Histoplasmosis

Sometimes called Darling’s disease, histoplasmosis is caused by a fungus, Histoplasma capsulatum. The fungus lives in dirt, especially dirt that is mixed with bird or bat droppings.

The fungus causes a short-term lung infection usually. However, the disease can spread to other parts of the body (disseminated histoplasmosis). In that form, it can be fatal. Even mild cases of histoplasmosis can cause a serious eye disease called ocular histoplasmosis syndrome that causes blindness.

Symptoms

Symptoms of histoplasmosis can range from being unoticeable to being fatal. They vary greatly depending on the form of the disease.

When histoplasmosis affects only the lungs, the signs show up in five to 18 days after being exposed to the fungus. It usually takes 10 days for the symptoms to appear.  They include tiredness, fever, chills, chest pains and a dry cough. When the lung infection is ongoing rather than short-term, histoplasmosis is like tuberculosis.  This form appears mostly in people who already have lung disease.  It can develop over months or even years. It leaves scars on the lungs.

The widespread version of the disease -- disseminated histoplasmosis – is serious.  It can affect all of the body’s organs, the blood and the linings of the brain. The liver and spleen become enlarged. Sores develop in the mouth or the digestive tract. Other symptoms include fevers, headache, neck stiffness or joint pain.  There may be sores, lumps or rashes on the skin.  With treatment, a person with disseminated histoplasmosis will die. 

Causes

People get histoplasmosis when they breathe in dust that has the fungus. The fungus is most likely to be found in dirt that has been mixed with bat and bird droppings. The histoplasmosis fungus in the United States is mostly found in the Midwestern and southeastern states and along the Ohio and Mississippi river valleys. It is, however, found around the world.

The fungus produces spores.  These are hardy forms of the fungus that can live in the environment for a long time. When the spores get into the lungs, they turn into yeast. It is the yeast that causes histoplasmosis.

The disease is not spread from person to person. If plants fertilized with bat droppings are then burned, the smoke becomes infectious. 

Risk Factors

Anyone can get histoplasmosis. Men are more likely to develop the chronic, lung infection form of the disease.  This is especially so if they already have chronic lung disease. The widespread form occurs mostly in people with weakened immune systems.  This includes babies, young children and people with HIV infection or cancer. 

Prevention

Avoid areas where the fungus might be growing.  This includes old chicken houses, in caves or other areas where bats live and around the roosts of starlings and blackbirds. Avoid disturbing dust or droppings in areas where there is a possibility of contamination.  Dirt should be sprayed with water before it is disturbed.

When gardening or working in high-risk areas, wear a dust mask that covers the mouth and nose and disposable clothing.

Diagnosis

To diagnose histoplasmosis, a doctor will do a blood test or try to grow the fungus in the laboratory from a sample of blood, lung tissue, sputum, bone marrow or the fluid that surrounds the brain and spinal cord.  (This is called a culture.) Tests for signs of a protein that shows the body is fighting histoplasmosis infection may be done on samples of blood, urine or spinal fluid.

An X-ray will show distinct patterns in the lungs.

Treatment

Without treatment, eight out of 10 people with widespread histoplasmosis will die. With treatment, three out of four survive.
People at high risk of getting the widespread form of histoplasmosis will be treated with fungus-killing medicines. Persons with mild disease usually get better on their own. Severe cases of acute histoplasmosis and all cases of chronic and disseminated disease are treated with fungus-killing medicines.

A person with HIV who is infected with histoplasmosis is usually treated first with amphotericin.  This is a strong drug that can cause damage to the kidneys. This may be followed by treatment with itraconazole or ketoconazole.

Histoplasmosis can cause serious complications.  These include inflammation of the sac that lines the heart (pericarditis) and of the joints (arthritis). It can also lead to fibrosing mediastinitis.  This is a scarring in the chest that traps lymph nodes, the heart, the esophagus (which carries food from the mouth to the stomach) or the blood vessels that carry blood to and from the heart.  Another serious complication is mediastinal granuloma.  This is a swelling of the lymph nodes inside the chest. As they get larger, they can press on the esophagus or the blood vessels going to and from the lungs.