Fungal Infection (Histoplasmosis) in Cats

Many cats can completely clear a histoplasmosis infection and remain asymptomatic. Prognosis is good if treatment is started shortly after infection. Once the fungus disseminates throughout the body, the prognosis is guarded. Any cat that is exhibiting a reduction of appetite, weight loss, or difficulty breathing needs to be examined by a veterinarian as soon as possible.

Histoplasmosis is a rare, potentially fatal infection caused by the fungus Histoplasma. The fungus can be found worldwide and is more prevalent in India, Southeast Asia, and the Americas. Histoplasmosis is endemic in the Ohio, Mississippi, and Missouri River Valleys.

Both indoor and outdoor cats are susceptible to histoplasmosis.

Some felines may be unable to completely eliminate the fungus, which results in a dormant infection. Dormant infections can become active if the cat becomes immunocompromised.

Cats are more susceptible to Histoplasma infection than dogs. Histoplasmosis can affect any age of cat but is more common in cats under the age of 4 years. Persian cats seem to be more susceptible.

Histoplasma spore inhalation is the most common route of infection. Ingestion of spores is rare, but possible. After inhalation, the fungus replicates in the lungs and spreads through the body.

Histoplasma grows best in warm organic matter such as bird or bat droppings, soil, and decaying wood. Indoor cats can contract histoplasmosis and potting soil, soil in unfinished basements, or fungal spores brought in on footwear.

Symptoms of disseminated disease depend on which organs are affected.

Diagnosis of histoplasmosis is confirmed with blood work, diagnostic imaging, and cytology from infected tissues.

Treatment consists of antifungal medication and supportive care. Supportive care for severe cases includes oxygen therapy, antibiotics, a feeding tube, and IV fluids.

Cats continue treatment for at least one month beyond resolution of symptoms. Monthly physical exams and bloodwork are used for monitoring response to treatment. Monitoring also includes repeating X-rays periodically.

Symptoms occur 2-3 weeks after infection. Histoplasmosis can take several months to treat and it is common for cats to undergo treatment for at least six months. Prognosis for respiratory histoplasmosis is good if treatment is started prior to the illness spreading to the rest of the body. Cats with disseminated disease have a guarded prognosis.

Prevention involves avoiding environmental reservoirs for the fungus. Areas high in bird or bat droppings are a particularly important reservoir.

Histoplasmosis is not considered contagious, but the organism can theoretically be transferred through inoculation (i.e. accidental needle puncture).

Feline histoplasmosis is uncommon.

Typical treatment consists of:

• Antifungal medication
• Antibiotics for secondary infections
• Oxygen therapy
• Feeding tube placement
• IV fluid therapy