Quantification of experimental transmission of bovine herpes-virus 1 in cattle vaccinated with marker vaccines

Abstract

An attenuated and an inactivated bovine herpesvirus 1 (BHV1) gE-negative vaccine and an experimental BHV1 gD-subunit vaccine were evaluated for their ability to reduce BHV1 transmission. For that purpose, experiments to quantify transmission among vaccinated and unvaccinated cattle were carried out. Three separate experiments, including 90 cattle, were performed. Each group was housed separately. Two groups were vaccinated, each with a different marker vaccine, and the third served as an unvaccinated control group. At 4 weeks after the second vaccination, from each group five animals were taken out, and the remaining five were challenged intranasally with 10⁵ TCID₅₀ of the Dutch Lam strain of BHV1. After 24 hours, the animals were placed back into their original stables. The transmission of the virus to and among the five non-challenged, in-contact animals was then monitored. An animal was defined as being infected when it shed virus from its nasal fluids or developed antibodies to glycoprotein gE of BHV1. Based on the findings, the R, i.e. the average number of secondary cases per infectious individual, was calculated. Only the attenuated gE- negative vaccine was able to significantly reduce the transmission of BHV1.