In vitro permissivity of bovine peripheral blood mononuclear cells to bovine viral diarrhoea virus is dependent on the animal specific immune status

A longitudinal study of bovine viral diarrhea virus in a semi-closed management dairy cattle herd, 2020-2022

Introduction

Bovine viral diarrhea virus (BVDV) brings great economic loss to the cattle industry worldwide. Developing a control/prevention strategy requires the prior assessment of certain epidemiological parameters. To determine the BVD incidence rate and associated risk factors, a dairy cattle herd in the eastern region of Saudi Arabia was monitored between 2020 and 2022.

Methods

Nasal swabs (n = 190), rectal swabs (n = 190), and sera (n = 190) were collected from 79 cows in this herd. Collected sera and swabs were tested using the commercially available ELISAs for the BVDV antibodies and antigens, respectively. Collected sera were also tested for the presence of BVDV nucleic acids using commercial real-time RT-PCR kits.

Results and discussion

Our data show BVDV seroprevalence (18.8%, 15%, and 8.2%) in the tested animals in 2020-2022, respectively. None of the collected nasal swabs, rectal swabs, or sera tested positive for the BVDV antigen, whereas 10.1%, 10%, and 18.1% of the tested sera were positive for BVDV nucleic acid in 2020-2022, respectively. The incidence rate was estimated at 0.02446 new cases/year despite the detection of BVDV in seronegative animals on single or two occasions at ≥6-month intervals. Young calves and bulls remained apparently unexposed to BVDV despite their presence with BVDV-infected females, with no significant physical separation. Both seropositivity and nucleic acid detectability showed significant positive and negative correlations, respectively, with reproductive performance. Collectively, the present study provides useful clues about the transmissibility of BVDV in the presence of possibly persistently infected animals. To the best of our knowledge, this is the first longitudinal study of BVDV in the Eastern Region of Saudi Arabia. Further detailed characterization of the circulating BVDVs is encouraged.

BVDV permissiveness and lack of expression of co-stimulatory molecules on PBMCs from calves pre-infected with BVDV

Bovine viral diarrhea virus (BVDV) has been detected in peripheral blood mononuclear cells (PBMCs) of immunocompetent animals, not being clear whether the development of a specific humoral immune response can prevent BVDV infection. The aim of this study was to evaluate the ability of non-cytopathic BVDV to replicate and produce infectious virus in PBMCs from calves pre-infected with BVDV and to elucidate the immunomodulatory effect of BVDV on these cells in an in vitro model. Quantification of virus was by quantitative PCR, while its replicative capacity and shedding into the extracellular environment was evaluated by viral titration. Apoptosis was assessed by flow cytometry analysis of annexin V and propidium iodide, and by expression of caspase-3/7. Flow cytometry was used to analyze the expression of CD14/CD11b/CD80, CD4/CD8/CD25, MHC-I/MHC-II and B-B2 markers. Our results showed that PBMCs from cattle naturally infected with BVDV were more susceptible to in vitro BVDV infection and showed a more severe apoptosis response than those from naïve animals. Non-cytopathic BVDV in vitro infection also resulted in a lack of effect in the expression of antigen presentation surface markers. All these findings could be related to the immunosuppressive capacity of BVDV and the susceptibility of cattle to this infection.