AimTo evaluate the efficiency of gene amplification technique used in detecting the specimens colleted from rodents to identify natural epidemic foci of scrub typlus. MethodMice of Kunining strain were experimentally infected by a certain amount of Oriential tsutsugamushi. The specimens of blood clot and spleen from the infected animals were detected by nested polymerase chain reaction(nPCR)specific to O. T sutsugamush at the day 3,6 and 9 of post-infection. Then the technique was used for detection of samples collected from field. As an infected index ,the specimen was considered to be positive only if a 88-bp DNA fragment from Sta 58kDa gene of O. Tsutsugamushi could be produced. According to the study ,it was estimated whether or not that the sampling area is a natural epidemic focus of the disease. ResultsThe specimens of both blood clot and spleen from the mica at day 3 of post-infecction showed negative to the specific PCR product ,but positive when detected at day 6 and hereafter. Of 111 spleen samples from the field collections in the northwest of Fujian province,one was positive, and another positive sample was in the 29 blood clots from Jiangxi province. It is demonstrated that these areas have been the natural epidemic foci. Conclusion The nPCR method is of highly sensitive and specific to be used in the etiologic study on specimens from field rats.