Risk factors for West Nile virus seropositivity of equids in Guadeloupe

In Guadeloupe, West Nile virus (WNV) activity was first observed in equids in 2002, and a high seroprevalence was found in 2003. The objective of our study was to determine individual and environmental factors associated with the risk of WNV seropositivity during 2002-2003. Fieldwork was conducted to retrospectively determine the location of equids at the time of virus circulation and to collect information regarding environmental and individual variables. Sera were collected from 369 equids out of an estimated total population of less than 500. Thirty-four environmental and individual variables were investigated. Equids had a higher risk (p<0.001) for WNV seropositivity if they lived within the proximity "distance less than 1.5km" of marshes or swamp forests "a large freshwater formation behind mangroves" or if they remained outside after dusk. Equids living within the proximity of ouassous shrimp (Macrobrachium rosenbergii) basins or sugar cane fields had a lower risk (p<0.001) for WNV seropositivity. These results confirm that WNV circulation is more likely in the humid coastal areas of Guadeloupe. The identification of risk factors is useful for predicting future emergence sites of WNV in the archipelago and other Neotropical islands, and to better target sentinel surveillance in the region.