According to their report in the July 16 issue of the journal Science, satellite data can help predict Rift Valley Fever outbreaks up to six months in advance. Linthicum consulted with Assaf Anyamba, a Goddard geographer who uses satellites to study the effects of El Nino, a phenomenon that occurs when sea-surface temperatures rise in the eastern Pacific Ocean. They found that some El Nino episodes over the past five decades led to large Rift Valley Fever outbreaks. During an El Nino, East Africa often receives more rain than normal, but El Nino alone does not ensure an outbreak. According to Anyamba, the decisive factor is the warming of the Indian Ocean along with the Pacific, which occurred in two of five El Ninos over the last 17 years.
Satellites provide synchronous measurements of ocean temperature and vegetation conditions.
The close relationship between ocean temperature, rainfall and land vegetation helps scientists determine which areas received the most rain and are greener than normal, making them likely habitats for the mosquitoes that carry the Rift Valley Fever virus. The Rift Valley Fever virus is passed into the eggs of Aedes mosquitoes. The mosquitoes lay their eggs in moist soil when floodwaters recede. The young insects hatch when the area is re- flooded and feed on local livestock. A second kind of mosquito, the Culex, then causes the large outbreaks by contracting the virus from infected livestock and spreading it rapidly.