Monitoring and predicting disease outbreaks early enough to prevent them or reduce their impact on society is a major goal of the DoD Armed Forces Health Surveillance Center's Global Emerging Infections System (AFHSC-GEIS) Operations Division. A collaborative project between AFHSC-GEIS GIMMS Group at NASA Goddard Space Flight Center (NASA/GSFC), and the USDA-ARS Center for Medical, Agricultural, and Veterinary Entomology (USDA-ARS CMAVE) accomplishes that goal, at least for one disease: Rift Valley fever (RVF).
Using near-real-time satellite vegetation measurements and associated climate data sets, including sea surface temperatures (SSTs) and satellite derived cloudiness indices (outgoing longwave radiation, or OLR) and knowledge of vector biology and ecology, monitoring and prediction of areas at risk for the emergence of RVF epidemics in Africa and the Arabian Peninsula can be made several months before an outbreak occurs. Primarily a disease of sheep, cattle, and goats, RVF virus (RVFV) can be transmitted to humans by a wide variety of Aedes spp., Culex spp., and Mansonia spp. mosquitoes. Outbreaks can be devastating to the agricultural economies of sub-Saharan Africa, Egypt, and the Arabian Peninsula, and can cause significant human morbidity and mortality as experienced following recent epidemics/epizootics in East Africa (2006-2007), Sudan (2007), Southern Africa (2008-2011), Madagascar (2008), and Mauritania (2012).
Outbreaks of RVF are now well known to be coupled with interannual variability of rainfall in East Africa and Southern Africa. In East Africa, above-normal rainfall is associated with SST warming events in the western equatorial Indian Ocean and El Niño events in the Pacific; in Southern Africa the tendency is for outbreaks to occur during cold ENSO or La Niña events which lead to above normal rainfall and flooding. Monitoring the state of SSTs, rainfall, and ecological conditions guides efforts to identify areas of potential risk of RVF outbreaks. Our demonstrated ability to map such areas of potential RVF activity 2 to 5 months before outbreaks occur provides a real opportunity to conduct field surveillance for emergence of RVFV mosquito vector populations and the presence of RVFV in mosquitoes and sentinel animals, develop vaccination and quarantine strategies for domestic animals, distribute information and preventive strategies to affected populations, and implement appropriate targeted mosquito control programs.
The AFHSC-GEIS, NASA/GSFC, and USDA-ARS CMAVE are posting current satellite-based climate and vegetation data as well as maps of areas at risk of RVF outbreaks on this web site. This is a part of a continuing effort in disease monitoring and surveillance. Although the information contained in this report has significant potential implications for disease prevention and control, we do not suggest that this information is absolute with regard to actual disease occurrence nor can it be used as the only basis for public policy on this disease. Rather, it is intended as a vehicle for identifying geographic areas where field surveillance and validation of risk can be conducted. Persons with information that can help corroborate or refine the information contained in these pages are urged to contact us; accurate information and feedback from the field may lead to valuable improvements in the predictive model.
In addition, all constructive comments related to the presentation of these materials are welcome. Given this intent, persons who use this information do so at their own risk. The DoD and AFHSC-GEIS, NASA/GSFC, and USDA-ARS CMAVE cannot and do not take any responsibility for the consequences of any actions based on this information. All users are therefore cautioned to treat this information in the manner intended — as a statement of research in progress for the purpose of scientific validation and review.Updates will be posted to the RVF web site on a regular basis.