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Intervet/Schering-Plough Animal Health IPVS Symposium 2010

A PRRS vaccination strategy to create PRRS-negative growersgilts in SPF herds re-infected with PRRS

Geertjan van Groenland1, Victor Geurts2, Toine Cruijsen2

1Topigs International, Postbox 86, 5268 ZH Helvoirt, The Netherlands,2Intervet Nederland BV, Boxmeer, The Netherlands (


PRRS infections still lead to severe economic losses in the pig industry (1). It is possible to create PRRS-negative farms by depopulation and repopulation with negative piglets and gilts from PRRS-free farms. Despite stringent hygienic procedures on these farms, it is difficult to keep them PRRS-free in pig dense countries like the Netherlands. Between Febr-2006 and May-2008, 5 farms in the Netherlands became PRRS-free by depopulation and repopulation with SPF- pigs or by introducing SPF pigs in a new farm, and all of them became infected after 6 to 22 months. The PRRS-infection-route could not always be identified. Therefore, farmers choose to produce PRRS- negative growers and gilts via a system of vaccination together with testing and optimization of biosecurity. Vaccination of piglets was ceased as soon as there could not be detected PRRS-fields virus anymore in the outflow (by serological and virological tests). A conventional boar- producing farm followed the same strategy. The chosen PRRS vaccine (Porcilis® PRRS) reduces vertical transmission and reduces virus circulation in the population following vaccination [Ro <1] (3, 4). Furthermore, to reduce the risk of transmission between pigs by needle injection, a needle-less vaccination system was used (IDAL®, intra dermal applicator of liquids, Intervet/Schering-Plough animal health). The vaccine had already been effective in eradicating PRRS from farms(5).

Materials and methods

Step 1. Once PRRS infection had been diagnosed on SPF farms, a cross-section of sows, piglets, fatteners and breeding gilts were sampled in combination with pooled virus isolation or PCR in order to investigate the spread. All biosecurity measures were checked and optimized and all pigs older than 2-weeks were vaccinated (herd vaccination, i.e. all sows, gilts, piglets, growers, fatteners). Sows were vaccinated 2-4 times with intervals of 2-4 weeks, thereafter all sows/gilts were vaccinated in mid- gestation (day 60) and during lactation (day 6). After the initial herd vaccination piglet vaccination was started at 14- 21days of age. On farm 3, only (pregnant) gilts and boars were present that were vaccinated only once. Step 2. After 3-6 months, again sows, breeding gilts, and pigs of 4, 10, 16, and 22-26 weeks of age were sampled for serological, and virus isolation or PCR. When the tests for PRRS field virus were negative, piglet vaccination was ceased. Step 3. Farms which had stopped piglet vaccination were monitored by the same sampling procedure as in Step 2, every 4 months.


Until now (February 2010), five out of six farms succeeded in producing PRRS negative gilts/growers/boars. Only one farm got re-infected during the trial, the isolated strain was an US-type PRRS strain. No vaccinations were added after this herd became re-infected (sow/gilts vaccination was continued) partly due to the fact that no clinical signs were seen after re-infection and the spread was limited (most cohorts were PRRS negative). From September on sera from 10-weeks-old pigs tested negative for PRRS.

Conclusion and discussion

Via testing, adjustments to biosecurity and targeted vaccination, it was possible to create PRRS-negative pigs from SPF farms that were infected with PRRS. In a pig dense country as the Netherlands where the estimated introduction risk of PRRS is high, this system proved to be effective in controlling PRRS. On all farms, except for farm 3, sow vaccination (day 6- day 60) was continued to minimize the risk of vertical transmission because viremic born piglets will further spread the infection through the herds. Sequence analyses on farms helps to identify the likely routes of re-infection. Two such routes were discovered during this trial/survey: (i) an aerosol infection originating from a neighboring farm and (ii) via infected replacement gilts. Because almost all SPF-farms in the Netherlands became infected after depopulation/repopulation it seems that (i) either regional approach or (ii) air-filtration of incoming air will be necessary for farms in pig dense areas such as The Netherlands to remain PRRS-free(2). In the meantime vaccination of sows and gilts, together with well- defined internal biosecurity can be used to produce PRRS- negative offspring in infected breeding farms as well as in farms that are “at risk”.

References al,(2005) J..Am.Vet.Med.Ass. 227, no3,
2. Dee al,(2008) Proc.20th IPVS congr., Vol.1, p57
3. Astrup al, (2002) Proc.17th IPVS congr.,p380
4. Grosse Beilage al, (2009) Prev.Vet.Med. 92:31-37
5. Voglmayr al (2006)Tierärzt.Praxis 34,241-248

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