Investigation of animal reservoirs of the Hepatitis E virus in Germany

Hepatitis E is a notifiable disease in Germany, which is caused by the hepatitis E virus (HEV). In 2010, 220 hepatitis E cases have been recorded; 165 cases of these have been acquired in Germany. The reason for these cases has still to be elucidated but a zoonotic transmission seems to be likely. Wild boars and domestic pigs are worldwide regarded as the main animal reservoirs of HEV and several studies report food-borne hepatitis E cases after the consumption of undercooked or raw meat of wild boars or pigs. Other animal species, especially rats, have been discussed as HEV reservoir but so far only HEV-specific antibodies have been detected in these animals. By 2008, no data about the HEV prevalence in Germany in wild as well as domestic animals are available. Hence, the aim of the studies was to assess the HEV prevalence in different animal species in Germany, which are considered as HEV animal reservoirs, and to reveal possible zoonotic transmission routes. After the development and establishment of suitable detection methods, wild boars, domestic pigs and rats from different regions in Germany have been investigated for the presence of HEV or HEV-specific antibodies. In average, 14.9% (22/148) of the investigated wild boar liver samples have been tested positive for HEV RNA using real time RT-PCR. However, in the rural regions of Brandenburg and Thuringia a significantly higher prevalence rate (25.9% & 23.8%, respectively) have been found compared to the cities Berlin and Potsdam (4.1%). From the HEV positive wild boars the HEV genotypes 3a, 3c, 3h and 3i have been detected, which show a high sequence identity to human HEV strains from autochthonous hepatitis E cases. The genome of the strain wbGER27 has been sequenced completely and represents the first full-length sequence of HEV genotype 3i. In a second study, the HEV seroprevalence has been determined in domestic pigs using three different immunoassays, which results have been compared to each other. In general, the HEV seroprevalences determined ranged between 21.7% and 64.8% depending on the used immunoassay. By the development of a novel HEV broad-spectrum RT-PCR it was possible to detect for the first time an HEV-like virus in faecal samples of wild Norway rats from Germany showing about 50 to 60% sequence identity to other HEV genotypes. Using electron microscopy an HEV-like virus of 32-34 nm in diameter was demonstrated tentatively designated as rat HEV. Screening of organ samples of further wild Norway rats trapped at the same location resulted in the detection of two full-length genomic sequences of rat HEV. Phylogenetic analyses showed that rat HEV builds a separated branch between mammalian and avian HEV genotypes, probably representing a novel HEV genotype. Using a specific real time RT-PCR for rat HEV and immunohistochemical methods a hepatotropism of rat HEV could be revealed. In summary, in wild boars and domestic pigs HEV or HEV-specific antibodies have been detected; in rats an HEV-like virus has been discovered. Thus, a zoonotic HEV transmission from animal reservoirs to humans might be possible in Germany. Further studies are needed, investigating the presence of infectious HEV in meat of wild boars and domestic pigs and assessing the transmissibility of rat HEV from rats to humans. In addition, rat HEV might be used for the establishment of a rodent model for human hepatitis E. Using such a rodent model, the efficiency of different transmission routes may be assessed. Finally, other animal species should be screened for the presence of HEV-like viruses using the novel detection methods.