Calvin Mehl

• Lymphocytic choriomeningitis virus (LCMV) is a neglected zoonotic arenavirus transmitted, primarily, by house mice (Mus musculus). In humans, LCMV infection may cause encephalitis and meningitis, or severe birth defects in embryos. In New World primates (family callitrichidae), LCMV causes acute and fatal callitrichid hepatitis (CH), presenting with lesions in the liver and brain. LCMV research in Germany is severely limited and outdated. Here, LCMV was detected for the first time in the Netherlands, and two viral lineages were continuously detected in house mice from a zoological garden in Germany. The total LCMV RNA prevalence in house mice tended to increase between 2021 and 2023. This was primarily driven by lineage I, while the occurrence of lineage II tended to decrease. Despite both lineages I and II being present in house mice, only lineage II was detected in NW primates with CH. The detection of three LCMV genome segments in house mice was interpreted as the emergence of a reassortant virus containing an S-segment of lineage II and an L-segment of lineage I. Additionally, a novel viral lineage was detected in wood mice (Apodemus sylvaticus) from the south of Germany, suggesting a wider range of potential host species than previously thought. The high prevalence of LCMV within the house mouse population of the zoological garden not only poses a potential health threat for employees and visitors of the zoological garden, and potentially other zoo animals. The occurrence and reassortment of two viral lineages provides a unique opportunity to advance our understanding of arenavirus evolution.