Motivated by the desire for more accurate prediction of malaria risk at longer lead times, Pascual and her colleagues analyzed epidemiological records of malaria incidence in northwest India and used statistical and computer climate models to test potential links between sea surface temperatures, monsoon rains in northwest India, and malaria epidemics there.
They found that most malaria epidemics in northwest India, which peak in October or November, occur when rainfall in the preceding summer monsoon season equals or exceeds a rainfall threshold presumably required to support the growth of Anopheles mosquitoes.
The researchers looked for a correlation between global sea-surface temperatures and epidemic malaria in northwest India. They identified a broad region in the tropical South Atlantic, west of Africa, where cooler-than-normal sea-surface temperatures are significantly associated with increases in both monsoon rainfall and malaria incidence in northwest India.
July sea-surface temperatures in the tropical South Atlantic proved to be remarkably accurate at predicting malaria outbreaks in northwest India during the following fall. In a retrospective analysis of malaria epidemics in the region between 1985 and 2006, the researchers found that July sea surface temperatures correctly anticipated nine out of 11 epidemic years and 12 out of 15 non-epidemic years.
"For this region of India and for this window of time in recent decades, the tropical South Atlantic appears to play a dominant role on rainfall and, through rainfall, on malaria," Pascual said.
Malaria is caused by the Plasmodium parasite, which is transmitted via the bites of infected mosquitoes. In the human body, the parasites multiply in the liver and then infect red blood cells.
|Contact: Jim Erickson|
University of Michigan