A common fungus could be the newest weapon in the fight against malaria, researchers have suggested.
Mosquitoes carry malaria
A UK team found that it can prove fatal to mosquitoes which come into contact with the fungus when it is sprayed onto surfaces.
The study in Science showed over 90% of mosquitoes were killed within 14 days of being infected.
However, other experts cautioned there would be difficulties in ensuring the fungus was widely used.
Malaria kills at least one million people each year.
It is an extremely difficult disease to treat, as the parasite easily becomes resistant to the drugs used to treat it, and the mosquitoes develop resistance to the pesticides designed to kill them.
The University of Edinburgh and Imperial College, London researchers looked at whether there was a way of halting the mosquitoes in their tracks.
After the insects have fed on human blood, they find somewhere to rest for a few hours - usually a nearby ceiling or wall.
The researchers wanted to identify something which could infect them during this period.
They tested a type of fungus from the species Beauveria bassiana by applying inert spores directly, and as a spray, onto cage mesh.
When a mosquito touches the spores, the fungus germinates, penetrates the mosquito and grows within it, eventually killing the insect.
Not only were over 90% of mosquitoes killed within 14 days of being infected with the fungus, it effectively overwhelmed their body, slowing the insects down so that in their last few days of life they were less able to fly, and thus spread disease.
In laboratory tests, fungal infection reduced malaria transmission by 98%.
The key is to infect the insect as soon as possible after it has fed on infected blood.
It takes about two weeks after this for parasite levels in the insect to reach the point where they can infect another person bitten by the same insect.
If the insect is killed during this time, then it would have no opportunity to pass malaria on.
Professor Andrew Read, of the University of Edinburgh, who worked on the research, told the BBC News website: "It seems this fungus is eating them up from the inside."
He said the formulation of fungal sprays used to protect fields from locusts could be the model for anti-mosquito sprays.
Dr Matt Thomas of Imperial College, who led the study, said: "There is no evidence that insects can develop resistance to fungi.
"However, even if mosquitoes were to become resistant, it is extremely unlikely that they would also be resistant to chemical pesticides.
"It should be possible to use the chemical and biological pesticides together or in rotation to prolong their usefulness".
People 'need convincing'
A second paper in Science, by researchers from the Ifakara Health Research and Development Centre in Tanzania, the Swiss Tropical Institute in Basel and Wageningen University in The Netherlands found mosquitoes which rested on fungus-impregnated sheets in houses became infected and died.
Researcher Kija Ng'habi said: "This technology needs to be developed to be manageable and affordable."
Dr Joe Lines of the London School of Hygiene and Tropical Medicine told BBC News website: "It is always great to have something new, and the way this works is exciting."
He said the fungus was unusual because it attacked adult mosquitoes - most control measures tackle larvae.
But he said the fact that using the fungus would confer benefit on the community, rather than the individual, would mean that people may need a lot of convincing to use it themselves.
"When mosquitoes come into the house, some are young and will bite a person, getting malaria to pass on to somebody else.
"Other mosquitoes will be old, and have already got malaria from other people, and will give it to you."
"So the fungus wouldn't prevent you getting malaria from the mosquitoes which were already infected."