Prevalence of PRRS virus in Wallonia (Belgium)

Porcine reproductive and respiratory syndrome (PRRS) causes major economical losses in pig farms. In different parts of the world, there is a growing consensus that PRRS virus (PRRSv) eradication should be performed on a regional basis, particularly in low density areas of pig production. The objective of the present study was to evaluate the apparent prevalence of PRRSv in Wallonia, a low density area of pig production (0.05 pig farms/km²). At this stage of the study, a phone survey has been addressed to 61/276 Walloon breeding pig owners. Fifty-eight answered to the questionnaire: 51 are responsible of a farrow-to-finish farm, 6 of a farrowing farm and 1 of a PRRS-free boar station. In 35% of the tested farms, sows are vaccinated with a modified live virus (MLV) PRRS vaccine (n=11) or with a killed PRRS vaccine (n=9). In two farms, both sows and piglets are vaccinated with a MLV PRRS vaccine. Replacement gilts are purchased in 33% farms. Among the 38 farms raising replacement gilts, 39% purchase boar(s). Boar semen is purchased in 86% of the farms: 56% purchase only boar semen; 30% purchase both semen and boar(s) and 14% of farms only purchase boar(s). In 22/57 tested farms, clinical signs evocative of PRRSv infection were observed over the last 10 years. In 30 farms a PRRS diagnostic test was performed in the past with a positive result in 17. When the pig owner did agree and if no vaccination was carried out on sows or on piglets, a serological Elisa test was performed in 10 breeding pigs and/or 5 feeder pigs >70 kg (or in all available sera if a smaller number of pigs was present). Globally, at herd level and at animal level, the apparent prevalence were respectively 35.2% (95% CI: 23.0-47.4%) and 23.4% (95% CI: 20.1-26.6%).