confirmed cases of histoplasmosis or histoplasma-like syndromes in cats or cat owners in nonendemic areas are encouraged to notify their respective state health departments.

Published: February 12, 2010

Source: Oregon State Public Health Veterinarian