Science - April 14, 2005

New: malaria prediction

Wageningen scientists are soon likely to be able to predict where and when malaria mosquitoes are active. Ninety-five percent of the mosquito larvae mature in shallow puddles. Entomologists and meteorologists are now researching how they can predict the swarming of young malaria mosquitoes using a model of the puddles.

The system is relatively simple, explain entomologist Dr Willem Takken and meteorologist Dr Adrie Jacobs. The researchers work out the topography of an area using geographic information. This is checked in the field, and then it is possible to calculate how many shallow pools there are in an area.

Using a new meteorological model, the researchers go on to estimate how quickly the mosquito population in the water will mature. By combining all the data they can predict how many mosquitoes will be produced. The more mosquitoes there are, the higher the chance that they will infect humans with the malaria parasite Plasmodium.

Local social workers can use the predictions to work together with the local population on filling up the pools. Some of the pools are naturally formed; others are where rainwater collects in tyre tracks and footprints. According to Takken this method is cheaper than using biological pest control against malaria. He thinks the method will be particularly useful in villages and towns. ‘In ten years’ time half of the African population will be living in urban areas.’

The work is new territory for both entomologists and meteorologists. ‘We still know nothing about how the larvae in the shallow pools mature,’ tells Takken. Around the equator the temperature in the pools can vary between 15 and 50 degrees Celsius, and how the larvae react to these differences is still a mystery for entomologists. How sunlight influences temperature is something meteorologists know little about, according to Jacobs.

AIO Krijn Paaijmans is doing field research at the moment near the large town of Kisumu in Western Kenya. He dug shallow puddles and suspended measuring equipment in them to see how the temperature fluctuates, and what the effects of the fluctuations are on the mosquito larvae in the puddles. Paaijmans’ results are to be used to test and extend Jacobs’ model.

The prediction system should provide a simple and cheap way of preventing malaria, especially in more densely populated areas. In the district around Kisumu, eighty percent of the children suffer permanently from malaria, says Takken, and a quarter of all child deaths are the result of malaria. ‘If we can reduce these figures, even by just a little, we are on the right track.’ / MW