Isolation, identification, and pathogenicity evaluation of a novel Cluster 3 Tembusu virus isolated from geese in China.

Tembusu virus (TMUV) is a significant pathogen that poses a considerable threat to the waterfowl farming industry in China and is classified into three distinct genetic clusters. In 2024, a suspected outbreak of TMUV infection was reported at a goose farm in Guangdong Province, China. A strain of TMUV, designated GDE19-2024, was successfully isolated using chicken embryos. Homology and genetic evolutionary analyses suggest that GDE19-2024 is categorized within cluster 3 of TMUV and exhibits a close genetic affiliation with other strains in this cluster. Nonetheless, GDE19-2024 has experienced two distinct mutations at the 149th and 157th amino acid positions of the E protein, setting it apart from other TMUV strains within cluster 3. The pathogenicity assay revealed that the GDE19-2024 strain possesses the ability to infect both geese and ducks, leading to viremia and effective viral replication in multiple organs. Notably, GDE19-2024 demonstrated considerable pathogenicity in goslings, resulting in a mortality rate of 62.5 % among 7-day-old goslings and causing hemorrhagic lesions in various organs of the infected geese. Conversely, GDE19-2024 exhibits relatively low pathogenicity in ducks, as evidenced by the manifestation of only mild and transient clinical symptoms in infected ducklings, without resulting in mortality. Furthermore, the extent of organ damage in ducks is less severe compared to that observed in infected goslings. This observation suggests that cluster 3 TMUV may be more adapted to geese, exhibiting increased pathogenicity in this species. Our findings provide a foundational basis for understanding the genetic evolution and pathogenicity of cluster 3 TMUV in China.