Rift Valley Fever

Scientists are learning that the key to predicting certain epidemics - like Rift Valley fever in Africa or Hanta virus in the U.S. - lies in an unexpected place: the ocean.

On the dusty savannahs of eastern Africa, where livestock sustain the economy, about twice a decade an epidemic whips through to decimate the herds. Nearly all of the pregnant animals spontaneously lose their fetuses. Among those already born - the lambs and kids - the mortality rate can reach 90 percent.

It's called Rift Valley fever.

Humans can be infected as well, either through mosquitoes that carry the disease, or by handling infected tissue. Few die, but the illness can cause serious complications: meningoencephalitis, an inflammation of the brain, and lesions of the retina, which leave victims with at least some permanent loss of vision. During the most recent and devastating outbreak in 1997-98, an embargo banned exports of East African meat for one and a half years.

While no easy treatment exists for the disease, Rift Valley fever can be controlled. Animals can be vaccinated, insecticides can be spread into the soil to keep infected mosquitoes from hatching. But the disease's unpredictability has been a sticking point: without knowing when and where the disease will strike, it's hard to know how to use those controls efficiently.

more Rift Valley fever was first identified during the 1930's when it struck residents of Kenya's great Rift Valley, pictured here.

But the disease might not be so capricious after all, says Assaf Anyamba of NASA's Goddard Space Flight Centre.

Anyamba and colleagues at Goddard and at the Walter Reed Army Institute of Research have discovered that outbreaks of Rift Valley fever follow sudden floods triggered by El Niño and a similar (yet lesser-known) climate disturbance called the "Indian Ocean Dipole." Using weather satellites to track sea surface temperature patterns in the Indian and Pacific oceans, they now believe they have found a way to predict outbreaks up to five months in advance.