Histoplasmosis

Summary

A disease caused by infection with a particular fungus, histoplasma capsulatum.

Alternative names

Darling's Disease.

What is this?

A fungal infection primarily affecting the lungs, which can sometimes spread elsewhere in the body, becoming disseminated histoplasmosis, which is a serious illness and can be fatal unless treated.

What causes this? A fungus which is found in most parts of the world, and is especially rife in some parts of the US, where skin tests show that as many as 80% of the inhabitants have been infected at some time in their lives, even if they may not have become noticeably ill. Normally, your immune system deals with the infection efficiently. The fungus grows in soil especially where it has been contaminated by bird and bat droppings. Thus it's more common around poultry farms, caves, and bird roosts. Infection generally occurs due to inhaling spores, which change their form when at body temperature. Birds themselves are not infected with histoplasmosis, as their body temperature is too high, but they carry the fungus on their feathers. It is not found among domestic pet birds.

What are its symptoms?

Within around a couple of weeks after exposure to the fungus, symptoms may appear, though a majority of those who become infested notice no symptoms or problems. Otherwise, in the acute phase, it produces flu-like symptoms. Chronic cases may resemble tuberculosis, and the disseminated form adversely affects multiple body organs, and can cause enlargement of lymph glands, and of the liver, spleen and adrenal glands. On healing, the infected areas may calcify. Histoplasmosis can also cause an eye infection, spreading there via the blood, and, by damaging the retina, can cause blindness.

Again, as with other infections, people with reduced effectiveness of their immune system, especially those with HIV infection, are much more susceptible to developing the most serious disseminated form of the infection. Symptoms include malaise, mouth and intestinal ulcers. Without treatment this form of the disease is fatal in around 90% of cases.

How is it diagnosed?

Samples of sputum, blood, bone marrow, and blood may be tested and cultured , as may be biopsies from ulcers or lymph nodes. The fungus may be slow to grow, delaying diagnosis by this means. Blood tests give more rapid results.

How is it treated?

Unnecessary in the common mild form. In severe and disseminated infections, treatment is with anti-fungal drugs, such as amphoteracin B, and itraconazole.

What is the prognosis?

For the mildest form, spontaneous cure is likely. For the most severe forms, careful treatment can be successful, but there is still a substantial death rate, and chronic lung disease is also possible.

When to call your doctor

If you may have been exposed to the fungus, and develop a chest infection.

How can it be prevented?

Avoid areas contaminated by bird and bat droppings. This is especially essential for people with any weakness of their immune system should avoid such areas of potential contamination and infection. Wearing a face-mask and spraying areas like chicken coops with water (to limit the release of spores into the air ) before working there, may reduce the risk.

Singer Bob Dylan was admitted to hospital with histoplasmosis in 1997, and had to cancel scheduled concerts.