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Histoplasmosis

Definition

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

Alternative Names

Ohio River Valley fever

Causes, incidence, and risk factors

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

Symptoms depend on the type of infection:

  • Acute asymptomatic pulmonary (lung) histoplasmosis -- no symptoms
  • Acute symptomatic pulmonary histoplasmosis:

Signs and tests

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.

Treatment

The main treatment for histoplasmosis is antifungal therapy. In the case of pulmonary histoplasmosis, this may include oral (taken by mouth) medicines such as itraconazole or ketoconazole. In some cases, long-term treatment with anti-fungal drugs may be used after treatment with amphotericin, in patients who are immunosuppressed (for example, people with AIDS).

Expectations (prognosis)

Prognosis depends on the clinical syndrome. Mortality is highest in disseminated histoplasmosis (up to 80% without treatment; decreased to 25% with treatment).

Complications

  • Fibrosing mediastinitis -- scarring in the chest that may entrap structures in the chest cavity:
    • Lymph nodes
    • Heart
    • Great vessels (the major blood vessels carrying blood to and from the heart)
    • Esophagus (food pipe)
  • Mediastinal granuloma -- enlarged chest-cavity lymph nodes, which may compress structures such as the esophagus and lung blood vessels

In individuals with weakened immune systems, disseminated disease may occur and involve the meninges (causing meningitis)

Side effects of medications (can be severe with amphotericin) are complications of histoplasmosis.

Calling your health care provider

Notify your health care provider if you live in an area where histoplasmosis is common, and you develop flu-like symptoms, chest pain, cough and shortness of breath. While there are many other illnesses that have similar symptoms, you may need to be tested for the possibility of histoplasmosis.

Prevention

Minimize exposure to dust in contaminated environments such as chicken coops and bat caves. Wear protective equipment such as masks if you work in these environments.

Review Date:9/5/2006
Reviewed By:D. Scott Smith, M.D., MSc, DTM&H, Chief of Infectious Disease & Geographic Medicine, Kaiser Redwood City, CA & Adjunct Assistant Professor, Stanford University. Review provided by VeriMed Healthcare Network.

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