Indirect immunofluorescence antibodies in natural and acquired Rickettsia tsutsugamushi infections of Philippine rodents.

Antibodies against Rickettsia tsutsugamushi detected by the indirect fluorescent-antibody test (IFAT) were present in most rats trapped from a human focus of scrub typhus in the Philippines. Rickettsiae were isolated only from rats with positive IFATs. Naturally acquired antibodies persisted for at least 11 months, and antibodies resulting from experimental infections of rats persisted for at least 7 months. A common Philippine rodent, Rattus mindanensis, tolerated experimental infections with both local and standard Karp strains of R. tsutsugamushi, and such infections always produced a positive IFAT.