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Plague outbreaks in Europe over the last few centuries, particularly widespread episodes of viral hemorrhagic fever, may have given some Europeans genetic protection against HIV infection, according to a study by U.K. researchers, Agence France-Presse reports. The plagues spared people who carried a genetic mutation called CCR5-delta 32, which prevented plague-causing viruses from attaching to the CCR5 receptors on the surface of the body's cells, a necessary step in the infection process. HIV also uses the CCR5 receptor to infect immune system cells, and the genetic mutation appears to prevent HIV from similarly infecting the cells. Because the plagues spared those people carrying the mutation, future populations throughout Europe included a higher proportion of people with the mutation--and with a natural ability to fight off HIV infection. About 10% of Europeans carry the CCR5 mutation, write the researchers in the Journal of Medical Genetics. In Scandinavia, which suffered through the particularly virulent Plague of Copenhagen in 1711, as many as 14% to 15% carry the HIV-protective mutation, the researchers say.