# Emergence and Phylodynamics of Influenza D Virus in Northeast China Reveal Sporadic Detection and Predominance of the D/Yamagata/2019 Lineage in Cattle

## TL;DR

Influenza D virus in cattle in Northeast China is sporadically detected and dominated by a specific lineage, with evidence suggesting it was introduced from outside the region.

## Contribution

The study identifies the D/Yamagata/2019 lineage as predominant in cattle and reveals the phylodynamics and sporadic nature of IDV in China.

## Key findings

- IDV was detected in 1.2% of cattle nasal swabs in Jilin Province, with two viable isolates recovered.
- Genomic analysis shows high similarity to Chinese D/Yamagata/2019 strains and no reassortment.
- Phylogenetic analysis suggests cross-border introduction around 2017 and a decline in global IDV diversity during 2020–2022.

## Abstract

Influenza D virus (IDV), an emerging orthomyxovirus with zoonotic potential, infects diverse hosts, causes respiratory disease, and remains poorly characterized in China despite its global expansion. From October 2023 to January 2025, we collected 563 nasal swabs from cattle across 28 farms in Jilin Province, Northeast China, and identified seven IDV-positive samples (1.2%), recovering two viable isolates (JL/YB2024 and JL/CC2024). Full-genome sequencing revealed complete, stable seven-segment genomes with high nucleotide identity (up to 99.9%) to contemporary Chinese D/Yamagata/2019 strains and no evidence of reassortment. Maximum-likelihood and time-resolved Bayesian phylogenies of 231 global hemagglutinin-esterase-fusion (HEF) sequences placed the Jilin isolates within the East Asian D/Yamagata/2019 clade and traced their most recent common ancestor to approximately 2017 (95% highest posterior density: 2016–2018), suggesting a cross-border introduction likely associated with regional cattle movement. No IDV was detected in parallel surveillance of swine, underscoring cattle as the principal reservoir and amplifying host. Bayesian skyline analysis demonstrated a marked decline in global IDV genetic diversity during 2020–2022, coinciding with livestock-movement restrictions imposed during the COVID-19 pandemic. Collectively, these findings indicate that IDV circulation in China is sporadic and geographically localized, dominated by the D/Yamagata/2019 lineage, and shaped by multiple independent incursions rather than a single emergence. Both the incorporation of IDV diagnostics into routine bovine respiratory disease surveillance and cattle-import quarantine programs, and the adoption of a One Health framework to monitor potential human spillover and future viral evolution, were recommend.