Wild boar: an increasing concern for Aujeszky's disease control in pigs?

Abstract

Background: The goal of this study was describing the temporal evolution of Aujeszky's disease virus (ADV) contact prevalence among Eurasian wild boar (Sus scrofa) populations under different management regimes and contact likelihoods with domestic pigs. Given the recent increase in wild boar abundance throughout Europe, we hypothesized that wild boar contact with ADV would remain stable in time even after significant reduction of ADV prevalence in domestic pigs.

Results: Sera from 1659 wild boar were collected from 2000 to 2010 within 6 areas of the Iberian Peninsula and tested for the presence of antibodies against ADV by ELISA. According to sampling date, wild boar were grouped into three time periods. ADV prevalence was compared through period both globally and by geographic area. Overall seroprevalence for the ten-year study period was 49.6 ± 2.4%. The highest seroprevalence was recorded in areas with intense wild boar management. The annual proportion of positive wild boar sampling sites remained stable through the study period, while the percentage of domestic pig AD positive counties decreased from 70% in 2003 to 1.7% in 2010.

Conclusions: Results presented herein confirmed our hypothesis that ADV would remain almost stable in wild boar populations. This evidences the increasing risk wild boar pose in the final stages of ADV eradication in pigs and for wildlife conservation.

Figure 1

Sampled areas and Aujeszky's disease virus (ADV) seroprevalences. Map of the Iberian Peninsula showing the six sampled areas for the study (upper panel). Seroprevalences (and associated 95% standard errors) for each area during the three considered seasons (2000-2003, 2004-2007, 2008-2010) are shown in the lower panel. Within each area, significant differences in overall season seroprevalence are marked with an asterisk.

Figure 2

Temporal trends on Aujeszky's disease virus (ADV) seroprevalences in wild boar and pig. Time trend (2000-2010) of the annual proportion of sampling sites with seropositive wild boar (black diamonds), and of the proportion of counties in Spain with ADV in domestic pig (grey squares; based on data from the Spanish Ministry of the Environment and Rural and Marine Affairs, MARM). Numbers on the black line indicate the number of wild boar sampling sites per year. Numbers in grey indicate the number of reported counties per year. The discontinuous grey line is an estimated prevalence of positive counties before 2003 as data were not available before this date. The dotted line represents the hypothetical relative risk of ADV spill-back from wild boar to domestic pig, based on the difference between the pig and wild boar ADV proportions.

Figure 3

Aujeszky's disease virus (ADV) seroprevalence and wild boar relative abundance and spatial aggregation changes in a private hunting estate. Wild boar relative abundance (FBII; diamonds), aggregation index (Z; squares), and ADV seroprevalence (black triangles, 95% CI) in an estate where wild boar management drastically changed during the study period.