Malaria vaccine announced

Staff Writers | 19 Dec 2006
Agence France Presse

An experimental vaccine that could eliminate the deadly parasite that causes malaria was announced in the U.S. today.

The vaccine, which so far has only been tested in mice, would not offer people immunity like most regular shots.

Instead, the goal is to use the blood of a vaccinated person to kill immature malaria parasites inside the mosquitoes that host the parasite and allow it to spread.

That could effectively prevent the mosquitoes from further spreading malaria.

"It's a transmission-blocking vaccine that attempts to get rid of the parasite reservoir inside its mosquito host," explained Owen Rennert, scientific director of the U.S. National Institute of Child Health and Human Development.

Borne by mosquitoes, malaria afflicts mainly people in the tropical parts of Africa, Asia and South and Central America, and kills up to three million people a year, many of them children.

Scientists have spent decades searching for a way to prevent the disease.

But numerous experimental vaccines tried against the form of the Plasmodium falciparum parasite that resides in humans have been unsuccessful, or produced only limited immunity.

Plasmodium falciparum incites the most deadly of several forms of malaria, all caused by parasites from the Plasmodium genus.

In this study, reported in the Proceedings of the National Academy of Sciences, the scientists decided to go after the early-stage form of the parasite living in the gut of the mosquito, before it matures and transfers to humans through bites from its mosquito host.

The researchers created a vaccine using a 'souped-up' version of a protein taken from the malaria parasite, and injected it into mice to create antibodies.

When serum was taken from the mice several months later and mixed in a test tube with the parasite cells, the mouse antibodies prevented the parasite cells from developing, effectively ending their life cycle.

A vaccine made in this way would not offer humans a first-line of defense against the disease, Rennert said. The vaccinated person would still likely be infected by the mature parasite when first bitten by the mosquito.

But in feeding on their blood, the mosquito would absorb antibodies from the vaccine that would wipe out the immature Plasmodium cells inside the insect's gut.

The result, they hope, could be to reduce the number of malaria cases down the line, as growth and transmission of the parasite is stifled.

But scientists at the National Institutes of Health, which includes the Child Health and Human Development institute, are also looking at ways to combine this vaccine with one of the experimental vaccines that offer direct protection from infection.

"The two combined might give you a better response than either alone," said Rennert.

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