In late December, the Institute for Medical Research in Malaysia released about 6,000 genetically modified (GM) mosquitoes into the country's Eastern forests. They were designed by the U.K. company Oxitec as an experimental method to help prevent the spread of dengue fever, a mosquito-borne virus that impacts 50 to 100 million people every year and for which there is no cure. Last year, nearly 46,000 Malaysians caught the fever, which generally does not result in death, but causes headaches, fatigue, joint and muscle aches, nausea and vomiting.

All the mosquitoes were sterile male Aedes aegypti. Because female Aedes aegypti only breed once in a lifetime, introducing sterile males into a population is thought to be one way of greatly reducing the number of offspring and hence the number of dengue-carriers in the next generation. Actually, the males were not exactly sterile, but they carried a “lethal” gene that kills offspring early on; any survivors are not fit for reproduction. And since this was an experiment, the Institute simultaneously released 6,000 unmodified Aedes aegypti into the wild, with plans to track how many of each group survive.

Malaria-Proof Mosquito Created

Problem? Malaysians claim they were unaware that this trial was going on until late January, after it had ended. In the meantime, two Malaysian groups opposed to the use of GM mosquitoes appealed to the National Biosafety Board to cancel the study. They didn't know it was already happening.

What's wrong with using this biotechnology to try and reduce the risk of a raging illness among mosquito-infested areas? Some groups, including Greenpeace, worry that reducing the population of just one species will only make it easier for other species to proliferate in the wild — and Aedes aegypti is not the only dengue carrier. Others worry that, since tiny percentages of the GM mosquitoes will actually be female and/or will survive, they will live on reproducing in the wild, posing unknown ecological threats. The researchers claim to have killed all the remaining mosquitoes with insecticide at the end of the trial in order to prevent this. But it seems unlikely — dare I say impossible? — that they could catch every stray mosquito weeks after releasing them, though a few lingering bugs compared to a few thousand might be inconsequential.

Even further skeptics are wary of Oxitec itself, claiming the company is losing millions each year but has a loan to pay back by 2013, and it's rushing into the mosquito trials as a result of panic. But as the company's chief scientific officer, Luke Alphey, tells ScienceInsider

"We are a for-profit company and finance is not irrelevant," he says. "But anyone who realizes that there are 50 to 100 million cases of dengue every year would feel a sense of urgency."

Skeptics or not, no one has much real data to judge with yet. The only other trial releasing GM mosquitoes into the wild so far took place last year in the Cayman Islands. Researchers there measured an 80 percent reduction in overall mosquito population where the modified animals were released. Here is a video about that trial:

Photo: David Wrobel/Getty Images