Has Vector-Rodent Relationship Changed in Plague? Experiences of Plague Affected Hilly Terrains of Himachal Pradesh, India.

Background: The present study was conducted with objectives to elucidate the existence of sylvatic cycle of plague and to document the changing pattern of relationship between rodents and fleas. Methods: Collection of samples was done from 15 sites (25 locations) from plague affected areas of Shimla district of Himachal Pradesh, India during 5 visits between June 2011 to July 2012, which were thereafter entomologically investigated in a BSL-3 laboratory Results: 57 fleas (3 species) from 243 rodents (3 species) were collected in domestic (n=16), peridomestic (n=3) and wild (n=6) locations. Rattus rattus (n=197) and Nosopsyllus fascitus (n=43) was most frequently trapped rodent and flea species respectively. Rattus rattus (domestic rodent species) was also trapped from wild areas and Nosopsyllus fascitus (domestic flea species) was also isolated from Rattus norvegicus (wild rodent species). One rare rodent species Cornilurus albipes was also found. Most common rodent-flea association was Rattus norvegicus-Nosopsyllus fascitus. The recovery of rodents and flea was higher in months of June and December respectively. Conclusions: The study concluded that sylvatic cycle persisted in study area and rodent and flea mixing was widely prevalent between domestic and wild area. This demands regular and intensive surveillance in plague prone hilly areas of Himachal Pradesh.