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.

First Identification and Genetic Characterization of a Novel Duck Astrovirus in Ducklings in China.

Four divergent groups of duck astroviruses (DAstVs) have been identified that infect domestic ducks. In March 2021, a fatal disease characterized by visceral urate deposition broke out in 5-day-old Beijing ducks on a commercial farm in Guangdong province, China. We identified a novel duck astrovirus from the ducklings suffering from gout disease. The complete genome sequence of this DAstV was obtained by virome sequencing and amplification. Phylogenetic analyses and pairwise comparisons demonstrated that this DAstV represented a novel group of avastrovirus. Thus, we designated this duck astrovirus as DAstV-5 JM strain. DAstV-5 JM shared genome sequence identities of 15-45% with other avastroviruses. Amino acid identities with proteins from other avastroviruses did not exceed 59% for ORF1a, 79% for ORF1b, and 60% for ORF2. The capsid region of JM shared genetic distances of 0.596 to 0.695 with the three official avastrovirus species. suggesting that JM could be classified as a novel genotype species in the Avastrovirus genus. Meanwhile, JM shares genetic distances of 0.402-0.662 with all the other known unassigned avastroviruses, revealing that it represents an additional unassigned avastrovirus. In summary, we determined that the DAstV-5 JM strain is a novel genotype species of avastrovirus.

Isolation and characterization of a new goose orthoreovirus causing liver and spleen focal necrosis in geese, China.

Since July 2020, an infectious disease characterized by liver and spleen white focal necrosis has been spreading widely through geese farms in many regions of China. A novel goose orthoreovirus (GRV), designated GRV-GD2020, was isolated from the liver and spleen of dead geese. Phylogenetic analysis and sequence comparison revealed that all the genes of GRV-GD2020 clustered with other waterfowl-origin orthoreovirus. However, the gene constellation of GRV-GD2020 was not similar to that of any particular strain. Instead, the genomic segments of GRV-GD2020 showed 27.5-97.3% similarities to that of other waterfowl-origin orthoreovirus isolates. Waterfowl-origin orthoreovirus infections characterized by liver and spleen focal necrosis had not emerged in recent years. The re-emergence of the disease may be related to the recombination of the genome segments of Muscovy duck reovirus (MDRV), GRV, and new-type duck orthoreovirus. In summary, we determined that the GRV-GD2020 strain, causing goose liver and spleen focal necrosis, is a new variant of waterfowl-origin orthoreovirus.