Molecular analysis of the full-length F gene of Brazilian strains of canine distemper virus shows lineage co-circulation and variability between field and vaccine strains.

Canine distemper is a highly contagious systemic viral disease, with worldwide distribution that affects a wide variety of terrestrial carnivores. This study characterized full-length fusion (F) genes from 15 Brazilian wild-type canine distemper virus (CDV) strains collected between 2003-2004 (n = 6) and 2013-2016 (n = 9). Using deduced amino acid (aa) sequence analysis, 14 strains were classified into Europe 1/South America 1 (EU1/SA1) lineage, with a temporal clustering into past (2003-2004) and contemporary (2013-2016) strains. One strain clustered to Rockborn-like lineage, showing high similarity (98.5%) with the Rockborn vaccine strain. In analyzed strains, the fusion protein signal-peptide (Fsp) coding region was highly variable at the aa level (67.4%-96.2%). The Brazilian strains were more Fsp-divergent from the North America 1 (NA1) strains (24.5%-36.3%) than from the Rockborn (11.2%-14.9%) vaccine strain. Seventeen cysteine residues in the full-length F gene and four non-conserved glycosylation sites in the Fsp region were detected. The results reveal that past and contemporary CDV strains are currently co-circulating. This first analysis of full-length F genes from Brazilian wild-type CDV strains contributes to knowledge of molecular epidemiology of CDV viral infection and evolution.