Characterization of BoHV-5 field strains circulation and report of transient specific subtype of bovine herpesvirus 5 in Argentina

Reactive oxygen species favors Varicellovirus bovinealpha 5 (BoAHV-5) replication in neural cells

Varicellovirus bovinealpha (BoAHV) 1 and 5 are closely related neurotropic alphaherpesviruses with distinct neuropathogenic potential. BoAHV-5 causes meningoencephalitis in calves whereas encephalitis by BoAHV-1 infection is sporadic. the mechanisms underlying the differences in tropism and clinical outcomes of the infections are not yet completely understood. Here, we used neuroblastoma SH-SY5Y cells as non-differentiated in comparison with the SH-SY5Y neuronal-like cells obtained after exposing SH-SY5Y undifferentiated cells to trans-retinoic acid. We aimed to establish whether there was a relationship between the production of reactive oxygen species (ROS) and the kinetics of virus replication. We demonstrated that ROS production after BoAHV infection was higher in differentiated cells. Generation of ROS was also dependent on the infecting BoAHV strain. Higher ROS levels were produced during BoAHV-5 infection concomitantly with enhanced viral replication. We propose that increased ROS production mechanistically contributes to the tissue damage and neuroinflammation induced by BoAHV-5 infection. Future studies will determine specific targets of ROS that mediate the effects on viral replication.

Bovine herpesvirus meningoencephalitis in the State of Tocantins, Brazil

Three outbreaks of herpesvirus meningoencephalitis in cattle have been reported in three municipalities in the northern region of the State of Tocantins, Brazil. In one outbreak, 41 predominantly young bovines were affected, with 2-3 deaths in some cases. The animals showed neurological signs of incoordination, blindness, and recumbency, with death occurring within approximately 4-5 d. At necropsy, hyperemia and leptomeningeal hemorrhages were observed in the brain. Histology revealed more intense lesions in the rostral portions of the brain, mainly affecting the frontoparietal cerebral cortex, with nonsuppurative encephalitis and meningitis, glial nodules, neuronophagia, and eosinophilic intranuclear inclusion bodies in the astrocytes and neurons. This study shows the presence of bovine herpesvirus in Tocantins, probably the highly neurotropic type 5 strain, and emphasizes its importance in the differential diagnosis of bovine neuropathies.

A Qualitative PCR Assay for the Discrimination of Bubaline Herpesvirus 1, Bovine Herpesvirus 1 and Bovine Herpesvirus 5

Bubaline herpesvirus 1 (BuHV-1), Bovine herpesvirus 1 (BoHV-1) and Bovine herpesvirus 5 (BoHV-5) are classified in the genus Varicellovirus, subfamily Alphaherpesvirinae. BoHV-1 is the causative agent of infectious bovine rhinotracheitis, BoHV-5 induces moderate disease in adult cattle while BuHV-1 has instead been associated with a decline in livestock production of water buffaloes. The aim of this study was to develop a qualitative PCR assay that allows the discrimination of BuHV-1, BoHV-1 and BoHV-5. The alignment of homologous genes identified specific nucleotide sequences of BuHV- 1, BoHV-1 and BoHV-5. The design of the primers and the optimization of the PCR assay were focused on the target sequences located on the portions of gD, gE and gG genes. This assay involved the use of three different PCR end-points: the PCR of a portion of the gD gene identified only the presence of BoHV-1; the PCR of a portion of the gE gene confirmed the presence of both BoHV-5 and BuHV-1; the PCR of a portion of the gG gene discriminated between BoHV-5 and BuHV-1, as the amplification product was observed only for BoHV-5. This qualitative PCR assay allowed the differentiation of BoHV-1 and BoHV-5 infections both in cattle and water buffaloes and heterologous BuHV-1 infections in bovine.

Whole-genome analysis of natural interspecific recombinant between bovine alphaherpesviruses 1 and 5

Bovine alphaherpesviruses 1 and 5 (BoHV-1 and BoHV-5) are closely related viruses that co-circulate in South America and recombine in the field. The complete genomes of three natural gB gene recombinant viruses between BoHV-1 and BoHV-5 were obtained by Illumina next-generation sequencing. Complete genome sequences of the three recombinant strains (RecA1, RecB2, and RecC2) have a similar size of approximately 138.3kb and a GC content of 75%. The genome structure corresponds to herpesvirus class D, with 69 open reading frames (ORFs) arranged in the same order as other bovine alphaherpesviruses related to BoHV-1. Their genomes were included in recombination network studies indicating statistically significant recombination evidence both based on the whole genome, as well as in the sub-regions. The novel recombinant region of 3074 nt of the RecB2 and RecC2 strains includes the complete genes of the myristylated tegument protein (UL11) and the glycoprotein M (UL10) and part of the helicase (UL9) gene, and it seems to have originated independently of the first recombinant event involving the gB gene. Phylogenetic analyzes performed with the amino acid sequences of UL9, UL 10, and UL11 indicated that RecB2 and RecC2 recombinants are closely related to the minor parental virus (BoHV-1.2b). On the contrary, RecA1 groups with the major parental (BoHV-5), thus confirming the absence of recombination in this region for this recombinant. One breakpoint in the second recombinant region lies in the middle of the UL9 reading frame, originating a chimeric enzyme half encoded by BoHV-5 and BoHV-1.2b parental strains. The chimeric helicases of both recombinants are identical and have 96.8 and 96.3% similarity with the BoHV-5 and BoHV-1 parents, respectively. In vitro characterization suggests that recombinants have delayed exit from the cell compared to parental strains. However, they produce the similar viral titer as their putative parents suggesting the accumulation of viral particles for the cell exit delayed on time. Despite in vitro different behavior, these natural recombinant viruses have been maintained in the bovine population for more than 30 years, indicating that recombination could be playing an important role in the biological diversity of these viral species. Our findings highlight the importance of studying whole genome diversity in the field and determining the role that homologous recombination plays in the structure of viral populations. A whole-genome recombinant characterization is a suitable tool to help understand the emergence of new viral forms with novel pathogenic features.

A new molecular method for the rapid subtyping of bovine herpesvirus 1 field isolates

Bovine herpesvirus 1 (BoHV-1) causes several clinical syndromes in cattle worldwide. There are 3 subtypes of BoHV-1: 1.1, 1.2a, and 1.2b. Several molecular methods are commonly used in the detection and characterization of BoHV-1. Among them, restriction endonuclease analysis (REA) and single-nucleotide polymorphism (SNP) analysis of the complete viral genome allow classification of BoHV-1 into different subtypes. However, developing countries need simpler and cheaper screening assays for routine testing. We designed a standard multiplex PCR followed by a REA assay allowing straightforward subclassification of all BoHV-1 isolates tested into 1.1, 1.2a, and 1.2b subtypes based on the analysis of fragment length polymorphism. Our standard multiplex PCR-REA was used to analyze 33 field strains of BoHV-1 isolated from various tissues. The assay confirmed the subtype identified previously by REA. In addition, non-polymorphic or undigested fragments were sequenced in order to confirm the mutation affecting the RE HindIII site. Our PCR-REA method is an affordable and rapid test that will subtype all BoHV-1 strains.

Bovine alphaherpesvirus type 5 replicates more efficiently than bovine alphaherpesvirus type 1 in undifferentiated human neural cells

Bovine herpesvirus (BoHV) types 1 and 5 are two closely related alpha-herpesviruses of cattle with neuroinvasive potential. BoHV-5 causes non-suppurative meningoencephalitis in calve whereas encephalitis caused by BoHV-1 has been occasionally reported. As an initial step to understand the biology of both BoHV types in neural cells, undifferentiated SH-SY5Y human neuroblastoma cells were infected with BoHV-1 strains Cooper and Los Angeles (LA), BoHV-5 strain 97/613 and A663, a BoHV-5/BoHV-1 natural recombinant. Cytopathic effect (CPE) in these cells was evident earlier for BoHV-5 strain 97/613 and CPE progression was slower for BoHV-1, particularly for Cooper strain. Virus antigen was detected as early as 8 h post-infection (hpi) for all strains, with the exception of BoHV-1 Cooper for which antigen expression was detectable by 24 hpi. All strains released detectable infectious virus in the extracellular medium by 8 hpi, confirming that undifferentiated SH-SY5Y cells are fully permissive to BoHV infection. Significantly different extracellular virus titers among the different strains were detected by 24 hpi, with BoHV-5 97/613 reaching the maximal virus production. The lowest extracellular titer was recorded for BoHV-1 Cooper at all the evaluated time-points. BoHV-1 Cooper, BoHV-1 LA and BoHV-5 97/613 had a steady increase in intracellular virus production. The evaluation of lysis plaques formation revealed that BoHV-5 A663 produced the largest plaques followed by BoHV-5 97/613. Both BoHV-1 strains produced smaller plaques when compared with BoHV-5. Despite a slower replicative cycle, strain A663 is more efficient in cell to cell dissemination. Thus, it is evident that BoHV-5 strains have growth advantages in undifferentiated neural cells compared with BoHV-1. This in vitro model might be useful to analyze the neuropathogenic potential of bovine alphaherpesviruses.

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.

Bovine herpesvirus type 5 in semen samples from bulls in Iran

Bovine herpesvirus 5 (BoHV-5) is an important pathogen of the central nervous system and has already been described in the genital tract of cattle and in semen. This virus is responsible for sporadic epizootics of fatal meningoencephalitis of calves. The objective of the present study was the identification and characterization of BoHV-5 in semen samples from bulls for the first time in Iran. DNA was extracted from bull semen samples, and the glycoprotein D (gD) gene of BoHV-5 and also the thymidine kinase (tK) gene of bovine herpesvirus 1 (BoHV-1) were amplified by PCR assay. The results showed a high prevalence of BoHV-5 (73.2 %) and BoHV-1 (25.89 %) in Iranian bull semen samples. In addition, in order to identify and compare BoHV-5 isolated from Iranian bulls with other isolates from all over the world, the gD gene of this virus was cloned and sequenced. A BLAST search showed that the sequence of the gD gene of BoHV-5 from Iran was 99 % identical to other sequences in the GenBank database. The present study indicated that semen samples are important transmission sources of BoHV-5 virus in Iranian bulls.

Bovine herpesvirus 5 encodes a unique pattern of microRNAs compared with bovine herpesvirus 1

Bovine herpesvirus type 5 (BoHV-5) and bovine herpesvirus 1 (BoHV-1) are two closely related viruses. However, BoHV-5 is responsible for fatal meningitis in calves, while BoHV-1 is associated with infectious rhinotracheitis in cattle, and the mechanism by which the two viruses cause different symptoms is not well understood. In this study, we identified 11 microRNA (miRNA) genes, encoded by the BoHV-5 genome, that were processed into 16 detectable mature miRNAs in productive infection as determined by deep sequencing. We found that 6 out of 16 miRNA genes were present as two copies in the internal repeat and terminal repeat regions, resulting in a total of 17 miRNA-encoding loci distributed in both DNA strands. Surprisingly, BoHV-5 shared only one conservative miRNA with BoHV-1, which was located upstream of the origin of replication. Furthermore, in contrast to BoHV-1, no miRNAs were detected in the unique short region and locus within or near the bovine infected-cell protein 0 and latency-related genes. Variations in both the 5′ and 3′ ends of the reference sequence were observed, resulting in more than one isoform for each miRNA. All of the 16 miRNAs were detectable by stem–loop reverse transcriptase-PCR. The miRNAs with high read numbers were subjected to Northern blot analysis, and all pre-miRNAs and one mature miRNA were detected. Collectively, the data suggest that BoHV-5 encodes a different pattern of miRNAs, which may regulate the life cycle of BoHV-5 and might account for the different pathogenesis of this virus compared with BoHV-1.

Validation of a reference control for an SYBR-Green fluorescence assay-based real-time PCR for detection of bovine herpesvirus 5 in experimentally exposed bovine embryos

The objective of this study was to optimize an internal control to improve SYBR-Green-based qPCR to amplify/detect the BoHV-5 US9 gene in bovine embryos produced in vitro and experimentally exposed to the virus. We designed an SYBR-Green-based binding assay that is quick to perform, reliable, easily optimized and compares well with the published assay. Herein we demonstrated its general applicability to detect BoHV-5 US9 gene in bovine embryos produced in vitro experimentally exposed to BoHV-5. In order to validate the assay, three different reference genes were tested; and the histone 2a gene was shown to be the most adequate for normalizing the qPCR reaction, by considering melting and standard curves (p < 0.05). On the other hand, no differences were found in the development of bovine embryos in vitro whether they were exposed to BoHV-5 reference and field strains comparing to unexposed embryos. The developed qPCR assay may have important field applications as it provides an accurate BoHV-5 US9 gene detection using a proven reference gene and is considerably less expensive than the TaqMan qPCR currently employed in sanitary programs.

Multiplex PCR followed by restriction length polymorphism analysis for the subtyping of bovine herpesvirus 5 isolates

Background

Several types and subtypes of bovine herpesviruses 1 and 5 (BoHV-1 and BoHV-5) have been associated to different clinical conditions of cattle, making type/subtype differentiation essential to understand the pathogenesis and epidemiology of BoHV infections. BoHV-5 subtyping is currently carried out by BstEII restriction enzyme analysis (REA) of the complete virus genome. This method allowed the description of three subtypes, one of which is the most widespread while the remaining two have so far only been found in South America. The present work describes a multiplex PCR followed by REA for BoHV-5 subtyping.

Results

The method consists in the simultaneous amplification of glycoprotein B and UL54 gene fragments of 534 and 669 base pairs (bp), respectively, BstEII digestion of amplicons, separation of products in 1% agarose gels, and analysis of fragment length polymorphims. The multiplex PCR detected up to 227 BoHV-5 genome copies and 9.2 × 10⁵ BoHV-5 genome copies when DNA was extracted from purified virus or infected tissue homogenates, respectively. The applicability of multiplex PCR-REA was demonstrated on 3 BoHV-5 reference strains. In addition, subtyping of two new isolates and seventeen previously reported ones (17 BHV-5a and 2 BHV-5b) by this method gave coincident results with those obtained with the classic BstEII REA assay.

Conclusions

Multiplex PCR-REA provides a new tool for the fast and simple diagnosis and subtyping of BoHV-5.

Evaluation of developmental changes in bovine in vitro produced embryos following exposure to bovine Herpesvirus type 5

BACKGROUND

Bovine Herpesvirus type-5 (BoHV-5) is a neurovirulent α-Herpesvirus which is potentially pathogenic for cows and suspected to be associated with reproductive disorders. Interestingly, natural transmission of BoHV-5 by contaminated semen was recently described in Australia. Additionally, BoHV-5 was also isolated from the semen of a healthy bull in the same country and incriminated in a natural outbreak of reproductive disease after artificial insemination. In contrast with BoHV-1, experimental exposure of in vitro produced bovine embryos to BoHV-5 does not affect embryo viability and seems to inhibit some pathways of apoptosis. However, the mechanisms responsible for these phenomena are poorly understood. In this study, we examined mitochondrial activity, antioxidant protection, stress response and developmental rates of in vitro produced bovine embryos that were exposed and unexposed to BoHV-5.

METHODS

For this purpose, bovine embryos produced in vitro were assayed for cell markers after experimental infection of oocytes (n = 30; five repetitions), in vitro fertilization and development. The indirect immunofluorescence was employed to measure the expression of superoxide dismutase 1 (SOD1), anti-oxidant like protein 1 (AOP-1), heat shock protein 70.1 (Hsp 70.1) and also viral antigens in embryos derived from BoHV-5 exposed and unexposed oocytes. The determination of gene transcripts of mitochondrial activity (SOD1), antioxidant protection (AOP-1) and stress response (Hsp70.1) were evaluated using the reverse transcriptase polymerase chain reaction (RT-PCR). MitoTracker Green FM, JC-1 and Hoechst 33342-staining were used to evaluate mitochondrial distribution, segregation patterns and embryos morphology. The intensity of labeling was graded semi-quantitatively and embryos considered intensively marked were used for statistical analysis.

RESULTS

The quality of the produced embryos was not affected by exposure to BoHV-5. Of the 357 collected oocytes, 313 (+/- 6.5; 87.7%) were cleaved and 195 (+/- 3.2; 54.6%) blastocysts were produced without virus exposure. After exposure, 388 oocytes were cleaved into 328 (+/- 8.9, 84.5%), and these embryos produced 193 (+/- 3.2, 49.7%) blastocysts. Viral DNA corresponding to the US9 gene was only detected in embryos at day 7 after in vitro culture, and confirmed by indirect immunofluorescence assay (IFA). These results revealed significant differences (p < 0.05) between exposed and unexposed oocytes fertilized, as MitoTracker Green FM staining Fluorescence intensity of Jc-1 staining was significantly higher (p < 0.005) among exposed embryos (143 +/- 8.2). There was no significant difference between the ratios of Hoechst 33342-stained nuclei and total cells in good-quality blastocysts (in both the exposed and unexposed groups). Using IFA and reverse transcriptase polymerase chain reaction (RT-PCR) for the set of target transcripts (SOD1, AOP-1 and Hsp 70.1), there were differences in the mRNA and respective proteins between the control and exposed embryos. Only the exposed embryos produced anti-oxidant protein-like 1 (AOP-1). However, neither the control nor the exposed embryos produced the heat shock protein Hsp 70.1. Interestingly, both the control and the exposed embryos produced superoxide dismutase (SOD1), revealing intense mitochondrial activity.

CONCLUSION

This is the first demonstration of SOD1 and AOP-1 production in bovine embryos exposed to BoHV-5. Intense mitochondrial activity was also observed during infection, and this occurred without interfering with the quality or number of produced embryos. These findings further our understanding on the ability of α-Herpesviruses to prevent apoptosis by modulating mitochondrial pathways.

Role of bovine herpesvirus type 5 (BoHV-5) in diseases of cattle. Recent findings on BoHV-5 association with genital disease

Bovine herpesvirus type 5 (BoHV-5) belongs to the family Herpesviridae, subfamily Alphaherpesvirinae, genus Varicellovirus. This virus is a major causative agent of non-suppurative meningoencephalitis in young cattle. It was first isolated in 1962 from a neurological disease outbreak in Australia. BoHV-5 is genetically and antigenically related to bovine herpesvirus type 1 (BoHV-1), a highly prevalent virus responsible for respiratory and genital disease in cattle. Initially, BoHV-5 was considered a subtype of BoHV-1 (BoHV-1.3). However, the exclusive presentation of outbreaks of neurological disease suggested that the virus was a new agent with characteristics of neuropathogenicity. Even though both are neurotropic viruses, only BoHV-5 is capable of replicating extensively in the central nervous system and inducing neurological disease. Occasionally, encephalitis caused by BoHV-1 has been reported. Like other alpha-herpesviruses, BoHV-5 can establish latency in nervous ganglia and, by stress factors or glucocorticoid treatment, latent virus can be reactivated. During episodes of reactivation, the virus is excreted in nasal, ocular and genital secretions and transmitted to other susceptible hosts. Recently, BoHV-5 has been associated with infection of the reproductive tract. The virus has been isolated and the presence of viral DNA has been demonstrated in semen samples from Brazil and Australia and natural transmission of the virus through contaminated semen has also been described. Embryos and oocytes are permissive for BoHV-5 infection and BoHV-5 DNA has been detected in the central nervous system of aborted fetuses. The objective of this review is to compile the limited information on the recent association between BoHV-5 and reproductive disorders in cattle.

Comparative study on the in vitro and in vivo properties of two bovine herpesvirus-5 reference strains

BACKGROUND

Bovine herpesvirus 5 (BoHV-5) is an alphaherpesvirus responsible for meningoencephalitis in young cattle and it is antigenically and genetically related to bovine herpesvirus 1. BoHV-5 outbreaks are sporadic and restricted in their geographical distribution, being mostly detected in the Southern hemisphere. The N569 and A663 strains are prototypes of the "a" and "b" subtypes of BoHV-5, however, scarce information about their in vitro and in vivo properties is currently available.

METHODS

For the in vitro comparison between BoHV-5 A663 and N569 strains, viral growth kinetics, lysis and infection plaque size assays were performed. Additionally, an experimental infection of cattle with BoHV-5 A663 and N569 strains was carried out. Viral excretion, development of neurological signs, presence of specific antibodies in serum and nasal swabs and presence of latent BoHV-5 DNA in trigeminal ganglion, were analyzed. Histopathological examination of samples belonging to inoculated animals was also performed.

RESULTS

The lytic capacity and the cell-to-cell spread was lower for the A663 strain compared to the N569 strain, however, the production of total infectious viral particles was similar between both strains. Concerning the in vivo properties, the A663 and N569 strains are able to induce similar degrees of pathogenicity in cattle.

CONCLUSIONS

Our results show that the A663 strain used in this study is less adapted to in vitro replication in MDBK cells than the N569 strain and, although slight differences were observed, both strains are able to induce a similar degree of virulence in the natural host.