What is Histoplasmosis?

Histoplasma capsulatum is a dimorphic fungus usually found in soil contaminated with bird or bat feces. It can change form depending on the temperature. In the outside environment, it typically grows as a mold but once inside the human body, it can form into yeast and mulitply in the lungs. Credit: Centers for Disease Control and Prevention

Histoplasmosis is a respiratory disease caused by a dimorphic fungus named Histoplasma capsulatum. It is prevalent in the Mississippi Valley of the United States, Central America, South America, Africa, Australia, and Asia. The microbe has two forms: it typically grows as mold in the outside environment and can form into yeast once inside the human body. The fungal pathogen is mostly found in soil contaminated with bat or bird feces.

People can get histoplasmosis by inhaling the fungal spores in the air. The disease cannot be transmitted from person to person. Only few individuals exposed to the fungal pathogen experience symptoms. The groups that are mostly affected are children, elderly, and people with weakened immune system.

Histoplasmosis is similar in many ways to that of tuberculosis in terms of the disease course. After inhalation by an individual, the spores enter the alveoli and engulfed by macrophages where it can survive and multiply. Lesions form from focal infections and can lead to calcification that is similar to the Ghon lesions of tuberculosis. Histoplamosis can have a secondary activation and become chronic just like tuberculosis along with spreading to other parts of the body such as spleen or liver.

Fever, headache, and weakness with some chest pain are some signs and symptoms of pulmonary histoplasmosis. Initial diagnosis include radiographs of chest and fungal cultures using Sabouraud’s agar. To detect the pathogen, Giemsa staining and direct fluorescence antibody staining can be used. Other diagnostic tests include histoplasmin sensitivity and complement fixation assay. In most cases, these infections are controllable even without the use of antifungal medications. However, in chronic stages, antifungal medications such as amphotericin B can effectively treat the disease. In immunocompromised patients where the disease is more serious, itraconazole may be effective.

Source:

OpenStax Microbiology. Histoplasmosis. Accessed November 23, 2019

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