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

Abstract

Abstract. 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-naïve boars were obtained and inoculated intranasally with a wildtype 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 (ϮSD) for the duration of PRRSV shedding in semen was 51 Ϯ 26.9 days, 7.5 Ϯ 4.9 days, and 28.3 Ϯ 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.

Characterization of the carrier state in porcine reproductive and respiratory syndrome virus infection

“…Given the high specificity of the RTnPCR assay demonstrated in this experiment, i.e., 4 false positives among 780 samples from animals known to be PRRS virus negative, these results suggest the detection of inactivated virus in previously infected animals .. Overall, the results of this and previous studies are in agreement: PRRS virus infection results in persistently-infected swine (Allende et al, 2000;Christopher-Hennings et al, 1995;Christopher-Hennings et al, 2001;Wills et al, 1995;Wills et al, 1999). The current study differed from previous studies in that a higher proportion of carriers was detected than previously reported.…”

“…The detection of PRRS virus in tonsil and/or oropharyngal scrapings has previously been reported (Allende et al, 2000;Benfield et al, 1997;Christopher-Hennings et al, 2001;Wills et al, 1997;Wills et al, 1999). In this study, virus was detected somewhat more frequently in oropharyngeal scraping samples than tonsil tissue samples.…”

“…These include the postulated role of virus-specific factors, i.e., hypothesized differences among virus isolates relative to their ability to persist in pigs, and host-specific factors , i.e., postulated effects of age or breed on the duration of persistent infection (Christopher-Hennings et al, 2001;Halbur et al, 1998). Although the North American prototype PRRS virus (ATCC VR-2332) was used frequently (Benfield et al, 1997;Christopher-Hennings et al, 1995), but not exclusively (Allende et al, 2000;Benfield et al, 1997;Christoper-Hennings et al, 2001;Swensen et al, 1995;Wills et al, 1997;Wills et al, 1999;Zimmerman et al, 1992), there are too many inconsistencies in experimental design to be able to compare the data and determine whether strain variation exists.…”

Diseases in swine transmitted by artificial insemination: An overview

“…Infected animals can shed PRRSV in saliva, nasal secretions, urine, feces, and also in semen. The virus can be shed in semen, even in the absence of viremia and in the presence of neutralizing antibodies [31,32]. This virus most likely reaches the tissues of the reproductive tract and semen by migration of infected monocytes and macrophages [49].…”

Nested Polymerase Chain Reaction Detection and Duration of Porcine Circovirus Type 2 in Semen with Sperm Morphological Analysis from Naturally Infected Boars

“…4 Landrace, Yorkshire, and Hampshire boars infected experimentally with PRRSV demonstrate variability in the duration of PRRSV seminal shedding among breeds. 3 The observed trend of differences in breed susceptibility to PRRSV-shedding in semen requires further study of variable host factors in PRRSV persistence and resistance. Porcine circovirus type 2 DNA was detected in semen from Duroc and Landrace boars only; however, the semen of the Hamline, Large White maternal, Large White paternal, and Meishan-synthetic boars were negative for PCV2 DNA.…”