http://timesofindia.indiatimes.com/articleshow/1051719.cms

NEW YORK: Devastating epidemics that swept Europe during the Middle Ages seem to have had an unexpected benefit — leaving 10 per cent of today's Europeans resistant to HIV infection, researchers say.

However, they are divided on which one was responsible for it. Researchers, the Nature magazine reported, claimed this week that plague helped boost our immunity to HIV, but rival teams are arguing that the credit should go to smallpox.

But what is clear is that something has boosted the prevalence of a mutation that helps protect against the virus. The mutation, which affects a protein called CCR5 on the surface of white blood cells, prevents HIV from entering these cells and damaging the immune system, the magazine reported.

Around 10 per cent of today's Europeans carry the mutation, a significantly higher proportion than in other populations, researchers found.

Geneticists know that the mutation, called CCR5-32, appeared some 2,500 years ago — long before HIV reared its head. "You need something that has been around for generation upon generation," explains Christopher Duncan of the University of Liverpool, UK, who led the latest analysis. Plague fits the bill, he and his colleagues conclude from a modelling study.

Ferguson says "smallpox seems the most parsimonious explanation as it largely affected children."