Isolation, Characterization and Virulence Assessment of Type 1d CP Bovine Viral Diarrhea Virus Originating from Inner Mongolia, China

Luyao Hao Fengmiao Zhao Ting Guo Yuan Gao Yongqing Hao ^*

• Inner Mongolia Agricultural University, Hohhot, China

In recent years, bovine viral diarrhea virus (BVDV) has been associated with increased respiratory and gastrointestinal diseases in cattle. Comprehensive monitoring and investigations into the virus's pathological features are crucial for developing effective prevention strategies. During 2021 and 2022, our team examined bovine farms implementing BVDV elimination procedures, identifying 33 positive cases of BVDV nucleic acid from 103 samples, resulting in a positivity rate of 32.04%. We isolated five strains of Noncytopathic Bovine Viral Diarrhea Virus (NCP-type BVDV) with a separation rate of 15.15%, and one strain of Cytopathic Bovine Viral Diarrhea Virus (CP-type BVDV), with a 3.03% separation rate. The CP strain, named HH839, was isolated from a severely symptomatic calf in Hohhot, Inner Mongolia. This study conducted a comprehensive investigation into the biological characteristics of the BVDV HH839 strain through various technological assays, including an assessment of cytopathic effects, electron microscopy, serum neutralization tests, whole genome sequencing, sequence comparison, and an evaluation of replication kinetics. Moreover, the pathogenicity associated with various biotypes of BVDV, including those within the CP-type BVDV-infected group, NCP-type BVDV-infected group, and the mixed-infection group of CP-type and NCP-type BVDV, was scrutinized utilizing New Zealand Large White rabbits as model laboratory animals. The HH839 strain caused significant cytopathic effects in MDBK cells, including cellular crumpling and syncytia formation, and had a concentration of 5.23 log10TCID50/0.1 mL. Under electron microscopy, it appeared spherical with a diameter of 40-60 nm. Genetic analysis revealed its close relation to the BVDV FBS-D8 strain from the BVDV 1-d subtype. Pathogenicity trials demonstrated slight fever and a minor decline in body weight in infected subjects,with BVDV detected in the trachea, lungs, spleen and small intestines, predominantly in the spleen. Histopathological examinations showed varying degrees of damage, with the NCP group exhibiting the least damage and the mixed infection group exhibiting more severe lesions compared to the CP group. The isolation of BVDV HH839, which causes serious clinical symptoms, and our detailed analyses provide a foundation for further research into BVDV's regional prevalence and the need for enhanced epidemiological surveillance.