2004 Ridremont1 Ipvs

SCREENING ON PRRS SEROLOGICAL PROFILES ON GROWING PIGS IN FRENCH INFECTED AND NON VACCINATED FARMS B. Ridremont1, V. Auvigne 2 (1) Intervet S.A., BP 17144, 49071 Beaucouzé, France (2) Ekipaj, 4 allée Charles Gounod, 35760 Saint Grégoire, France Introduction Serological profiles, useful to evaluate age of growing pigs at seroconversion and precisely age at infection (1), are an important tool in farms to analyze clinical and economical consequences of diseases and to adapt control and eradication measures. Intervet S.A. proposed to the French pig veterinarians a partnership for realization of PRRS serological profiles in French farms (with “all in/all out” management system). Here is described a complete analysis on PRRS serological profiles done on a one-year period. Materials and Methods Present study is a screening with a total of 375 « non negative » profiles (at least one positive pig per profile), with at least three age groups (with a mean of 5 sera within each age group) and realized from February 2002 to February 2003. All these profiles have been done by 62 different veterinarians. In all these farms, growing pigs have not been vaccinated. A total of 7.734 serologies have been included in this study. PRRS serologies have been realized by Elisa tests (90% of them with Idexx kit). Results The mean serological profile seems quite classical in French farms (Figure 1) : maternal antibodies are present in 40% of the piglets and decrease to reach a minimum at 8 to 10 weeks of age (i.e. at end of post-weaning period or at beginning of fattening period). Seroconversion to wild virus is then observed in fattening period : more than 80% of pigs at the end of fattening period are seropositive. Figure 1 : Mean serological profile

Figure 2 : Results per pig batch % p ig b a tc h e s

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Analysis per geographical area has been conducted by selecting 114 profiles with at least 4 age groups sampled between 5 and 16 weeks of age and by considering pig batch as the statistical unit. Four different areas have been considered (mostly in West of France) : Finistère department (n=48), Côtes d’Armor and Morbihan departments (n=40), Ille et Vilaine, Manche and Mayenne departments (n=18), other departments (n=3). From a geographical area to the other , serological profiles are statistically different in post-weaning and beginning of fattening periods . For instance, in Finistère department, more than 2 piglets on 5 are positive at the beginning of post-weaning period (5 to 7 weeks of age), i.e. one piglet more than in other departments. In East part of Brittany (Ille et Vilaine, Manche and Mayenne departments), serological profiles showed a high prevalence at the beginning of fattening period : more than 3 piglets on 5 are positive between 11 and 13 weeks of age, i.e. 1.4 more on average than in other departments or areas . Then there is no statistical difference between sampling seasons (spring/summer versus autumn/winter) Discussion

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The mean serological profile showed a progressive seroconversion but, within each pig batch, serological response is mainly « quite positive or quite negative » (Figure 2). We observed that pig batches are either completely negative (36% of batches : 5 negative sera/ 5 sera), or highly positive (38% of batches : 4 or 5 positive sera/ 5 sera). This confirms that pig batch is the “epidemiological” unit within farm, and that virus spreading is often explosive within pig batches.

In this study, we observed differences between geographical areas in growing pigs from 5 to 13 weeks of age. Serologies on older pigs, which are convenient to establish a diagnosis of PRRS infection, do not provide pertinent data about epidemiology of virus infection in farms. However these results must be considered cautiously because selection of profiles was not random. Nevertheless, we could conclude that there would be structural factors which could influence PRRS virus spreading in growing pigs (herd size, farm management, health status,…). If these factors could be specified, then it would be possible to define subgroups of farms and to maximize vaccination schedules without having to realize complete and regular serological profiles within each farm. Reference 1. Pommier P et al. 2003. Proc. J.R.P., 35, 369-374.

Proceedings of the 18th IPVS Congress, Hamburg, Germany, 2004 – Volume 1

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