Deletion of the thymidine kinase gene attenuates Caprine alphaherpesvirus type 1 in goats

Caprine alphaherpesvirus 1 (CpHV-1) is a pathogen associated with systemic infection and respiratory disease in kids and subclinical infection or reproductive failure and abortions in adult goats. The enzyme thymidine kinase (TK) is an important viral product involved in nucleotide synthesis necessary for virus replication. Therefore, it is a common target for herpesvirus attenuation. Here we deleted the tk gene of a CpHV-1 isolate and characterized the recombinant CpHV-1ΔTKin vitro and in vivo. In vitro characterization revealed that the recombinant CpHV-1ΔTK replicated to similar titers and produced plaques of similar size to the parental CpHV-1 strain in BT and CRIB cell lines. Upon intranasal inoculation, of young goats, the parental virus replicated more efficiently and for a longer period than the recombinant virus. In addition, infection with the parental virus resulted in mild systemic and respiratory signs whereas the kids inoculated with the recombinant CpHV-1ΔTK virus remained healthy. Goats inoculated with the parental virus also developed higher neutralizing antibody titers when compared to CpHV-1ΔTK inoculated animals. Dexamethasone (Dx) administration on days 35 to 39 post-inoculation did not result in virus shedding in nasal secretions, indicating lack of reactivation from latency. However, viral DNA was present in trigeminal ganglia of animals euthanized at 14 days post-Dx, indicating that both viruses successfully established latent infection. Our results show that the recombinant CpHV-1ΔTK presents an attenuated phenotype when compared to the parental virus, and hence may represent a promising strain to be used as a vaccine to prevent CpHV-1 disease in goats.