Development of an in vivo system to measure antibody-blocking of ovine herpesvirus 2 entry

Ovine herpesvirus 2 (OvHV-2), the causative agent of sheep-associated malignant catarrhal fever (SA-MCF), has never been propagated in vitro. Thus, an alternative to in vitro virus neutralization is needed to assess neutralizing antibody activity to OvHV-2 in SA-MCF vaccine development. An in vivo system in sheep and rabbits was evaluated to determine whether it could be used to assess the ability of antibodies to block OvHV-2 at the entry site by mixing virus and anti-OvHV-2 serum before challenge by intranasal nebulization. A dose of OvHV-2 (106 viral DNA copies) incubated with sheep sera (1:4 final dilution) at 37 °C for 1 hr was delivered by intranasal nebulization to sheep and rabbits. All sheep became infected, but the positive serum reduced viral infectivity by approximately 1000 fold based on delayed detection of viral DNA and seroconversion as compared to the negative control group, which received virus treated with negative sheep serum. All rabbits that received the virus mixed with the positive sheep serum, either with or without complement, were protected from the infection while all rabbits in the control groups developed SA-MCF. The data indicate that this type of in vivo system, sheep or rabbits, can be used to assess antibody's ability to block OvHV-2 entry, which is a significant tool for the analysis of protective antibody responses to the virus.