Bat and Soil Studies for Sources of Histoplasmosis in Florida

An autochthonous case of histoplasmosis in a college student in Florida, the second case on record in the State, was the impetus for an investigation of the distribution of Histoplasma capsulatum in bats and their environment. The patient had explored a sinkhole cave that was inhabited by bats. H. capsulatum was isolated from one of 20 Myotis austroriparius collected from this cave. Examination of cave dwelling bats demonstrated this fungus to be present in 48 percent of the 170 bats of this species only. Bats from which H. capsulatum was isolated were collected in the vicinity of Floral City, Gainesville, Marianna, Newberry, Ocala, and Tampa, Fla. H. capsulatum was not isolated from the 101 Pipistrellus subflavus or 71 Tadarida cynocephala specimens studied. H. capsulatum was also isolated from 10 of 147 guano-enriched soil samples (6.8 percent) collected in nine bat caves. M. austroriparius, the only species found to be infected with H. capsulatum in Florida, is known to prefer caves with permanent pools of water and a relative humidity of 99 to 100 percent. It is suggested that the wet caves may tend to inhibit spore dispersal and thereby account for the low rate of histoplasmin sensitivity and the rarity of clinical histoplasmosis among native Floridians. Prolonged incubation up to 8 weeks increased the yield of H. capsulatum from bat tissue with 10 percent of the isolates not appearing until the fifth to eighth week.