Systemic infection induced by intranasal inoculation of Bovine herpesvirus 1.1 in pregnant and non-pregnant rabbits

53BP1, a known chromatin-associated factor that promotes DNA damage repair, is differentially modulated during bovine herpesvirus 1 infection in vitro and in vivo

Bovine herpesvirus 1 (BoHV-1) productive infection induces the formation of DNA double-strand breaks (DSBs), the most severe form of DNA lesions in cultured cells. 53BP1, a chromatin-associated factor, plays an essential role in DNA damage repair. In this study, we demonstrated that BoHV-1 productive infection in bovine kidney (MDBK) cells increased the expression of phosphorylated form of H2AX protein (γH2AX) and promoted the formation of γH2AX foci in the nucleus, indicative of enhanced DNA lesions. However, despite the elevated total 53BP1 protein levels, its recruitment to the nucleus and formation of 53BP1 foci was impaired, suggesting the disruption of 53BP1-mediated DNA damage repair (DDR). Furthermore, immunohistochemistry (IHC) studies showed that γH2AX was readily detected in trigeminal ganglia (TG) neurons of New Zealand White rabbits during both acute infection (day 3) and dexamethasone (DEX)-stimulated reactivation from latency, indicating the occurrence of DNA damage in vivo. This was consistent with the substantial reduction of 53BP1 protein expression in these tissues. Interestingly, 53BP1 was detected in a subset of TG neurons from both mock-infected and latently infected rabbits, but the localization profile of 53BP1 looks largely different, suggesting that 53BP1 may play a role in viral latency. Taken together, our findings demonstrated that BoHV-1 lytic infection impaired 53BP1-dependent DNA damage repair through differing mechanisms in vitro and in vivo, potentially promoting the accumulation of DNA damage. Moreover, virus latency altered the 53BP1 localization, underscoring the importance of 53BP1 signaling in the virus pathogenicity.

Evaluation of Antiviral Activity of Ivermectin against Infectious Bovine Rhinotracheitis Virus in Rabbit Model

Infectious bovine rhinotracheitis (IBR) caused by bovine herpes virus 1 (BoHV-1) can lead to enormous economic losses in the cattle industry. Vaccine immunization is preferentially used to decrease its transmission speed and resultant clinical signs, rather than to completely stop viral infection. Therefore, a drug effective in treating IBR is urgently needed. Our previous work demonstrated that ivermectin significantly inhibited viral replication in a cell infection model. This study aimed to investigate its antiviral effects in vivo by using a rabbit infection model. The viral inhibition assay was first used to confirm that ivermectin at low concentrations (6-25 nM) could reduce viral titers (TCID50) significantly (p < 0.001) at 24 h post-infection. In rabbits, ivermectin was administrated with one to three doses, based on the recommended anti-parasite treatment dosage (0.2 mg/kg bodyweight) through subcutaneous injection at different days post-infection in the treated IBRV infection groups, while non-treated infection group was used as the control. The infected rabbits showed hyperthermia and other clinical signs, but the number of high-fever rabbits in the ivermectin treatment groups was significantly lower than that in the non-treated infection group. Furthermore, in ivermectin treatment groups, the cumulative clinical scores correlated negatively with drug doses and positively with delay of administration time post-infection. The overall nasal shedding time in ivermectin-treated groups was two days shorter than the non-treated challenge group. At the same time point, the titer of neutralizing antibodies in the treatment group with triple doses was higher than the other two-dose groups, but the difference between the treatment groups decreased with the delay of drug administration. Correspondingly, the serious extent of lung lesions was negatively related to the dosage, but positively related to the delay of drug administration. The qPCR with tissue homogenates showed that the virus was present in both the lung tissues and trigeminals of the infected rabbits. In conclusion, ivermectin treatment had therapeutic effect by decreasing clinical signs and viral shedding, but could not stop virus proliferation in lung tissues and trigeminals.

Protective immunity following vaccination with a recombinant multiple-epitope protein of bovine herpesvirus type I in a rabbit model

Bovine herpesvirus type 1 (BoHV-1) causes considerable economic losses to the cow industry. Vaccination remains an effective strategy to control the diseases associated with BoHV-1. However, live vaccines present safety concerns, especially in pregnant cows; thus, nonreplicating vaccines have been developed to control the disease. The envelope glycoproteins of BoHV-1 induce a protective immune response. In this work, selected epitopes on glycoproteins gD, gC, and gB were constructed in triplicate with linker peptides. Vaccination of rabbits demonstrated that P2-gD/gC/gB with AAYAAY induced higher specific antibodies than that with GGGGS linker. P2-gD/gC/gB with AAYAAY linker was fused with bovine interleukin-6 (BoIL-6) or rabbit IL-6 (RaIL-6) and bacterially expressed. Rabbits were intramuscularly immunized with 100 μg of P2-gD/gC/gB-BoIL-6, P2-gD/gC/gB-RaIL-6, P2-gD/gC/gB, P2-gD/gC/gB plus BoIL-6, P2-(gD-a)3-BoIL-6, or P2-(gD-a)3 emulsified with ISA 206 adjuvant thrice at 3-week intervals. P2-gD/gC/gB-BoIL-6 generated a higher titer of BoHV-1-specific antibodies, neutralizing antibodies, interferon (IFN)-γ, and IL-4 compared with P2-gD/gC/gB plus BoIL-6, P2-gD/gC/gB-RaIL-6, or other formulation. P2-gD/gC/gB-BoIL-6 triggered similar levels of antibodies and significantly higher titer of IFN-γ and IL-4 compared with inactivated bovine viral diarrhea (BVD)-infectious bovine rhinotracheitis (IBR) vaccine. Rabbits vaccinated with P2-gD/gC/gB-BoIL-6 dramatically reduced viral shedding and tissue lesions in lungs and trachea after viral challenge and reactivation compared with those with P2-gD/gC/gB plus BoIL-6 or P2-gD/gC/gB-RaIL-6. P2-gD/gC/gB-BoIL-6 provided protective effects against viral shedding and tissue pathogenesis similar to those of the inactivated vaccine. The data confirmed the safety and immunogenicity of multiple-epitope recombinant protein and a potential vaccine candidate to control the disease, especially for pregnant cattle.