猪繁殖与呼吸综合征病毒NSP2基因不同变异毒株对仔猪致病性研究

Pathogenicity of Porcine Reproductive and Respiratory Syndrome Virus Isolates with Different NSP2 Variation in Piglets

为了评价猪繁殖与呼吸综合征病毒(PRRSV)不同分离毒株致病性差异,选择4株PRRSV分离毒株,即YX0907、BB0907、SY0909(属于NSP2基因亚型Ⅰ,具有30aa缺失特征)和NT0801(属于NSP2基因亚型Ⅱ,其NSP2上不存在缺失)进行动物接种试验。将23头45日龄PRRSV、猪圆环病毒2型和副猪嗜血杆菌阴性健康仔猪随机分为5组,第1～4组各5头猪,分别颈部肌内注射上述4株PRRSV分离株(均为第3代)2×104.32TCID50.(mL.头)-1,第5组3头猪作为空白对照,隔离饲养21d,每天观察临床症状。攻毒后不同时间测定病毒血症,并对死亡猪和第21天处死猪进行病理剖解、观察大体病理变化和组织病理变化。结果显示,BB0907毒株毒力最强,试验猪感染后体温明显升高,临床症状明显,可引起3/5死亡,病猪肺脏组织具有明显病理变化;YX0907毒株毒力较强,试验猪临床症状和病理变化明显,可引起2/5死亡;NT0801毒力较弱,部分试验猪感染后出现1～2d体温升高和轻度临床症状,未引起死亡;SY0909毒株毒力最弱,感染猪出现1～3d体温升高,临床症状不明显,病理变化较轻;而对照猪无临床异常表现和病理变化。该研究结果表明,PRRSV分离株毒力存在明显差异,具有NSP2相同基因缺失类型的3个PRRSV分离株毒力差异较大,PRRSV毒力与NSP2 30aa基因缺失没有直接联系。

This study was conducted to evaluate the pathogenicity of different porcine reproductive and respiratory syndrome virus（PRRSV） isolates.Based on the NSP2 sequence of PRRSV isolates,four different isolates named as YX0907,BB0907,SY0909 and NT0801 were selected to study pathogenicity in piglets.Among them,YX0907,BB0907 and SY0909 isolates have 30 aa deletion in NSP2 and NT0801 isolate has no amino acids deletion.Twenty-three 45-day old piglets,free of PRRSV,porcine circovirus 2 and Haemophilus parasuis infection,were selected and randomly separated into 5 groups.The 4 experimental groups were inoculated individually with 4 PRRSV isolates by injection of 2 mL of 2×104.32TCID50·mL-1 per pig.Three pigs in the control group were mock inoculated.After challenging,the rectal temperature of every pig was daily recorded.The sera were collected at 7,14 and 21 day post inoculation（dpi） for viremia detection.The pigs dead and sacrificed at 21 dpi were autopsied and the gross lesions were valued.The results showed that BB0907 isolate had the highest virulence,which caused obvious fever and clinical signs with great pathological changes and 3 of 5 pigs were dead after infection.Compared with BB0907,YX0907 isolate was less virulent.The pigs in BB0907 inoculated group also showed apparent clinical syndrome and gross lesions and 2 pigs were dead after inoculation.But NT0801 isolate has relatively lower pathogenic ability and causes pigs had 1-2 days fever with slight clinical signs.SY0909 isolates has the lowest virulence,some pigs in this group only experienced 1-2 days fever without clinical signs.Meanwhile,the pigs in the control group performed well and without any clinical signs.These results revealed that the order of virulence of these four isolates is BB0907 YX0907 NT0801 SY0909,which indicating that the isolates with the same 30 aa deletion have different pathogenic ability and the 30aa deletion has no relationship with the virulence of isolate.