The Black Death first appeared in Europe in 1347. Over the next three years it swept through Europe, killing 40% of its inhabitants. Over the next three centuries the disease was ever present, culminating in the Great Plague of London in 1665. While Black Death dwindled in Western Europe, in Eastern Europe it remained active until 1800. While the spread of the Black Death across Europe was a terrible tragedy, it is hardly news. However the legacy it has left is. One in ten Europeans posses a gene whose development was greatly encouraged by the Black Death in the Middle Ages. This gene, called CCR5-delta 32, prevents HIV from entering white blood cells.

Since 1900, historians have spread the idea that the Black Death was caused by bubonic plague. However, according to Professor Christopher Duncan and Professor Susan Scott of the University of Liverpool, this idea is incorrect. They say the plagues of Europe were instead outbreaks of a lethal, viral, haemorrhagic fever which used the CCR5 mutation as a gateway into the immune system.

In an article on the University of Liverpool website, “Lethal, viral haemorrhagic fevers were recorded in the Nile valley from 1500 BC and were followed by the plagues of Mesopotamia (700-450BC), the plague of Athens (430BC), the plague of Justinian (AD541-700) and the plagues of the early Islamic empire (AD627-744).  These continuing epidemics slowly raised the frequency from the original single mutation to about 1 in 20,000 in the 14th century simply by conferring protection from an otherwise certain death.” In short, those who had the CCR5 gene survived while those who didn’t, and were infected, suffered a 100% mortality rate. Professor Duncan added: “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. This maintenance of haemorrhagic plague provided continuing selection pressure on the CCR5-delta 32 mutation and explains why it occurs today at its highest frequency in Scandinavia and Russia.”