Highlight 2003: On the trail of the Malaria mosquito

In the highlands of Kenya, malaria is not active all the year round. But after long rainy spells, the disease reappears, killing many people. ICIPE researchers have recently developed a way to prevent this.

The small town of Kisii is a thriving trading post and has a colourful market. The surrounding countryside is hilly, green and fertile. The main problem for the people here is not lack of food, but diseases, of which malaria is the worst. In the area around Kisii there are several malaria epidemics every year. Thousands of malaria patients are cared for in the local hospitals. The doctors do their best with limited supplies of medicine, and the farmers try to prevent being stung by using mosquito nets.

Until recently, no one had asked where these malaria-carrying mosquitoes, the anopheles mosquitoes, came from. Might there not be a way to deal with the mosquitoes rather than with the illness? The ICIPE research scientist for insects, Francois Omlin, wanted to find out. He spent months travelling round the area, making notes on the landscape and the people. He took samples from ponds and puddles and found the answer: the problem was the puddles left by the brick makers! In recent years many farmers have started making bricks; the heavy soil around Kisii is ideal for this. But no one had realised the consequences. When the farmers dug out the clay, they left little hollows which quickly filled with water, and it was here that the mosquitoes bred so plentifully.

When Francois Omlin took samples from these puddles he made an astounding discovery. There were far more anopheles mosquito larvae there than in the lakes and larger ponds. The reason was easy to find. The larvae’s natural predators, for example mud fish and the other insects that feed on the larvae, live in the lakes and ponds, but not in the puddles. Francois Omlin began careful research to find a biologically sound way of destroying the larvae. He discovered that when he spread an extract from the neem tree onto the water the larvae stopped growing. They either died or developed into crippled mosquitoes which did not harm humans. Francois Omlin has turned his discovery into a simple treatment from which farmers can already profit. A sack is filled with neem powder and this oversized tea bag is then laid into the puddle. This gets rid of the danger. Together with BioVision, Omlin intends to pass this simple and effective method onto the brick makers and the farmers as quickly as possible. He hopes that the results will be seen soon, with fewer patients in hospitals and greater happiness in the faces of the people. More information about the project