Those living within countries that were conquered by the Romans are more susceptible to HIV because of variations in a gene that confers resistance to the virus. The gene in question codes for a protein receptor called CCR5, which is the receptor that HIV binds to before entering cells. One gene varient, CCR5-Delta32 has 32 DNA base pairs missing and produces a receptor that HIV cannot bind to - and so prevents the virus from entering cells. People with this gene variant have some resistance to HIV infection and take longer to develop AIDS.
In general, only people in Europe and western Asia carry the variant, which becomes less frequent the further south a population is. More than 15% of people in some areas of northern Europe carry CCR5-Delta32 compared with less than 4% of Greeks. The HIV pandemic itself occurred too recently to have influenced the distribution of the variant. However, the changing frequency of the variant reflects the changing boundaries of the Roman Empire from 500 BC to AD 500, according to Eric Faure and Manuela Royer-Carenzi from the University of Provence. They looked at the links between Roman colonisation and the frequency of the CCR5-Delta32 variant in nearly 19 000 DNA samples from across Europe. They found that the gene variant was less common in regions conquered by the Romans.
Faure thinks that the Romans introduced a disease to which people carrying the CCR5-Delta32 gene were particularly susceptible and as the Romans moved north, the disease killed off people with this variant.
