Investigating the evolution of the Arctic lineage of canine distemper virus circulating in Italy

Canine distemper virus (CDV) can cause fatal viral infection in domestic and wild animals globally. Several lineages are known, originating from distinct geographical regions and hosts, and can spread naturally or through human intervention into new geographic areas. The Arctic lineage was first described in carnivores of the Arctic ecosystems and subsequently reported in several European and Asian countries, yet its origin, evolution, and ecology remain partially unresolved. In this study, we generated genome sequence data of (n = 16) CDV strains of Arctic lineage collected from dogs in Italy over a nearly 15-year period, providing an extensive dataset to investigate the evolution of this particular lineage. We also generated genome data of seven Europe strains of another major lineage collected during the same period from red foxes (n = 3) and dogs (n = 4). Inter-lineage recombination events were identified in two CDV sequences. Sequence 2008 of the European lineage acquired a fragment from an Arctic lineage virus between the N and P genes. Sequence 2015 of the Arctic lineage displayed a more complex recombination pattern with fragments from Europe, America-2, and Rockborn lineages across multiple genes and hosts. Phylogenetic tree showed that the oldest Italian Arctic lineage from 2006 was more similar to the oldest Arctic CDV isolates, whilst a well-defined sub-cluster circulated from 2009 onwards in domestic and wild carnivores. These results provide novel insights into CDV evolution in Europe and emphasize the importance of ongoing genomic monitoring.