Acute pulmonary histoplasmosis is a respiratory infection caused by inhaling the spores of the dimorphic (exists in two forms) fungus Histoplasma capsulatum. This fungus is commonly found in the soil along river valleys. It gets into the soil mostly from bird and bat droppings. The fungus exists as a mold in nature and transforms into a yeast in the human body.

Histoplasmosis is caused by a fungus found in the Central and Eastern United States, Eastern Canada, Mexico, Central America, South America, Africa, and Southeast Asia.

Most patients have no symptoms (asymptomatic) or experience a mild flu-like illness and recover uneventfully. Acute pulmonary histoplasmosis may occur in an epidemic, which is a widespread local outbreak of disease. Progressive and chronic disease can also occur, particularly amongst those with impaired immune systems, such as people with HIV.

Risk factors include travel to or residence in the Central or Eastern United States near the Ohio and Mississippi River Valleys), and exposure to the droppings of birds and bats. Having a compromised immune system increases a person's risk for more frequent, symptomatic (causing symptoms), and severe disease.

Most patients with acute primary infection have very mild symptoms. The most common symptoms are:

• Fever
• Chills
• Shortness of breath
• Muscle aches and stiffness
• Cough
• Rash
• Joint pain and stiffness

In the very young, elderly, or immunocompromised, more severe symptoms can occur. They include serious lung infections, severe joint pains, and inflammation around the heart.

• Chest x-ray (might show obvious lung infection or pneumonia)
• Sputum culture (often not positive)
• CBC (complete blood count)
• Bronchoscopy (usually only performed in patients with severe disease or abnormal immune systems)
• Antibody tests for histoplasmosis (serologies)
• Biopsy of site of infection
• Chest CT scan
• The most common test to diagnose histoplasmosis in clinical use is detection of urinary histoplasmosis antigen. This test is especially useful in patients with severe disease

Treatment for acute pulmonary histoplasmosis is usually not necessary. Amphotericin B, an antifungal medication, may be given for severe cases. Treatment with amphotericin B is given for 2 weeks to children under 2 years of age, because they are at risk for developing disseminated histoplasmosis. If additional therapy is needed, or if the disease is not serious enough to require intravenous (IV)therapy, itraconazole may be given.

When severe and progressive, the illness may last for 1 to 6 months, but is rarely fatal. It can be a very serious illness in people with weak immune systems, such as those who have had bone marrow or solid organ transplants, or those who have AIDS.

Histoplasmosis can spread to other organs through the bloodstream (dissemination). This is usually seen in infants, young children, and immunosuppressed patients.

Acute histoplasmosis can progressively worsen or can become chronic histoplasmosis.

Call your health care provider if symptoms of histoplasmosis occur, especially if you have an immune disorder, have been recently exposed to bird or bat droppings, or if you are being treated for histoplasmosis and new symptoms develop.

Avoid contact with bird or bat droppings if you are in an area where the spore is coommon, especially if you are immunosuppressed.