Experts identify key triggers in malaria vaccine hunt

Indian flood victims suffering from malaria lie on hospital beds in Alindra, 90 km (56 miles) south of the western Indian city of Ahmedabad August 18, 2004.

HONG KONG (Reuters) - Scientists have identified two surface molecules in the malaria parasite that could lead to developing a vaccine against the disease that kills at least one million people each year, a medical journal said on Wednesday.

The molecules, or antigens, appear to trigger powerful immune responses in patients that help protect them from falling ill in subsequent infections.

Led by Freya Fowkes at the Walter and Eliza Hall Institute of Medical Research in Melbourne, Australia, researchers plowed through 33 previous studies which analyzed people who had suffered from malaria in the past but were now immune.

What they found was that two antigens -- MSP-3 and MSP-119 -- triggered particularly powerful antibodies in patients, which protected them from falling ill subsequently with malaria by 54 and 18 percent, respectively.

"People in malaria endemic areas develop natural immunity to malaria, what (these studies) have done is go into these communities and see what antigens (the people) have immunity to and see if we can use these antigens to make vaccines," Fowkes told Reuters ahead of the publication of the team's findings.

"We've reviewed all the literature that looks at surface antigens ... results suggest that response to the two (antigens) were most indicative of protection against clinical disease. There may be other antigens out there that may be protective but they have just not been well studied."

The study was published in the latest issue of PLoS Medicine on Wednesday.

ELUSIVE VACCINE

The malaria parasite multiplies by invading red blood cells in its victims.

"The parasite uses different antigens to attach to the different molecules on the surface of red blood cells ... once inside the red blood cells the parasite rapidly divides and multiplies, and red blood cells burst and release even more (parasites) that infect even more red blood cells," Fowkes said.

"You can get hundreds of thousands of infected red blood cells in a person."

A malaria vaccine has been difficult to make because the parasite is very diverse with many antigens on its surface.

"With measles, you get just one measles infection and you are immune for life," Fowkes said.

"With malaria, you need multiple infections to develop long term immunity to disease. The actual parasite itself is very diverse with lots of different antigens on the surface ... and it takes a while to develop enough immunity to all the different antigens to give long term protection against malaria."

"Some molecules will be more effective at stimulating an immune response than others. We have to prioritize the antigens and also look at others in making a vaccine."

(Reporting by Tan Ee Lyn; Editing by Raju Gopalakrishnan)