Histoplasmosis in Cats: An Overview
Definition of Histoplasmosis in Cats
Histoplasmosis is a systemic fungal infection that can affect companion animals and people. It is caused by exposure to the soil-dwelling fungus, Histoplasma capsulatum.
How Histoplasmosis Affects Cats
Histplasmosis can affect cats of any breed, age or gender, although typically it is seen in younger animals. Early on, infected cats become depressed, have difficulty breathing, become anorexic and lose weight. The respiratory tract rather than the gastrointestinal tract is the target of this infection in cats. They also can develop a cough, lameness, abnormal eye redness, eye swelling and discharge, and diarrhea. As the fungus disseminates throughout the cat’s body, the liver, spleen and bone marrow can become affected. Enlarged lymph nodes, a high fever and significantly increased respiratory effort also are common. Histoplasmosis can be fatal in a short matter of weeks. Fortunately, this infection can be diagnosed by fungal culture (diagnosis is not necessarily simple) and usually can be treated successfully with an extended course of oral anti-fungal medications.
Cause of Histoplasmosis in Cats
Histoplasmosis is caused by exposure to Histoplasma capsulatum. This fungal organism is found in moist soils organically rich in bird and bat manure and is endemic in many temperate regions of the world. In the United States, it is most commonly found in the Mississippi, Missouri and Ohio River basins, although it has been reported in Tennessee, Texas, California, the southeastern states and the Great Lakes region, as well. Cats become infected by either inhaling (or less commonly, ingesting) fungal spoors, which infiltrate the lower airways (or intestinal lining), germinate and become yeast, reproducing by a process called “budding.” The cat’s immune system responds to the infection by mobilizing certain cells that envelop the yeast, which continue to replicate. At this point, affected cats typically show only respiratory signs. However, over time, the fungi can disseminate throughout the cat’s body through either the lymphatic or general circulatory systems.
The best way to prevent cats from developing this disease is to prevent their exposure to the fungal spores. This entails avoiding outdoor activities in known endemic areas (temperate climate with moist soil rich in organic material containing bird and/or bat feces). There currently is no vaccine available against Histoplasma capsulatum.
The prognosis for cats with histoplasmosis ranges from good to guarded depending upon how far the disease has progressed at by the time it is diagnosed. Again, with prompt recognition of clinical signs and proper treatment, the infection almost always can be resolved successfully.
While companion animals and people are susceptible to infection from this microorganism, it is not known to spread from animals to people, or vice versa. However, people can inhale the organism from the same source and at the same time as their cats or dogs, and can become simultaneously infected.