Pathogenesis

Histoplasmosis is an infection caused by breathing in spores of a fungus often found in bird and bat droppings.

The infection is most commonly spread when these spores are inhaled after taking to the air, such as during demolition or cleanup projects.

Lungs are the initial site of infection which occurs after inhalation of spores where Histoplasma converts to a yeast form at body temperature
Majority of infections are asymptomatic in immunocompetent hosts but clinical disease is common in immunosuppressed patients
Pulmonary disease is most common; however, as part of disseminated disease gastrointestinal histoplasmosis may cause diarrhea, bleeding, pain, nausea, vomiting, flu-like symptoms or obstruction
Large bowel is affected in approximately half of patients with gastrointestinal histoplasmosis and infection of multiple sites is common
Ulcers, nodules, hemorrhages, masses or lymphoid hyperplasia may be present and histopathologic findings include lymphohistiocytic infiltrates, the presence of variable numbers of primarily intracellular small yeast within histiocytes, lymphoid hyperplasia, infiltrates of eosinophils, neutrophils, necrotizing granulomas or plasma cells; importantly well formed granulomas are uncommon in disseminated disease

Itraconazole may be used as prophylaxis for immunosuppressed patients; disseminated disease is treated with amphotericin

Soil contaminated by bird or bat droppings also can spread histoplasmosis, putting farmers and landscapers at a higher risk of the disease.

In the United States, histoplasmosis commonly occurs in the Mississippi and Ohio River valleys, though it can occur in other areas, too.

It also occurs in Africa, Asia, Australia, and in parts of Central and South America.