Detection and duration of porcine reproductive and respiratory syndrome virus in semen, serum, peripheral blood mononuclear cells, and tissues from Yorkshire, Hampshire, and Landrace boars

Because transmission of porcine reproductive and respiratory syndrome virus (PRRSV) can occur through boar semen, it is important to identify persiste ntly infected boars. However, even for boars given the same PRRSV strain an d dose, variability in the duration of viral shedding in semen has been obs erved, suggesting that host factors are involved in PRRSV persistence. To d etermine whether there are host genetic factors, particularly litter and br eed differences related to the persistence of PRRSV, 3 litters from 3 pureb red swine breeds were used for this study. It was also determined whether P RRSV could be detected for a longer period of time in serum, semen, or peri pheral blood mononuclear cells (PBMC) and if PRRSV could still be detected in tissues after these antemortem. specimens were PRRSV negative for a mini mum of 2-3 weeks. Three Hampshire, 3 Yorkshire, and 2 Landrace PRRSV-naive boars were obtained and inoculated intranasally with a wildtype PRRSV isola te (SD-23983). All boars within each breed were from the same litter, and l itters were within 9 days of age. Serum and PBMC were collected twice weekl y 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 viru s neutralization titers and enzyme-linked immunosorbent assay S/P values. S emen was collected twice weekly from 7 of 8 boars and analyzed by PCR. Afte r all specimens were PRRSV negative for a minimum of 2-3 weeks, each boar w as euthanized, and 21 tissues plus saliva, serum, feces, and urine were col lected. All postmortem specimens were evaluated by virus isolation. Specime ns 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 w as 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 size s and large SDs, the differences in duration of PRRSV shedding in semen bet ween breeds were not considered significant. However, the trend suggested t hat Yorkshire boars were more resistant to PRRSV shedding in semen than wer e Landrace boars, requiring further investigation using a larger numbers of boars. PRRSV was detected for a longer period in semen than in serum or PB MC 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-negativ e 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 wit hin the tonsil even though antemortem specimens are PRRSV negative.