A Deeper Insight into Evolutionary Patterns and Phylogenetic History of ORF Virus through the Whole Genome Sequencing of the First Italian Strains

Orf virus (ORFV) is distributed worldwide and is the causative agent of contagious ecthyma
that mainly occurs in sheep and goats. This disease was reported for the first time at the end of 18th
century in Europe but very little is currently known about the temporal and geographic origins of
this virus. In the present study, the use of new Italian whole genomes allowed for better inference on
the evolutionary history of ORFV. In accordance with previous studies, two genome types (S and G)
were described for infection of sheep and goats, respectively. These two well-differentiated groups of
genomes originated for evolutive convergence in the late 1800s in two different areas of the world
(Europe for S type and Asia for G type), but it was only in the early 1900s that the effective size of
ORFV increased among hosts and the virus spread across the whole European continent. The Italian
strains which were sequenced in the present study were isolated on the Mediterranean island of
Sardinian and showed to be exclusive to this geographic area. One of them is likely representative
of the early European forms of ORFV which infected sheep and became extinct about one century
ago. Such an ancient Sardinian strain may have reached the island simple by chance, where it quickly
adapted to the new habitat.