First evidence that GM mosquitoes reduce disease

Releasing genetically modified mosquitoes appears to have helped reduce cases of dengue in a town in Brazil. The news comes as the US is considering whether to approve the use of the same mosquitoes. 

The trial involved Aedes mosquitoes that had been modified to kill off wild mosquitoes of the same species, and was carried out in the town of Piracicaba. Just by eliminating the standing water where the mosquitoes that carry dengue and other diseases like Zika breed, Piracicaba was able to halve the number of dengue cases during the 2015-16 dengue season, compared with last year. But in the areas where the GM mosquitoes were released too, cases of dengue fell by more than 90 per cent.

This result is significant because regulators have been demanding evidence that this control method not only reduces wild mosquito numbers – as previous trials have shown – but also brings down disease incidence.

Piracicaba has a population of 400,000 people, and the areas where the GM mosquitoes were trialed are home to only around 5,000. Although this small trial doesn’t provide rigorous evidence of the standard that epidemiologists require, it shows potential, says Hadyn Parry, chief executive of Oxitec, the UK firm that developed the mosquitoes.

Independent experts agree. “It is very encouraging,” says Philip McCall of the Liverpool School of Tropical Medicine in the UK. However, it is not a randomised controlled trial, he adds. Oxitec is now working with the World Health Organisation to plan a much larger trial that will provide more rigorous evidence.