Scrub Typhus

Scrub typhus, a disease caused by the rickettsial organism, Rickettsia tsutsugamushi, has had many animals used in the process of trying to develop a human model and a model to use for the development of a vaccine. Animals used include monkeys, mice rabbits, rat, guinea pigs, gerbils, and dogs. Hamsters, chickens, goats, horses, cats, calves and pigeons have also been shown to be susceptible. The selection of a species for use as an animal model for human Scrub typhus has not been clear cut. Approximately 45% of wild-caught cynomolgus monkeys have antibody to R. tsutsuhamushi. However, wild-caught silvered leaf monkeys, due to arboreal nature, rarely have antibody. Based on studies completed thus far, the cynomolgus monkey is probably the monkey model of choice. The mouse is the animal of choice for the isolation of the agent and for most other experimental studies. Pathological manifestations of Scrub typhus at necropsy are not striking. The course of death is generally equally attributed to circulatory failure, secondary pneumonia or encephalitis.