Histoplasmosis

Half million cases per year in the U.S.

Endemic infection in most of the U.S.

H.capsulatum is a dimorphic fungus highly endemic in the Ohio-Mississippi valleys.

Grows as a mold in the environment and a yeast at body temperature.

Mold spores are dispersed by soil disturbance, and can be inhaled by humans.

Following inhalation spores reaching lung temperature convert into budding yeast.

Mold colonies have septate hyphae and large round thick walled macroconidia, with cylindrical surface projections.

40 million people in the U.S. are infected with 500,000 new cases each year.

Ordinarily causes self-limiting or slowly progressive chronic infection.

Causes a latent infection that can reactivate years after a patient has left an endemic area, especially when CD4 T lymphocyte count falls below 100 per cubic millimeter.

With disseminated disease adenopathy is almost always present.

Patients with disseminated disease present with fever, weight loss, respiratory symptoms, hepatosplenomegaly, anemia, lymphadenopathy and sepsis.

A complication of long-term steroids, AIDS, leukemia and lymphoma and other immunocompromised states.

Occurs in bout 5% of patients with HIV/AIDS in areas where the process is endemic like the Central U.S., particularly the Mississippi, Ohio and Missouri river valleys, the Caribbean, Central and South America.

Associated with the use of low-dose methotrexate.

Not transmissible from person to person contact.

Infections caused by spores from sources such as soil, bird roosts, and buildings contaminated with bird or bat droppings.

Occurs by inhalation of airborne conidia.

The mycelial form is found in soil and they produce the spores which when become airborne can be inhaled into the alveoli of the lung.

Immunoassay for urinary enzyme Histoplasma capsulatum antigen is highly sensitive for the diagnosis.

Amphotericin B or one of its lipid-bound formulations is recommended for immunocompromised and/or seriously ill patients.

Itraconazole is the treatment of choice for infected patients with mild to moderately severe symptoms.

Fluconazole not as effective as itraconazole and more likely to be associated with development of drug resistance.

Achieves excellent concentrations in the CNS and is used for maintenance therapy after amphotericin B or its formulations for Histoplasma meningitis.

Disseminated infection is associated with fever, weight loss and fatigue.

Disseminated disease occurs in up to 30% of patients with AIDS and is AIDS defining disease in up to 50% of those patients.

Up to 12% of AIDS patients with disseminated histoplasmosis have GI involvement, most commonly in the colon.

70% of patients with disseminated infection have chest x-ray abnormalities of interstitial or reticulonodular infiltrates.

The most sensitive rapid test is an analysis of urine for Histoplasma antigen, which is positive in 90% of patients with disseminated disease.

Serologic tests for H capsulatum positive in 70-80% of patients with disseminated disease.

Fungal blood cultures should be performed in all patients suspected of having disseminated disease, and 50-70% of such cultures will be positive.

Common cause of splenic calcification.

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