猪圆环病毒2型与链球菌7型协同感染研究

Study on Synergistic Infection of Porcine Circovirus Type 2 and Streptococcus suis Type 7

2016年10月,在山东省发现猪圆环病毒2型(PCV-2)和链球菌7型协同感染病例。猪场小猪40日龄发病,持续至100日龄时死亡率高达30%,病猪表现为精神沉郁、发热、四肢无力和呼吸困难,最后衰竭死亡。采用血液学检测,病理组织学观察,细菌、病毒分离鉴定和动物回归试验验证。结果表明,血液中大量红细胞变形,淋巴细胞、中性粒细胞数量增多;分离的细菌为短链状排列的革兰阳性球菌,直径1μm^2μm;16SrRNA PCR测序结果显示为链球菌7型;病毒PCR结果显示为PCV2阳性,猪瘟病毒、猪伪狂犬病病毒、猪繁殖与呼吸综合征病毒、猪细小病毒均为阴性;遗传进化分析表明PCV-2检测株与PCV-Y16同源性最高,为99.7%。随后,PK-15细胞连续传代显示PCV-2在PK-15细胞中增殖。动物回归试验中,临床数据统计结果、剖检病变以及组织病理学观察证实两种病原具有协同致病性。根据猪群临床症状、剖检病变、组织学病变、病原检测结果以及动物回归试验,最终确诊该猪群发生PCV-2与链球菌7型的混合感染,并呈现致病上的协同作用。

In October 2016,the synergetic infection cases with porcine cirovirus type 2（PCV-2）and Streptococcus suis type 7 in Shandong province were discoveried.An outbreak of diseases occurred in swine herd of a farm.The symptoms were first seen at 40-day-old.The mortality reached 30% at 100-day-old.The main symptoms were characterized by emaciation,depression,fever,limbs weakness and dyspnea,eventually died of organs failure.The blood smear,histopathological observation,bacterial and viral isolation and identification methods were used for diagnosis.The morphology of red blood cells was deformed,increased number of lymphocytes and neutrophilic granulocytes in blood were found.Gross and histopathological observations showed the synergetic pathogenic effect.The bacterial morphs showed that there were a large number of Streptococcus suis,1-2μm in diameter.16 sRNA identification showed Streptococcus suis type 7.Furthermore,PCR technique was used.The special test of PCR detection was taken with porcine circovirus,classical swine fever virus,porcine pseudorabies virus,porcine reproductive and respiratory syndrome virus and porcine parvovirus.PCR results showed that PCV-2 was positive,the rest of the viruses were negative.Phylogenetic analysis showed that the homology was over 99.7% of PCV-2 with PCV-Y16.Subsequently,PCV-2 positive specimen was innocutated in PK15 cells for continuous passages to isolate the virus,the results showed that PCV-2 replication in PK15 cells was good.According to the swine herd morbidity situation,clinical symptoms,histopathological observation,all the findings observed in these cases were considered to be related with the PCV-2 and Streptococcus suis type 7 synergistic infection.