Evaluation of passive immunity from dams previously immunized with an inactivated glycoprotein E-deleted infectious bovine rhinotracheitis marker vaccine after challenge infection with wild-type bovine alphaherpesvirus 1 in calves

Bovine alphaherpesvirus 1 (BoAHV-1) is a major cattle pathogen that causes infectious bovine rhinotracheitis (IBR) and other respiratory and reproductive disorders, resulting in substantial global economic losses to the cattle industry. Although glycoprotein E (gE)-deleted IBR marker vaccines are widely used to manage BoAHV-1, the protective efficacy of passive immunity in dams vaccinated with these vaccines remains unclear. In this study, we aimed to test the hypothesis that passive immunity transferred from dams previously vaccinated with an inactivated gE-deleted IBR marker vaccine protects calves against wild-type (wt) BoAHV-1. To test this hypothesis, we conducted an experiment in which 12 calves aged 3–6 months were divided into four groups (A, B, C, and D). Calves in groups A and C were immunized with neutralizing antibodies derived from passive immunity at titers of 1.00 log 10 and 1.61 log 10 , respectively. Groups B and D represent negative controls. All calves were challenged with BoAHV-1, and the clinical scores and rectal temperatures were recorded at different time points after the challenge. Nasal swabs and blood samples were collected for virological and serological investigations, respectively. The findings did not support our hypothesis, as typical clinical signs, viremia, and immunological responses to IBR were observed in all groups. In summary, these findings demonstrate that passive immunity does not protect calves from wt BoAHV-1 infection, suggesting the necessity of future studies to develop appropriate vaccination strategies for calves with passive immunity to protect them against wt BoAHV-1. • Passive immunity does not protect calves from bovine alphaherpesvirus type 1 infection. • Calves with maternal antibodies show clinical signs, viral shedding, and fever. • Viral challenge increases antibody levels, but the protection remains inadequate. • Maternal immunity may suppress active immune responses in calves. • The study calls for better vaccines and focuses on cell-mediated immunity in calves.