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Injecting human volunteers with malaria parasites instead of exposing them to live mosquitoes could speed up clinical trials of new treatments for the disease, researchers have reported.

In usual trials people are exposed to infected mosquitoes, but it can be difficult to ensure that all receive the same dose of the infection.

Now, researchers at the Radboud University Nijmegen Medical Centre, Netherlands, have infected healthy volunteers with an injectable formulation of malaria parasites, potentially opening up a faster way to develop a malaria vaccine.

The formulation is an "enabling technology" that can be manufactured on a large scale, says Stephen Hoffman, co-author of the study published last week (13 November) in the American Journal of Hygiene and Tropical Medicine.

"For the first time this will allow investigators in any clinical facility in the world to test malaria drugs. It is going to change the face of testing of these new products," he says. Currently, five centres are looking at how best to administer the formulation.

Researchers took 18 healthy volunteers, split them into three groups and gave them differing doses of Plasmodium falciparum parasites (sporozoites) that had been frozen.  

Fifteen volunteers, five from each of the three groups, became infected with the disease. As soon as parasites were detected in blood smears the volunteers were given anti-malaria drugs for three days and were confirmed malaria free.

The sporozoites were harvested from the salivary glands of mosquitoes. The glands were dissected and the sporozoites were purified, bottled and then frozen in liquid nitrogen.  

Hoffman is also chief executive of Sanaria, a US-based biotechnology firm, which is looking at developing a vaccine by taking the sporozoites and irradiating them so they give people immunity but not malaria.

Brian Greenwood, professor of clinical tropical medicine at the London School of Hygiene and Tropical Medicine, and an expert on malaria, said that the injectable formulation is a major achievement.

He added that using live mosquitoes is complicated as researchers have to ensure they are at the right stage of infection.

"With this formulation you go to the freezer and get out your test tube. It makes the process much easier and quicker. It will also make it possible to do volunteer challenge studies in Africa, which is very difficult because no African centres have a colony of mosquitoes," he said.  

Link to full paper


American Journal of Hygiene and Tropical Medicine doi: 10.4269/ajtmh.2012.12-0613 (2012)