Human Immunodeficiency Virus (HIV) affects 25 million people in sub-Saharan Africa today, an HIV burden greater than any other region of the world. Around 90 per cent of people in Africa carry the genetic variation, meaning that it may be responsible for an estimated 11 per cent of the HIV burden there.

Based on data from a 25-year study of thousands of Americans of different ethnic backgrounds, the research showed that the particular genetic variation found only in people of African descent increased their susceptibility to HIV infection by up to 40 per cent.

Conversely, the same gene variation also indicates tendencies to prolong survival of those infected with HIV by approximately two years.

"It turns out that having this variation is a double-edged sword. The finding is another valuable piece in the puzzle of HIV-AIDS genetics," said lead author of the study, Professor Sunil K. Ahuja, from The University of Texas Health Science Center at San Antonio in the United States.

The discovery marks the first genetic risk factor for HIV found only in people of African descent, and sheds light on the differences in genetic makeup that play a crucial role in susceptibility to HIV and AIDS.

"The big message here is that something that protected against malaria in the past is now leaving the host more susceptible to HIV," Professor Robin Weiss, co-author of the research, was quoted as saying by the Science Daily online.