Role of sow and piglet vaccination in stabilizing a closed herd without depopulation after a PRRS outbreak

Different strategies have been described to stabilize a farm after a PRRSv outbreak, with vaccination being a very effective one. This experience describes how correct use of MLV PRRS vaccination (Porcilis® PRRS, MSD AH) in sows and piglets, combined with biosecurity and management, achieves stabilization of a closed herd after a PRRSv outbreak without depopulation.

The events occurred in a PRRS(-) closed 500 sow herd. In Apr 2014, reproductive disorders such as late term abortions and early farrowings were detected. PRRSv outbreak was diagnosed by several (+) PCRs in blood samples of aborted sows. Sequencing of field strain confirmed a 95% homology with Lelystad virus. Depopulation was not a feasible option and main objective was to stabilize the farm in the shortest time possible. In May 2014, a sow mass vaccination with Porcilis® PRRS (with IDAL) was initiated; revaccination was done one month later and then maintained every 3 months. Gilt new entries were stopped for 4 months and biosecurity measures were established, as well as strict unidirectional piglet flow. Two months after revaccination, newborn piglets were checked by PCR to ensure that there were no viremic piglets (15 piglets/week). In Sep 2014, the first negative PCRs were detected in newborn piglets. After 3 consecutive weeks of negative PCRs, Strategic Piglet Vaccination was initiated (Oct 2014). Fourteen day old piglets were vaccinated with Porcilis PRRS using IDAL over a 16 week period. While Strategic Piglet Vaccination was established, PCR of 2 week old piglets were done every 2 months to ensure no new recirculation. After this 16 wk period, piglet vaccination was stopped. First non-vaccinated piglets were sampled at 3, 6 and 9 wks of age for PRRS serology and PCR.

First PCR negative newborn piglets were obtained in Sep 2014, 5 months after the outbreak. Sampling was repeated every two months, and all PCRs were negative (last sampling Nov 2015). Serological results of first non-vaccinated piglets showed that there was no recirculation of PRRSv before 9 wks of age (last sampling Sep 2015). Nevertheless PRRS recirculation was detected in 12 week old piglets in the fattening units. Although this requires further investigation, this was most likely the result of a horizontal infection from pigs already present in the units.

The right combination of vaccination, biosecurity and management allows PRRSv stabilization after an outbreak in a short period of time without depopulation. Therefore, sows mass vaccination and Strategic Piglet Vaccination are a very effective combination to obtain PRRS negative piglets to enter the fattening units.

Disclosure of Interest: None Declared.