Spatio-temporal analysis of the progression of Aujeszky's disease virus infection in wild boar of Saxony-Anhalt, Germany

Aujeszky’s disease (AD, pseudorabies) is a notifiable disease caused by Suid herpesvirus 1 (SuHV-1), also named pseudorabies virus (PrV). The study aimed at determining the occurrence and spatio-temporal trend of specific antibodies to AD virus (ADV) among wild boar of Saxony-Anhalt, a landlocked federal state situated in the western part of eastern Germany. To this end, a total of 7,209 blood samples were collected and tested from 2000 to 2011. An average seroprevalence of 6.8% was found for the entire observation period, whilst seroprevalence increased significantly between time periods January 2000-March 2009 (n = 3,605; prevalence = 4.5%) and March 2009-December 2011 (n = 3,604; prevalence = 9.1%). Spatial analysis revealed an extremely heterogenous distribution of seropositive samples with cluster formation [relative risk (RR) up to 41, P = 0.001] in the east. A comparison of spatial clusters between the aforementioned time intervals showed an expansion of the disease in the north to north-westerly direction. A test for spatial shift involving the entire territory of Saxony-Anhalt detected a spread of ADV infection in the latter direction (P = 0.079) at the average speed of 3.3 km/year. Detailed study of the distribution and spread of the disease among wild boar, including assessment of the speed of spatial spread, has not been done in the region before. Saxony-Anhalt has been officially recognised as being free of AD in domestic pigs since 1996. Despite increasing ADV seroprevalences in the wild boar population of Saxony-Anhalt and other federal states in the east of Germany, no spill-over to domestic pigs have been reported. The currently implemented monitoring will be continued in conjunction with surveillance of classical swine fever (CSF) to further trace ADV infections in the wild boar population of Saxony-Anhalt.