Early warnings of Rift
Valley fever outbreaks can help save people and livestock like these Ethiopian
women and their bull, who are vulnerable to disease-carrying mosquitoes that
reproduce in stagnant and slow-moving water. Photo courtesy Food and
Agriculture Organization/Marc Bleich.
Top: Particles of
Phlebovirus, the causal agent of Rift Valley fever. Bottom: The map
links to a
that provides detailed geographic distribution and other information about the
disease. The website is hosted by the Food and Agriculture Organization.
Images courtesy FAO.
Model Successfully Predicts Rift Valley Fever
Outbreak By Kim
Kaplan February 16, 2007
A Rift Valley fever outbreak was successfully predicted several months
in advance for the first time with a model developed by a team assembled by an
Agricultural Research Service (ARS)
In October 2006, when the model predicted that Rift Valley fever would
flare up within three months in sub-Saharan Africa, a warning was sent to the
United Nations Food and Agriculture
Organization and the World Health
Organization, which then passed on the warning to countries such as Kenya,
Ethiopia, Tanzania, Uganda and Somalia.
The early warning allowed the countries most likely to be in harm's
way to step up surveillance and control of insect vectors for the
disease--actions that may have mitigated the outbreak. Rift Valley fever is
primarily spread to livestock and humans by biting insects such as mosquitoes.
An outbreak of Rift Valley fever was blamed for the deaths of hundreds
of people in Kenya in 1997-1998. Twenty years earlier, in 1977-1978, a Rift
Valley fever epidemic in Egypt involved 200,000 human cases and 600 fatalities.
The disease also attacks cattle, sheep, camels and goats.
So far, Rift Valley fever has not reached the United States, but
having a model that can predict outbreaks allows the U.S. to know when to step
up its own watch to prevent its spread to this country, according to
J. Linthicum, director of the ARS
for Medical, Agricultural and Veterinary Entomology in Gainesville, Fla.,
who established the team. The team included researchers from the Department of
Defense's Global Emerging Infections
System and the National Aeronautics and Space Administration's
For the U.S. livestock industry, a Rift Valley fever outbreak would be
devastating because the World Organization for
Animal Health imposes a four-year ban on exports of beef, sheep or goat
products from any country that has an outbreak.
The model is based on analyzing satellite images to find when
vegetation is growing at a rapid rate in an area as a surrogate for weather
conditions that include heavy rainfall, elevated humidity and heavy cloud
cover. Such conditions give rise to major increases in the number and longevity
of insects that spread the disease.
The model also can help predict outbreaks of other diseases of
livestock and people such as malaria and cholera.
ARS is the U.S. Department of
Agriculture's chief scientific research agency.