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

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.classical swine fever / wild boar / spatial / monitoring / serology

Control and eradication of Classic Swine Fever in wild boar

“…Barriers such as the fenced motorways and large rivers lakes and low density areas seem able to stop disease spreading (Schnyder et al, 2002;Rossi et al, 2005b; Figure 13). …”

“…o At first, infection dynamics behave as epidemic (epidemic or invasion phase): while the disease is spreading geographically, at a local level such as the municipality, the proportion of infected increases (the year of disease emergence) to a peak and then decreases; the proportion of immune animal increasing afterwards (Rossi et al,2005b).…”

“…During that 2 nd phase the proportion of infected decreases slowly until it fades out or is not detected. In parallel the host populations quickly compensated the mortality induced by the epizootic and the seroprevalence (of non vaccinated populations) rapidly decreases due to the turnover of the population (Laddomada et al, 1994;Rossi et al, 2005b). Due to the lack of time resolution of the data collected by the EFSA questionnaire, it was not possible to cross validate the decrease in seroprevalence.…”

“…In huge forested areas (green corridors) with no barriers or open fields stopping of drive hunts did not prevent the spreading of the virus (Rossi et al, 2005b;Pol et al, 2008). Restriction of hunting had been implemented in the field in small areas relatively isolated by physical barriers such as the Ticino region (Switzerland, part of the outbreak starting from Varese) and more recently in the Thionville region (France, part of the outbreak starting from Eifel) with some evidence of success (Schnyder et al, 2002;Pol et al, 2008).…”

Six recommendations for improving monitoring of diseases shared with wildlife: examples regarding mycobacterial infections in Spain

“…These meetings prompted a more widespread interest in wildlife disease surveillance. In the last decades, classical swine fever in Eurasian wild boar (Sus scrofa; Rossi et al 2005) and highly pathogenic avian influenza (Chen et al 2005) further contributed to a growing interest on diseases shared Communicated by A. Aguirre M. Boadella (*) : C. Gortazar : T. Carta : M. P. Martín-Hernando : J. de la Fuente : J. Vicente with wildlife such as zoonotic diseases and diseases that have potential risk for domestic species ). Detection of these relevant diseases in wildlife was identified as a determinant of the structure and function of European surveillance schemes (Leighton 1995).…”