LOS ANGELES, April 27 (Xinhua)-- Most wild mosquitoes in Mali have already gained resistance to malaria parasite, scientists reported on Thursday. Genetic clues in these mosquitoes could be used in new malaria control strategies, the researchers said.

    The mosquito, called Anopheles gambiae (A. gambiae), is the major vector of human malaria in Africa caused by Plasmodium falciparum, the malaria parasite. Although scientists have found some wild mosquitoes are genetically resistant to malaria parasites, until now the mechanism of such natural resistance in mosquitoes were not known.

    But researchers from the United States and Mali discovered that quite a number of wild mosquitoes in Mali are actually immune to malaria parasites. Their findings appeared in the April 28 issue of the journal Science.

    In this study, the researchers collected female mosquitoes inside huts in Mali and let each produce one generation of offspring. Then, they let the resulting pedigrees feed on blood from a malaria-infected villager.

    After 7 to 8 days, they sliced open the insects and counted the oocysts-a stage in Plasmodium's life cycle-inside the insect gut. The lower the number, the more resistant the individual.

    Of the 27 mosquito pedigrees that met criteria for genotyping, the researchers found 22 had no infected individuals at all despite feeding on infected blood. This suggests that mosquito resistance to the malaria parasite is common.

    The researchers further found that in those insects without parasite oocysts, a small piece of the 2L chromosome protected mosquitoes from infection. The Plasmodium Resistance Island, as the researchers dubbed it, contains almost 1000 genes.

    Using several techniques to shake out genes of relevance, they pinpointed one gene, APL1, which appears to play a particularly important role. The researchers indicated that most wild mosquitoes are naturally immune to malaria infection, while those susceptible are minority.

    "We speculate that the wild-type mosquito phenotype is resistance and that susceptibility should be attributed to specific points of failure or loss of function in the mosquito immune system," the researchers wrote in the Science paper.

    According to Kenneth Vernick, an associate professor at the University of Minnesota who led the study, this finding may bring new strategies to control malaria, one of the most obstinate diseases that kills over 1 million people worldwide.

    "Using some insect-devouring fungi that preferentially kill Plasmodium-infected mosquitoes, maybe we can wipe out those with minority susceptibility alleles," he said. Enditem