A histoplasmosis infection usually has a gradual onset with chronic, mild symptoms. In rare cases, the infection will be acute with rapid develop in multiple organs. Left untreated, this type of infection can become fatal in two to three weeks. Acute histoplasmosis often disseminates into a systemic disease affecting the gastrointestinal tract, spleen, liver, lymph nodes and on occasion, the eyes. The infection is much more difficult to treat when it has reached this state and may lead to death. Veterinary treatment should be sought as soon as symptoms begin to show. 

Histoplasma capsulatum is a fungus that grows in decomposing organic material. It releases spores into the air to spread. When a cat inhales these spores, the particles enter the respiratory system. These particles are small enough to reach the lower respiratory tract. The presence of these fungal spores creates an infection in the cat’s lungs. In a healthy cat, the infection may stay within the respiratory system, but a cat who is under two years of age or has immune deficiencies may experience an infection that spreads to other organs. 

The type and range of symptoms that develop with histoplasmosis in cats will have very much to do with the severity of the infection and whether or not it has spread to numerous organs. If multiple symptoms develop quickly, emergency veterinary attention should be sought. Symptoms to watch for include:

The Histoplasma capsulatum fungus can be found in 31 States across America. Areas near the Mississippi River carry greater risk of exposure. Outdoor cats come into contact with the fungus far more than indoor cats. All known causes are as follows:

Upon arrival to a veterinary clinic or animal hospital, you will be asked to provide your cat’s medical records. This can help identify any potential complications from a compromised immune system. The veterinarian will perform a complete physical examination of the cat. During this process, the vet will attempt to match your cat’s symptoms to the signs of histoplasmosis. X-rays will be taken of the chest and abdomen to see the progression of the infection and to determine which organs have been effected. These images will also show any fluid collection in the abdominal cavity.

A fine needle aspiration biopsy of infected tissue may be collected to identify the microscopic fungal organisms. Often a Wright’s-Giemsa stain will be used to differentiate the small organisms on a blood smear. Histoplasma capsulatum can be identified by its ovular shape. A fungal culture may also be performed with the collected tissue. Cytology of bone marrow is another method of diagnosing a histoplasmosis infection. Blood work will be run, including a complete blood count to reveal anemia in the cat, and a serum chemical profile to look for hypoalbuminemia (low levels of albumin in the blood.) Urinalysis may also show the spilling of protein into the urine.

In very mild cases of histoplasmosis, treatment may not be deemed necessary, however most veterinarians prescribe treatment as a preventative measure to ensure the infection does not progress. If symptoms are severe or if the cat has a deficient immune system, immediate treatment should be sought.

Most cats who have been diagnosed with histoplasmosis will receive a long course of treatment with oral antifungal medication. Medications such as fluconazole and itraconazole are the preferred prescription, with ketoconazole being a less expensive but potentially more toxic alternative. In very severe infections, amphotericin B may be prescribed, but regular monitoring of urine will be needed to look for signs of toxicity. Treatment generally lasts from four to six months.

Cats suffering from multiple organ infections may need hospitalization to stabilize their organ function. Oxygen supplementation and antibiotic administration may be needed during this time.

Antifungal medication is successful at ridding histoplasmosis in most instances. You will have to bring the cat to the veterinarian once a month during treatment for assessment and dosage adjustments. Antifungal medication can produce adverse side effects. If the cat is refusing to eat, the dose may need to be reduced. Medication should be administered until the cat has been symptom-free for one month. The cat will need two more check-up appointments, one at three months symptom-free and one at six months, to test for organism presence.

Do all you can to keep your cat out of infected environments to prevent re-exposure to the fungus. Keeping your cat indoors may be the best way to ensure your cat does not contact Histoplasma capsulatum. Change any indoor plant soil to purchased topsoil from a fungus-free area. Most cats do make a complete recovery from histoplasmosis. It should be noted that if the infection progresses to the point of affecting the central nervous system, prognosis is guarded although recovery is still possible.