Immune responses in bats following intranasal infection with Histoplasma capsulatum

Groups of bats (Artibeus lituratus) were infected by the intranasal instillation of a suspension of mycelia and spore particles of Histoplasma capsulatum containing either 10(4) or 10(6) viable units. Bats infected with the high dose had viable H. capsulatum in the lungs, liver, spleen and gut as early as 2 weeks post-infection. Complement-fixing antibodies to the organism were detectable 3 weeks after infection, whereas precipitating antibodies were not persent until 5 weeks. Significantly delayed hypersensitivity to histoplasmin was noted at 2 and 4 weeks after infection. By 9 weeks, delayed hypersensitivity had waned, while antibodies could still be demonstrated. The observation that bats are susceptible to respiratory infection with H. capsulatum suggests a mechanism by which the disease may be maintained within a colony. Delayed hypersensitivity appears to be a sensitive, but transient, indicator of active histoplasmosis in bats.