The researchers grow the altered parasites in dishes of human blood, which they feed to bloodthirsty female mosquitoes. Each mosquito can harbor 30,000 to 40,000 developing parasites that, when mature, migrate to the insect’s salivary glands. Then the mosquito injects what is now a potential anti-malaria vaccine like a fusillade of tiny torpedoes into a lab mouse or a human volunteer.
“The problem with whole-organism vaccines is how to make them safe,” Kappe says. An earlier version of his vaccine only partially weakened the parasite, meaning it could still cause malaria in rare cases, but Kappe believes his lab has since fully disabled the parasite by deleting three genes crucial for its development. Similar versions of the new vaccine protected 100 percent of lab mice in early tests.
This summer, Kappe and colleagues will expose a dozen human volunteers to vaccine-harboring mosquitoes, followed eventually by a batch of bugs with the full-strength malaria parasite. If the vaccine proves itself in this and subsequent clinical trials, the next challenge will be scaling up production of the crippled parasites and injecting them via needles instead of mosquitoes.
[This article originally appeared in print as "Anti-Malarial Drugs, Injected by Mosquito."]