Brussels, 10 Mar 2005

Biologists at the University of Liverpool in the UK have published new research suggesting that the reason why ten per cent of Europeans are immune to HIV infection is because of the plagues that swept the continent in ancient times.

Scientists have known for some time that these individuals carry a genetic mutation (of the gene known as CCR5) that prevents the HIV virus from entering their immune system. What has puzzled them is the fact that HIV has emerged only recently, and thus cannot have played a role in raising the frequency of the mutation to the high levels found in some parts of Europe today.

New research by Christopher Duncan and Susan Scott, however, attributes the high prevalence of the mutation to the fact that it also offers protection from another deadly viral disease that ravaged Europe in historic times.

According to Professor Duncan: 'The fact that the [...] mutation is restricted to Europe suggests that the plagues of the Middle Ages played a big part in raising the frequency of the mutation. These plagues were also confined to Europe, persisted for more than 300 years, and had a 100 per cent case mortality.'

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Whereas some historians have tried to suggest that the many plagues that swept Europe in past times were outbreaks of bubonic plague, which is a bacterial disease, Professor Duncan and Dr Scott have shown that they were in fact epidemics of a lethal, viral, haemorrhagic fever that used the CCR5 gene as an entry point into the immune system.

Using computer models, the two researchers demonstrated how outbreaks of this disease throughout history provided the necessary selection pressure - simply by conferring protection from an otherwise certain death - to force up the frequency of this genetic mutation from 1 in 20,000 at the time of the Black Death in 1347 to the values of 1 in 10 today.

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'Haemorrhagic plague did not disappear after the Great Plague of London in 1665-66 but continued in Sweden, Copenhagen, Russia, Poland and Hungary until 1800,' concluded Professor Duncan. 'This maintenance of haemorrhagic plague provided continuing selection pressure on the [genetic mutation] and explains why it occurs today at its highest frequency in Scandinavia and Russia.'

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