Genotypic Change of Porcine Circovirus Type 2 Detected in Healthy Pigs in Japan from 2009 to 2016

Abstract

Porcine circovirus type 2 (PCV2) causes a variety of diseases in pigs, collectively known as porcine circovirus-associated diseases (PCVAD). PCV2d is one of the five genotypes (a to e) and can be divided into two clusters, PCV2d-1 and PCV2d-2, the latter of which includes a mutant strain of PCV2 (mPCV2) identified in the U.S. mPCV2 proliferates at a high rate in pigs and is excreted from infected pigs more profusely than other PCV2 genotypes. Consequently, PCV2d-2 has become the predominant cluster worldwide. We previously reported three new PCV2 strains detected in serum samples from healthy pigs in Japan in 2015. These strains are closely related to mPCV2 and belong to the same PCV2d-2 cluster. To investigate the prevalence of PCV2d-2 strains in Japan, the incidence of PCV2 in rural areas and genotypic changes over time were evaluated using PCR and nucleotide sequence analysis of serum samples from healthy pigs collected from 19 different farms in 6 prefectures from 2009 to 2016. The results showed that PCV2d-2 strains have existed in Japan since at least 2012 and are now the predominant strains distributed among Japanese pig farms. Moreover, the PCV2e strain was detected for the first time in Japan in 2016. The genotypic change of PCV2d-2 over time and the date the strain was first detected in Japan were almost identical to those in the U.S. The data could provide useful information about the spread of PCV2 into Japan.