We present a simple predictive framework for monitoring and forecasting St. Louis
encephalitis virus (SLEV) transmission. We use a dynamic hydrology model to hindcast
water table depth (WTD) and quantify the relationship between SLEV transmission and
hydrologic conditions in Indian River County, Florida between 1986 and 1991, a period
that included a major south Florida SLEV epidemic. Virus transmission followed periods
of modeled droughtspecifically, low WTDs 12-17 weeks prior to virus transmission
that were followed by a rising of the water table 1-2 weeks prior to virus transmission.
Further evidence derived from collection of Culex nigripalpus (the major mosquito
vector of SLEV in Florida), suggests that during extended spring droughts, vector
mosquitoes and nestling, juvenile, and adult wild birds congregate in select refuges,
facilitating epizootic amplification of SLEV. When the drought ends and habitat
availability increases, the SLEV-infected Cx. nigripalpus and wild birds disperse,
initiating an SLEV transmission cycle. These findings demonstrate a mechanism by
which drought facilitates the amplification of the SLEV and its subsequent transmission
to humans. Using these results we present a seasonal forecast of SLEV transmission in
Indian River County Florida. We couple a three-month forecast of modeled land surface
hydrology with the association between model-simulated WTD and SLEV transmission.
SLEV transmission forecast skill is demonstrated, and a real-time seasonal forecast of
SLEV transmission is presented for the current season.
Species 1: Diptera Culicidae Culex nigripalpus (Florida SLE mosquito)
Keywords: seasonal forecast, SLE transmission
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