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Last Updated: Tuesday, 19 December 2006, 00:13 GMT
Stopping malaria before the bite
Image of a mosquito
The malaria parasite is spread by mosquitoes
Researchers are developing a malaria vaccine which blocks development of the disease-causing parasite while it is still inside the mosquito.

The vaccine targets Pfs25, a protein key to the parasite's development during its time in the mosquito's gut.

When a mosquito bites a vaccinated person it would ingest antibodies which would block the protein's action.

The US National Institutes of Health study appears in Proceedings of the National Academy of Sciences.

The experimental malaria vaccine shows great promise for combating a terrible disease that exacts a devastating toll on the world's children
Dr Elias Zerhouni
National Institutes of Health

The researchers said the vaccine had the potential to eliminate malaria from entire geographic regions.

However, experts warned that the vaccine would not prevent or limit disease in the person who had been vaccinated, and predicted this could make it difficult to sell the idea to infected communities.

Tests of other malaria vaccines are under way, but as yet none has been licensed for widespread use.

Most attempt to neutralise the malaria parasite - Plasmodium - while it is in humans.

But this has proved difficult, because Plasmodium cells escape the human immune system by hiding in liver and blood cells.

Big killer

Malaria kills up to three million people worldwide each year, with most of the deaths in sub-Saharan Africa.

More than a million children in Africa die from malaria each year.

The latest vaccine has so far only been tested in mice.

It is a combination of the Pfs25 protein, and other molecules which are more easily recognised by the immune system, and more likely to spur it into action.

The combination triggers the production of large quantities of antibodies which, when ingested by the mosquito, zero in on the malaria parasite in its gut.

A microscopic analysis of the guts of mosquitoes fed a serum containing the antibodies triggered by vaccination in the mice, showed that they were completely free of the malaria parasites.

In fact, the mice produced higher levels of antibodies when they were tested three and seven months after their initial set of jabs, than they did after one week.

The same technology has already been used to develop vaccines against diseases such as typhoid fever.

Dr Elias Zerhouni, director of the National Institutes of Health, said: "The experimental malaria vaccine shows great promise for combating a terrible disease that exacts a devastating toll on the world's children."

However, Dr Ron Behrens, a malaria expert at the London School of Hygiene and Tropical Medicine, said the potential problem with the vaccine was that it would protect communities, but not the individual to whom the jab was administered.

"Until now all other vaccines that have been developed have offered the individual some form of protection," he said.

"In this case, the individual has got to make a sacrifice in order to protect the community, and that might make it very difficult to sell."

Professor Brian Greenwood, also based at the London School, said transmission blocking vaccines were most likely to be used as part of a combined vaccine, with a second component offering direct protection for the vaccinated individual.

The vaccine has been developed to combat Plasmodium falciparum, the parasite responsible for the most severe form of malaria.

But the researchers said it was also likely to be effective against another form of the parasite, Plasmodium vivax.




SEE ALSO
Malaria
08 Feb 03 |  Medical notes

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