* Genetic method creates male-only offspring
* Malaria parasite spread by biting female mosquitoes
* Some 627,000 people die each year from malaria
* Hope is that new method could "crash" mosquito populations
By Kate Kelland
LONDON, June 10 (Reuters) - Scientists have found a way of genetically modifying mosquitoes to produce sperm that only creates males, offering a potential fresh approach to fighting and eventually eradicating malaria.
Researchers from Imperial College London tested a genetic method that distorts the sex ratio of Anopheles gambiae mosquitoes, the main transmitters of the malaria parasite, so that the female mosquitoes that bite and pass the disease to humans are no longer produced.
In a study published in the journal Nature Communications, the team reported that in the first laboratory tests, the technique created a fully fertile mosquito strain that produced 95 percent male offspring.
"For the very first time, we have been able to inhibit the production of female offspring in the laboratory and this provides a new means to eliminate the disease," said Andrea Crisanti, who led the research at Imperial's department of life sciences.
Nikolai Windbichler, who co-led the work, said what was most promising about the results is that they are self-sustaining.
"Once modified mosquitoes are introduced, males will start to produce mainly sons, and their sons will do the same, so essentially the mosquitoes carry out the work for us," he said.
In their experiments, which took more than six years, the scientists inserted a DNA cutting enzyme called I-PpoI into Anopheles gambiae mosquitoes.
The enzyme works by cutting the DNA of the female-producing X chromosome during production of sperm, so that almost no functioning sperm carry it. As a result, the offspring of the genetically modified mosquitoes was almost exclusively male.
The scientists introduced the genetically modified mosquitoes to five caged wild-type mosquito populations. In four of the five cages, this eliminated the entire population within six generations due to the lack of females.
The hope is that if this could be replicated in the wild, this would ultimately cause the malaria-carrying mosquito population to crash.
Experts not directly involved in the work were impressed with its results and enthusiastic about its potential.
"This is super cool work," said Michael Bonsall, a reader in zoology at Britain's University of Oxford. "Reducing mating potential of mosquitoes by modifying sperm is a population suppression technology. It will be very exciting to see how this ... is now taken forward."
Malaria kills some 627,000 people worldwide each year, according to the World Health Organisation, and the vast majority of its victims are babies and children in sub-Saharan Africa.
Malaria control has been threatened by the spread of insecticide resistant mosquitoes and malaria parasites resistant to drugs, and the WHO says more than 3.4 billion people remain at risk from contracting the disease.
"Malaria is debilitating and often fatal and we need to find new ways of tackling it," said Crisanti. "We think our innovative approach is a huge step forward." (Editing by Tom Heneghan)