Friday March 20 6:30 PM EST

Malaria Discovery May Aid Prevention

NEW YORK (Reuters) -- The identification of a chemical crucial to the life cycle of the malaria parasite may provide scientists with a new weapon to fight the mosquito-borne illness, researchers say.

Biologists at Imperial College in London believe their discovery could "lead to the development of new methods of interrupting malarial transmission."

Their report, published in the current issue of the journal Nature, focuses on the life cycle of the Plasmodium family of protozoa that cause malaria. The mature organisms live inside blood cells, and are passed from human to human via the bite of the Anopheles mosquito.

Once inside the mosquito digestive tract, the malaria protozoa undergo one stage in their life cycle, a process called gametogenesis that requires a specific pH environment (8.2-8.4).

However, the normal pH level of the mosquito gut -- 7.4 -- initially inhibits this type of growth. But scientists say the introduction of an (until now) "mystery" chemical seems to trigger a subsequent rise in pH, allowing the malarial life cycle to continue.

The London researchers now say they have identified this chemical as xanthurenic acid. Xanthurenic acid alone appears to adjust the mosquito's pH environment to Plasmodium-friendly levels: the investigators say experiments proved that the introduction of other, similar acids "failed to induce gametogenesis."

In their accompanying commentary in the same issue of Nature, malaria experts Richard Carter and Lisa Ranford-Cartwright of the University of Edinburgh in Scotland say xanthurenic acid may be "the 'ignition key' to transmission of malaria through mosquitoes."

They believe that mosquito-borne transmission might be interrupted by the introduction of a species of genetically-altered insects that lack the capacity to produce xanthurenic acid. Tests assessing the viability of Plasmodium in the bodies of these new types of mosquitoes could be a crucial next step in antimalarial research, they concluded.

SOURCE: Nature (1998;392:227-228, 289-292)

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