M.Battilani et al.
/
Virus Research
83 (2002) 149–157
153
The mutation in the 440 residue of the VP2
capsid protein has been found in the CPV-699
isolate. When comparing our Italian isolates with
other CPV strains isolated in various parts of the
world, the same mutation in two strains isolated
from wild feline in Asia were found (GenBank
reference number AB054221-AB054222). In fact,
in the VP2 protein tree (Fig. 1b), the CPV-699
formed a distinct cluster with these Asian isolates.
The 440 residue is located in the GH loop; this
large loop is composed of 267–498 residues and is
located between the bGandbH strands. The GH
loop intertwines with two other symmetry equiva-
lents to form a protrusion around each threefold
axis (Liljas, 1991). This region is exposed on the
surface of the capsid and forms the 22 A
,
threefold
spike; the greatest variability between par-
voviruses was observed in this antigenic region
(Chapman and Rossmann, 1993).
For estimation of viral phylogenetic relation-
ships, we constructed phylogenetic trees for the
VP2 gene and the VP2 protein: phylogenetic tree
analysis was performed using the ME method
along with the sequences of the foreign isolates
obtained from the GenBank and published by
other groups.
Representative minimal trees for the VP2 gene
and the VP2 protein are shown in Fig. 1a and b.
For the VP2 gene and the VP2 protein, more
than 50 minimal trees were obtained using the
Close-Neighbor-Interchange algorithm; the differ-
ences among those trees in each gene and protein
did not seem to be significant. However, we se-
lected the minimal trees showing the same topol-
ogy as those obtained by neighbour joining
method as representative trees method.
The phylogenetic tree of the VP2 gene showed
three branches with high confidence values (\
70%). One of the three groups includes the FPV
and the FPV-like virus isolated in species other
than dog; a second group consists of old type 2.
The third group includes all new type 2a, 2b
isolated in various parts of the world.
A cluster of the new types on the phylogenetic
tree was divided into three subgroups.
Twelve Italian isolates placed in a cluster to-
gether with Asian isolates were classified as CPV-
2a: nine Italian CPV-2a isolates formed a cluster
including Asian isolates; three Italian CPV-2a
strains (CPV-684, CPV-685 and CPV-632) were
placed in different branches to form three inde-
pendent lineages; it probably depends on the si-
lent changes in the VP2 gene of these isolates. In
fact analysing the phylogenetic tree of the VP2
protein, CPV-684 CPV-685 and CPV-632 were
included in the type 2a cluster.
Four Italian isolates classified as type 2b
formed a cluster denominated CPV-2b together
with Asian, American and African isolates. Inside
cluster 2b, the VP2 sequences of CPV-603, CPV-
616 and W42 (an Italian CPV-2b strain isolated
from wolf) were differentiated from other 2b
strains by 89% of the bootstrap replicates. This
group was maintained in the VP2 protein tree:
this may be due to the presence of the T265P
mutation in these isolates, which had never been
detected, in other foreign strains. CPV-598, an
Italian CPV type 2b, was included in a subgroup
together with Asian type 2b and type 2c isolates.
Instead, in the VP2 protein tree, this subgroup is
inserted in the 2a cluster; in fact, all these strains
have the S297A mutation, which resembles the 2a
strain.
The third subgroup is composed of the original
type 2a taken from American isolates (CPV-15
and CPV-31), a Japanese isolate (CPV-Y1) and
the African isolate (CPV-Africa9).
Unlike the phylogenetic tree of the VP2 gene,
the internal branches in the cluster of the new
types were not present in the phylogenetic tree of
the VP2 protein, indicating that the branches of
the phylogenetic tree of the VP2 gene are mainly
composed of silent changes.
In the VP2 protein tree, three CPV strains
LCVP-V140 and LCVP-V203 isolated from leop-
ard cats (Ikeda et al., 2000) formed an indepen-
dent lineage; an Asian isolate V208 (type 2b)
formed a cluster with CPV-598. CPV 699 formed
a cluster supported by 53% of the bootstrap repli-
cates with LCVP-V204 and LCVP-V139.
On the basis of phylogenetic analysis, the Ital-
ian strains showed great similarity to the recent
Asian isolates: all Asian strains examined were
isolated from domestic and leopard cats in Viet-
nam and Taiwan (Ikeda et al., 2000).