Introduction

Histoplasmosis is a systemic fungal infection that can affect companion animals and people. It is caused by exposure to a soil-dwelling fungus called Histoplasma capsulatum. This organism is found in soils organically rich in bird and bat manure and is endemic in many temperate regions of the world, including many areas of the United States. Cats infected with this organism often display signs of disseminated histoplasmosis, a form of the disease which occurs when the fungus invades multiple tissues and organ systems.

Symptoms of Histoplasmosis in Cats

There is no known feline breed predilection for contracting this infection. Importantly, many infected cats never develop outward signs of disease.

Most clinically affected cats are less than 4 years of age, and according to some reports females may be overly represented. Cats are affected primarily in their respiratory tract, but bone, bone marrow, liver, spleen, skin and lymph nodes can also become involved. Cats initially show nonspecific signs of the infection, such as depression, respiratory difficulty, inappetence and weight loss. Cats also can develop a cough, lameness, abnormal eye redness, eye swelling and discharge, and diarrhea. Cats normally do not show the significant gastrointestinal involvement that dogs do. As the fungus disseminates throughout a cat’s body, the liver, spleen and bone marrow may become involved. Enlarged lymph nodes, a high fever and significantly increased respiratory effort typically are found upon physical examination by the attending veterinarian.

If you notice any of the above signs in your cat, especially if you live in a high-risk geographical area, take your cat to a veterinarian as quickly as possible. Histoplasmosis can be fatal if treatments are not begun promptly. Fortunately, this fungal infection can be diagnosed through fungal culture (although diagnosis is not simple) and usually can be treated successfully with an extended course of antifungal oral medications.