New Delhi, July 26: People with blood groups A and B when infected with the malaria parasite Plasmodium falciparum are more likely to develop cerebral malaria than those with group , a study in India has shown.
The research bolsters evidence for earlier observations that group protects people from cerebral malaria and for the mechanism to explain why groups A and B increase the risk for this severe form of malaria.
A team of researchers in Odisha have shown that red blood cells (RBCs) from groups A and B, infected with the parasite, bind to uninfected RBCs, a process termed as rosetting which occurs much less frequently among group RBCs.
“Rosetting is a biological trick the parasite has developed to evade the elimination of infected RBCs through the spleen,” said Manoranjan Ranjit, a scientist at the Regional Medical Research Centre, Bhubaneswar. “But high levels of rosetting increases the risk of cerebral malaria.”
Ranjit and his colleagues analysed blood groups of patients with severe and relatively mild malaria and observed that the risk of cerebral malaria appears highest among people with group B, slightly lower among those with group A and lowest among those with group .
They also observed correlations between rosetting and blood groups.
The highest levels of rosetting occurred in RBCs from group B, lower levels in RBCs from group A, and the least in RBCs from group . Their findings appear this week in the British journal Transactions of the Royal Society of Tropical Medicine and Hygiene.
“Such studies are valuable in improving our understanding of the mechanisms of malaria,” said Amit Sharma, a group leader for structural and computational biology at the International Centre for Genetic Engineering and Biotechnology, New Delhi, who was not involved in the study.
“They raise questions about mechanisms which may be addressed through tools of molecular biology,” Sharma said.
The study was based on the analysis of the blood groups of 343 patients diagnosed with malaria at the Sriram Chandra Bhanj Medical College and Hospital, Cuttack, over a two-year period.
“The findings imply that doctors looking after malaria patients with blood groups B or A need to be extra vigilant about the risk of cerebral malaria,” said Biranchi Mohapatra, professor of internal medicine at the Veer Surendra Sai Medical College, Burla, a six-hour drive west of Bhubaneswar.
There is no nationwide data on the distribution of blood groups in the Indian population, Mohapatra said, but limited figures from blood bank collections suggest that about 50 per cent of people have group , about 35 per cent have group A, 10 per cent have group B, and the rest are AB.
Ranjit, a parasitologist for 20 years, said the study from Odisha establishes the link between rosetting and risk of cerebral malaria in the Indian population and adds to earlier evidence from Africa.
Five years ago, a team of malaria scientists in the UK, the US, and Mali in western Africa had suggested that people with blood group are protected against severe Plasmodium falciparum malaria through the mechanism of reduced rosetting.
“Rosetting leads to clusters of RBCs, several uninfected RBCs cluster around an infected RBC — it’s a trick the parasite has evolved to hide,” said Ranjit. “But such clusters of RBCs may obstruct routine blood flow through vessels carrying oxygenated blood to the brain — leading to the cerebral complications.”
The researchers believe future studies should seek to validate these findings in other states. “In the long-term, if medical researchers can find a safe way to block rosetting, it might open up new treatment strategies,” Ranjit said.
India’s health ministry claims only about 1,000 people die from malaria in the country each year, but doctors as well as public health experts believe the number is many times higher. Two years ago, a team of Indian and Canadian scientists estimated that the actual number of deaths could be as high as 2,05,000 each year.