A serological study was performed in 2009 in Madagascar highlands to evaluate the point prevalence rate of RVF antibodies in ruminants and identify environmental and trade factors potentially linked to RVF persistence and transmission. Nine hundred ruminants were randomly selected among 51 villages and sampled. Sera were analysed using a commercial validated ELISA test. For each ruminant, the following variables were recorded: age, location of the night pen, minimum distance from the pen to the closest water point and the forest, water point type, and the way owners use to renewal their herd: auto-renewal vs purchase. Serological data were analysed using a generalized linear mixed model, the individual serological status being the binomial response, and the above-mentioned variables the explicative factors, and the breeder as random effect. The overall IgG seroprevalence rate was 28% [IC95% 25-31]. The main effect on prevalence was due to age (P=10-4) suggesting an endemic RVF circulation in this area. The distance to the closest water point was a protective factor (P=5×10-3) but the type of water point had no effect on the prevalence rate: a substantial part of the transmission is due to vectors and several mosquito species are probably involved. Ruminants belonging to owners renewing their herd by purchase were significantly more infected than others (P=0.04), suggesting that cattle trade may contribute to the circulation of the virus in this area. This is the first evidence of a recurrent transmission of RVFV in such an ecosystem which associates a wet, temperate climate, high altitude, paddy fields, and vicinity to a dense rain forest. Persistence mechanisms need to be further investigated. (Texte intégral)