Long-term circulation and molecular evolution of rat hepatitis E virus in wild Norway rat populations from Berlin, Germany

Rat hepatitis E virus (ratHEV, Rocahepevirus ratti) is an emerging zoonotic pathogen which was recently identified in several human hepatitis patients. The virus has been demonstrated in its primary reservoir hosts, rats, in many countries of the world. However, little is known about the persistence and molecular evolution of ratHEV in a host population over time. Here, wild Norway rats (Rattus norvegicus) from Berlin, Germany, were screened for ratHEV, and virus strains and rats were genetically characterized. The ratHEV detection rate in 2023 (8.3 %, 11/131) was similar to that of 2009/2010 (11.5 %, 7/61). Generated virus genome sequences showed 89.3 % to 100 % nucleotide sequence similarity to each other. Phylogenetic analysis indicated clustering of the sequences from the rats and a human patient from Berlin, irrespective of year and separate from sequences from other parts of Germany. Strains from Berlin formed subclades according to sampling districts, and rivers were identified as possible barriers between subclades. Rat population genetics analysis indicated a stable rat population with a dominant genetic cluster containing most ratHEV-infected rats at both time-points, and the presence of closely related virus strains within a genetic subcluster. Analysis of all ratHEV strains identified variable amino acid positions in all four virus-encoded proteins. The results indicate long-term persistence of ratHEV in wild rat populations, which is mainly driven by local transmission of virus strains in small geographic areas. Environmental and rat surveillance for ratHEV, along with effective pest control, should be considered to reduce the risk of human infections in future.