Persistence of Porcine Reproductive and Respiratory Syndrome Virus in Serum and Semen of Adult Boars

Abstract

Abstract. Four seronegative adult boars were intranasally inoculated with porcine reproductive and respiratory syndrome virus (PRRSV) isolate VR-2332. Serum and semen were collected 2-3 times weekly for over 100 days postinoculation (DPI). Serum samples were assayed for PRRSV by virus isolation (VI) and a polymerase chain reaction (PCR) and screened for antibodies to PRRSV using the indirect fluorescent antibody (IFA) and virus neutralization (VN) tests. Semen was assayed for PRRSV RNA by PCR. Virus or viral RNA was detected in the serum of all boars within 1 DPI by VI and/or PCR. However, VI results indicated that viremia was transient and occurred from 1 to 9 DPI. Viral RNA was detected in serum from 1 to 31 DPI. In the acute stage of the infection, PRRSV RNA was detected in serum by PCR prior to the presence of viral RNA in semen. The PRRSV RNA was detected in semen as early as 3 DPI and persisted for 25 DPI in 2 of the boars and 56 and 92 DPI in the remaining 2 boars. Detection of PRRSV RNA in semen occurred 2-8 and 28-35 days prior to the detection of antibodies by IFA and VN, respectively. PRRSV was isolated from the bulbourethral gland of the boar that shed viral RNA in semen for 92 DPI. These results suggest that PRRSV RNA can be detected by PCR in boar serum and semen, and may persist for variable periods of time. Viremia and the serologic status of the boar are not adequate indicators of when PRRSV or PRRSV RNA is being shed in the semen. Preliminary findings also indicated that neither shipping stress nor reinoculation with homologous PRRSV resulted in viremia or viral RNA shedding in semen.Porcine reproductive and respiratory syndrome (PRRS) is an important disease in swine and occurs throughout the world. 8,13 The syndrome was first recognized in 1987 and is clinically characterized by poor conception rates, late-term abortions and stillborn and weak pigs from sows of reproductive age. Respiratory distress, fever, lethargy, and high mortality can occur in suckling, weaned, and grow-finish pigs. 8,12,16,24 The etiologic agent of this disease was first described in 1991 and was identified as a single-stranded RNA virus, currently classified as an arterivirus. 2,24 Although the primary route of PRRS virus (PRRSV) transmission may be through airborne spread, 13 recent investigations in the United Kingdom 12 and the United States 18,26 have indicated that infected boars can transmit PRRSV in semen. This information has heightened concern in the world swine industry, which is becoming more reliant on artificial insemination as a means to introduce new genetic information into "high health" status herds. There are also trade restrictions on the importation of semen from countries with PRRSV. 18 The contamination rate of semen and boars with PRRSV in the US and Europe is unknown. A polymerase chain reaction (PCR) assay using primers to open reading frame (ORF) 7 of the VR-2332 isolate has recently been developed to detect the PRRSV RNA in semen, and it was found to be more sensitive than virus isolation...

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].…”

“…This virus most likely reaches the tissues of the reproductive tract and semen by migration of infected monocytes and macrophages [49]. The duration of shedding in semen samples of experimentally infected boars varies widely, ranging from 2 d [33] to 92 d [31] after infection (Table 1). This marked variability may be due to various factors, including individual boar variation, possibly the type of virus strain, and the technique used for detection of the virus (i.e.…”

A review of evidence for immunosuppression due to Porcine Reproductive and Respiratory Syndrome Virus

“…This work expanded on the earlier observation of Christianson et al [18], who obtained similar results, but terminated their observations at 14 days post-infection. Certainly, PRRSV is known to persist in pigs for up to 2-3 months postinfection [1,19,26], so experiments such as those described should be extended to explore the long-term effects of PRRSV, if any, on the immune system. Not all the published data of sub-cell populations are in accord.…”

Article

“…After experimental infection, the presence of viral RNA in semen was detected by PCR on day 92 pi and viral isolation took place from the bulbourethral gland of one boar on day 101 pi [10].…”