Plague Circulation and Population Genetics of the Reservoir Rattus rattus: The Influence of Topographic Relief on the Distribution of the Disease within the Madagascan Focus

Abstract

BackgroundLandscape may affect the distribution of infectious diseases by influencing the population density and dispersal of hosts and vectors. Plague (Yersinia pestis infection) is a highly virulent, re-emerging disease, the ecology of which has been scarcely studied in Africa. Human seroprevalence data for the major plague focus of Madagascar suggest that plague spreads heterogeneously across the landscape as a function of the relief. Plague is primarily a disease of rodents. We therefore investigated the relationship between disease distribution and the population genetic structure of the black rat, Rattus rattus, the main reservoir of plague in Madagascar.Methodology/Principal FindingsWe conducted a comparative study of plague seroprevalence and genetic structure (15 microsatellite markers) in rat populations from four geographic areas differing in topology, each covering about 150–200 km2 within the Madagascan plague focus. The seroprevalence levels in the rat populations mimicked those previously reported for humans. As expected, rat populations clearly displayed a more marked genetic structure with increasing relief. However, the relationship between seroprevalence data and genetic structure differs between areas, suggesting that plague distribution is not related everywhere to the effective dispersal of rats.Conclusions/SignificanceGenetic diversity estimates suggested that plague epizootics had only a weak impact on rat population sizes. In the highlands of Madagascar, plague dissemination cannot be accounted for solely by the effective dispersal of the reservoir. Human social activities may also be involved in spreading the disease in rat and human populations.

Urban population genetics of the invasive black rats in Franceville, Gabon

“…Genetic diversity and N E levels estimated per district in Franceville were similar to those reported for rural or wild populations of R. rattus in Madagascar (Brouat et al ., ), or for urban populations of R. norvegicus in Brazil (Kajdacsi et al ., ). Such comparisons support the idea that urban environments are propitious habitats for commensal rodents, compared to more natural ones (Banks & Smith, ).…”

“…Potos and Ombele, separated by less than 500 m). The level of genetic differentiation observed in Franceville ( F ST = 0.03) was similar to that found at a same spatial scale (few kilometers) in rural habitats of Madagascar (Brouat et al ., ) or between forest sites in New Zealand (Abdelkrim, Byrom & Gemmell, ). A single genetic group was evidenced by STRUCTURE and DAPC analyses.…”

Highly Diverse Morbillivirus-Related Paramyxoviruses in Wild Fauna of the Southwestern Indian Ocean Islands: Evidence of Exchange between Introduced and Endemic Small Mammals

“…The data presented here indicate an important role for R. rattus in the transmission of UMRV paramyxoviruses and highlight these animals as potential intermediates in the dissemination of infectious agents that are endemic or otherwise isolated that facilitate disease emergence. The global dispersal of Rattus and their associated biota have been studied in many different contexts (25,51) and have particularly important implications within the SWIO (52), where many mammal species are endemic, particularly on Madagascar, and at risk from both macro-and microorganism invasions, and where active commercial trade results in considerable and largely uncontrolled exchange (24,53).…”

Dynamic, spatial models of parasite transmission in wildlife: Their structure, applications and remaining challenges

“…Since the relative importance of local and long‐distance processes is often unknown for pathogen transmission in wildlife, landscape genetic approaches like isolation by distance and spatial assignment can provide important information about levels of connectivity between different populations, and thus provide inferences about rates of migration and dispersal (Storfer, Murphy, Spear, Holderegger, & Waits, ; Streicker et al., ). Such techniques have been used to investigate host–pathogen systems like plague in rats and prairie dogs, chronic wasting disease in mule deer, and rabies or bTB in raccoons and Virginia possums (Brouat et al., ; Hennessy et al., ; Powell et al., ; Rioux Paquette, Talbot, Garant, Mainguy, & Pelletier, ). More recently, advances in phylogeography and full genomic sequencing approaches have enabled retroactive tracing of the evolution and spatial spread of bacteria like bTB and RNA viruses like FMD and rabies (Dellicour, Rose, & Pybus, ; Lemey, Rambaut, Welch, & Suchard, ; Trewby et al., ; Valdazo‐González et al., ).…”