A picture of trends in Aujeszky's disease virus exposure in wild boar in the Swiss and European contexts

Abstract

Background: In parallel to the increase of wild boar abundance in the past decades, an increase of exposure to the Aujeszky's disease virus (ADV) has been reported in wild boar in several parts of Europe. Since high animal densities have been proposed to be one of the major factors influencing ADV seroprevalence in wild boar populations and wild boar abundance has increased in Switzerland, too, a re-evaluation of the ADV status was required in wild boar in Switzerland. We tested wild boar sera collected from 2008-2013 with a commercial ELISA for antibodies against ADV. To set our data in the European context, we reviewed scientific publications on ADV serosurveys in Europe for two time periods (1995-2007 and 2008-2014).

Results: Seven out of 1,228 wild boar sera were positive for antibodies against ADV, resulting in an estimated seroprevalence of 0.57% (95% confidence interval CI: 0.32-0.96%). This is significantly lower than the prevalence of a previous survey in 2004-2005. The literature review revealed that high to very high ADV seroprevalences are reported from Mediterranean and Central-eastern countries. By contrast, an "island" of low to medium seroprevalences is observed in the centre of Europe with few isolated foci of high seroprevalences. We were unable to identify a general temporal trend of ADV seroprevalence at European scale.

Conclusions: The seroprevalence of ADV in wild boar in Switzerland belongs among the lowest documented in Europe. Considering the disparity of seroprevalences in wild boar in Europe, the fact that seroprevalences in Switzerland and other countries have decreased despite increasing wild boar densities and the knowledge that stress leads to the reactivation of latent ADV with subsequent excretion and transmission, we hypothesize that not only animal density but a range of factors leading to stress - such as management - might play a crucial role in the dynamics of ADV infections.

Fig. 1

Map of Switzerland showing the study units and the origin of sampled wild boar. Shades of grey refer to the landscape relief and main lakes are indicated in plain blue. Letters and transparent colored surfaces refer to the five study units: Purple, a = Geneva; Light blue, b = Jura Mountains; Orange, c = Thurgovia; Grey-blue, d = Swiss plateau; Green, e = Ticino. Sera were tested by ELISA for antibodies against ADV. Colored dots, stars and diamonds indicate the location of the sampled wild boar (2008-2013): Pink dots = seronegative; Yellow stars = seropositive; Green diamonds = doubtful

Fig. 2

Seroprevalence of ADV in free-living wild boar in Europe from 1995-2014. Compilation of published data obtained by ELISA for two time periods: (a) 1995-2007 [, , , , , , , , –, –50, 59, 60, 62, 64, 65]; (b) 2008-2014 [1, 17, 19, 38, 43, 44, 47, 61, 63, 64, 82]. Numbers refer to estimated seroprevalences for the regions where they are placed.*Fenced animals included. ¹Data obtained over both time periods