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One man’s mosquito trash is another man’s malaria treasure

June 7, 2010 - 19:46 -- Mark Benedict

There is a vision currently being researched in mosquito laboratories; the possibility that it may be possible to release mosquitoes containing some genetic factor that would drive through wild populations and disable their capacity to transmit disease. Not likely you say?

This once-ridiculed vision is close to testing for Aedes aegypti using the cytoplasmic incompatibility approach that I have blogged about previously . Because Wolbachia do not occur naturally in anophelines (my pet genus), a related approach is being developed using homing endonuclease genes (HEGs) by Austin Burt, Andrea Crisanti and others under a Grand Challenges in Global Health program.

With regard to the potential of gene drive systems for An. gambiae and African malaria more generally, the question frequently arises, “How will you handle the different types of An. gambiae, and what will you do about the multiplicity of vectors? Won’t each one require a separate intervention, and isn’t this impractical?” This is a valid concern since the spread of a genetic element between isolated genetic pools will be at least slowed and at most prevented. This may necessarily mean that numerous strains be produced and released. The answer will hinge in part on the relative diseases contribution of various forms and species. An accurate answer to this will be provided when – and if - a drive system effectively reduces the transmission contribution by one major vector - probably An. gambiae S – over a wide area.

Only one vector you say? Think what a remarkable achievement that would be! Concerns that the intervention has not eliminated all transmission by all vectors in Africa sets a very high threshold indeed for its attractiveness. This is particularly true considering the relatively small investment that is likely to be needed to produce and distribute such strains. The power of the technology – at least as envisioned - is that the natural biology of the mosquitoes and the drive system do the work that now is done by millions of citizens, thousands of public health workers and tens of nations and donors. It would be a non-intrusive technology that would be only slightly short of miraculous.

Issues about the multiplicity of species and mating subpopulations should also be considered in a slightly different light: What level of certainty about the effects of the intervention would you require if all malaria vectors in Africa could be affected by release of a single kind of mosquito? A very, very, perhaps impossibly high level of certainty. While the technological simplification of one vector is undeniable, untoward epidemiological, biosafety and socio-economic effects could be rapid and uncontainable. Whatever negative effects the intervention had, the effects could be difficult to anticipate and prevent.

This is novel and powerful technology by its nature. At this time, we should welcome some technical hurdles to ensure that the effects are well-known before using the technology against additional vector targets. If the technology performs according to design in even a tiny insignificant population of vectors, the vision immediately becomes an intervention, and the technical problems of population structuring and multiplicity of species become footnotes.

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