Effect of experimental infections of various Tembusu virus strains isolated from geese, ducks and chickens on ducklings

Chicken-origin Cluster 3.2 Tembusu virus exhibits higher infectivity than duck-origin Cluster 2 Tembusu virus in chicks

In 2020, a chicken-origin Cluster 3 Tembusu virus (TMUV) caused outbreaks of a disease characterized by egg-drop syndrome in laying hens in China. In the present study, a TMUV strain, TMUV-GX, was isolated from tissue samples of laying hens with egg drop syndrome in south China. Phylogenetic analysis grouped TMUV-GX into TMUV Cluster 3.2, which was distinct from the prevalent TMUV Cluster 2 in duck flocks. To study the infectivity and pathogenicity of TMUV-GX in chickens and ducks, 7 day-old specific pathogen-free (SPF) chicks and SPF ducklings were infected with the same dose of the TMUV-GX. As a comparison, the duck-origin Cluster 2 strain, TMUV-JM, infection groups were set up in chicks and ducklings. Compared with the low infectivity and pathogenicity of TMUV-JM in chicks, the chicken-origin TMUV-GX displayed high replication competence in multiple tissues and caused tissues histopathological damage. In addition, the replication competence of TMUV-GX in ducklings was comparable to that of TMUV-JM. Our study revealed chicken-origin Cluster 3.2 TMUV exhibits high infectivity in chicks and ducklings, and suggested that chicken-origin Cluster 3.2 TMUV possesses a biological basis for widespread infection of chickens and ducks.

Non-Structural Protein 3 of Duck Tembusu Virus Induces Autophagy via the ERK and PI3K-AKT-mTOR Signaling Pathways

Despite autophagy’s pivotal role in the replication of viruses such as duck Tembusu virus (DTMUV), which has caused massive economic losses to the poultry industry in the world, the specific relationships between DTMUV and cellular autophagy remain largely unknown. In response, we investigated the interactions between autophagy and DTMUV, the effects of the structural and non-structural proteins of DTMUV on autophagy, and the autophagy-related signaling pathways induced by DTMUV. Among the results, DTMUV increased the autophagy flux in duck embryo fibroblasts (DEF) and BHK-21 cells, while autophagy facilitated viral replication. After we pharmacologically induced autophagy with rapamycin (RAPA), the replication of DTMUV increased by 15.23-fold compared with the control group of DEF cells. To identify which DTMUV protein primarily induced autophagy, all three structural proteins and seven non-structural proteins of DTMUV were transfected into cells, and the results showed that non-structural protein 3 (NS3) induced significant autophagy in DEF cells. By means of Western blot, immunofluorescence, and transmission electron microscopy, we confirmed that NS3 protein could significantly induce autophagy and autophagy flux. Furthermore, we showed that NS3 induced autophagy in DEF cells through extracellular signal-regulated kinase 2 (ERK2) and phosphatidylinositol-3-kinase (PI3K)/AKT and the mammalian target of rapamycin (mTOR) signaling pathways using specific inhibitors and RNA interference assays. Finally, autophagy induced by NS3 promoted DTMUV replication. These results provide novel insight into the relationship between DTMUV and autophagy, broadening the current understanding of the molecular pathogenesis of DTMUV.