In late 2005, sporadic cases of an acute onset disease of high mortality were observed in 10- to 16-
week-old growing pigs among several swine herds of the United States. Tissues from the affected pigs
in Kansas, Iowa, and North Carolina were examined, and porcine circovirus type 2 (PCV2) was
detected consistently among these tissues. Phylogenetically, PCV2 can be divided into two major
genotypic groups, PCV2-group 1 and PCV2-group 2. Whereas PCV2-group 1 isolates were detected in
all the diseased animals, only two of the diseased animals harbored PCV2-group 2 isolates. This observation is important because PCV2-group 1 isolates had never been reported in the United States
before (GenBank as of May 16, 2006), and they are closely related to the PCV2-group 1 isolates that
have been described in Europe and Asia, previously. Our analysis revealed that each genotypic group
contains a distinct stretch of nucleotide or amino acid sequence that may serve as a signature motif
for PCV2-group 1 or PCV2-group 2 isolates.