Around 10 percent of modern Europeans enjoy a natural protection against AIDS as a result of the suffering of their forbears as plague outbreaks spread from the Middle Ages, a pair of British scientists say.

The findings of Christopher Duncan and Susan Scott, researchers at the University of Liverpool in northwest England, have been published in the Journal of Medical Genetics, The Times newspaper said in its Friday edition.

Scientists have known for some time that people with a genetic mutation known as CCR5-delta32 remain free of AIDS even after contracting HIV, as the mutation prevents the virus entering the cells of their immune system.

The new theory suggests that the CCR5 mutation is a by-product of the European plagues, otherwise known as the Black Death.

Duncan and Scott claim that these plagues were not bubonic, but epidemics of viral haemorrhagic fever, which spared those carrying the CCR5 mutation, meaning future local populations contained a higher proportion of such people.

Bubonic plague is a bacterial disease rather than a virus, and cannot be blocked by a mutation.

The research notes that there appear to be higher levels of the CCR5 mutation the more recently plague swept through a region.

Thus in Scandinavian countries -- which endured the Plague of Copenhagen as reently as 1711 -- the resistance figure is as high as 14 or 15 percent, the report said.

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