Detection of hepatitis E virus in wild boars of rural and urban regions in Germany and whole genome characterization of an endemic strain

Abstract

Background: Hepatitis E is an increasingly diagnosed human disease in Central Europe. Besides domestic pigs, in which hepatitis E virus (HEV) infection is highly prevalent, wild boars have been identified as a possible source of human infection. In order to assess the distribution of HEV in the wild boar population of Germany, we tested liver samples originating from different geographical regions for the presence of the HEV genome and compared the detected sequences to animal and human HEV strains.

Results: A total of 148 wild boar liver samples were tested using real-time RT-PCR resulting in an average HEV detection rate of 14.9% (95% CI 9.6-21.6). HEV was detected in all age classes and all geographical regions. However, the prevalence of HEV infection was significantly higher in rural as compared to urban regions (p < 0.001). Sequencing of the PCR products indicated a high degree of heterogenicity of the detected viruses within genotype 3 and a grouping according to their geographical origin. The whole genome sequence of an HEV isolate (wbGER27) detected in many wild boars in the federal state of Brandenburg was determined. It belongs to genotype 3i and shows 97.9% nucleotide sequence identity to a partial sequence derived from a human hepatitis E patient from Germany.

Conclusion: The results indicate that wild boars have to be considered as a reservoir for HEV in Germany and that a risk of HEV transmission to humans is present in rural as well as urban regions.

Figure 1

Geographical origin of wild boar samples. In the map of Germany, the federal states of Brandenburg and Thuringia are coloured in blue, the cities of Berlin/Potsdam are in dark blue. The areas, in which HEV positive wild boars have been detected, are marked by red circles containing the number of positive animals. The total number of positives out of all samples investigated from a federal state or from the cities is indicated by red numbers.

Figure 2

Genotyping of wild boar HEV strains. The phylogenetic tree was constructed based on a 148 base pair nucleotide sequence of ORF-2 using reference sequences. The genotypes according to Lu et al. [8] are indicated in bold face. The actual isolates from wild boars are marked in coloured boxes with respect to their geographical origin and deduced genotype. Isolate wbGER27, which was selected for whole genome sequencing, is shown in red and marked by a red arrow. The tree is scaled in nucleotide substitution units.

Figure 3

Phylogenetic relationship between genotype 3 HEV strains derived from wild boars and humans from Germany. The tree was constructed on the basis of a 287 bp sequence fragment of ORF-1. The actual isolates from wild boars are shown in bold face. The closely related isolates wbGER27 from wild boar and V0706586 from human are indicated with a coloured box. The tree is scaled in nucleotide substitution units.

Figure 4

Comparison of the entire genome sequence of the wild boar isolate wbGER27 with 20 full-length sequences of HEV. Strain designations, accession numbers, host species and geographical origin of the isolates are indicated. Isolate wbGER27 is shown in red colour. Assigned genotypes are indicated with blue bars. The phylogenetic tree is scaled in nucleotide substitution units.