Development and application of a real-time RT-PCR assay for the specific detection of influenza D virus

Since the influenza D virus (IDV) was first isolated from a swine exhibiting respiratory disease symptoms in the United States in 2011, it has been detected in various animals across more than 20 countries worldwide, including cattle, pigs, goats, sheep, and camels. IDV has emerged as a significant pathogen associated with bovine respiratory disease complex (BRDC). In this study, specific primers and a TaqMan probe were designed based on the conserved region in the PB1 gene to develop a highly specific and efficient real-time RT-PCR assay (RT-qPCR) for IDV. The RT-qPCR assay demonstrated excellent specificity for IDV, without cross-reactions with other common BRDC-associated pathogens. Using in vitro transcribed PB1 RNA as a template, the assay's limit of detection was established at 100 copies/reaction. Furthermore, the developed RT-qPCR assay was evaluated using 417 cattle nasal swab samples collected from 10 different regions in Hebei Province, China, between 2021 and 2022. The results showed that 33 samples (7.91 %) tested positive for IDV. The IDV HEF gene was amplified and sequenced in these 33 positive samples, yielding 10 HEF gene sequences that all belonged to the D/Yama2019 lineage, with nucleotide homology ranging from 98.7 % to 99.1 %. This study successfully developed an RT-qPCR assay for the specific and sensitive detection of IDV, which performed well on the cattle nasal samples. Additionally, it is the first to demonstrate the presence of IDV in cattle herds in Hebei Province, China.