Vaccination of 1-day-old pigs with a porcine reproductive and respiratory syndrome virus (PRRSV) modified live attenuated virus vaccine is able to overcome maternal immunity

Abstract

BackgroundThe objective of the study was to evaluate the influence of maternally derived antibodies (MDA) on the efficacy of a PRRSV-1 based attenuated vaccine, when administered in 1 day-old piglets by the intramuscular route. The protective immunity of the modified live virus vaccine was evaluated in pigs born from seropositive sows, vaccinated at 1 day of age, upon inoculation with a PRRSV-1 isolate. The animals were challenged when the levels of MDAs detected by seroneutralization test (SNT) in the non-vaccinated control group became undetectable (10 weeks after vaccination).ResultsA protective effect of vaccination was observed since a significant reduction of viral load in serum compared to the control group was detected in all sampling days after challenge; efficacy was supported by the significant reduction of nasal and oral shedding as well as in rectal temperatures. Clinical signs were not expected after the inoculation of a PRRSV-1 subtype 1 challenge strain. However, the challenge virus was able to develop fever in 61% of the control pigs. Vaccination had a positive impact on rectal temperatures since the percentage of pigs that had fever at least once after challenge was reduced to 31% in vaccinated animals, and control pigs had significantly higher rectal temperatures than vaccinated pigs 3 days post-challenge. The lack of a vaccination effect in body weight gain was probably due to the short evaluation period after challenge (10 days). In the vaccinated group, 9/16 pigs (56%) experienced an increase in ELISA S/P ratio from the day of vaccination to 67 days post-vaccination. All vaccinated pigs were seropositive before challenge, indicating the development of an antibody response following vaccination even in the face of MDAs. In contrast to ELISA results, only 2/16 vaccinated pigs developed neutralizing antibodies detectable by a SNT that used a subtype 1 MA-104 adapted strain. Even in the absence of SN antibodies, vaccinated pigs were protected from challenge with a heterologous strain. The role of cell-mediated immunity should be considered, if protection was not mediated by SN antibodies only.ConclusionsThe efficacy of the attenuated PRRSV-1 vaccine in 1-day-old pigs seropositive to PRRSV prior to a PRRSV-1 challenge was demonstrated by improvement of clinical, virological and immunological variables. With the current experimental design, maternal immunity did not interfere with the development of a protective immune response against a PRRSV-1 challenge, after vaccination of 1 day-old pigs. Confirmation of these results under field conditions will be needed.

Maternally-derived neutralizing antibodies reduce vaccine efficacy against porcine reproductive and respiratory syndrome virus infection

“…In Jeong's study, all the piglets were MDA+ at vaccination (no MDA-group included) and thus this precluded to clearly evaluating the impact of MDAs on the vaccine efficacy. As the same, Balasch et al recently showed that vaccination of 1-day-old piglets using a new PRRSV-1 MLV in presence of MDAs induced a partial protection against a challenge at 67 days pv [18]. In Balasch's study, NAs were quantified in piglets at the vaccination time but here also the absence of comparison with vaccinated piglets without MDNAs limits the conclusions of the study.…”

Efficacy of a Modified Live Virus Vaccine against Porcine Reproductive and Respiratory Syndrome Virus 1 (PRRSV-1) Administered to 1-Day-Old Piglets in Front of Heterologous PRRSV-1 Challenge

“…Due to the fact that the onset of immunity of vaccinated piglets is delayed and usually detectable around 3-4 weeks after vaccination [16], a gap in protection may occur if vaccination is given late in the suckling period or at weaning. In particular, the potential early circulation of PRRSV in piglets after weaning has led to the development of vaccines with an approval for usage from the first day of life for both PRRSV-1 and PRRSV-2 [17,18].…”

A DNA Prime Immuno-Potentiates a Modified Live Vaccine against the Porcine Reproductive and Respiratory Syndrome Virus but Does Not Improve Heterologous Protection

“…Finally, we found that a partial heterologous protection was achieved in the absence of detectable NAbs at the challenge time-point. PRRSV has often been reported to induce very low NAb titers which appear late in infection [37,38] or which were even non-detectable upon infection or MLV administration in several cases [39,40,41,42,43,44]. The non-detection could be due to the currently used in vitro techniques which may not capture the neutralization of the virus occurring in vivo.…”