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Abstract
Porcine circovirus type 2 (PCV2) is the primary cause of Postweaning Multisystemic
Wasting Syndrome (PMWS) in pigs. PCV2, however, is found in both PMWS-affected herds
and non-affected herds. The objective of this study was to clarify if PCV2 genome
nucleotide sequences isolated from pigs from PMWS-affected herds and non-affected
herds cluster phylogenetically in two separate groups. All isolates (45) belonged
to PCV2 group 1 and shared a nucleotide sequence identity of 99.4-100% indicating
a very homogeneous PCV2 population in Denmark. Phylogenetic analysis of the PCV2 isolates
revealed no distinctive clustering of case- and control-herds suggesting that there
is no link between PCV2 sequences and herd disease status. The appearance of only
PCV2 group 1 isolates in this study (isolates from 2003/2004) led us to determine
if PCV2 nucleotide sequences had changed in Denmark over time. Interestingly, all
PCV2 isolates from before the first outbreak of PMWS (2001) belonged either to a new
PCV2 group identified for the first time in this study and named group 3 (isolates
from 1980, 1987 and 1990) or PCV2 group 2 (isolates from 1993 and 1996). The shift
from PCV2 group 2 to 1 was confirmed on a more global scale by placing all full genome
PCV2 sequences submitted to GenBank from 1997 to 2006 in either of the groups by phylogenetic
analysis. The analysis showed that the shift happened in 2003 or even earlier. This
may indicate that PCV2 group 1 is a more adapted form of PCV2 and possibly could be
more pathogenic.