Canine Distemper Virus in Sardinia, Italy: Detection and Phylogenetic Analysis in Foxes †

Abstract

Canine distemper is a contagious infectious disease caused by the canine distemper virus (CDV). The disease affects carnivores and is present in different geographical areas. This work aimed to characterize CDV strains infecting foxes in Sardinia (Italy) from 2014 to 2023, through clinical, anatomic–histopathological, and phylogenetic analysis. Neurological, respiratory, and gastrointestinal clinical signs, including fever, depression, ocular and nasal muco-purulent discharge, and diarrhea, were reported. Necropsy and histopathological examination revealed interstitial pneumonia and mild, diffuse, non-purulent meningoencephalitis with multifocal, moderate to severe demyelination, respectively. Immunohistochemical analysis detected specific CDV positivity in lung and brain sections. For the phylogenetic analyses, a dataset with the sequences of the gene coding for the hemagglutinin (H gene) obtained from fox strains was set up, including a canine strain sequence to assess possible differences. The genetic sequences of the fox strains clustered within an exclusively Sardinian clade. This clade is a sister clade of sequences recently analyzed from central Italy, with a mean genetic divergence of more than 5%. Together, these clades form a sister clade of the Central Europe-Wildlife lineage, with a mean genetic divergence of more than 5% between these clades and the Central European lineage. Sardinian sequences belong to a newly proposed “Sardinia-Wildlife” lineage of CDV. The circulation of this lineage in the investigated foxes and dogs suggests the transmission of the virus between wild and domestic animals. Central Italian viruses may also constitute a new separate CDV lineage.