Opportunities and challenges for plague vector control in Madagascar

Plague is a rodent-borne disease transmitted to humans by the bite of fleas infected with the bacterium Yersinia pestis. Flea control is a key part of the overall plague management strategy. Insecticide-based strategies are designed to reduce or eliminate fleas from the environment in order to stop the disease transmission cycle during outbreaks. Many efforts have been directed toward monitoring flea susceptibility to insecticides using standardized bioassay methods recommended by the World Health Organization (WHO). Several studies have reported the development of insecticide resistance in vector species across Madagascar, which could be one of the factors contributing to the re-emergence of plague in endemic foci. However, the assessment of the operational efficacy of vector control in the field has received less attention. Furthermore, the mechanisms conferring flea resistance to insecticides remain poorly explored. In this review, we summarize the current understanding of (i) the effectiveness of insecticides for flea vector control in Madagascar, (ii) longitudinal surveillance of insecticide resistance in flea vector populations across the country, and (iii) insecticide resistance mechanisms in these fleas. Current vector control methods, including WHO standard methods for assessing the susceptibility or resistance of adult fleas, are presented and discussed. In addition, we propose recommendations for future research to improve the effectiveness of vector control and insecticide resistance mitigation for more effective control of plague-vector fleas in Madagascar.