ABSTRACT
H. capsulatum exists in nature as a mold (hyphae form) growing particularly well in soil mixed with droppings from bats or birds such as starlings or chickens. Chicken coops, caves inhabited by bats, or new construction sites on grounds formerly used as starling or blackbird roosts serve as prime resting sites for this fungus. Physical disturbance of these areas may cause aerosolization of the spores. Infection occurs when airborne
spores are inhaled and deposited in pulmonary alveoli. Conversion of the organism into the pathogenic yeast form then takes place with phagocytosis by macrophages and dissemination to lymph nodes and organs of the reticuloendothelial system (liver, spleen, and bone marrow). Low-level exposure in healthy persons generally results in asymptomatic or minimally symptomatic pulmonary infection in about 90% of those exposed. Heavier exposure may cause acute and at times severe pulmonary disease. Chronic pulmonary disease may occur in susceptible hosts with preexisting chronic lung disease. Progressive disseminated disease primarily occurs in individuals who are immunocompromised.
