Potential role for the plague as a selective force in Sardinia

Selective pressure on isolated populations can determine increases in the frequency of specific genetic traits. The presence of genes associated with resistance or susceptibility to diseases has been investigated in Sardinia primarily with respect to the effects of malaria on its population and subpopulations. Because of its location at the crossroads of maritime trade routes in the Mediterranean Sea, Sardinia also suffered frequent and often protracted plague epidemics. While fragmentary and incomplete, the historical and demographic data reviewed here support that plague epidemics caused substantial mortality crises in the Sardinian population in the XIV-XVII centuries with an almost generational frequency. Plague epidemics almost invariably were introduced to the northern territories to then spread to the rest of the island mainly via the principal north-south road that runs through the western part of the island. We propose here that, in addition to malaria, the plague is also likely to have exerted a significant selective pressure on the Sardinian population. In particular, the plague may have selected genetic traits resulting in an aberrant immune response to Y. pestis that could contribute to the high frequency of autoimmune diseases found in the island today. A detailed analysis of the demographic impact of the plague in the island through the centuries will be needed for the validation of this hypothesis in a population genetic framework.