# Genomic characterization and pathogenicity assessment of a novel strain of duck reovirus identified in China

## TL;DR

A new duck reovirus strain, SD416, was identified in China and found to cause severe disease in young ducklings, with unique genetic and pathogenic features.

## Contribution

The study reports the genomic characterization and age-dependent pathogenicity of a novel duck reovirus strain, SD416, isolated from China.

## Key findings

- The SD416 strain has a distinct genome with significant divergence from other duck reovirus isolates.
- The virus causes severe hepatic and splenic lesions in 1-day-old ducklings but milder effects in older ducklings.
- The σC protein-coding sequence of SD416 shows high genetic variability compared to other genotyping clusters.

## Abstract

The global duck industry faces substantial challenges due to the emergence of novel duck reovirus (NDRV) infections, which are pathologically characterized by splenomegaly, hemorrhagic manifestations, and necrotic lesions in affected birds. Surviving ducklings often suffer from severe growth retardation. Here, we investigated an outbreak of hepatic necrosis in commercial ducklings from Shandong Province, China. After excluding other potential pathogens, an NDRV strain was isolated and designated SD416. This strain demonstrated infectivity in both chicken and duck embryos and induced syncytial formation in Vero cells. Full-genome sequencing revealed a 23,420-bp dsRNA genome consisting of 10 segments, displaying significant genetic divergence from other Chinese duck reovirus isolates. Phylogenetic analysis indicated that SD416 is genetically distinct from known DRV strains, particularly within the M2 and S3 genes. Furthermore, its σC protein-coding sequence exhibited notably high genetic variability compared to strains from other genotyping clusters. To evaluate the age-dependent pathogenicity of SD416, 1-, 7-, and 14-day-old ducklings were intramuscularly inoculated with 0.1 mL of allantoic fluid containing the virus at a titer of 1 × 10⁶ TCID₅₀/0.1 mL. The strain exhibited pronounced age-related virulence: 1-day-old ducklings developed severe hepatic and splenic lesions resulting in mortality, whereas ducklings inoculated at 7 and 14 days of age exhibited only splenic pathology and survived throughout the study. The SD416 strain was comprehensively characterized in terms of tissue tropism, pathogenesis, genomic structure, and evolutionary relationships. Our findings reveal a unique genomic and virulence pattern associated with this novel isolate, providing important insights into the biology of NDRV. These results underscore the need for enhanced surveillance and development of targeted intervention strategies to limit the spread of this virus in global waterfowl production systems.