Scientists may soon be able to predict some malaria outbreaks by monitoring sea surface temperatures. In tomorrow's Journal of the American Medical Association, researchers report that malaria epidemics in Venezuela appear to be closely linked to warmer ocean water and droughts that are both associated with the weather phenomenon known as El Niño. The finding could help tropical disease experts prepare for outbreaks at least a year in advance.
Researchers have long noticed that outbreaks of malaria come in cycles. In parts of South America, for example, major epidemics occurred every 5 years in the early 1900s. In 1994, researchers suggested that El Niño, which periodically brings warmer waters to the eastern Pacific and droughts to South America's western coast, might explain the pattern.
Now, Menno Jan Bouma and Christopher Dye of the London School of Hygiene and Tropical Medicine, United Kingdom, have found that El Niño does herald the arrival of malaria. The pair compared data on 11 El Niño events since 1910 with death and medical records collected in 21 Venezuelan states. They found that malaria deaths and illnesses increased, on average, 37% in the year after an El Niño event, which is marked by droughts.
The researchers aren't sure why the droughts bring on epidemics. One idea is that the dry weather kills fish and other predators that control mosquito larvae. Whatever the exact mechanism, the findings "demonstrate that epidemics don't just come out the blue, and that climate can play a significant role in public health," says Bouma, who has found similar climate-malaria associations in other South American nations and East Africa.
The ability to use climate information to predict malaria epidemics would be extremely helpful, says Robert Wirtz of the Centers for Disease Control and Prevention in Atlanta. The disease kills more than 2 million people a year.