By: Paula Plummer, LVT, VTS (ECC, SAIM)

TVMA Member
College Station, TX

Published March 2017

What Is Histoplasmosis?

Histoplasmosis is a fungus that is caused by Histoplasma capsulatum. Both humans and animals can contract the fungus, and it is the second most common systemic fungal disease diagnosed in cats. Both dogs and cats of any age, species or breed can become infected. It is considered infectious but not zoonotic, meaning the disease is not transmissible to people. Histoplasmosis is transmitted by inhalation of the microconidia, which are small enough to reach the lower respiratory tract on inhalation. The incubation period is 12-16 days. After inhalation, the microconidia convert to the yeast phase and bud (reproduce). The yeast is infused in the body’s circulation and undergoes replication. Infection spreads throughout the body due to circulation and the lymphatic system.

Clinical Signs

Most dogs and cats will have a wide range of clinical signs, including mental depression, weight loss, fever, anorexia, pale mucous membranesepithelial tissue that secretes mucus and that lines many body cavities and tubular organs including the gut and respiratory passages., coughing, respiratory distress, facial abnormalities and rapid respiratory rates.

Diagnostic and Treatment Options

Veterinarians usually diagnose the disease by ultrasound-guided aspiratesdraw (fluid) by suction from a vessel or cavity of infected organs. The fungus can also be seen on bone marrow, the lungs, spleen, urinary bladder, liver and/or lymph node aspirates. After aspirates are obtained and prepared properly, the yeast must be identified to obtain a definitive diagnosis. Antigena toxin or other foreign substance that induces an immune response in the body, especially the production of antibodies tests are run on blood or urine, but the results are not as reliable as a positive identification on cytology.

Prognoses vary, depending on the extent of the disease. In the most severe and critical phase of the disease, supportive therapy is necessary for successful treatment. Most patients are dehydrated and not eating, so fluid therapy, nutritional support with feeding tubes and antifungal drugs will get them on the road to recovery.

Treatment of histoplasmosis with antifungal medications is the mainstay of treatment. It is an oral medication that needs to be given up to one year. Routine exams and lab work will need to be performed on your pet to monitor his or her recovery. Every patient is different, so the exact time it will take for your pet to fully recover is unknown.

Preventative Measures

The fungus flourishes and accelerates in soil containing nitrogen-rich organic matter, which is found in bird and bat feces. Keeping pets away from those areas in the environment will help reduce the chances of them becoming infected. However, no preventative is 100 percent, and any pet can contract histoplasmosis in endemic areas.

If histoplasmosis were left untreated, it would be fatal to your pet. If you are concerned about your pet being infected, seek veterinary medical attention immediately.

Histoplasmosis can survive in almost any environment but thrives in warm, humid, moist areas, so it is common in the state of Texas. It has been reported on every continent except Antarctica, but it is most prevalent in the Americas, India and southeastern Asia. In the U.S., 31 states have reported the fungus. Most clinical cases are reported in the Midwestern and southern regions.

Paula Plummer, LVT, VTS (ECC, SAIM), is a licensed veterinary technician who graduated from Murray State College in Tishomingo, Oklahoma. Ms. Plummer works in the Feline Internal Medicine Department at the Texas A&M University Veterinary Teaching Hospital in College Station, Texas.

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