Wednesday, March 28, 2007


Recently I read an interesting article in the Science and Technology section of the Sunday Times. The article was on genetically modified insects, specifically mosquitoes in order to control disease.

We are all aware of Malaria, but not many of us know how it “works” or what it actually is. Malaria is caused by a parasite (representatives of the genus Plasmodium) that infects the blood and is transmitted to potential hosts through the saliva of the mosquito. According to the article, Malaria is second only to HIV and AIDS when it comes to how many people it kills each year. This is estimated to be around 2.7 million lives annually.

What scientists have done is to genetically engineer a mosquito that is resistant to the parasite itself, which can drastically impact the efficiency of transmission. The proposal is to release these mosquitoes into the wild where malaria is prevalent and where the natural biodiversity exists which includes the genetic component of the wild mosquitoes. In wild mosquitoes, the actual infection with malaria parasites does impact that mosquito’s reproductive potential, however previous studies with genetically modified mosquitoes proved that the wild forms were still fitter. Basically what this means is that even though genetically modified mosquitoes could have been introduced into the wild population earlier, they would have been out-competed by the wild forms which were genetically predisposed to survive better in the environment. Now unfortunately, the scientists seem to have unlocked this barrier and have now produced a genetically modified form that is fitter than the wild form!

So you may ask what this has to do with biodiversity then? Well, since a component of biodiversity is genetic, the introduction of a genetically modified mosquito would eventually cause the local extinction of the wild gene pool. What is more alarming is the apparent lack of forethought in the scientists who have not even mentioned the concern over the effects of co-evolution in parasitism, which can occur at a faster rate in the parasite than in the host. The Red Queen Hypothesis explains that parasites and their hosts are in a continuous battle or evolutionary “arms race” and that each has to keep up to remain within the folds of a dynamic equilibrium. If the mosquitoes that are introduced have a genetically predisposed higher resistance to the actual parasite, it is almost certain that this would fuel a reciprocal response in the parasite’s evolution in order to survive. If this response is to produce more aggressive forms of Plasmodium spp., the result could be even worse for infected people…

Something to think about.

David Vaughan
Senior aquarist, Quarantine
Two Oceans Aquarium
Cape Town, South Africa
+27 21 418 38 23

Article in Sunday Times, 25 March 2007, Science and Technology, page 33.

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