Washington: A common type of malaria that used to be powerless to infect certain groups of Africans is becoming more potent, putting tens of millions of people at risk, scientists said today.
Caused by a mosquito-borne parasite called Plasmodium vivax, the infection is rarely fatal but can lay dormant in the liver and cause chronic recurrences if left untreated.
"If this is on the move into continental Africa, it is going to complicate all the efforts of malaria elimination that have begun to make some progress there," Peter Zimmerman, professor of international health, biology and genetics at the Case Western Reserve School of Medicine, told AFP.
Zimmerman presented the latest research on the evolving nature of P vivax in the US capital at the American Society of Tropical Medicine and Hygiene annual meeting.
P vivax already causes over 100 million cases of malaria annually, but Africans and African-Americans in a certain blood group called Duffy negative have enjoyed natural immunity to the parasite.
Researchers first learned of this resistance, which is quite common among populations in sub-Saharan Africa and exists throughout the continent, in the early 20th century.
"It is sort of a bizarre start to the story," said Zimmerman.
Back then, people with syphilis, which was untreatable before the advent of penicillin, were being infected with malaria as a way to alleviate symptoms of psychiatric disturbances and paralysis.
After the practice spread through Europe, it reached the American medical community in 1922, he said.
"And right away, when African-Americans were treated with plasmodium vivax as the parasite that caused malaria in malaria therapy, it was observed that African-Americans were highly resistant to Plasmodium vivax infection."
Subsequent research confirmed this finding.
While P vivax causes some 65 per cent of malaria in India and is endemic in many other parts of the world, much of Africa has remained immune.
That is not the case for P falciparum, the most deadly type of malaria and the kind that is largely blamed for the estimated 660,000 people -- mainly children in Africa -- killed by the infection in 2010 according to the World Health Organisation.
While P vivax is not nearly as deadly and is sometimes called "benign malaria," it can cause chronic infection, fever chills, headache, vomiting, diarrhea and an enlarged spleen.
It is also growing increasingly resistant to current drug treatments, according to the Malaria Vaccine Initiative.
