ARMING mosquitoes with the venom of a scorpion sounds like a terrible idea. But researchers in Mexico say malaria could be stopped in its tracks by genetically engineered mosquitoes that produce a scorpion toxin in their gut.
For years, scientists have dreamed of displacing wild mosquitoes with genetically modified insects that cannot carry the malaria parasite Plasmodium (New Scientist, 5 August 1995, p 36). Two weeks ago, researchers in Europe announced the first successful attempt at genetically modifying the malaria-carrying Anopheles mosquito. Now, in experiments on a different insect, Lourival Possani and his colleagues at the National Autonomous University of Mexico in Cuernavaca have shown that a little scorpion venom can block the malaria parasite's development.
Possani, who studies compounds derived from scorpions, recently discovered that the venom of Pandinus imperator contains a peptide, which he calls scorpine, that blocks the development of malaria parasites growing in culture. To see whether scorpine has the same effect in living insects, he and his colleagues created transgenic fruit flies that express the gene for the peptide in their gut.
The researchers then injected young Plasmodium parasites directly into the abdomens of the transgenic flies and their wild counterparts, and compared how many of these parasites matured. Over 40 per cent of the normal flies had mature malaria parasites. But only 12 per cent of the flies that made scorpine had parasites that continued to grow, Possani told researchers at a recent meeting at the Howard Hughes Medical Institute in Chevy Chase, Maryland. "I think it's a very promising result," he says.
Possani did his experiments in fruit flies because at the time no one had managed to genetically modify Anopheles mosquitoes. He knew, however, that David Schneider of the Whitehead Institute for Biomedical Research in Cambridge, Massachusetts, had shown that Plasmodium parasites injected into the guts of fruit flies develop in much the same way as they do in mosquitoes. Details of Schneider's technique were published in Science last week (vol 288, p 2376).
"It's wonderful to know that someone else can do it," Schneider says. "My guess is that the way we should do things is to model them in the fly first and then hop into the mosquito."
While other types of mosquitoes have been genetically altered before, it's only now that Fotis Kafatos of the European Molecular Biology Laboratory in Heidelberg and his colleagues have succeeded in modifying the malaria-carrying Anopeles (Nature, vol 405, p 959). In addition to introducing the scorpine gene, researchers would like to try a whole slew of other modifications to the mosquito.
Because Plasmodium affects mosquitoes' lifespan and ability to reproduce, researchers suspect that altered mosquitoes would outcompete the wild ones. But many questions remain. "Once you make this thing, how do you drive it into the environment?" wonders Schneider. "I'm not sure we understand the ecology of it enough."
Author: Nell Boyce
New Scientist issue: 8th July 2000
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