The 90 per cent of Africans who carry the DNA variation are 40 per cent more likely to contract HIV than those without it, after similar exposure to the virus, scientists from Britain and America have found.
As the genetic change is common among people of African ancestry but virtually unknown among other ethnic groups, it could explain in part why HIV-Aids is more prevalent in sub-Saharan Africa. The United Nations estimates that 22.5 million people there are HIV-positive, more than two thirds of the global total of approximately 33.2 million.
The variant, known as “Duffy-negative”, is so common in Africa that it could be responsible for about 11 per cent of the continent’s HIV burden, or 2.5 million cases, scientists said.
“It could certainly be a contributing factor to the scale of the epidemic in sub-Saharan Africa. It’s the first time, so far as we understand, that a genetic factor that increases susceptibility to infection has come into play.”
Sexual behaviour is also involved in the epidemic in Africa, the only part of the world in which it predominantly affects heterosexuals.
The Duffy-negative gene has probably spread so widely through the African population because it provides resistance to a form of malaria called Plasmodium vivax. Professor Weiss believes it may also once have increased resistance against a precursor of the most deadly malaria parasite, Plasmodium falciparum.
These traits would have been highly advantageous in evolutionary Africa. As HIV is a new human pathogen, thought to have jumped from chimpanzees to people between 1910 and 1950, the gene’s effect on the virus would have had no negative consequences until recently. “Something that protected against malaria in the past is now leaving the host more susceptible to HIV,” Professor Weiss said.
Matthew Dolan, of the San Antonio Military Medical Centre in Texas, said: “After thousands of years of adaptation, this Duffy variant rose to high frequency because it helped protect against malaria. Now, with another global pandemic on the scene, this same variant renders people more susceptible to HIV. It shows the complex interplay between historically important diseases and susceptibility in contemporary times.”
For the study, published in the journal Cell Host & Microbe, scientists examined a group of US Air Force personnel, of whom more than 1,200 are HIV-positive, and who have been followed for nearly 22 years. The Duffy-negative genotype was seen almost exclusively in African-Americans.
A continent cursed
— Sub-Saharan Africa is the globe’s most Aids-affected region. In 2005, 24.5 million of its people were living with HIV and of all Aids sufferers, 64 per cent live there
— In 2005, about 2.7 million people became infected with HIV and more than two million died
— More than two million children under 15 are HIV-positive and more than 90 per cent live in Africa
— About 12 million African children under 17 have lost one or both parents to Aids
— About 72 per cent of all people needing anti-retroviral treatment live in Africa, and only one in six receives the necessary medicine
— Swaziland has the highest HIV rate, at 33.4 per cent of population. Botswana has 24.1 per cent and Zimbabwe 20.1 per cent