Sterile mosquitoes use sex to kill in dengue trial

* Genetically sterile mosquitoes designed to kill species
* Early trial shows 80 percent cut in population in 6 months
* Dengue infects 50 million people a year, kills 25,000
Kate Kelland, Reuters AlertNet 11 Nov 10;

LONDON, Nov 11 (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.

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 programmed to do."

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

The World Health Organisation 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 antidote...so 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.

FACTBOX-Dengue fever a risk for 2.5 billion people
Reuters AlertNet 11 Nov 10;

Nov 11 (Reuters) - British scientists have created genetically sterile mosquitoes who use sex to kill off others in their species and researchers say early field trials suggest the idea could help halt the spread of dengue fever. [nLDE6AA1FD]

Here are some facts about dengue fever:

* Dengue is transmitted by the bite of an Aedes aegypti mosquito infected with any one of the four dengue viruses. Symptoms appear in 3 to 14 days after the infective bite.

* Dengue fever is a severe, flu-like illness that affects babies, young children and adults.

* It is often known colloquially as bone-break fever for the severe muscle and joint pains it induces, the disease causes death only when it develops into a more severe form, dengue haemorrhagic fever.

* Early clinical diagnosis of dengue haemorrhagic fever and careful clinical management by experienced doctors and nurses often saves lives.

* Global incidence of dengue has grown dramatically in recent decades.

* Around 2.5 billion people -- two fifths of the world's population -- are now at risk from dengue. The World Health Organisation (WHO) currently estimates there may be 50 million dengue infections worldwide every year.

* With no specific treatment for the four viruses, health officials focus on eradicating mosquitoes to prevent infections.

* More than 70 percent of the disease burden is in southeast Asia and the western Pacific area. Africa and the Eastern Mediterranean are much less affected.

* According to the WHO, the incidence and severity of disease are increasing rapidly in Latin America and the Caribbean.

* An increase in international air travel is facilitating the rapid global movement of dengue viruses. This increases the risk of dengue haemorrhagic fever epidemics by introducing new dengue viruses into susceptible populations.

* French drugmaker Sanofi-Aventis is one of various groups and firms seeking to develop a dengue vaccine and is currently testing it in late stage clinical trials.

SOURCE: Reuters/World Health Organisation.