Sheep infection by caprine lentivirus

SUMMARY The objective of this study was to demonstrate iatrogenic transmission of small ruminant lentivirus (SRLV) from goats to sheep and horizontal transmission between sheep. The study was conducted on a farm with separate goat and sheep rearing, and animals were monitored for lentivirus occurrence by clinical examination and testing by immunoblotting (IB), agar gel immunodiffusion (AGID), and nested polymerase chain reaction (nPCR). Positive results had not been observed in the sheep flock until this study. Conversely, virus positive dairy goats were known. For this reason, the farm performed the caprine arthritis-encephalitis (CAE) control program. The study was designed with a sheep group that presented positive animals for SRLV by nPCR. It was verified that three newborn animals in this group were rejected by their mothers and consequently received milk from the goat herd. These three animals remained with another 20 sheep of the same age, totaling 23 animals. After one year, during monitoring, 11 of the 23 animals in the group presented positive results in the nPCR and three demonstrated seroconversion by IB. Of the animals that had received goat milk, two had positive results in the nPCR and IB. The 11 animals positive in the nPCR were followed and it was verified that five animals did not present further positive results in the nPCR, nor seroconversion; two continued presenting positive results in the nPCR but were negative in the IB and AGID and four were positive in the nPCR, IB, and AGID. Thus, it was possible to demonstrate iatrogenic interspecific infection and the occurrence of horizontal caprine lentivirus transmission among sheep.摘要 本研究旨在证实小反刍动物慢病毒（small ruminant lentivirus, SRLV）从山羊向绵羊的医源性传播（iatrogenic transmission），以及绵羊之间的水平传播。本研究在一个分别饲养山羊与绵羊的养殖场开展，通过临床检查以及免疫印迹试验（immunoblotting, IB）、琼脂凝胶免疫扩散试验（agar gel immunodiffusion, AGID）和嵌套聚合酶链反应（nested polymerase chain reaction, nPCR）三种检测方法，对受试动物的慢病毒感染状况进行监测。直至本研究启动前，该绵羊群未检出慢病毒阳性样本；反之，该场早已检出存在病毒阳性的奶山羊群。为此，该养殖场启动了山羊关节炎-脑炎（caprine arthritis-encephalitis, CAE）防控方案。本研究设置了一组绵羊，该组内经nPCR检测存在SRLV阳性个体。经确认，该组中的3只新生羔羊被母羊拒哺，因此饮用了山羊群的乳汁。这3只羔羊与另外20只同龄绵羊混群饲养，试验组总规模达23只。饲养满1年后的监测结果显示，该组23只受试动物中有11只nPCR检测呈阳性，另有3只经IB试验检出血清转换阳性。在饮用过山羊乳汁的3只羔羊中，有2只的nPCR与IB检测结果均为阳性。研究团队对11只nPCR检测阳性的绵羊进行了后续跟踪监测，结果显示：5只绵羊后续的nPCR检测与血清转换检测均未呈阳性；2只持续呈nPCR阳性，但IB与AGID检测结果为阴性；另有4只nPCR、IB与AGID三项检测均呈阳性。综上，本研究成功证实了慢病毒的医源性跨物种感染，以及山羊慢病毒在绵羊群体中的水平传播现象。