Evolved malaria parasites concern scientists

Malaria parasites evolving in laboratory mice injected with a trial malaria vaccine became more lethal to unvaccinated mice, according to research from Penn State University.

The mice were injected with an important component of multiple candidate human malaria vaccines that are in clinical trials. While the research showed that the more-virulent parasites evolved after the vaccination, the mechanism of the evolution was unclear, Ivanhoe Newswire reports.

"Our research shows immunization with this particular type of malaria vaccine can create ecological conditions that favor the evolution of parasites that cause more severe disease in unvaccinated mice," Andrew Read, a biological sciences professor at Penn State, said, according to Ivanhoe Newswire. "We are a long way from being able to assess the likelihood of this process occurring in humans, but our research suggests the need for vigilance. It is possible that more-virulent strains of malaria might evolve if a malaria vaccine goes into widespread use."

The complexity of the malaria parasite has made the creation of an effective malaria vaccine particularly difficult. There has yet to be a malaria vaccine approved for widespread use.

"Our laboratory experiments followed clues from theoretical studies and earlier experiments that suggested that some malaria vaccines could favor the evolution of more-virulent malaria parasites," Read said, according to Ivanhoe Newswire.

If the vaccine candidates are unable to destroy all of the malaria parasites, the parasites remaining could evolve and be transferred from the vaccinated person to a new host, in a process called leaking.

"Vaccines are one of the most fantastically cost-effective health gains we've ever had, so there is no question that we should proceed on all fronts to develop a safe and effective vaccine against malaria," Read said, according to Ivanhoe Newswire. "At the same time, our research is revealing new reasons to proceed with vigilant caution."