抗体监测在规模猪场猪繁殖与呼吸综合征防控中的预警作用

Early warning effect of antibody monitoring on prevention and control of porcine reproductive and respiratory syndrome in large-scale pig farms

为了揭示猪繁殖与呼吸综合征(PRRS)抗体水平在免疫猪群与非免疫猪群中的变化规律,本研究选取福建省龙岩市两个规模相似的自繁自养猪场,其中一个场免疫国内某厂家的TJM-F92株,另一个场不进行免疫。试验采用ELISA方法对两个场不同周龄的商品猪进行PRRS抗体检测及分析,通过RT-PCR方法对临床样品中检测到的两株PRRSV的ORF5基因进行测序,并结合参考株进行序列分析。抗体检测结果表明,未免疫场248份血清中PRRS抗体阳性率从4周龄的70.0%下降至10周龄的26.7%,14周龄后抗体阳性率开始上升直至18周龄,保持在97.1%~100%;免疫场170份血清中未免疫的2周龄抗体水平较高,阳性率为100%,免疫后除6周龄、8周龄、10周龄分别为80%、70%、90%,其他周龄均为100%。ORF5基因遗传演化分析表明,免疫场检出毒株为HP-PRRSV,与HP-PRRSV(JXA1、HuN4等)、疫苗株HP-PRRSV TJM-F92等的同源性为70.5%~93.8%,并与JXA1、HuN4等处于同一小分支。未免疫场检出毒株与PRRSV NADC30株同源性为87.2%,属于NADC30-like分支。因此,当发现PRRS抗体阳性率较低、出现个别S/P值高且离散度大时,猪场要立刻采取处理措施预防因PRRSV感染而引起的继发感染。表明抗体定期监测在疫苗免疫场和阳性稳定场PRRS防控上可发挥有效的预警作用。

In order to reveal the variation rule of PRRS antibody levels in immunized and non-immunized pigs,two self-propagated pig farms of similar scale were selected in Longyan city,Fujian province.One farm was immunized with TJM-F92 strains from a domestic manufacturer,while the other was not immunized.PRRS antibody was detected and analyzed in commercial pigs of different weeks of age in two farms by ELISA method.ORF5 gene of two PRRSV strains detected in clinical samples was sequenced by RT-PCR method,and sequence analysis was performed in combination with reference strains.The antibody detection results showed that the positive rate of PRRS antibody in 248 sera from the unimmunized field decreased from 70.0%at 4 weeks of age to 26.7%at 10 weeks of age,and the positive rate of PRRS antibody began to rise after 14 weeks of age until 18 weeks of age,maintaining 97.1%-100%.Among 170 sera from the immunization field,the antibody level was higher at 2 weeks of age and the positive rate was 100%.After immunization,the antibody levels were 80%,70%and 90%at 6 weeks of age,8 weeks of age and 10 weeks of age,respectively,and the other weeks of age were 100%.The genetic evolution analysis of ORF5 gene showed that the strain detected in immune field was HP-PRRSV,which had 70.5%~93.8%homology with HP-PRRSV(JXA1,HuN4,etc.)and vaccine strains HP-PRRSV TJM-F92,and was in the same subbranch with JXA1,HuN4,etc.The homology between the strain detected in non-immune field and NADC30 was 87.2%,belonging to NADC30-like clade.Therefore,when the positive rate of PRRS antibody is low and individual S/P values are high and the dispersion degree is large,treatment measures should be taken immediately to prevent secondary infection caused by PRRSV infection in pig farms.This study indicated that regular antibody monitoring could play an effective early warning role in the prevention and control of PRRS in vaccine immune field and positive stable field.