The latency related gene of bovine herpesvirus types 1 and 5 and its modulation of cellular processes

Characterization of BoHV-1 gG-/tk-/gE- Mutant in Differential Protein Expression, Virulence, and Immunity

Infectious bovine rhinotracheitis (IBR), caused by bovine alphaherpesvirus 1 (BoHV-1), is an important disease affecting cattle worldwide resulting in great economic losses. Marker vaccines are effective in controlling infectious diseases including IBR, because they allow the discrimination between the natural infection and the vaccination. Therefore, a triple gene deleted strain BoHV-1 gG-/tk-/gE- was developed and evaluated in vivo and in vitro as a marker vaccine. In cell culture, this triple mutant virus showed significantly slower growth kinetics and smaller plaques when compared to wild-type (wt) BoHV-1 and double mutant BoHV-1 gG-/tk- (p < 0.01). On proteomic level, it revealed downregulation of some virulence related proteins including thymidine kinase, glycoproteins G, E, I, and K when compared to the wt. In vitro, the triple mutant virus showed a significantly lower and shorter viral shedding period (p < 0.001) in calves compared to double mutant. Moreover, the immunized calves with triple mutant virus showed protection rates of 64.2% and 68.6% against wt BoHV-1 and wt BoHV-5 challenge, respectively, without reactivation of latency after dexamethasone injection. In conclusion, BoHV-1 gG-/tk-/gE- is a safer marker vaccine against IBR although its immunogenicity in calves was decreased when compared to double mutant virus.

Distinctive features of bovine alphaherpesvirus types 1 and 5 and the virus-host interactions that might influence clinical outcomes

Bovine herpesvirus types 1 (BoHV-1) and 5 (BoHV-5) are two closely related alphaherpesviruses. BoHV-1 causes several syndromes in cattle, including respiratory disease and sporadic cases of encephalitis, whereas BoHV-5 is responsible for meningoencephalitis in calves. Although both viruses are neurotropic, they differ in their neuropathogenic potential. This review summarizes the findings on the specific mechanisms and pathways known to modulate the pathogenesis of BoHV-1 and BoHV-5, particularly in relation to respiratory and neurological syndromes, which characterize BoHV-1 and BoHV-5 infections, respectively.

Functional analysis of the latency-related gene of bovine herpesvirus types 1 and 5

Bovine herpesvirus type 1 and type 5 (BoHV-1 and BoHV-5) are two alphaherpesviruses that affect cattle with two different syndromes. While BoHV-1 mainly produces respiratory symptoms, BoHV-5 is highly neuropathogenic and responsible for meningoencephalitis in young cattle. The latency-related (LR) gene, which is not conserved between these two herpesviruses, is the only viral gene abundantly expressed in latently infected neurons. The antiapoptotic action of this gene has been demonstrated during acute infection and reactivation from latency and seems to be mainly mediated by a LR protein (ORF-2) which is truncated in amino acid 51 in the case of BoHV-5. In this work, we show that the BoHV-5 LR gene is less efficient at cell survival and apoptosis inhibition in transient as well as in established neuronal cell lines compared to its BoHV-1 homolog. We hypothesize that the BoHV-5 LR gene may have novel functions that are lacking in the BoHV-1 LR gene and that these differences may contribute to its enhanced neuropathogenesis.

Bovine herpesvirus type 5 replication and induction of apoptosis in vitro and in the trigeminal ganglion of experimentally-infected cattle

Bovine herpesvirus (BoHV) types 1 and 5 are neuroinvasive. Cases of BoHV-1-induced encephalitis are not as frequent as those caused by BoHV-5. In this study, the capability of BoHV-5 to induce apoptosis in cell cultures and in the trigeminal ganglion during acute infection of experimentally-infected cattle was analyzed. Apoptotic changes in cell cultures agree with the ability of the viral strains to replicate in each cell line. Marked differences were observed between the in vitro induction of apoptosis by BoHV-1Cooper and BoHV-5 97/613 strains. Apoptotic neurons were clearly evident in the trigeminal ganglion of BoHV-1-infected calves. For BoHV-5 a fewer number of positive neurons was observed. There is an association between the magnitude of bovine herpesviruses replication and the induction of apoptosis in trigeminal ganglion. These findings suggest that the induction of apoptosis and the innate immune response orchestrate the final outcome of alpha herpesviruses infection of the bovine nervous system.