Researchers could be a step closer to a cure for malaria after discovering people with blood group O are naturally protected from its most severe forms.
Edinburgh University has found blood type O people are significantly less likely to experience the most life-threatening effects of malaria.
It is hoped the discovery will help develop drugs which mimic the properties of red cells.
Red cells in O group blood prevent malaria worsening.
"We may be able to reduce the number of children dying from severe malaria in sub-Saharan Africa"
Scientists at Edinburgh University and researchers in the US, Mali and Kenya studied African children and found that those with blood type O were two-thirds less likely to experience unrousable coma or life-threatening anaemia.
Both conditions are characteristic of severe malaria. Their findings are published in the journal PNAS.
In fatal malaria, it is often found that red blood cells which are infected by parasites block blood vessels which supply oxygen to the brain.
Malarial parasites arm the blood cell's surface with proteins which stick to blood vessel walls.
Malaria parasites
These proteins recruit healthy red blood cells to stick to the parasite, encasing the infected red blood cell inside a so-called rosette. It makes the blockage, and the disease, worse.
However, the team's latest findings suggest that group O red blood cells do not easily join rosettes as the cell's surface structure prevents it from sticking fully.
The researchers found that the process of rosetting is associated with severe malaria in all blood groups except O, and that rosettes are less well formed in group O red blood cells.
They suggest that reduced rosetting of malaria parasites is the reason why people with group O blood are less likely to suffer severe malaria.
It is estimated that malaria claims up to two million lives annually around the world.
Dr Alex Rowe, of Edinburgh University's School of Biological Sciences, said: "This discovery explains why some people are less likely to suffer from life-threatening malaria than others, and tells us that if we can develop a drug or a vaccine to reduce rosetting and mimic the effect of being blood group O, we may be able to reduce the number of children dying from severe malaria in sub-Saharan Africa."
The research was funded by the Wellcome Trust and the National Institutes of Health.
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