3.5 High substitution rates for CPV-2 without evidence of
recombination
We investigated the substitution rate of CPV-2 based on the 199
full-length genome sequences. The mean substitution rate was found to be
2.49 x 10-4 nt/s/y, and similar rates were estimated
for individual genes coding for the nonstructural and structural
proteins at 3.16 x 10-4 and 3.06 x
10-4 nt/s/y, respectively. Since the phylogenetic tree
divided the CPV-2 into Asian and Western clades, the substitution rate
was estimated for each clade, suggesting the Asian CPV-2 evolutionary
rate at 2.12 x 10-4 nt/s/y was faster than that in the
Western clade at 1.69 x 10-4 nt/s/y (Table 4).
To further explore possible recombination in Vietnamese CPV-2 evolution,
we investigated the recombination analysis in all detected Vietnamese
CPV-2 genomes compared to the other CPV-2 strains in GenBank using the
RDP method. However, no recombination breakpoints were found in any of
the Vietnamese CPV-2 strains.