GM mosquito could help slash dengue vectors

[LIMA] The release of genetically modified (GM) mosquitoes could help reduce the numbers of dengue-transmitting wild mosquitoes, although it is unlikely to eliminate them entirely, according to a study.

Dengue fever is the world's fastest spreading tropical disease, according to a WHO report released last week (16 January): every year it infects around 50 million people and it represents a "pandemic threat".

The suppression of dengue through releasing GM versions of the Aedes aegypti mosquito — the  vector for dengue fever — might soon become possible, with early tests already showing success in Brazil and the Cayman islands.

But before the wide-scale release of transgenic mosquitoes can take place, national regulatory bodies are likely to seek additional evidence that proves such a release will work in natural habitats.

This is where detailed spatial models can help, says the new modeling study, which was published in PLOS One last month (21 December).

Laboratory experiments, field tests and even general mathematical models are not sufficient to account for various environmental factors that may affect the success of a large-scale GM mosquito release, the study says.

So the researchers developed a biologically detailed model that tracks the development of GM mosquitoes in individual breeding sites, and used it to simulate the release of such mosquitoes in Iquitos, Peru.

The simulation was made using a strain of GM mosquitoes, with an inserted gene that prevents female mosquitoes from flying, and therefore from mating or biting, meaning that the insects die soon after birth.

Male mosquitoes that carry such a transgene can be released in control programmers. They pass the transgene on to offspring, of which the biting females die, while the surviving males mate and transmit the transgene to another generation, carrying the suppression effect through multiple generations.

The researchers found that a number of factors boosted the campaign's success.

These included: releasing mosquitoes uniformly rather than at random sites; treating the wild populations with pesticides to reduce their numbers before the GM mosquito release; and releasing GM strains that have several independent transgenes inserted.

But the researchers did not study whether suppression of numbers of wild mosquitos leads to a reduction in the actual burden of dengue fever, lead author Mathieu Legros, an entomologist at North Carolina State University, United States, tells SciDev.Net.

"The relationship between vector density and dengue transmission is complex and further studies are needed to evaluate carefully how this approach could help reduce dengue incidence," says Legros.

César Cabezas, a tropical medicine expert and chief of Peru's National Institute of Health, tells SciDev.Net that the value of models for studying infections whose dynamics depend on many variables, as is the case with dengue, may be limited.

Such vector-borne infections will need a selection of different interventions to keep them in check, Cabezas says.  

Link to full study

Link to WHO report on neglected tropical diseases