17MB PDF - Association for Mexican Cave Studies

HISTOPLASMOSIS91In 1906 an organism, Histoplasma capsulatum, was discoveredand named; and the accompanying disease was called Histoplasmosis.It was originally thought to be a protozan but later proved to be afungus. Further studies of the organism did not take place until1934. Much research is needed before the fungus and its effects aare sufficiently understood.Histoplasmosis is very common in the Ohio and MississippiRiver Valleys and in the eastern and central United States. Thefungus lives in bird, especially pigeon and starling, dung andchicken dung as well as bat guano and other soils with high organiccontent. Indications are that it will not grow in dry, dusty soil.The fungus is circumglobal in distribution. It is estimated that30 million persons now living have had Histoplasmosis and one-halfmillion new infections occur yearly in the United States. The deathrate is very small, because all but a small percentage of thesepersons develop an effective degree of immunological resistance veryearly in the disease.Histoplasma ca~sulatum belongs to the group of fungi calledFungi ImperfectI.t is dimorphic, growing as a filamentous mold inthe soil and as a yeast in animal and human hosts. In the soil itsends out hyphae which produce chlamydospores. These are theinfecting agents. They are airborne and are distributed to the dryparts of the cave where they are picked up by inhalation. They getinto the lungs and germinate, producing a yeast-like asexual stagein which the fungus is in individual, small, spherical, budding,thick-walled cells 3 to 5 microns in diameter. These grow mainly inthe alveoli of the lungs, where they are frequently walled off byprotective calcifying agents; i.e. the same mechanism that wards offtuberculosis, though many people have positive tests for TB. Ifthis fails the yeast cells invade the spleen, liver, and bone marrowand can cause death.Infection is frequently recurring, usually in a mild form.Sometimes it spreads rapidly causing severe illness or death. Themajority of the infections remain entirely asymptomatic, and mostof the rest are mild, during which time an effective degree ofimmunological resistance develops. Most of these cases are neverdiagnosed as histoplasmosis, and spontaneous cure results with noneed for therapy other than general supportive measures. Even whenmore severe, the outlook is usually good. Symptoms appear withinfive to eighteen days after exposure.The mycosis is characterized by irregular fever, emaciation,leukopenia, anemia, and splenomegaly. There may also be papular orUlcerative skin and mucous membrane lesions. It is diagnosed bythe demonstration of the fungus in mucous membrane smears, in theblood system, in bone marrow, and by skin tests.Amphotericin B (Fungizone) is an antifungal antibiotic usefulin treatment of many mycotic infections. It is produced by a strainof strePto~ces nodosus. Fungizone is the most satisfactory treatmentfor h~toplasmosis. It is administered intravenously for anaverage of three months. Use of the drug, however, is obviouslylimited to severe cases.Barbara HershbergerAustin, Texas