AG index page FAO homepage
Print this page | Close

ARCHIVE Rift Valley Fever (RVF) Maps

Disclaimer

The maps shown here represent areas at risk of RVF vector amplification. The designations employed and the presentation of material in the maps do not imply the expression of any opinion whatsoever on the part of FAO concerning the legal or constitutional status of any country, territory or sea area, or concerning the delimitation of frontiers.

Map. Hotspots for Rift Valley fever (RVF) vector amplification and potential RVF epizootic for October 2013 in Senegal & Mauritania

Hotspots for Rift Valley fever (RVF) vector amplification and potential RVF epizootic for October 2013 in Senegal & Mauritania

 

Rift Valley Fever (RVF) virus amplification and spread depends on environmental factors that influence vector abundance and distributions. Mosquitoes populations (e.g. Aedes and Culex) that are involved in the transmission of RVF virus are strongly influenced by climate.

Outbreaks are closely associated with periods of heavy rains and prolonged flooding, which increase habitat suitability for vector populations, thus influencing the risk of disease emergence, transmission and spread. This relation is particularly strong in the Horn of Africa, where precipitation usually correlates to ENSO (El Nino Southern Oscillations) (Anyamba et al. 2009). In Senegal and Mauritania, the onset of RVF outbreaks appears to be also associated with dry spell events, which are rainless periods of about ten days preceded and followed by an intense rainfall event during the late rainy season. These rainy events leads to the filling of temporary ponds, causing mass hatching of Aedes eggs potentially infected by the RVF virus (e.g., Caminade et al. 2014).

The risk monitoring and mapping system of RVF epizootic implemented by FAO-EMPRES in Senegal and Mauritania is based on the integration of two risk modelling approaches that capture different ecological conditions for vector amplification: a) a published scientific method on cumulative rainfall anomalies developed by the NASA, which has been calibrated for the region of interest, and b) a published method on the identification of dry spell events. Every month, the risk of RVF epizootic is assessed through monitoring precipitation and cumulative Normalized Difference Vegetation Index (NDVI) anomalies.

The risk maps available in this website show hotspots of vector amplification and potential of RVF outbreaks based on average cumulative NDVI anomalies over 3 months period as well as dry spell events. The RVF historical distribution obtained using available RVF outbreaks data (from 1998 to 2015) and kernel density methods is shown for model interpretation. In addition, when available, an overview of the wet season per year is provided together with the RVF distribution of the same year. Considering the high uncertainty associated with the RVF reporting system, RVF outbreak locations as well as the unavailability of recent field data on vector abundance and dynamic and RVF serological data, the RVF maps represent a monitoring tool for VF emerge to be used together with results of other surveillance activities (e.g., sentinel herd monitoring). Further analysis and calibration will be conducted as soon as field data become available.