RESULTS AND DISCUSSION
Of the 158 tested serum samples from dogs, 17.7% (n=28) were positive
for P1, 16.5% (n=26) for PCVL258, and 8.9% (n=14) for PCVL264 based on
PCR. In 41 samples from cats, 17.1% (n=7) were positive for P1, 9.8%
(n=4) for P4, and 14.6% (n=6) for PCVL258. No PCV2, PCV3, and PCV4
strains were identified in the PCR assays (data not shown). The results
also revealed a co-infection of P4 and PCVL258 in a cat.
To further study the molecular epidemiology of these agents, we obtained
the full-length genomic sequences from 18 strains, representing 4 P1, 3
PCVL258, and 2 PCVL264 strains in dogs, and 5 P1, 2 P4, and 2 PCVL258
strains in cats, all of which have been deposited in GenBank (accession
nos. MH379143, MH379144, MT318811-MT318826). All 9 P1 viruses in this
study had a circular genome length of 648 nt and shared 96.8 to 100%
nucleotide identity with other available P1 genomes in GenBank. Compared
with the nucleotide sequence of the prototype P1 strain (GenBank
EF514716), the dog-origin P1 strain NJ01 (MH379143) and the cat-origin
P1 strain NJ03 (MT318822) were similar to the prototype elongated ORF1
strain (KU323639) and had a nucleotide substitution at position 77 (T to
C), which would result in a codon shift of the putative ORF1 starting at
nt position 419 and a stop codon at aa position 122. The ORF1 sequence
of other strains in this study had a stop codon at aa position 114.
Alignment of the whole genomic sequences of the 21 P1 strains showed
that there were multiple point or region mutations, for example,
variations in 6 positions appeared specific for the cat-origin strain
HeB02 (MT318824), including residues 331 (A to T), 337 (T to C), 344 (C
to T), 371 (T to G), 376 (G to T), and 379-383 (CCCCC to TTGTT). The 2
P4 cat-origin strains NJ01 and NJ02 had a genome length of 710 nt. The
nucleotide sequence of the cat-origin strain NJ01 was identical to that
of NJ02. The overall nucleotide identity of strains NJ01 and NJ02 in the
whole genome to other pig-origin strains ranged from 98.3% (MF802838)
to 100% (MF802836). Whether of pig-origin or not, all PCVL258 and
PCVL264 sequences were identical.
A corresponding phylogenetic tree (including 12 reference P1 sequences,
2 reference P4 sequences, 1 reference PCVL258 sequence, and 1 reference
PCVL264 sequence) was constructed based on the full-length sequence.
Phylogenetic analysis suggested that all P1 sequences from this study
were scattered within the P1 viral lineage except one cat-origin strain
(MT318824), the sequence of which showed more variation and was located
in a separate branch. All P1 strains in this study were more closely
related to other PCVL258 and PCVL264 strains than to P4 strains (Figure
1).
PCV2 is responsible for several multifactorial disease syndromes
(especially for postweaning multisystem wasting syndrome (PMWS) in pigs.
Furthermore, PCV2 can be transmitted across species barriers, and may
cause severe fatal disease in other species (such as mink) (Wang et al.,
2016). In addition, porcine circovirus-like agents, newly emerging
causative agents in pigs, have a close evolutionary relationship with
PCV2, based on phylogenetic analysis of genomic DNA sequences. The P1
viruses detected in dogs and cats in our study had high homology with P1
strains from pigs, goats, cattle, and rabbits.