Study on the Movement of Rattus rattus and Evaluation of the Plague Dispersion in Madagascar

Abstract

Plague affects mainly the rural areas in the central highlands of Madagascar. Rattus rattus is the main rodent host of Yersinia pestis in these localities. Since the introduction of plague, endemic foci have continued to expand, and spatiotemporal variability in the distribution of human plague has been observed. To assess the movements of R. rattus and evaluate the risk of dispersion of the disease, a field study at the scale of the habitats (houses, hedges of sisals, and rice fields) in the plague villages was carried out during high and low seasons of plague transmission to humans. The systemic oral marker Rhodamine B was used to follow rats' movements. Baits were placed in different habitats, and trapping success was carried out once a month for 3 months after the bait distribution. Plague indicators (reservoirs' abundance, flea index, Y. pestis prevalence in fleas, and Y. pestis antibody prevalence in rats) were determined. The highest abundance of rats and marking efficiency were observed in the sisal hedges and the rice fields. Marked rats were captured most commonly near the points where baits were initially placed. The main movements of rats were observed between the houses and sisal hedges. Major differences were observed between the seasons of high and low plague transmission. During the season of low plague transmission, rats were more abundant in the sisal hedges and rice fields, with rats moving from the houses to the rice fields. During the high plague transmission season, rats moved from the hedges of sisal to the rice fields. Important indicators of vector abundance and plague transmission were higher during the high plague transmission season. The three study habitats were the risk areas for plague transmission, but the risk appeared highest in the houses and sisals. Rats' movements according to the season were likely directed by the availability of food.

Landscape and Residential Variables Associated with Plague-Endemic Villages in the West Nile Region of Uganda

“…That is, as host abundance and flea infestation rates increase, so does the probability of epizootic activity. 1,2,19,20,[31][32][33][34][35][36] Human risk of exposure has been associated with behaviors that increase the probability of contact with infectious fleas or practices that increase the availability of food or harborage for rodents. 21,25 Rodent movement is often driven by food availability and appropriate habitat.…”

“…21,25 Rodent movement is often driven by food availability and appropriate habitat. 34,37 Therefore, behaviors that attract flea-infested rodents into peridomestic settings may increase the probability of human exposure to plague-infested fleas or rodent hosts. 38 In an attempt to identify areas of elevated risk of human exposure to plague bacteria in the West Nile region, a fineresolution model was recently created based primarily on RS variables.…”

Climate Predictors of the Spatial Distribution of Human Plague Cases in the West Nile Region of Uganda

“…Rodent movement is often driven by food availability and appropriate habitat. 60,61 Thus, properly dried grains that are stored within human habitations may increase rat abundance in the home and peridomestic setting where most human exposures are believed to occur. 11,62 It is not clear if the rainfall variables for particular months emerged as significant because they affect crop production during key points in the life cycle of rodents, which in turn affects both rodent and flea abundance, or if these months provided the best fit to the data because they represent divergent distributions in rainfall over the plague risk area.…”

Free-living animals as a source of zoonotic microorganisms

“…Jakkolwiek szczury są istotnym rezerwuarem Y. pestis wywołującej infekcję człowieka, to niejednokrotnie zakażanie spowodowane tym patogenem również powoduje ich śmierć (9,14,71,74). W związku z powyższym gryzonie nie przyczyniają się znacząco do utrzymywania się Y. pestsis w środowisku (71).…”