The parasite depends on mosquitoes for more than just transport, however. Plasmodium goes through much of its complex life cycle inside the mosquito, passing through the gut as it goes.
Here lies the bottleneck: While mosquitoes may ingest anywhere from 100 to 1,000 immature cells during a blood meal, by the time the parasite ends up in the mosquito’s gut, only five or fewer spores, known as oocysts, remain.
This is where researchers targeted their attack. The gut is a complicated place, full of bacteria that help break down nutrients and digest food. Perhaps some of these bacteria could be enlisted to break down the Plasmodium spores as well.
Researchers at the Johns Hopkins Malaria Research Institute devised a genetically modified version of the Pantoes agglomerans bacteria that naturally lives in the mosquito gut. The new P. agglomerans acts much the same as ordinary P. agglomerans, and should be able to spread through wild mosquito populations. Except the engineered bacteria has one unique and deadly trait: It produces proteins that destroy Plasmodium oocysts.
This isn’t the first use of genetic modification strategies to quell mosquito-spread disease. In November we reported on a project that has introduced genetically modified mosquitoes into the wild. The new mosquitoes carry genes that kill their young—when they mate with native mosquito populations, the offspring die before they can fly.
This new approach doesn’t require modifying the mosquitoes directly, just their gut bacteria, which makes the technique more portable. More than 100 species of mosquito transmit malaria, and although the researchers only tested two, they wrote in the Proceedings of the National Academy of Sciences that the strategy "may well be 'universal' as effectiveness does not appear to be influenced by mosquito species." And effective it was: the genetically enhanced bacteria suppressed populations of both the human malaria parasite Plasmodium falciparum and the rodent malaria parasite Plasmodium berghei by 98 percent.
Image of Anopheles stephensi mosquito via Wellcome Images on Flickr