# First assessment of plague in terrestrial small mammals and fleas from Makira Natural Park and surroundings, North-eastern Madagascar

## TL;DR

This study confirms the presence of plague in small mammals and fleas in northeastern Madagascar, highlighting the risk of human transmission.

## Contribution

The study provides the first assessment of plague circulation in terrestrial small mammals and fleas in northeastern Madagascar.

## Key findings

- Yersinia pestis was confirmed in one seropositive rat and one PCR-positive flea.
- Xenopsylla brasiliensis, a known plague vector, was prevalent in the area.
- The black rat (Rattus rattus) was the most commonly trapped species and likely contributes to plague transmission.

## Abstract

Plague, a zoonosis caused by Yersinia pestis, is endemic in Madagascar but knowledge on the epidemiological situation in the northern focus remains unclear. The aim of this study was to investigate the circulation of Y. pestis in terrestrial small mammals in north eastern Madagascar, where suspected plague outbreaks have been reported.

Sampling of terrestrial small mammals and their fleas was carried out in 22 trapping sites within 9 localities of the two sectors (1 and 3) of Makira Natural Park (MNP) and surroundings, from 2020 to 2022. Yersinia pestis was investigated in terrestrial small mammal spleen samples and their fleas using bacteriological, serological and molecular methods.

A total of 614 terrestrial small mammals composed of eight species and 1,754 individual fleas were collected following 4,880 trap-nights. The black rat (Rattus rattus) represented the majority (87.8%) of the small mammal species caught. Flea infestation rate was higher in sector 3 compared to sector 1. In sector 3, Xenopsylla brasiliensis, a plague vector, represented 66.4% of fleas identified. Further, one plague seropositive R. rattus individual, captured inside a house, and one Ctenocephalides felis specimen, collected on another R. rattus, was positive on PCR in this sector.

Despite low detection rates, we confirmed the circulation of Y. pestis in our study area (one rat seropositive and one flea PCR positive) and highlight the risk of potential human transmission. Our results also suggest that R. rattus contributes to the maintenance and transmission of plague in MNP, as described for other areas in Madagascar. Further, these findings contribute to documentation of the known geographic distribution of the endemic plague vector S. fonquerniei and X. brasiliensis.

The confirmation of the circulation of the Y. pestis through serological and molecular diagnostics in small mammals and fleas underscores the urgent need to assess awareness levels of risk factors and symptoms to monitor among local communities and health workers and ensure that trained rapid response teams are prepared to intervene promptly upon suspect case detection. The risk and epidemiology of plague circulation in remote rural areas of Madagascar remains insufficiently studied. Addressing this gap is crucial, as a more comprehensive understanding of the distribution and dynamics of the wild animal hosts, their vectors and host-vector interactions will enhance risk assessment and prevention for plague emergence and improve mitigation and early control of potential outbreaks.

Plague, a zoonosis caused by Yersinia pestis, is an endemic disease and major public health problem in Madagascar. Almost all of the available data are from the central highlands and little is known regarding the epidemiology of the disease in the northern region, despite suspect cases. The aim of this study was to investigate the circulation of Y. pestis in terrestrial small mammals and their fleas in north eastern Madagascar, where suspected plague outbreaks have been reported in the last decade. Sampling of terrestrial small mammals and their fleas was carried out in 22 trapping sites located in two different sectors (1 and 3) of Makira Natural Park (MNP) and its surroundings, from 2020 to 2022, to investigate the presence of Y. pestis. A total of 614 terrestrial small mammals composed of eight species and 1,754 flea individuals were collected. It is important to note that Xenopsylla brasiliensis, a known plague vector in Africa, represented about 65% of the fleas collected. After biological screening, one plague seropositive R. rattus individual, captured inside house as well as one PCR positive Ctenocephalides felis specimen collected on R. rattus were identified confirming the circulation of Y. pestis in the region and the importance of further investigation to understand the epidemiology of the disease in this plague focus and mitigate future outbreaks.