Canadian researchers have discovered" an unexpected link" between AIDS and smallpox, opening new frontiers for developing ways to block AIDS.

The finding clarifies why some people are immune to HIV infection while enhancing hopes that human beings would eventually eradicate AIDS as they did with smallpox in the late 1970s.

Local media said Friday that the discovery was made by researchers in the University of Western Ontario and the University of Alberta.

The researchers have found that "the two most important human plagues in history" use the same route of entry to invade cells.

The conclusion coincides with the fact that the AIDS virus, or HIV, is not able to enter the cells of about 1 percent of Caucasians, who do not have chemokine receptors as a result of genetic mutation of 1,000 years.

Scientists speculate that the mutation protecting people from HIV emerged under an environmental pressure from an infectious disease.

It was smallpox that likely caused this mutation to spread in the human population, according to Canadian researchers.

People without this "lock" survived the epidemic hundreds of years ago, passing the lucky mutation on to their descendants, who then enjoy an immunity to AIDS as well, they said.

"People who have the mutation are otherwise healthy," said Grant McFadden, a professor and world-renowned expert in pox viruses with the University of Western Ontario.

"That means there might be tricks you could develop to mimic the genetic mutation, and prevent people from getting HIV," he added.

The "groundbreaking" discovery began with a series of experiments in Professor McFadden's lab and with University of Alberta graduate students brainstorming over beer, according to local media reports. (Xinhua)