MONITORING OF PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME VIRUS-INFECTION IN BOARS

A major concern exists on transmission of porcine reproductive and res piratory syndrome virus (PRRSV) via semen and effect of vaccination on PRRSV shedding in semen. Recent reports suggest that the virus can be transmitted by semen from boars infected experimentally or from natur al sources. Seminal shedding, viremia, and changes in semen quality in boars with or without vaccination were examined. Nine boars were divi ded into three groups (three boars/group). Group I boars were vaccinat ed with 2 ml of RespPRRS vaccine (NOBL Laboratory) intramusculary and groups II and III were non-vaccinated. At 28 post-vaccination study da ys, group I and group II boars were challenged with virulent PRRSV VR- 2332 at 2 ml of 10(4.0) TCID50 per boar intranasally. Group III served as non-vaccinated and non-challenged control. Semen and serum samples were collected from -9 pre-vaccination study days to 85 post-challeng e study days and tested for the presence of PRRSV by virus isolation a nd reverse transcription-nested polymerase chain reaction (RT-nPCR). P rior to detection of PRRSV RNA from samples, conditions for RT-nPCR we re optimized. Two primer sets, an external and an internal, were selec ted for RT-nPCR. The first round of PCR using an external primer set c ould detect 10 TCID50 of PRRSV/reaction. However, nested PCR could det ect as little as 0.01 TCID50 of PRRSV/reaction. PRRS vaccine virus was not isolated from vaccinated pigs, but the vaccine virus RNA was dete cted from three boars, at day 6 to 15, 9 to 12, and 15 to 21 post-vacc ination by RT-nPCR. Following challenge, two of non-vaccinated/challen ged boars shed virus into semen up to 50 and 57 days post-challenge, r espectively. The group I vaccinated boars did not shed virus into seme n after challenge. The non-vaccinated/challenged group featured sperm abnormalities in the form of significantly increased incidence of prox imal droplets and abnormal tails at 36-50 days post-challenge. The lat ter defect was observed to increase similarly in vaccinated/challenged boars as well. (C) 1997 Elsevier Science B.V.