Molecular detection of Orientia tsutsugamushi in ectoparasites & their small mammal hosts captured from scrub typhus endemic areas in Madurai district, India.

BACKGROUND OBJECTIVES: Scrub typhus, caused by Orientia tsutsugamushi present in small mammals harbouring the ectoparasites. A study was undertaken to detect the pathogen present in small mammals and its ectoparasites in the scrub typhus-reported areas.

METHODS: The small mammals (rodents/shrews) and its ectoparasites were screened for O. tsutsugamushi using nested PCR amplification of the groEL gene. Small mammals were collected by trapping and screened for ectoparasites (mites, ticks and fleas) by combing method.

RESULTS: All the chigger mites collected were tested negative for O. tsutsugamushi. Interestingly, adult non-trombiculid mites (Oribatida sp., Dermanyssus gallinae), fleas (Xenopsylla astia, X. cheopis, Ctenophalides felis and Ctenophalides sp.) and ticks (Rhipicephalus sanguineus, R. haemaphysaloides) screened were found to be positive for O. tsutsugamushi, which the authors believe is the first report on these species globally. Bandicota bengalensis with O. tsutsugamushi infection is reported for the first time in India. The O. tsutsugamushi groEL sequences from the positive samples were similar to the reference strains, Karp and Ikeda and phylogenetically clustered in clade IV with less evolutionary divergence. The blood samples of Rattus rattus, Suncus murinus and B. bengalensis collected from this area were tested positive for O. tsutsugamushi; interestingly, the sequence similarity was much pronounced with their ectoparasites indicating the transmission of the pathogen to host or vice versa.

INTERPRETATION CONCLUSIONS: The outcome of the present investigations widened our scope on the pathogens present in ectoparasites and rodents/shrews from this area. This will help to formulate the required vector control methods to combat zoonotic diseases.