Comparison of Growth Characteristics and Genomics of Two Canine Distemper Virus Strains Isolated From Minks in China

Canine distemper (CD) caused by the HI542N/Y549H variant of CD virus (CDV) has become an epidemic in fur-bearing animals (minks, foxes, and raccoon dogs) since its outbreak in 2012 in China. To understand the detailed characteristics of the CDV variant, we determined the viral growth kinetics and complete genome sequences of two CDV variants, SDZC(17)M2 and LNDL(17)M4, isolated from CDV-infected minks in Shandong and Liaoning provinces of China, respectively, in 2017. SDZC(17)M2 showed higher viral titers and CDV-induced syncytia in BHK-minkSLAM cells than LNDL(17)M4. Although both strains belonged to an independent clade, SDZC(17)M2 strain harboring I542N/Y549H substitutions in the H protein shared high similarity (99.3–99.6% nt) with other variant strains, whereas LNDL(17)M4 with only the Y549H substitution shared lower identity (97.7–97.9% nt) with variant strains. A novel R223K substitution was identified in the conserved cleavage site (RRQKR) of the F protein in the SDZC(17)M2 variant strain. The R223K substitution did not significantly change the relative cell fusion activity in BHK cells, though LNDL(17)M4 F (R332K) substitution exhibited an increase and SDZC(17)M2 F (K223R) exhibited a decrease in the relative fusion activity when combined with SDZC(17)M2H or LNDL(17)M4H. The genomic variations of the two isolates will support further analysis of virulence determinants and the evolutionary trend of CDV.