Histoplasmosis is a fungal infection caused by Histoplasma capsulatum. It primarily affects the lungs but may spread to other organs.

Histoplasmosis is a fungal infection that can occur almost anywhere in the world. In the United States, it is most common in the southeastern, mid-Atlantic, and central states.

The lungs are the point of entry for this infection. Histoplasma grows as a mold in the soil, and infection results from breathing in airborne particles. Soil contaminated with bird or bat droppings may have a higher concentration of histoplasma.

Histoplasmosis may have no symptoms. There may be a short period of active infection, or it can become chronic and spread throughout the body. Most patients with symptomatic histoplasmosis will have a flu-like syndrome and pulmonary (lung) complaints related to underlying pneumonia or other lung involvement. Individuals with chronic lung disease (e.g., emphysema, bronchiectasis) may be at higher risk of a more severe infection.

If the body responds to infection with extreme inflammation (irritation and swelling, with presence of extra immune cells in affected area), up to 10% of patients may have complications involving the skin, bones or joints, or the lining of the heart (pericardium).

In a small proportion of patients, histoplasmosis may be widespread (disseminated histoplasmosis), and involve the blood, meninges (linings of the brain), adrenal glands, and other organs. Very young or very old people, or those who have underlying immune disorders such as AIDS, are at higher risk for disseminated histoplasmosis.

Symptoms depend on the type of infection:

• Acute asymptomatic pulmonary (lung) histoplasmosis -- no symptoms
• Acute symptomatic pulmonary histoplasmosis:
  • Fever
  • Chills
  • Cough
  • Chest pain when breathing in

• Chronic pulmonary histoplasmosis:
  • Cough
  • Shortness of breath
  • Chest pain
  • Excessive sweating
  • Fever - may resemble symptoms of pulmonary tuberculosis and include coughing up blood (hemoptysis)
• Disseminated histoplasmosis:
  • Fevers
  • Headache
  • Neck stiffness
  • Skin lesions
  • Mouth sores
• Other histoplasma symptoms:
  • Joint pain
  • Skin nodules (lumps)
  • Rashes

The diagnosis of histoplasmosis depends on the suspected location of infection. Tests may include analysis of the organism in sputum, lung tissue, blood, cerebrospinal fluid (CSF), or bone marrow tissue, as well as antigen tests performed on blood, urine, or CSF.

In addition, certain abnormal findings may be seen in tissues, which may support the diagnosis of histoplasmosis.