Abstract
BackgroundPorcine reproductive and respiratory syndrome virus (PRRSV) is widespread in commercial pig farms worldwide, and has a significant cost to the swine industry. Herd owners need a vaccine that will confer long-lasting immunity to prevent PRRSV infection and transmission. The studies described here evaluated duration of immunity conferred by a European-derived PRRS (isolate 94,881) modified live virus (MLV) vaccine, Ingelvac PRRSFLEX® EU, at 20, 24, and 26 weeks post-vaccination. Primary endpoints were the assessment of gross and histological lung lesions and viral RNA load in lung tissue 10 days following heterologous PRRSV challenge. Secondary endpoints included clinical observations, average daily weight gain (ADWG) and viral RNA load in serum 10 days post-challenge. Three blinded, vaccination-challenge efficacy studies were performed using separate cohorts of pigs (n = 56 per study). Pigs received either Ingelvac PRRSFLEX® EU (Group 1) or placebo (Groups 2 and 3). Groups 1 and 2 were subsequently challenged with heterologous European PRRSV isolate 205,817 at 20, 24 or 26 weeks post-vaccination.ResultsMean gross lung lesion scores were significantly lower in Group 1 than in Group 2 at 24 and 26 weeks (p < 0.0001), but not at 20 weeks (p = 0.299). Significantly lower mean histological lung lesion scores were observed in Group 1 versus Group 2 at 20 (p = 0.0065), 24 (p < 0.0001) and 26 weeks (p < 0.0001). Mean viral RNA load in lung tissue was significantly lower in Group 1 than in Group 2 (p < 0.0001) at 20 (p < 0.0001), 24 (p < 0.0001) and 26 weeks (p < 0.0001). Cumulative viral RNA loads in serum during days 1–10 post-challenge were significantly lower in Group 1 than in Group 2 (p < 0.0001) in all studies. A significant increase in ADWG was observed in Group 1 compared with Group 2 at 20 weeks (p = 0.0027) and 24 weeks (p = 0.0004), but not at 26 weeks (p = 0.1041). There were no significant differences in clinical signs post-challenge in any study.ConclusionThese results suggest that Ingelvac PRRSFLEX® EU confers long-term immunity to European heterologous PRRSV, which is maintained up to 26 weeks after vaccination, corresponding to the expected lifespan of commercial pigs.
Highlights
Porcine reproductive and respiratory syndrome virus (PRRSV) is widespread in commercial pig farms worldwide, and has a significant cost to the swine industry
In the 20-week study, the lung lesion score of Group 1 animals was in a similar range to that of Group 1 animals in the two adjacent studies; significance could not be reached due to the fact that lung lesions in Group 2 pigs were low as well. These findings suggest that Ingelvac PRRSFLEX® EU vaccine is highly effective in providing long-term immunity against a virulent challenge with PRRS
Following challenge at 26 weeks, average daily weight gain (ADWG) in Group 1 pigs was increased compared with Group 2, but this increase did not reach statistical significance. These results indicate that Ingelvac PRRSFLEX® EU is effective at diminishing weight gain reduction caused by PRRS, possibly representing substantial economic importance
Summary
Porcine reproductive and respiratory syndrome virus (PRRSV) is widespread in commercial pig farms worldwide, and has a significant cost to the swine industry. The disease has profound economic consequences, causing significant losses to the worldwide swine industry, and an estimated annual loss of 1 billion US dollars in North America alone [5]. There are two major genetic lineages: Type 1, which was originally isolated in Europe in 1990 [6], and Type 2, which was first isolated in North America [7]. These two genotypes emerged at approximately the same time, but their nucleotide sequences differ by approximately 40% [8, 9].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
