Pathogenicity study on susceptible piglets with PRRSV isolated from domestic pig and wild boar in Shaanxi Province | 野猪源与家猪源PRRSV陕西流行毒株对仔猪的致病性试验

Chinese. 研究野猪源Shaanxi-2及家猪源Shaanxi-1 猪繁殖与呼吸综合征病毒（PRRSV）变异株对易感仔猪的致病性及发病规律，进一步弄清PRRSV变异株的病原特征及其与“猪高热病”发生的关系。选取PRRSV和猪圆环病毒2型（PCV2）抗原、抗体检测均为阴性的健康仔猪（40日龄）9头，随机分为3组，用家猪源Shaanxi-1及野猪源Shaanxi-2 PRRSV变异株分别感染其中一组仔猪，每头肌注6 mL，滴鼻2 mL；另一组作为阴性对照，按相同剂量和方法接种正常Marc-145细胞处理液。攻毒后各组分圈饲养，每天定时测量体温，绘制体温变化曲线，观察临床症状，记录发病情况。攻毒后采血及咽喉、眼、鼻分泌物和粪便，采用RT-PCR方法检测PRRSV、猪瘟病毒（CSFV）、PCV2、猪伪狂犬病毒（PRV）核酸，用ELISA试验及血清中和试验检测血清抗体。Shaanxi-1与 Shaanxi-2攻毒组均出现体温升高及典型临床症状，但未见死亡病例；攻毒组CSFV、PCV2、PRV核酸检测均为阴性，咽喉、眼、鼻分泌物和粪便在一定时间段可检测到PRRSV核酸；PRRSV特异性抗体检测均为阳性，仅Shaanxi-2攻毒组在第35天检测到中和抗体；Shaanxi-2与Shaanxi-1相比，感染猪的体温较高，临床症状明显，病毒血症的维持时间较长，抗体水平较高。野猪源Shaanxi-2及家猪源Shaanxi-1 PRRSV变异株对易感仔猪具有一定的致病性，能使感染动物发病但不能致死，Shaanxi-2毒株的致病性相对较强。攻毒后第7天出现病毒血症，持续14～21 d后逐渐消退，仔猪感染PRRSV变异株后，病毒可通过鼻、眼、咽喉分泌物及粪便等排出，其中鼻分泌物排毒最早、排毒时间最长，眼、咽喉分泌物与鼻分泌物、粪便相比排毒较晚、持续时间较短。

English. The research was to study the pathogenicity of susceptible piglets and occurrence regularity of two American PRRSV variant strain virus Shaanxi-2 and Shaanxi-1, which were isolated from wild boar and domestic pig respectively. The relationship between PRRSV genomic characteristics and development of high fever syndrome was further clarified. 40-day-old piglets free of antigen and antibody to PRRSV and PCV2 were divided into three groups randomly with three piglets in each group. Two groups were inoculated intramuscularly with 6 mL of PRRSV isolates, and intranasally with 2 mL. The piglets in the control group were mock inoculated with the same dosage of Marc-145 cell culture supernatant. After inoculation, each group was housed. Rectal temperatures and clinical indexes in a different isolation room were monitored daily. Serum samples and eye, nasal, throat feces swabs were used for the detection of antibodies for PRRSV by ELISA test and the detection of PRRSV nucleic acid for PRRSV, CSFV, PCV2, PRV by RT-PCR. Shaanxi-1 and Shaanxi-2 inoculated piglets started to develop elevated body temperatures, with typical clinical symptoms, but no death. The antigens of CSFV, PCV2, PRV detected negative after challenge, but positive PRRSV was detected in serum of some piglets in a certain period. Only the Shaanxi-2 challenge group was detected the neutralizing antibody at the 35th day. Compared with Shaanxi-1 infected group, fervescence and clinical symptoms were more obvious in Shaanxi-2 infected group, and showed longer time of viraemia and higher antibody level. Two American PRRSV variant strains Shaanxi-2 and Shaanx-1 have certain pathogenicity on susceptible animal, and susceptible piglets challenged with these isolates develop clinical signs, but no mortality. Shaanxi-2 isolate of wild boar showed relatively stronger pathogenicity than Shaanxi-1 isolate. The viremia appear on the 7th day of challenge, continue for 14-21 d, then remove gradually. The virus could eliminate through the nose, eye, throat and faeces secretions from vitro. Compared with nasal and feces, eyes and throat secretions eliminate later and have shorter time, whereas nasal secretions eliminate earlier and longer.