Scientists have released genetically modified mosquitoes in an experiment to fight dengue fever in the Cayman Islands, British experts said Thursday.
It is the first time genetically altered mosquitoes have been set loose in the wild. Scientists believe the trial could lead to a breakthrough in stopping the disease, but critics argue the mutant mosquitoes might wreak havoc on the environment.
"Anything that could selectively remove insects transmitting really nasty diseases would be very helpful," said Andrew Read, a professor of biology and entomology at Pennsylvania State University, who was not involved in the project.
Dengue is a potentially fatal mosquito-borne disease that can cause fever, muscle and joint pain and hemorrhagic bleeding. More than 2.5 billion people are at risk, and the World Health Organization estimates there are at least 50 million cases every year. There is no treatment or vaccine.
Unlike malaria, which is also spread by mosquitoes, dengue outbreaks are unpredictable and bed nets are of limited use because dengue-spreading mosquitoes also bite during the day.
Sterile male mosquitoes were created by researchers at British company Oxitec by manipulating the insects' DNA. Scientists in the Cayman Islands released 3 million of the mutant mosquitoes to mate with wild female mosquitoes, which bite humans and spread diseases.
The sterile mosquitoes were released from May to October in a 40-acre area. By August, mosquito numbers in that region dropped by 80 percent compared with a neighboring area where no sterile male mosquitoes were released.
Luke Alphey, Oxitec's chief scientific officer, said the company estimates an 80 percent reduction in mosquitoes should result in far fewer dengue infections.
Some scientists worry that the release of mutant mosquitoes could be an environmental nightmare.
"If we remove an insect like the mosquito from the ecosystem, we don't know what the impact will be," said Pete Riley, campaign director of GM Freeze, a British nonprofit group that opposes genetic modification.
Humans have a patchy track record of interfering with natural ecosystems, Riley said. In the past, such interventions have led to the overpopulation of species including rabbits and deer. "Nature often does just fine controlling its problems until we come along and blunder into it."