Isolation and pathogenicity characterization of a tembusu virus from 817 broilers with decreased egg production

Tembusu virus (TMUV) is widely distributed in duck and goose populations in Asia, causing significant economic losses to the poultry industry. In this study, a TMUV strain, designated 24SD, was isolated and characterized from 817 broilers with decreased egg production in Shandong province of China, in 2024. The 24SD replicated efficiently in BHK-21 cells and SPF chicken embryos, reaching titers 10^6.833 TCID₅₀ per 0.1 mL and 10^3.681 ELD₅₀ per 0.3 mL, respectively. The virus also replicated in duck embryos and caused obvious pathological lesions. Whole-genome sequencing (WGS) and phylogenetic analysis indicated that 24SD belongs to TMUV Cluster 3. The 24SD strain showed high nucleotide sequence identities (99.00-99.03 %) with other Cluster 3 strains, including YN2020, CTLN, and SD2021. Animal pathogenicity studies demonstrated that 24SD could infect both chickens and ducklings, with stronger replication in chickens. The virus induced transient viremia, replicated efficiently in multiple organs, including the heart and liver, leading to varying degrees of tissue damage and inflammation, and was excreted via feces. Overall, this study expands the genomic dataset of chicken-origin TMUV strains within Cluster 3 and provides valuable information for surveillance and control of TMUV in poultry.