Genetic diversity and expanded epidemic area of novel tick-borne pathogen wetland virus in ticks, wild and domestic animals, and patient in China

Wetland virus (WELV) is a recently identified segmented orthonairovirus associated with human febrile illness in northeastern China. To elucidate its ecological drivers and transmission patterns, we conducted multi-host surveillance in seven eco-climate regions across China through an integrated approach combining molecular and serological profiling. Over 33,000 questing and feeding ticks representing 11 species were systematically screened WELV-RNA alongside 1,493 wild small mammals, while 2,578 domestic animals and 3,921 patients presenting with outdoor field or tick exposure history underwent both WELV specific molecular and serological evaluation. WELV-RNA detection via real-time RT-PCR revealed low but widespread infection, including 0.54% (8/1,493) in wild rodents (<i>Apodemus chevrieri</i>, <i>Rattus norvegicus</i>), 1.12% (29/2,578) in domestic animals, and 0.86% (275/33,091) in ticks, including five newly confirmed vector species. Serological analysis via enzyme-linked immunosorbent assay (ELISA) demonstrated 2.44% (63/2,578) IgG seroprevalence in livestock. Clinical surveillance identified acute WELV infections in 1.81% (71/3,921) of febrile patients, predominantly as monoinfections (77.46%, 55/71). Coinfected patients exhibited elevated disease severity markers, with hospitalization rates doubling compared to single-infection cases (87.50% vs. 36.36%). Spatiotemporal analysis showed spring-summer predominance of WELV for both ticks and human patients. Phylogenetic analyses revealed remarkable genetic conservation patterns of WELV strains across diverse hosts and tick vectors; and clustering across geographical regions. These findings establish WELV as an emerging tick-borne virus with trans-regional spread across heterogeneous landscapes in China. The intersecting transmission cycles among wildlife reservoirs, domestic amplifier hosts, and expanding tick vectors underscore the imperative for integrated surveillance strategies to mitigate this growing public health threat.