RESUMEN
In the last two decades, in France, Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) stabilization protocols have been implemented using mass vaccination with a modified live vaccine (MLV), herd closure and biosecurity measures. Efficient surveillance for PRRSV is essential for generating evidence of absence of viral replication and transmission in pigs. The use of processing fluid (PF) was first described in 2018 in the United States and was demonstrated to provide a higher herd-level sensitivity compared with blood samples (BS) for PRRSV monitoring. In the meantime, data on vertical transmission of MLV viruses are rare even as it is a major concern. Therefore, veterinarians usually wait for several weeks after a sow mass vaccination before starting a stability monitoring. This clinical study was conducted in a PRRSV-stable commercial 1000-sow breed-to-wean farm. This farm suffered from a PRRS outbreak in January 2018. After implementing a stabilisation protocol, this farm was controlled as stable for more than 9 months before the beginning of the study. PF and BS at weaning were collected in four consecutive batches born after a booster sow mass MLV vaccination. We failed to detect PRRSV by qPCR on PF and BS collected in a positive-stable breeding herd after vaccination with ReproCyc® PRRS EU (Boehringer Ingelheim, Ingelheim, Germany).
RESUMEN
The influence of maternally-derived antibodies (MDAs) on the post-vaccination humoral and cellular immune responses in piglets vaccinated against PRRS was studied. The piglets came from a vaccinated breeding herd. Thirty piglets with a low (A-) or high level (A+) of PRRSV-neutralizing MDAs were vaccinated (V+) with a modified live vaccine at 3 weeks of age. Blood samples were collected before vaccination and then at 2, 4, 8 and 14 weeks post-vaccination (WPV). The samples were analysed to detect the vaccine viraemia (RT-PCR) and quantify the post-vaccination humoral (ELISA and virus neutralisation test) and cellular (ELISPOT IFNγ) immune responses. PRRSV vaccine strain was detected in 60%, 64%, 36% and 0% of A-V+ piglets 2, 4, 8 and 14 WPV respectively. No virus was detected in A+V+ piglets during the first four WPV but 32% and 6% of A+V+ piglets were PCR-positive at 8 and 14 WPV. Eighty-five percent of A-V+ piglets and 0% of A+V+ piglets seroconverted (ELISA) between 2 and 4 WPV. Neutralising antibodies appeared 4 WPV in the A-V+ piglets and 14 WPV in the A+V+ piglets. The number of PRRSV-specific IFNγ-secreting cells was significantly higher in A-V+ piglets at 2 and 4 WPV than in A+V+ piglets. These results show that MDAs can affect both post-vaccination humoral and cellular immune responses in piglets. Further studies are required to assess the impact of MDAs on vaccine efficacy following a PRRSV challenge and its ability to reduce viral transmission.
