Mosquito trial to cut dengue infection gets go-ahead in Malaysia
12 November 2010
Dengue is a potentially fatal disease that is passed on from the bite of an infected female mosquito of the Aedes aegypti strain. Bednets are of little use, because this strain of mosquito also bites during the day. With more than 2.5 million people at risk of infection, methods to control the mosquito population and combat the spread of disease are urgently needed.
Oxitec has created a genetically modified strain of Aedes aegypti that is effectively sterile and unable to reproduce. When the sterile males are released into the wild, they compete with other male mosquitoes to mate with females. But if a wild female mates with a sterile male, she will have no offspring that can survive to adulthood, and so the population of the next generation of mosquitoes is reduced.
Male mosquitoes do not bite and cannot spread disease, and will only mate with females of the same species. So the release of sterile male mosquitoes offers a safe alternative to insecticides. Because they only last for a generation, releasing the GM mosquitoes can't permanently alter the ecosystem.
Approval for the Malaysian trial follows the success of a smaller-scale trial conducted in the Cayman Islands earlier this year, which resulted in a significant reduction in the local mosquito population. See a video about the trial, conducted in collaboration with the Mosquito Research and Control Unit of Grand Cayman.
Scientists released batches of the sterile male mosquitoes in cages, three times a week over a 16-hectare area between May and October of this year. By August, mosquito numbers in the trial area had dropped by 80 per cent compared with a neighbouring area where no sterile mosquitoes were released.
Oxitec's Chief Scientific Officer, Luke Alphey, explains: "The results from the Cayman trial show that our method works in principle, but with such a small area involved, it would have been difficult to detect a drop in dengue cases. Our estimates suggest that an 80 per cent reduction in mosquitoes should result in fewer dengue infections and we are hopeful that these effects will begin to be seen in the larger Malaysian trial."
Ted Bianco, Director of Technology Transfer at the Wellcome Trust, commented: "There is a general recognition that the threat to human health from dengue infection is growing. With no medication or vaccine currently available, our methods of limiting the spread of dengue have to centre on controlling the mosquito population. As innovative approaches to vector controlemerge, it is important that they are evaluated rigorously, and in real world situations, so they can find their rightful place in the armamentarium of the public health agencies. It is for this reason that we are pleased to be supporting Oxitec's demonstration project and we look forward to the results of the Malaysian trial.”
Elsewhere, healthcare research company Roche has begun a clinical trial of a drug to treat dengue at the Oxford University Clinical Research Unit in Vietnam, with support from the Wellcome Trust. The drug was initially developed against the closely related hepatitis C virus but now researchers are looking to see whether it has any effects in patients infected with the dengue virus.
Dengue infection manifests itself with the sudden onset of fever, with associated headaches and severe muscle and joint pain that gives it the nicknames 'break-bone fever' or 'bonecrusher disease'.
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Image: A mosquito full of blood. Credit: Hugh Sturrock, Wellcome Images.
