Comparative study of the virulence of three major Korean porcine circovirus type 2 genotypes (a, b, and d)

Abstract

Porcine circovirus type2 (PCV2) is an economically important swine pathogen beacuse it is the most common causative agent of several disease and syndromes including porcine circovirus-associated disease (PCVAD). Based on its genotypes, PCV2 have been distinguished and identified as PCV2a, PCV2b, PCV2c, PCV2d, and PCV2e. In this study, we compared virulence between the three major Korean PCV2 genotypes, PCV2a, PCV2b, and PCV2d based on clinical signs, PCV2 viremia and antibody titers, lymphoid lesion scores and numbers of PCV2 antigens. A population of forty piglets was selected as healthy and colostrum fed, 14 days old from sows in a commercial farm which was determined to be free of porcine reproductive and respiratory syndrome virus (PRRSV) and also Mycoplasama hyopneumoniae-free based on monitoring results, serological testing, and long term clinical history. We designed to 4 groups of pigs and 10 piglets per group. Each group was intranasally inoculated with 2mL of tissue culture supernatant containing 105 TCID50/mL of PCV2a, PCV2b, and PCV2d. The negative group was intranasally inoculated with 2mL of uninfected cell culture supernatant. Compare to the negative group, all 3 of experimental groups had more severe clinical signs, but no significant difference among PCV2a-, PCV2b-, and PCV2d-infected groups. Throughout the time of challenge, average daily weight which was calculated over the time period between 49 and 77 days of age showed no significant difference in infected groups. There were no detection of genomic copies of PCV2 from all 4 groups, and all infected groups were appeared to have similar PCV2 antibody levels, regardless of genotype. Regardless of infected PCV2- genotypes, PCV2 antibodies were come out into similar results for all four groups. For pathological part the negative control group, all three PCV2a-, PCV2b-, and PCV2d-infected groups showed significantly higher number of lymphoid PCV2-positive cells and lymphoid lesion scores than the negative control group. Therefore, this study exhibits that there is no significant difference in virulence between the three major Korean PCV2 genotypes, PCV2a, PCV2b, and PCV2d.

The objective of this study was to compare the virulence of three major PCV2 genotypes in terms of clinical signs, PCV2 viremia and antibody titers, lymphoid lesions, and PCV2-antigen within lymphoid lesions in experimentally infected pigs. Pigs were infected at 7 weeks with PCV2a, PCV2b, and PCV2d strains and necropsied at 28 days post infection. No statistical differences were observed in clinical signs, PCV2 viremia and antibody titers, lymphoid lesions scores, and numbers of PCV2 antigens among the three major Korean PCV2 genotypes. The results in this study indicate that the three major Korean PCV2 genotypes, PCV2a, PCV2b, and PCV2d have similar virulence.

돼지 써코바이러스는 양돈 산업에서 경제적 손실을 가져오는 가장 흔한 원인체이고, 주요 유전자형에 기반해 써코 바이러스는 PCV2a, PCV2b, PCV2c, PCV2d, PCV2e로 분류된다. 본 실험은 한국의 돼지 써코 바이러스 주요 유전자형인 PCV2a, PCV2b, PCV2d를 임상학적, 바이러스학적, 면역학적, 병리학적 기법을 통해 비교 분석한 것이다. 실험에 앞서 돼지 생식기 호흡기 증후군과 마이코 플라즈마성 폐렴 검사를 통해 감염 이력이 없는 돼지 농장에서 초유 수유가 이루어진 건강한 14일령 돼지 40마리를 선별하였다. 실험에는 14일령 돼지를 10마리씩 4개 그룹으로 나누어 진행하였다. 3개 그룹은 각각 PCV2a, PCV2b, PCV2d로 감염된 세포의 상층액을 2mL씩 비강 내 접종하였고, 대조군에는 감염되지 않은 세포의 상층액을 2mL 비강 접종하였다. 대조군은 접종 전후에 유의적 변화는 관찰되지 않은 것에 비해 감염된 상층액이 접종된 3그룹은 모두 접종 이후로 심한 임상학적 변화가 관찰되었다. 감염이 이루어진 3 그룹은 임상학적, 바이러스학적, 면역학적, 병리학적 측면에서 모두 유의한 차별점 없이 비슷한 변화 양상을 보였으며, 이를 통해 한국의 돼지 써코 바이러스 유전형, PCV2a, PCV2b, PCV2d의 병원성 정도에는 유의한 차이가 없음을 확인하였다.