Christopher-Hennings J, Holler L D, Benfield D A, Nelson E A
Animal Disease Research and Diagnostic Laboratory, South Dakota State University, Brookings 57007-1396, USA.
J Vet Diagn Invest. 2001 Mar;13(2):133-42. doi: 10.1177/104063870101300207.
Because transmission of porcine reproductive and respiratory syndrome virus (PRRSV) can occur through boar semen, it is important to identify persistently infected boars. However, even for boars given the same PRRSV strain and dose, variability in the duration of viral shedding in semen has been observed, suggesting that host factors are involved in PRRSV persistence. To determine whether there are host genetic factors, particularly litter and breed differences related to the persistence of PRRSV, 3 litters from 3 purebred swine breeds were used for this study. It was also determined whether PRRSV could be detected for a longer period of time in serum, semen, or peripheral blood mononuclear cells (PBMC) and if PRRSV could still be detected in tissues after these antemortem specimens were PRRSV negative for a minimum of 2-3 weeks. Three Hampshire, 3 Yorkshire, and 2 Landrace PRRSV-naive boars were obtained and inoculated intranasally with a wild-type PRRSV isolate (SD-23983). All boars within each breed were from the same litter, and litters were within 9 days of age. Serum and PBMC were collected twice weekly from each boar and analyzed for the presence of PRRSV by virus isolation and the polymerase chain reaction (PCR). Serum was also used to obtain virus neutralization titers and enzyme-linked immunosorbent assay S/P values. Semen was collected twice weekly from 7 of 8 boars and analyzed by PCR. After all specimens were PRRSV negative for a minimum of 2-3 weeks, each boar was euthanized, and 21 tissues plus saliva, serum, feces, and urine were collected. All postmortem specimens were evaluated by virus isolation. Specimens that were PRRSV negative by virus isolation were then evaluated by PCR. The mean number of days (+/-SD) for the duration of PRRSV shedding in semen was 51+/-26.9 days, 7.5+/-4.9 days, and 28.3+/-17.5 days for Landrace, Yorkshire, and Hampshire boars, respectively. Because of small sample sizes and large SDs, the differences in duration of PRRSV shedding in semen between breeds were not considered significant. However, the trend suggested that Yorkshire boars were more resistant to PRRSV shedding in semen than were Landrace boars, requiring further investigation using a larger numbers of boars. PRRSV was detected for a longer period in semen than in serum or PBMC in 4 of 7 boars. Viremia could be detected for a longer period in serum than in PBMC in 6 of 8 boars. After a minimum of 2-3 weeks of PRRSV-negative serum, semen, and PBMC, PRRSV could still be detected in the tonsil of 3 of 8 boars by virus isolation, indicating that boars still harbor PRRSV within the tonsil even though antemortem specimens are PRRSV negative.
由于猪繁殖与呼吸综合征病毒（PRRSV）可通过公猪精液传播，因此识别持续感染的公猪很重要。然而，即便给公猪接种相同毒株和剂量的PRRSV，精液中病毒排出持续时间仍存在差异，这表明宿主因素与PRRSV的持续存在有关。为确定是否存在宿主遗传因素，特别是与PRRSV持续存在相关的窝别和品种差异，本研究使用了3个纯种猪品种的3窝猪。还确定了在血清、精液或外周血单个核细胞（PBMC）中是否能更长时间检测到PRRSV，以及在这些生前样本PRRSV阴性至少2 - 3周后，组织中是否仍能检测到PRRSV。获取了3头汉普夏、3头约克夏和2头长白未感染PRRSV的公猪，并经鼻接种一株野生型PRRSV分离株（SD - 23983）。每个品种内的所有公猪来自同一窝，且窝内仔猪年龄相差在9天以内。每周从每头公猪采集两次血清和PBMC，通过病毒分离和聚合酶链反应（PCR）分析PRRSV的存在情况。血清还用于获得病毒中和滴度和酶联免疫吸附测定S/P值。每周从8头公猪中的7头采集两次精液，并通过PCR进行分析。在所有样本PRRSV阴性至少2 - 3周后，对每头公猪实施安乐死，并采集21种组织以及唾液、血清、粪便和尿液。所有死后样本通过病毒分离进行评估。病毒分离PRRSV阴性的样本再通过PCR进行评估。长白、约克夏和汉普夏公猪精液中PRRSV排出持续时间的平均天数（±标准差）分别为51±26.9天、7.5±4.9天和28.3±17.5天。由于样本量小且标准差大，各品种间精液中PRRSV排出持续时间的差异不被认为具有显著性。然而，这一趋势表明约克夏公猪在精液中排出PRRSV方面比长白公猪更具抵抗力，需要使用更多公猪进行进一步研究。7头公猪中有4头在精液中检测到PRRSV的时间比在血清或PBMC中更长。8头公猪中有6头在血清中检测到病毒血症的时间比在PBMC中更长。在血清、精液和PBMC PRRSV阴性至少2 - 3周后，通过病毒分离在8头公猪中的3头扁桃体中仍能检测到PRRSV，这表明即便生前样本PRRSV阴性，公猪扁桃体中仍存有PRRSV。
