New research shows Africans and people of African descent could be up to 40 percent more likely to get HIV, the virus that causes AIDS,  than people of other races.  The study marks the first discovery of a genetic risk factor for HIV. More from VOA's Carol Pearson.

For years, researchers have been trying to find out why some people seem more vulnerable to HIV than others, and why some people can be repeatedly exposed to the virus but do not get infected.

They have also been puzzled by the racial makeup of people who get AIDS.  

Dr. John Bartlett from the Johns Hopkins School of Medicine in Baltimore speculates. "We have been puzzled by the fact that there has been so much AIDS in the African-American community," Dr. Bartlett said.

The study's authors say sexual behavior and other social factors did not fully explain why HIV affects so many Africans and African-Americans.

It turns out that race could be a factor. That's what researchers at U.S. and British universities found.  They discovered that a genetic variation in people of African descent
that once protected them against malaria seems to a play a role in increasing susceptibility to HIV and AIDS.

"What they showed is that there is a genetic difference in African-Americans and Africans that do make that race more susceptible to HIV infection," Dr. Bartlett said.

In the United States, African-Americans are 13 percent of the population, but they account for nearly half the cases of HIV and AIDS.

In sub-Saharan Africa, HIV affects 25 million people, far more than in any other region of the world.

The researchers analyzed data from more than three thousand members of the American military over a 25-year period.  

What they found was that 60 percent of African-Americans carry the genetic variation. Previous studies had shown that up to 90 percent of Africans have the same variation.

The scientists say their discovery could lead to research on more effective treatments for HIV and AIDS.  It may also help in developing a vaccine AIDS patient against the disease.