Genetically altered mosquitoes thwart dengue spreaders

An outdoor trial of mosquitoes genetically engineered to sabotage Aedes aegypti mosquitoes, which spread dengue fever, has been declared a success by scientists in the field.
The trial is first time genetically modified mosquitoes have been released in the wild. The strategy promises to provide a new weapon against dengue, a disease that infects 50 million people annually and kills 25,000. In the past year, dengue has reappeared in the US for the first time in 65 years, and in southern Europe.
By the end of the six-month trial on a 16-hectare plot, populations of the native insects, which spread the dengue virus had plummeted.
"It's a proof of principle, that it works," says Angela Harris of the Mosquito Control and Research Unit on the Caribbean island of Grand Cayman, where the trial took place. The MCRU conducted the trial with Oxitec, the company in Oxford, UK, that bred the GM mosquitoes.
Combating disease
The only current method of combating dengue is to kill and control the mosquitoes that pick up and spread the virus when they feed on blood from infected individuals. "There's no vaccine, no preventative drugs as there are with malaria, and no therapeutic drugs," says Luke Alphey, the chief scientist and founder of Oxitec.
The only control measures are therefore to kill the mosquitoes with insecticides or monitor and restrict the small pools of water, saucers and receptacles where they breed. "The range of options really is extremely limited," says Alphey, adding that the disease poses a threat to 40 per cent of the world's population.
Oxitec breeds millions of males carrying an altered gene called tTA which they pass down when they mate with females. The lethal gene overcommits the gene-reading machinery of larva and pupae, preventing them from growing properly and causing them to die before adulthood, breaking the insects' life cycle.
In the six months of the trial, the researchers released males in batches of 50,000. A total of 3.3 million were released.

**Published in "New Scientists"