AI Article Synopsis

  • Scrub typhus cases are frequently reported in Puducherry and surrounding areas, but there's limited knowledge about the presence of its causative agent, Orientia tsutsugamushi, and its vectors.
  • The study involved collecting and identifying trombiculid mites from rodents and shrews, using tests and DNA extraction to detect the pathogen.
  • Results showed a significant presence of the known vector, Leptotrombidium deliense, and a high rate of antibodies against O. tsutsugamushi in the sampled animals, indicating a high risk of scrub typhus transmission in the villages studied.

Article Abstract

Background & Objectives: Human cases of scrub typhus are reported every year from Puducherry and adjoining areas in southern India. However, information on the presence of causative agent, Orientia tsutsugamushi, and its vectors is lacking. Hence, the objective of the study was to find out the vector as well as pathogen distribution in rodents and shrews present in the scrub typhus-reported areas in southern India.

Methods: Trombiculid mites were collected by combing rats and shrews collected using Sherman traps and identified to species level following standard taxonomical keys. The serum samples of the animals were used for Weil-Felix test and the clots containing blood cells were used for DNA extraction and polymerase chain reaction (PCR).

Results: A total of 181 animals comprising four rodent species and one shrew species were collected from 12 villages. High proportion of chiggers was collected from the shrew, Suncus murinus (79.1%) and Rattus rattus (47.6%). A total of 10,491 trombiculid mites belonging to nine species were collected. Leptotrombidium deliense, the known vector of scrub typhus pathogen, was the predominant species (71.0%) and the chigger (L. deliense) index was 41.1 per animal. Of the 50 animals screened for the pathogen, 28 showed agglutination against OX-K in Weil-Felix test indicating the presence of antibodies against O. tsutsugamushi, the causative agent of scrub typhus. PCR carried out with the DNA extracted from blood samples of two of the animals were positive for GroEl gene of O. tsutsugamushi.

Interpretation & Conclusions: L. deliense index was well above the critical limit of chigger load, indicating that all the villages were receptive for high risk of transmission of scrub typhus to human. Pathogen positivity was higher among animals collected from villages recorded for higher chigger indices due to active transmission between the chigger mites and reservoir host animals. The results are suggestive of routine vector/pathogen surveillance at hot spots to initiate timely preventive measures.

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Source
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5433282PMC
http://dx.doi.org/10.4103/ijmr.IJMR_1390_15DOI Listing

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