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Research article2009Peer reviewed

Control and eradication of classic swine fever in wild boar

Algers, Bo; Blokhuis, Harry; Bötner, A; Broom, DM; Costa, P; Domingo, M; Greiner, M; Guemene, D; Hartung, J; Koenen, F; Müller-Graf, C; Morton, DB; Osterhaus, A; Pfeiffer, DU; Roberts, R; Sanaa, M; Salman, M; Sharp, JM; Vannier, P; Wierup, Martin

Abstract

Classical swine fever (CSF) is a disease that has been causing major socio-economic damages in the EU during the last decades. Although considerable progress has been made in the eradication and prevention of the disease, the threat for an epidemic still exists. The virus is endemic in the wild boar population of several member states (MS). Wild boar cannot be managed as domestic pigs. Hunting and vaccination have been tentatively used in order to stop transmission by reducing the number of susceptibles. Oral vaccination of wild boar with modified live vaccine based on the C-strain (the only suitable) is used; this vaccine does not allow serological differentiation between vaccinated and infected animals. The aim of the control measures for CSF in wild boar is to reduce the risk of transmission to domestic pigs, to prevent an “endemic phase evolution” or to reduce the endemic phase duration. In order to support and to improve the control and eradication measures as regards CSF in wild boar, EFSA was requested by the Commission to provide scientific advice on the efficacy of the available surveillance, hunting and vaccination measures to control and eradicate CSF in feral pig populations (wild boar), considering the possible use of new diagnostic tests and vaccines. In order to reply to the mandate data were collected from MS through two questionnaires (CSF vaccines, hunting practices and CSF vaccination in wild boar). Data were also extracted from the EU CSF wild boar data base, after requesting permission from the participating MS. Considering that the data received were rather limited and not comparable, the WG decided to use a model in order to fill the gaps in the available knowledge. For the evaluation of the efficacy of CSF control in wild boar a continuous metapopulation compartmental model developed in an EU research project (FP6-5015599-CSFVACCINE&WILDBOAR) was applied. Although the disease manifests in the same manner in both domestic pig and wild boar it is more difficult to identify in wild boar because clinical monitoring of these is hardly possible. Wild boar found dead constitutes the main alert sign of CSF. Hunters and gamekeepers should be instructed to report the finding of each dead wild boar to the competent authority at all times. In case of high-risk situations, a passive surveillance should be complemented by an active serological surveillance. The active sampling of wild boar is not as efficient as in domestic pigs considering that hunting is the sole practical system to obtain samples and that the aim of hunting is quite different. Consequently, the sample size is not controlled by authorities and fits rarely the aim of the survey in terms of detecting the presence of disease at a certain level. In addition, the interpretation of serological results is confounded by maternal derived antibodies (until the 6th month of age), vaccination and the sampling quality. There is no definition at EU level of spatial and temporal units for surveillance, neither for criteria defining a disease free wild boar population. The sample size is not the only factor that dictates the overall sensitivity of surveillance systems. Indeed, wild boar habitat, hunting patterns, and disease distribution should be included when assessing surveillance system sensitivity. After a vaccination campaign, PCR positive animals can be due to modified live vaccines (MLV) but these MLV-vaccinated animals can be cross-checked for wild type CSF virus (genetic DIVA – discriminatory PCR). A positive PCR diagnosis should be considered to indicate that an animal is or has been infected with the wild type or MLV virus but it is not necessarly still infectious. According to previous field experience and to model simulations of a CSF epidemic in a wild boar population and the possible outcomes regarding vaccination: the disease will fade out without any additional control measures in small populations (between 1000 and 1500); hunting is not efficient for CSF control and should not exceed the normal 45% per year. Hunting is currently needed for sampling; vaccination: increases population immunity progressively. The maximum population immunity is only reached after three double campaigns; by one isolated campaign cannot increase population immunity adequately to control CSF and might even aggravate the persistence of CSF; mainly prevents the spread of the infection in neighbouring vaccinated patches; promotes long-term eradication through a progressive reduction of virus transmission to neighbouring areas; always reduces the epidemic peak (number of infected animals/time). Endemic evolution of infection may occur when a low rate of vaccination is achieved; in both infected and not yet infected areas, reaching a minimum target of 40 % of susceptible animals is necessary to obtain a positive control effect, below 20% - will increase probability of endemic stability, above 60% - will always eradicate the infection

Keywords

classical swine fever; wild boar; surveillance; control; monitoring; vaccination; hunting; modelling; ecology; epidemiology

Published in

EFSA Journal
2009, number: 1, article number: 932
Publisher: EFSA