Histoplasmosis (also known as Darling’s disease) is a systemic fungal disease that can range in severity from symptom-free to minor self-limited to life threatening illnesses. Infection is quite common but clinical disease is not.

Histoplasma capsulatum/CDC
Histoplasma capsulatum/CDC

The fungus that causes histoplasmosis is Histoplasma capsulatum. This is a dimorphic fungus that grows as a mold in the environment and soil and as yeast in human and animal tissue.

The disease is seen in many areas of the world to include the Americas, Africa, eastern Asia and Australia. It is rarely seen in Europe.

In the United States, H. capsulatum is endemic in the Mississippi River valley, the Ohio River valley and along the Appalachian Mountains.

The fungus is found in soil with undisturbed bird droppings, in old chicken houses, in bat caves and around starling, blackbird and pigeon roosts. The fungus multiplies in bird droppings and bat guano.

Disturbing these contaminated areas and the wind can easily transport infectious fungal particles. Infections in humans and animals are typically due to inhalation of the airborne fungus. It is not transmissible person to person.

Animals that can get histoplasmosis include dogs, cats, cattle, horses, skunks and possums among others.

The majority of infections (90-95%) are asymptomatic or self-limiting flu-like illness. Others may have symptoms associated with active pulmonary disease; night sweats, cough, fever and weight loss.

In some people, the fungus disseminates through the bloodstream to the spleen, liver, kidneys, mouth, eyes, or central nervous system.

Disseminated histoplasmosis is especially dangerous in immunocompromised individuals and can result in a rapidly fulminant disease. Over 50% of AIDS patients from endemic areas develop histoplasmosis.

Symptoms typically appear within 10 days but may be shorter in heavy infections.

Histoplasmosis can be diagnosed by chest radiographs and laboratory culture. A biopsy culture of the affected organ and blood cultures are best.

The Infectious Diseases Society of America (IDSA) outlines treatment guidelines in the following Clinical Infectious Diseases.

Histoplasmosis made the news back in 1997 when rock legend Bob Dylan was stricken with a fungal infection of the sac surrounding his heart. He was treated successfully and released from the hospital. Dylan was quoted as saying “I’m just glad to be feeling better. I really thought I’d be seeing Elvis soon.”