Phylodynamic analysis of the historical spread of Toscana virus around the Mediterranean

All available sequences of the three genome segments of Toscana virus with date and location of sampling were analysed using Bayesian phylodynamic methods. We estimate that extant Toscana virus strains had a common ancestor in the late 16 th to early 17 th century AD, in territories controlled by the Ottoman Empire, giving rise to an ancestral genotype A/B in north Africa and to genotype C in the Balkans. Subsequent spread into western Europe may have occurred during the period of European colonization of north Africa in the 19 th and early 20 th centuries AD, establishing genotypes A and B in Italy and Spain respectively. Very little positive evolutionary selection pressure is detectable in Toscana virus, suggesting that the virus has become well adapted to its human hosts. There is also no convincing evidence of reassortment between genome segments, despite genotypes A and B now co-circulating in several countries.