母猪免疫PCV-2疫苗对仔猪感染PCV-3的影响

Effect of PCV-2 vaccination on piglets infected with PCV-3

为了解猪圆环病毒3型病毒(porcine circovirus 3 virus, PCV-3)ORF2基因的分子生物学信息,探寻防控PCV-3损害仔猪的可行方案。本研究通过对山西省某未免疫过PCV-2商品疫苗的规模化母猪场的妊娠母猪在产前45 d持续6批次免疫PCV-2疫苗,以所生仔猪生产成绩和PCV-3 ORF2基因阳性检出率为指标,评价母猪免疫PCV-2疫苗对仔猪PCV-3的感染和发病情况的缓解作用。临床数据显示母猪免疫PCV-2疫苗后生产的6批仔猪PCV-3 ORF2基因阳性率由45.0%逐渐降至20.0%,伤亡率由25.5%降至8.0%。试验结果显示,从死亡仔猪淋巴结分离出的6株PCV-3 ORF2基因序列同源性为98.4%~99.2%,均有17个磷酸化位点,预测Cap蛋白氨基酸N端不存在典型的信号肽结构,说明该蛋白位于胞外区的可能性更大,且未预测到跨膜结构存在;PCV-3 ORF2与PCV-2a同源性为32.5%~32.9%,与PCV-2b同源性为30.8%~31.7%,与PCV-2d同源性为32.6%~33.5%,与PCV-4同源性为33.9%~34.3%,说明同源性低,进化不同步。因此,推测母猪通过持续的免疫PCV-2疫苗可解除PCV-2感染造成的机体免疫抑制,增强自身健康情况,降低PCV-3传播给仔猪的风险,用于控制仔猪群PCV-3流行是可行的应急方式。

The purpose of this study is to understand the molecular biological information of ORF2 gene of porcine circovirus 3(PCV-3),so as to explore a feasible scheme to prevent and control the damage of PCV-3 to piglets.The pregnant sows of a large-scale sow farm in Shanxi Province that had never been immunized with PCV-2 commercial vaccine were immunized with PCV-2 vaccine45 d before delivery,and 6 batches of pregnant sows were immunized continuously.The production performance of piglets and the positive rate of PCV-3 ORF2 were used as indicators to evaluate the alleviating effect of sow immunized with PCV-2 vaccine on the infection and incidence of PCV-3 in piglets.Clinical data showed that the PCV-3 ORF2 positive rate of six batches of piglets produced by sows immunized with PCV-2 vaccine gradually decreased from 45.0% to 20.0%,and the casualty rate decreased from 25.5% to 8.0%.The results of biological information analysis showed that the sequence homology of the ORF2 gene of six PCV-3 strains isolated from the dead piglet lymph nodes was 98.4%-99.2%,and there were 17 phosphorylation sites in the sequences.There was no typical signal peptide structure in the N-terminus of amino acid of the Cap protein translated from the sequence,and no transmembrane structure was predicted,indicating that the protein was more likely to be extracellular.The homology of PCV-3 ORF2 with PCV-2 a ORF2 was 32.5%-32.9%,the homology with PCV-2 b ORF2 was 30.8%-31.7%,the homology with PCV-2 d ORF2 was32.6%-33.5%,and the homology with PCV-4 ORF2 was 33.9%-34.3%,suggesting that they evolved out of sync.Therefore,it is speculated that continuous immunization of sows with PCV-2 vaccine can relieve the immune suppression caused by PCV-2 infection,enhance the health of sows,and reduce the risk of PCV-3 transmission to piglets,which is currently a feasible emergency way to control the prevalence of PCV-3 in piglets.