November 11, 2010 / 4:14 PM / 9 years ago

Sterile mosquitoes use sex to kill in dengue trial

LONDON (Reuters) - British scientists have created genetically sterile mosquitoes which use sex to kill off others in their species, and researchers say early field trials suggest the idea could help to halt the rapid spread of dengue fever.

Patients suffering from dengue fever rests on a bed covered by a mosquito net at the Alonso Suazo hospital in Tegucigalpa, Honduras, July 20, 2010. REUTERS/Edgard Garrido

Scientists from a firm called Oxitec ran a small trial with the Mosquito Research and Control Unit (MRCU) in the Cayman Islands in the Caribbean. This found that releasing 3 million of the genetically altered bugs into a small area managed to cut the species population by 80 percent in six months.

Dengue fever, a disease which causes severe flu-like symptoms and can kill, is spread through the bite of infected female Aedes aegypti mosquitoes.

“The idea is based on releasing sterile males who will go out and mate with wild females,” said Luke Alphey, Oxitec’s chief scientist and co-founder.

“One of the main advantages is that the males actively look for the females — that’s what they are programed to do.”

Larvae are produced but most die before they hatch and the rest survive only a short time as mosquitoes.

The World Health Organization estimates there are 50 million cases of dengue fever a year, of which 25,000 are fatal, and about 2.5 billion people — two-fifths of the world’s population — are at risk, mostly in Africa and southeast Asia.

There is no vaccine or treatment for dengue, and experts say innovative ways of dealing with its spread are urgently needed, since global incidence has risen sharply in recent decades.

French drugmaker Sanofi-Aventis is one of various groups seeking to develop dengue vaccines. It is testing its candidate in late stage clinical trials, but experts say it could be many years before a vaccine is on the market.

Alphey’s team bred a version of the male Aedes aegypti mosquito which can attract and mate with females but is genetically modified to die if it is not fed on a certain antidote, in this case an antibiotic called tetracycline.

“We put a segment of DNA into the mosquito which means it will die unless it gets the antidote,” said Alphey told reporters at a briefing in London on Thursday.

“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 they die.”

Most of the offspring die as larvae, he said, but even those who manage to hatch face a very short life.

Angela Harris of the Cayman MRCU, said she was very encouraged by the results of the trial, which was conducted and monitored during April to October this year.

“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, there’s no vaccine and there are no drugs you can take to avoid it or get better from it. 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 Oxford-based firm is in talks with officials in various countries, including Malaysia, Brazil and Panama about conducting further and larger trials.

Editing by David Stamp

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