Primary acute histoplasmosis in guinea pigs exposed to aerosolized Histoplasma capsulatum.

Guinea pigs were examined as a possible in vivo model for human histoplasmosis. Guinea pigs were exposed to an aerosol of viable microconidia and mycelial fragments of Histoplasma capsulatum generated in a Henderson apparatus. Colonization and infection of the lungs occurred, with subsequent involvement of the regional lymph nodes and reticuloendothelial organs. Cultural recovery of the fungus from the nasopharynx and bronchoalveoli was initially high, but decreased with time. The mean number of colonies recovered from the lungs gradually increased, reaching a peak at 2 weeks, with involvement of the regional lymph nodes. Extrathoracic dissemination to the liver and spleen occurred in only a few animals. After 4 weeks, all tissues except the cervical and tracheobronchial lymph nodes were culturally negative; all specimens were culturally negative after 8 weeks. Disappearance of H. capsulatum from tissues appeared to correlate inversely with the development of hypersensitivity as measured by skin test reactivity. Histopathological studies supported cultural results and were similar to those described for primary human and canine histoplasmosis.