Long duration of immunity against a type 1 heterologous PRRS virus challenge in pigs immunised with a novel PRRS MLV vaccine: a randomised controlled study

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.

Dynamics and Differences in Systemic and Local Immune Responses After Vaccination With Inactivated and Live Commercial Vaccines and Subsequent Subclinical Infection With PRRS Virus

“…Despite the fact that many studies focused on PRRS immunoprophylaxis have already been published and many procedures are implemented in the agricultural industry, a universal model does not yet exist (46)(47)(48)(49)(50)(51)(52)(53)(54)(55)(56)(57)(58)(59)(60). The use of live attenuated vaccines is generally preferred as was also confirmed in our field study (61).…”

“…In another study the excretion of virus was described still for 21 days after vaccination with for Porcilis or Amervac vaccine (53). Demonstration of cell-mediated immunity and reduction in viral load correlate with studies by other authors and support the preferred use of MLV vaccines in the control of PRRS infection (29,46).…”

“…There are only a few papers published providing a comprehensive picture of immune response after vaccination against PRRSV (40)(41)(42)(43) because the majority of the existing studies are based mainly on the evaluation of the vaccination effectiveness by monitoring the immune responses found in the blood (5,30,33,(44)(45)(46). Our results show that antibodies after immunization and infection, and the virus after infection, can be detected in all the monitored compartments (blood, respiratory tract, intestine).…”

Codon Pair Deoptimization (CPD)-Attenuated PRRSV-1 Vaccination Exhibit Immunity to Virulent PRRSV Challenge in Pigs

“…Gross and histopathological lung lesions are the main indicators of PRRSV infection [50]. Tissue hyperplasia and hemorrhage in the lungs are the typical characteristics of PRRSV infection and were evident in unvaccinated and challenged animals (positive control).…”

Control integral del PRRSv mediante el concepto de las 5 fases: revisión crítica

“…La transmisión vía vertical, de la madre a los embriones o fetos en desarrollo vía transplacentaria (Christianson et al, 1992) ocurre durante el último tercio de gestación en cerdas activamente infectadas (Lager y Mengeling, 1995).…”