Malaria is still an enormous problem in many parts of the world. The World Health Organization estimates that every year there are 300 to 500 million cases of malaria worldwide and approximately 1 million deaths attributable to malaria (the disease is second only to tuberculosis in the toll it takes on humanity). Unfortunately the two main strategies for dealing with malaria, trying to kill mosquitoes with insecticides and treat the disease with medication, are both diminishing as pesticide-resistant mosquitoes and drug-resistant malaria strains are becoming more prevalent.
Several scientists around the world are working on a more exotic approach — a strain of mosquito that is genetically modified to destroy the malaria plasmodium. Malaria has a complex series of vectors, and gets passed to human beings after the mosquito first picks up the disease by taking blood from another infected animal.
Research into genetically modified mosquito strains has concentrated on adding genes that cause mosquitoes to have immune system reactions to the malaria bacteria so that the mosquitoes’ own natural defense mechanisms destroy the disease before the mosquito can pass it on to human beings. Working with the yellow-fever mosquito, researchers from MIchigan State University spliced a gene into insects that produced an antibody called defensin which was coded to go into action when the mosquito ingested blood. The genetically modified mosquitos had high levels of defensin in their blood stream for several weeks after feeding.
But the obstacles to be overcome are still daunting. Before it was possible to genetically modify insects, researchers had long been trying to use traditional breeding methods to produce malaria-resistant mosquitoes. The problem they ran into was that the malaria-resistant mosquitoes were always less robust than the natural mosquitoes, meaning releasing even large numbers of them would be pointless since they would be quickly selected out of the breeding population.
Dr. Jo Lines, a researcher in tropical medicine, outlined the problem for the BBC, saying “you would end up with insects that are highly inbred and devoid of genetic variability — the modified train of Aedes aegypti (yellow-fever mosquito) would come from a single egg, and that is bound to affect its competitiveness.”
Not to mention the problems of how researchers would breed the hundreds of millions of mosquitoes needed to even have a shot at displacing traditional mosquitoes. Still, such research is certain to advance our understanding of both mosquitoes and malaria, even if it doesn’t lead to realistic near-term solutions.
Sources:
Further progress in war on malaria. The BBC, July 24, 2000.
Mosquito attacks its own problem. Jonathan Amos, The BBC, July 25, 2000.