Phylogenetic Analysis
Based
on the evaluation of MEGA-X, an ML
phylogenetic
tree based on the full VP2 gene was constructed with the Tamura
3-parameter model plus gamma distribution with five rate categories
(T92+G+I).
According to the
phylogenetic
tree, the 27 strains fell into three clades(Figure 2). Clade CPV-2c Ⅰ
included all the CPV-2c variants in this study, and Asian CPV-2c
strains, along with one Italian CPV-2c strain. This clade was separated
from clade CPV-2c Ⅱ, which contained CPV-2c strains circulating in
European and American countries. CPV-2c strains belong to this clade
were characterized by four mutations:
Ala5Gly,
Phe267Tyr, Tyr324Ile, Gln370Arg. Six New CPV-2a strains in this study
were classified into another clade, New CPV-2a/b Ⅰ, containing Asian New
CPV-2a/b strains and two American New CPV-2a strains. All the strains
located within this clade shared three mutations, Phe267Tyr, Tyr324Ile,
and Thr440Ala, clustering away from other clades containing New CPV-2a
variants with different mutations. Two FPLV strains were located in
clade FPLV which included all the FPLV strains.