Genetically modified mosquitoes divide scientists
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It’s an excruciating disease that has earned the name “breakbone fever.” The World Health Organization estimates there are at least 50 million cases of Dengue fever around the world each year, primarily transmitted by the Aedes aegypti mosquito.
U.K.-based research company Oxitec is trying to change that through genetic modification of the culprit insects, which works much like bug birth control.
The hope is to eventually rid the world of Aedes aegypti. But doubt and questions of unforeseen side effects surround the technology.
A group of scientists at Oxitec nurture the very insect species responsible for passing the dengue virus to millions of people in recent decades.
The mosquitoes are fed animal blood and provided hotbeds to hatch their eggs. Of the new breed of insects, the males are selected for genetic transformation.
The genetic tweak makes the male insects dependent on tetracycline, an antibiotic that does not exist in their natural environment, said Dr. Andrew McKemey, a field trial manager at Oxitec.
The bugs are fed the tetracycline in the lab. When the male mosquitoes are released in the wild and mate, their progeny inherits the tetracycline-dependent gene. Without the antibiotic, the offspring dies at the larvae stage.
“The lethal trait is dominant,” said McKemey, adding it will surely be inherited. “Any offspring from these transformed mosquitoes will fail to develop.”
Aedes aegypti “lives with people,” said McKemey. The disease-transmitting mosquito thrives in drinking water containers and backyard puddles in the world’s most vulnerable areas.
Targeting the insects in all the places they hide through chemical pesticides is both impossible and dangerous, said McKemey. The genetic modification approach is “a more environmentally conscious technology that only targets the species you’re trying to control.”
A year after a field trial in parts of Brazil and the Cayman Islands, McKemey said, Oxitec noticed an 80 to 85 per cent decline in the Aedes aegypti population.
The same method could be applied to eradicate malaria. However, with many different species of mosquitoes causing the disease, at least a few of them have to be altered for the technology to work, said McKemey.
A plan to release altered insects in Key West, Fla., where there have been reported cases of Dengue fever, is being met with opposition. A local resident who created an online petition citing “unintended consequences” has so far garnered more than 100,000 signatures.
Some scientists have similar concerns.
“Any type of genetic modification is subject to mutation,” said Dr. Alfred Handler, a research geneticist at the U.S. Department of Agriculture. More experiments are needed to see if adverse mutation is possible, he said.
Handler, who does research on insects, also mentioned the small percentage of altered insects that survive after they’re released.
Although the survivor insects may be no more dangerous than regular Aedes aegypti, it is still important to know why they are surviving, said Handler, who worries the insects may eventually become resistant to genetic modification.
Oxitec says the survivors are too small in number to be significant.
Should a negative trait begin to occur in the modified insects, McKemey said, the fix is simple.
“If there’s a problem, you stop releasing new insects,” he said, adding the insects can only live up to eight days after their release.