Histoplasmosis

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at June 25, 2016
StartDiseasesHistoplasmosis

Histoplasmosis (also called spelunker's lung or caver's disease) is a health condition that is caused by a fungal infection. Though not everyone who breathes in these fungal spores gets sick, people with weakened immune systems can develop severe symptoms and life-threatening complications.

Contents

Definition & Facts

Histoplasmosis occurs when people breathe in microscopic Histoplasma spores that are normally present in soil contaminated with bird and bat droppings. It is called "spelunker's lung" or "caver's disease" because people are more likely to come into contact with the spores in these damp, underground areas.

Most people who breathe in these spores do not show any symptoms, but some people get an infection from the histoplasmosis and start to have lung issues. Though many people with histoplasmosis end up getting better without medical intervention, if the infection travels from the lungs to other organs, it can potentially be life-threatening.

Among young children and people with immune systems that are weak, histoplasmosis can spread from the lungs to other parts of the body. This type of histoplasmosis is called disseminated histoplasmosis, and it happens to about 1 in 2,000 people with histoplasmosis.

Symptoms & Complaints

It is quite common for a person to have histoplasmosis without even realizing it, since the symptoms are either very mild or not present at all. Nevertheless, the first symptoms of the fungal infection will show up between three to 17 days after the initial exposure to Histoplasma spores. It typically starts with a mild fever that gradually progresses.

Since the lungs are the primary affected area, a persistent cough and chest pain are also common among histoplasmosis patients. People who are infected with histoplasmosis may also experience extreme exhaustion, a headache, chills, and aching pains throughout the body. Disseminated histoplasmosis can cause rapid weight loss, blood clots, low blood pressure, renal failure, and encephalopathy. If left untreated, it is almost always fatal. 

Causes

The primary cause of histoplasmosis is the Histoplasma capsulatum fungus. The reproductive cells of this fungus are very lightweight, so they are easily inhaled. Certain conditions are more likely to cause a Histoplasma infection. When soil is damp and filled with organic material, the fungus grows rapidly.

It typically grows in areas filled with droppings from bats or birds, so it is particularly common in areas with caves or large bird populations. This fungal infection is most common in the Ohio and Mississippi River valleys, but it is also found in a few locations in Africa, Asia, Australia, Central America, and South America.

People are most likely to become infected with Histoplasma spores if they are breathing heavily when dirt or soil is disrupted. Therefore, it is particularly common among miners, farmers, construction workers, and people exploring caves. It can also occur at farms that raise chicken or other poultry.

Histoplasmosis cannot be spread between humans, so it is not contagious. It can only be caused by actually breathing in spores from the fungus itself. Since disseminated histoplasmosis only happens among people with very weak immune systems, having HIV/AIDS makes it far more likely for a person to develop this extremely severe complication.

Diagnosis & Tests

Because the symptoms are so varied, it can be very difficult to test for histoplasmosis. It is often misdiagnosed as a flu or some type of respiratory illness at first. Normally, a simple physical examination is not enough to tell if a patient has histoplasmosis. There are tests that can be done to determine the presence of histoplasmosis, so doctors often attempt to diagnose histoplasmosis with these tests if the patient has recently been in any area where the Histoplasma fungus is likely to grow.

Most tests work by looking for histoplasmosis antigens in either blood samples or urine samples. Urine antigen tests are typically seen as the fastest and most effective test for histoplasmosis, but some tests can take up to six weeks to confirm the diagnosis.

Lung sputum samples or biopsies from infected organs may occasionally be used to look for histoplasmosis too. There are also a few types of skin tests that can show if a person has been near Histoplasma, but skin tests do not actually confirm that a person has histoplasmosis.

Treatment & Therapy

For most people with a healthy immune system, histoplasmosis goes away on its own without any extra medical treatment. Some people may benefit from over-the-counter pain relievers to deal with histoplasmosis symptoms, but typically no medication is prescribed. However, if a person is already immunocompromised, a doctor may recommend that they begin taking antifungal medications to prevent disseminated histoplasmosis from occurring.

In rare cases, histoplasmosis does not go away, resulting in chronic histoplasmosis. Both chronic histoplasmosis and disseminated histoplasmosis always require antifungal medications. The normal treatment method starts with intravenous antifungal medications such as amphotericin B.

Other antifungals that patients may take include itraconazole, posaconazole, fluconazole, or voriconazole. Patients may take these antifungals orally until all signs of histoplasmosis are gone. Extremely severe cases may require up to a year of regular medication, but most people dealing with chronic or disseminated histoplasmosis are cured between six weeks to three months after beginning treatment.

Prevention & Prophylaxis

The most effective form of histoplasmosis prevention is entirely avoiding areas with contaminated soil. People who are concerned about histoplasmosis, particularly immunocompromised people, should not enter caves or go to places that raise birds.

If it is impossible to avoid areas with potential Histoplasma contamination, a person can wear a mask that filters out any airborne organisms as they breathe. Spraying down soil with water before working with it also helps to prevent histoplasmosis because it keeps the fungal spores from floating through the air.