Histoplasmosis

Key facts

• Histoplasmosis is a fungal infection caused by Histoplasma capsulatum, a mold that lives in soil enriched by bird and bat droppings.
• Most infections are mild and self-limiting, but in people with weakened immune systems the fungus can spread beyond the lungs and become life-threatening.
• Mild to moderate disease is treated with an oral antifungal, usually itraconazole, for several months; severe or disseminated cases often need initial intravenous treatment in hospital before stepping down to oral therapy.
• Persistent fever, unexplained weight loss, or breathing difficulty after exposure to caves, old buildings, or bird roosts warrants prompt medical assessment.

Who is most at risk

Histoplasma lives in soil enriched by bird and bat droppings, particularly around caves, old buildings, and dense bird roosts. People who explore cave systems, work in construction or demolition, or clean out old buildings face a recognised risk of inhaling spores. People living with HIV, transplant recipients, and anyone on long-term immunosuppressive therapy are far more likely to develop severe or disseminated disease once infected.

How antifungals address the infection

Mild to moderate histoplasmosis is typically treated with an oral antifungal for several months. Itraconazole is the standard agent for non-severe disease and for maintenance therapy, working by disrupting the fungal cell membrane. Severe or disseminated cases usually require initial intravenous treatment in hospital before stepping down to oral therapy once the infection is under control.

When to see a doctor

If you develop persistent fever, unexplained weight loss, or breathing difficulties after visiting a cave or another high-risk environment, seek medical assessment promptly, particularly if your immune system is weakened.

This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.