World - Attack on dengue intensifies with two new weapons

Things are looking up for countries struggling to prevent dengue fever, with the development of two new tools.

Dengue fever affects up 100 million people each year worldwide, killing around 22,000. The existing method of control is to kill the mosquitoes that spread it by spraying their breeding sites – stagnant puddles – with pesticide. This is only partially effective, though.

In a clinical trial involving 4000 children in Thailand, a vaccine developed by Sanofi-Pasteur gave some protection from three of the four dengue virus strains. The children produced antibodies to the fourth strain, though the response was not strong enough give statistically meaningful protection. This meant that overall the vaccine only reduced the risk of contracting the disease by 30 per cent, not the 70 per cent hoped for.

The fact that the strain that wasn't protected against was the one circulating in the region at the time skewed the results, The New York Times reports.

Full approval will depend on the results of a much larger trial in 31,000 people in 10 Asian and Latin American countries. The hope is that this will include enough people to show activity against all four strains.

Weedy offspring

The second tool is a method of limiting the spread of mosquitoes by exposing them to millions of males genetically engineered to produce weakened offspring. The effectively sterile engineered males crowd out local rivals and the weakened offspring die before they can reproduce.

In a trial in the Cayman Islands, the native population fell by 80 per cent within six months. "This is clear evidence it can work," says Luke Alphey, chief scientist at Oxitec, the company in Oxford, UK, that bred the mosquitoes.

Oxitec is currently seeking permission to carry out another trial of the mosquitoes in Florida, and says the US Food and Drug Administration has now agreed to oversee the application.

The publication of the Cayman Islands trial results in a peer-reviewed journal was welcomed by critics of the approach, such as UK based lobby group GeneWatch and Friends of the Earth. But many remain sceptical and oppose further trials. "It adds to doubts about the efficacy of the approach, as releases of males had to be increased significantly beyond what Oxitec anticipated to achieve the desired results," says Helen Wallace GeneWatch UK.

Another concern cited by opponents is that other species of mosquito that transmit dengue would occupy niches left by the reduction of the original mosquito population, simply restoring the problem.

Wallace also argues that an effective vaccine would make the mosquito approach redundant.

Duane Gubler, who has been researching the dengue virus for many years at Duke National University of Singapore, disagrees. "Both vaccines and new tools for vector control are desperately needed if we are to succeed in controlling dengue," he says. "It's an exciting time with several vaccines in trials, all of which look promising, and several new tools to control the principal vector, including the sterile male approach, and mosquitoes genetically resistant to dengue infection, which also look promising."

Journal references: The Lancet, DOI: 10.1016/S0140-6736(12)61428-7

Nature Biotechnology, DOI: 10.1038/nbt.2350

Andy Coghlan

http://www.newscientist.com/