Local-scale diversity of Yersinia pestis: A case study from Ambohitromby, Ankazobe District, Madagascar

Climatic variations and Yersinia pestis host-vector abundance: a case study in Ankazobe district to understand plague epidemiology in Madagascar

BACKGROUND

Plague, a disease caused by the bacterium Yersinia pestis remains a major public health concern in Madagascar despite numerous multidisciplinary studies. The persistence of human plague infections is thought to be linked to fluctuations in mammalian host and flea populations, which are affected by climatic and environmental variations. This study explored local macro- and microclimatic variations along with mammal and flea population dynamics across different microhabitat types within plague endemic rural and forested habitats of Madagascar. Understanding these variables and their interdependent relationships may help us better understand the complexities of Y. pestis transmission in the Madagascan Highlands.

METHODS

Small mammals and their fleas were captured in different microhabitats within plague focus in the Ankazobe District of Madagascar. Simultaneously, climatic data including temperature and humidity, were collected to assess the potential relationship between flea population dynamics and climatic variations. Specialized equipment was used to monitor microclimate conditions across various microhabitat types and compare them with macroclimate. Monitoring was performed inside and outside rodent burrows located inside and outside houses and in adjacent forested areas.

RESULTS

A greater abundance of fleas was observed inside dwellings compared to other microhabitats, such as outside houses and forest, whereas small mammal species diversity was significantly higher in forest environments. We also revealed significant differences in microclimates across microhabitat types, with lower temperatures and higher humidity inside rodent burrows compared to outside burrows, outside houses and the forest. Inside houses, temperature variations were more stable although temperatures were higher and humidity lower inside rodent burrows compared to other microhabitats.

CONCLUSION

This study highlights microclimate variation across different microhabitat types, which also differ from the macroclimate, and maps small mammal and flea abundance to these locations. These data suggest that it is important to further explore the relationship between microclimatic variations in the different microhabitats and the dynamics of flea and rodent populations as potential markers for plague persistence and transmission in these endemic foci.

Plague in Small Mammals From an Endemic Focus of the Malagasy Central Highlands: A Longitudinal Survey With a Special Reference on Black Rats (Rattus rattus)

Plague, a zoonotic disease caused by Yersinia pestis, remains a major public health threat in several parts of the world, including Madagascar. Factors underlying long-term persistence and emergence of the pathogen remain poorly understood. We implemented a longitudinal survey to provide insights into plague reservoir ecology within an endemic focus. Six trapping sessions (TS) were conducted in six different localities of the Ankazobe district from 2018 to 2020 in order to monitor small mammal communities. A total of 2762 individuals composed of six species (Rattus rattus, Rattus norvegicus, Mus musculus, Setifer setosus, Suncus murinus and Tenrec ecaudatus) were caught over the six successive TS. R. rattus represented 88% of all captures, with the highest relative abundances observed during the dry season (June to August 2019). None of the micromammals tested positive for the presence of Y. pestis, neither with qPCR nor bacterial culture. However, 11 seropositive individuals (6 R. rattus, 2 M. musculus and 3 S. murinus) were retrieved following ELISA, thus leading to a global seroprevalence of 0.4%. Our study highlighted the significant influence of climatic data on the seasonal variations of R. rattus abundance and suggest that black rat control should be conducted before the dry season, that is, during high reproduction period of rats, in order to reduce the number of reproducing animals and prevent subsequent increase in abundance. As three S. murinus and two M. musculus plague seropositive were identified in the present study, their potential role in plague eco-epidemiology in Madagascar should be explored further.

Population dynamics of plague vector fleas in an endemic focus: implications for plague surveillance

Plague is a zoonotic vector-borne disease caused by the bacterium Yersinia pestis. In Madagascar, it persists in identified foci, where it is a threat to public health generally from September to April. A more complete understanding of how the disease persists could guide control strategies. Fleas are the main vector for transmission between small mammal hosts and humans, and fleas likely play a role in the maintenance of plague. This study characterized the dynamics of flea populations in plague foci alongside the occurrence of human cases. From 2018 to 2020, small mammals were trapped at sites in the central Highlands of Madagascar. A total of 2,762 small mammals were captured and 5,295 fleas were collected. The analysis examines 2 plague vector species in Madagascar (Synopsyllus fonquerniei and Xenopsylla cheopis). Generalized linear models were used to relate flea abundance to abiotic factors, with adjustments for trap location and flea species. We observed significant effects of abiotic factors on the abundance, intensity, and infestation rate by the outdoor-associated flea species, S. fonquerniei, but weak seasonality for the indoor-associated flea species, X. cheopis. A difference in the timing of peak abundance was observed between the 2 flea species during and outside the plague season. While the present study did not identify a clear link between flea population dynamics and plague maintenance, as only one collected X. cheopis was infected, the results presented herein can be used by local health authorities to improve monitoring and control strategies of plague vector fleas in Madagascar.