SciDev.Net

[LUSAKA] Different strains of the plasmodium parasites that cause malaria may be behind the failure to develop an effective malaria vaccine, according to a study conducted in Mali.

Research published in PLoS Medicine this month (12 March) indicates that the immune response generated by a vaccine might be less effective — or even ineffective — if its contents do not match the particular parasite causing malaria in a given location.

Lead researcher Christopher Plowe of the University of Maryland School of Medicine said the study demonstrated the importance of determining the genetics of pathogen populations before starting vaccine trials.

Without this, he said, the effectiveness of a vaccine cannot be determined accurately and potentially useful vaccines might be abandoned if tested on inappropriate populations. 

Plowe and colleagues looked at a specific parasite protein, MSP-119, used in malaria vaccines. The MSP-119 gene has six genetic variations that occur in various combinations in different strains of the malaria parasite.

The researchers used DNA sequencing to examine the MSP-119 gene in samples from over 1300 infections in 100 Malian children over three years.

They discovered that the type of MSP-119 used to produce a trial vaccine accounted for just 16 per cent of infections.

The findings show that most parasites at the Malian test site have a different form of MSP-119 than the one contained in the vaccine.

The director of the Tropical Diseases Research Centre in Zambia, Emmanuel Kafwembe, said there is a lack of effective malaria vaccines that can be used continent-wide.  

"[The study] may be the beginning of the discovery of a vaccine that can be used beyond boundaries," Kafwembe told SciDev.Net.

According to the World Health Organization there are more than a million deaths from malaria each year globally and around 90 per cent of these occur in Africa, mostly in young children.

Link to full paper in PLoS Medicine

Reference: PLoS Medicine doi: 10.1371/journal.pmed.0040093 (2007)