Dec. 3, 2010, 7:53 a.m.
Scientists use sterile males to mate with infected females in fight to curtail spread of disease that kills 25,000 people a year
Dengue fever is transmitted by the bite of the female mosquito. Photograph: Rex Features
Swarms of genetically modified mosquitoes could be released into the wild to combat dengue fever around the world.
British scientists today said a small-scale trial of the strategy, which was carried out in the Cayman Islands, had cut mosquito numbers by 80% in six months.
The trial – which used 3 million modified insects – was run with the Mosquito Research and Control Unit (MRCU), and has raised hopes that the disease may be curtailed in countries such as Brazil, Malaysia and Panama.
Dengue fever causes severe flu-like symptoms and can be lethal. It spreads through the bite of infected female aedes aegypti mosquitoes.
Researchers at the Oxford-based firm Oxitec modified male mosquitoes to carry a gene that means they can only survive if they get regular feeds of an antibiotic called tetracycline. Without the drug, the mosquitoes die within a few days.
When the mosquitoes are released into the wild, they mate with females but produce offspring that inherit the gene and so die almost immediately.
"One of the main advantages is that the males actively look for the females – that's what they are programmed to do," Luke Alphey, a scientist at Oxford University and co-founder of Oxitec, said.
"By giving them tetracycline in the lab, we can keep them alive and breed large numbers of them, but when we release the males into the environment and they mate with wild females, all the offspring inherit a copy of the gene that kills them if they don't get the antidote ... so they die."
The World Health Organisation estimates there are 50m cases of dengue fever a year, of which 25,000 are fatal. About 2.5 billion people – or two-fifths of the world's population – are at risk, mostly in Africa and south-east Asia.
There is no vaccine or treatment, and experts say new ways of controlling it are urgently needed because of a sharp rise in global infection rates in recent decades.
A report by the World Health Organisation last year estimates that in eight countries in the Americas and Asia, dengue fever causes illness, disability and deaths that cost at least $440m a year.
Angela Harris, of the Cayman MRCU, said she was encouraged by the trial, conducted from April to October. "This kind of technology really has a place for reducing dengue and having an impact on human health," she said.
"One of dengue's main problems is that there's no cure. So the only control you can really come by ... is killing the mosquitoes and making sure they're not there to transmit the virus in the first place."
Alphey said his firm was in talks with officials in several countries about further and larger trials.
The French drug firm Sanofi-Aventis is among companies seeking to develop dengue vaccines. It is testing a drug in late stage clinical trials – but it could be many years before a vaccine is on the market.