Isolation and identification of type 1d CP bovine viral diarrhea virus from Inner Mongolia, China

Abstract Background In recent years, outbreaks of respiratory and gastrointestinal diseases in cattle is associated with bovine viral diarrhea virus (BVDV). BVDV infection is a persistent global issue, particularly concerning for calves health. Comprehensive epidemiological surveillance and research into its pathogenic characteristics are essential for effective control and prevention of this virus. Despite limited investigation into the epidemiology of BVDV in Inner Mongolia, there is a lack of comprehensive information in this area. Results From 2021 to 2022, within cattle farms implementing eradication plans for bovine viral diarrhea virus (BVDV), we detected 33 cases of BVDV nucleic acid positivity out of 103 samples (positive rate 32.04%). We isolated five strains of NCP-type BVDV (separation rate 15.15%) and one strain of CP-type BVDV (separation rate 3.03%). This CP BVDV strain was successfully isolated from the nasal swab of a calf with severe clinical symptoms in Hohhot, Inner Mongolia. Subsequently, we designated this strain as HH839 in this study. Non-cytopathic BVDV strains are common and participate in severe clinical acute infections, whereas cytopathic BVDV strains are rare and usually associated with mucosal disease outbreaks. Therefore, this study determined the biological characteristics of CP BVDV 1d strain HH839 using various assays, including cytopathic conditions, electron microscopy, serum neutralization test, whole-genome sequencing, sequence alignment, and replication kinetics. A cytopathic virus strain was isolated, and viral particles were observed within 40–60 nm using transmission electron microscopy. The growth curve showed that the virus propagated effectively in MDBK cells. Phylogenetic analyses based on the 5’untranslated region (5’UTR) and full-length genome sequences indicated that HH839 belonged to the BVDV-1d group and that the strain was in the same branch and had the closest genetic relationship with BJ-1308 (KT951841.1). New Zealand white rabbits were used to study the pathogenicity of different biotypes of BVDV, including the CP-type BVDV-infected group, NCP-type BVDV-infected group, and CP-type NCP-type BVDV mixed-infected group. The animal infection experiments showed that hematology and histopathology showed different degrees of changes, although the infected rabbits did not show typical disease symptoms. Conclusion We isolated a BVDV HH839 strain that can cause severe clinical symptoms in cattle. Genome-wide determination and infection experiments with HH839 provide material to further explore the regional prevalence of BVDV. We propose to reinforce the epidemiological surveillance of this virus.