Vet. Res. 36 (2005) 27-42
DOI: 10.1051/vetres:2004050

Long-term monitoring of classical swine fever in wild boar (Sus scrofa sp.) using serological data

Sophie Rossi^{a, b}, Marc Artois^a, Dominique Pontier^c, Catherine Crucière^d, Jean Hars^e, Jacques Barrat^f, Xavier Pacholek^b and Emmanuelle Fromont<sup>c

a</sup>  École Nationale Vétérinaire de Lyon, Unité Microbiologie, Pathologie infectieuse et Épidémiologie, 1 avenue Bourgelat, BP 83, 69280 Marcy-l'Étoile, France
^b  Direction Générale de l'Alimentation, Ministère de l'Agriculture, de l'Alimentation, de la Pêche et des Affaires Rurales, 251 rue de Vaugirard, 75732 Paris Cedex 15, France
^c  UMR 5558, Biométrie et Biologie Évolutive, Bâtiment Mendel, Université Claude Bernard Lyon 1, 43 Bd du 11 novembre 1918, 69622 Villeurbanne Cedex, France
^d  Agence Française de Sécurité Sanitaire des Aliments (AFSSA), 23 avenue du Général De Gaulle, 94706 Maisons-Alfort Cedex, France
^e  Office National de la Chasse et de la Faune Sauvage, 5 allée de Bethléem, ZI de Mayencin, 38610 Gières, France
^f  Agence Française de Sécurité Sanitaire des Aliments (AFSSA), BP 9, Domaine de Pixérécourt, 54220 Malzéville, France

(Received 12 March 2004; accepted 30 June 2004)

Abstract - In the European Community, epizootics of classical swine fever (CSF) in the wild boar (Sus scrofa) are compulsorily monitored because transmission may occur between wild boars and domestic pigs, causing heavy economic losses to the pork industry. The estimation of incidence in populations of wild boars is generally based on viroprevalence. However, viral isolation becomes rare when the incidence is low because the virus cannot be detected for more than a few weeks following infection. On the contrary, seroprevalence is detectable at low incidence levels, because antibodies can be detected for the lifetime of the infected animal. We thus attempted to analyse the long-term evolution of CSF incidence using serological data. The data came from France, where CSF had been monitored from 1992 to 2002, and where the virus has not been detected since 1997. We assumed that the overall seroprevalence would estimate the proportion of immune wild boars, that seroprevalence in juveniles would approximate incidence and that seroprevalence in different age classes would show the evolution of incidence in a given cohort. Spatial and temporal trends of incidence and seroprevalence were explored using logistic modelling and the spatial trend was analysed using polynomial regression. In 1992, incidence peaked in the northern area. After 1993, incidence decreased but remained the highest in the northern area. After 2000, no seropositive juvenile was observed, suggesting the extinction of the epizootic. Our results support the reliability of serological monitoring since it allowed a longer detection of viral transmission and provided more information on the spatio-temporal evolution of incidence than did viral isolation. We advocate that the highest persistence of infection in northeastern France is not independent from infection persistence in Reinland-Pfalz (Germany). Such persistence may be due to favourable local conditions and/or the social organisation of wild boars.

Key words: classical swine fever / wild boar / spatial / monitoring / serology

Corresponding author: Emmanuelle Fromont fromont@biomserv.univ-lyon1.fr

© INRA, EDP Sciences 2005