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Last Updated: Sunday, 9 October 2005, 23:02 GMT 00:02 UK
Glowing insects 'to cut malaria'
Abdominal segments (Nature Biotechnology)
A close-up of the glowing mosquito abdomen
A protein that makes the sex glands and sperm of male mosquitoes glow could help reduce malaria infection rates, UK scientists say.

They used the protein to tag male mosquito larvae, the genes of which can be manipulated to make them infertile.

As malaria is spread only by female mosquitoes, the scientists hope sending such sterile males into the wild could help kill off infective populations.

The Imperial College London research is reported in Nature Biotechnology.

Malaria causes 300-500 million cases and one million deaths each year.

Green glow

There are drugs that can treat malaria, but eradicating the mosquitoes that carry the disease is one way to prevent this killer.

Malaria is transmitted to humans only by biting female mosquitoes of the genus Anopheles.

Like others in the past, Professor Andrea Crisanti and colleagues believe that a good way to stop transmission would be to make sure the male mosquitoes these females mate with are infertile, hence killing off infective populations.

It's by no means the first genetic method for sex separation of mosquitoes, but it may be an advantageous one
Professor Chris Curtis
London School of Hygiene and Tropical Medicine

In theory, releasing sterile females into isolated populations would also work, but it would take longer because some fertile females would remain and both types of female while alive could still bite humans, which would be dangerous because it could increase malaria risk in the shorter term.

Mosquitoes go through four stages in their life cycle: egg, larva, pupa, and adult.

While still in the larval stage, it is possible to manipulate the insect's genes to render it infertile.

However, it has been difficult for scientists to then tell which of the larvae will become males and which will become female mosquitoes.

To get round this, Professor Crisanti's team used a protein that glows green to tag only male larvae.

They manipulated the genes of the larvae so that the males would make this protein in their gonads, which would fluoresce.

Using a machine that recognises this glow, the researchers were able to sort 18,000 larvae into male and female in only 10 hours.

"All individuals that had shown a green fluorescent phenotype at the larval stage emerged as males and all individuals that were negative for green fluorescence emerged as females," they said.

Disease control

When these males grow into adults their sperm also glows, which means scientists would also be able to trace the females with which they had mated.

The species that the researchers looked at are mainly found in Asia, but they believe it will apply to other Anopheles species.

Professor Chris Curtis, from the London School of Hygiene and Tropical Medicine, said: "It's a neat method. It's by no means the first genetic method for sex separation of mosquitoes, but it may be an advantageous one.

"And the fact that you can also identify the sperm of these males in the females they have mated with is another advantage."

It would mean researchers could check important parameters such as dispersal and whether there were other non-sterile males competing to mate with the females in a given region, he said.

He added that a number of machines would be required to reach the million or more sterile male mosquitoes that would need to be released into a population for eradication of pockets of malaria.




SEE ALSO:
Fungus 'may help malaria fight'
09 Jun 05 |  Health


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