Removing the green slime from streams and rivers could be a cheap and simple way to combat malaria. The algal gunk harbours larvae of the mosquitoes that transmit the disease.
Numerous attempts to combat malaria have focused on the mosquito larvae鈥檚 habitat. Draining the marshes near Rome in Italy, periodically emptying fish ponds in Java, and even clearing old car tyres where water accumulates in tropical cities have all led to lasting reductions in malaria. But running water is harder to tackle.
Now a study in Mexico has focused on making the water less hospitable for larvae. In the dry season along the Coat谩n river in the Mexican state of Chiapas near Guatemala, malaria is mainly carried by a species of Anopheles mosquito that breeds in riverside pools. The insect鈥檚 aquatic larvae shelter in and eat the green alga Spirogyra.
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Using garden rakes and netting, Guillermo Bond of the Centre for the Investigation of Malaria in Tapachula, Chiapas, and colleagues cleared the algae from a 3-kilometre stretch of river at the beginning of the dry season 鈥� about a day鈥檚 work for a dozen people. They monitored the effect by counting the number of mosquitoes attracted to light traps and human baits at night.
Virtually no malarial mosquitoes appeared for five to seven weeks in the cleared area, unlike a matched but uncleared stretch of river. The next year, the team cleared the other stretch but left the first untouched. Again mosquito numbers plummeted in the alga-free zone (Proceedings of the Royal Society, DOI: 10.1098/rspb.2004.2826).
No malaria outbreaks occurred during the experiment, but the scale of clearing was too small to say whether that was the reason, says team-member Trevor Williams of the University of Navarra in Pamplona, Spain. But now women in the neighbouring Mexican state of Oaxaca have adopted the technique. This has led to 鈥渁 dramatic reduction in the number of local cases of malaria鈥�, says Williams. 鈥淪tudies of malaria in that region had to be cancelled because there were no cases to evaluate.鈥�