Topic: Urban landscape and the movement of urban rodents as reservoirs of zoonotic agents: a study in Antananarivo, Madagascar.
Dates: March 2023 – March 2024
CBGP supervisor: G. Dobigny
University: Université de Tananarive
Background: The eco-epidemiology of zoonoses involving small mammals, particularly rodents, has been relatively understudied in urban settings. In Madagascar, most research and control efforts focus on rural areas, primarily in relation to plague. However, outbreaks of plague and the recent detection of other zoonotic pathogens with high potential health risks (e.g. Rickettsia spp., Leptospira spp.) in Malagasy cities, particularly in Antananarivo, suggest that urban socio-environments probably warrant special attention.
Reason: In particular, there is very little research into the general biology of small reservoir mammals in urban areas, especially their ability to move around within the urban environment. Yet this information is essential for describing and understanding the patterns and processes of pathogen transmission, and therefore the associated zoonotic risk.
Objectives: The aim of this thesis is to explore, for the first time, the movement patterns of small mammals involved in the ecology of major zoonotic pathogens (e.g. the causative agents of plague, typhus and leptospirosis) in relation to characteristic features of the urban landscape in Antananarivo.
Methodology: Rhodamine is a fluorochrome which, once ingested by rodents, is detectable at certain wavelengths in their mouths, digestive tracts and/or fur once metabolised. It has already been used successfully by researchers at the Plague Unit to study the movements of black rats (the main susceptible reservoir for plague in rural Madagascar) between rice fields, sisal hedges and houses (Rahelininirina et al., 2010). In order to document the extent of small mammals’ movements within the urban landscape, field experiments will be conducted in Antananarivo in two stages: first, rhodamine-labelled baits will be placed at pre-selected sites (see below), followed by trapping sessions to determine whether rhodamine is detectable in the trapped rodents, indicating that they have moved between the baiting site and the trapping site. It is planned to apply this protocol to investigate potential rodent movements (i) between markets and surrounding dwellings, (ii) across roads, (iii) around rubbish dumps, (iv) around sewage collectors and (iv) between rice fields and dwellings in slum areas. Finally, a gradient setup will be used to assess (v) the distance the animals can travel within residential areas (i.e. between adjoining dwellings, within the same blocks, etc.). Rhodamine ingestion will be verified using a UV lamp to examine the digestive tract of captured rodents, as well as through the analysis of their fur and whiskers under a fluorescence microscope.
Expected results: To the best of our knowledge, the results obtained will be entirely novel. We nevertheless hypothesise that rodents move relatively little within homogeneous residential areas (i.e. restricted territories) and that their movements are restricted by major road infrastructure but facilitated by open or underground drainage systems. Given the food resources they contain, markets could be attractive to rodents, thereby inducing inward movements. Conversely, movements between rice fields and dwellings in the lower districts (where food resources are likely to be abundant as well) remain entirely unexplored and will be documented for the first time.
