Comparative study on the in vitro replication and genomic variability of Argentinean field isolates of bovine herpesvirus type 4 (BoHV-4)

Isolation and complete genomic characterization of a Movar 33/63-like Japanese bovine herpesvirus 4 from a calf with respiratory disease

Bovine herpesvirus 4 (BoHV-4) is an indigenous virus in cattle prevalent mainly in North and South American countries and European countries, but the genomic sequences and genetic characteristics of Japanese strains have not been reported. BoHV-4 is suspected, but not proven, to be associated with various diseases. In the present study, we isolated BoHV-4 from a 10-month-old Japanese Black calf with respiratory symptoms in Japan. To identify the genetic characteristics of the isolate named strain SG20, complete genome sequencing was performed using a combination of next-generation and Sanger sequencing technologies. The complete long unique coding region (LUR) of SG20 was found to comprise 108,819 nucleotides with 41.4% GC content and contain at least 78 open reading frames. It shares 83.4 to 99.3% overall nucleotide identity with six BoHV-4 strains available in the database. The deduced amino acid sequence alignment revealed that SG20 contains genotype 1-specific features of BoHV-4, such as amino acid substitutions and insertions within the glycoprotein B region. Phylogenetic analyzes based on the nucleotide sequences of ORF20 indicated that the virus belonged to genotype 1 (Movar 33/63-like group). The strain was also analyzed using the complete LUR and placed in the same clade as a strain recently isolated from China, but it was distinct from American and European BoHV-4 strains of genotype 1. Although further genomic and epidemiologic information is needed, our results help elucidate the molecular epidemiology of BoHV-4 and provide a foundation for future studies.

Whole Genome Sequence-Based Analysis of Bovine Gammaherpesvirus 4 Isolated from Bovine Abortions

Bovine gammaherpesvirus 4 (BoGHV4) is a member of the Gammaherspivirinae subfamily, Rhadinovirus genus. Its natural host is the bovine, and it is prevalent among the global cattle population. Although the complete genome of BoGHV4 has been successfully sequenced, the functions of most of its genes remain unknown. Currently, only six strains of BoGHV4, all belonging to Genotype 1, have been sequenced. This is the first report of the nearly complete genome of Argentinean BoGHV4 strains isolated from clinical cases of abortion, representing the first BoGHV4 Genotype 2 and 3 genomes described in the literature. Both Argentinean isolates presented the highest nt p-distance values, indicating a greater level of divergence. Overall, the considerable diversity observed in the complete genomes and open reading frames underscores the distinctiveness of both Argentinean isolates compared to the existing BoGHV4 genomes. These findings support previous studies that categorized the Argentinean BoGHV4 strains 07-435 and 10-154 as Genotypes 3 and 2, respectively. The inclusion of these sequences represents a significant expansion to the currently limited pool of BoGHV4 genomes while providing an important basis to increase the knowledge of local isolates.

Effect of bovine viral diarrhea virus on subsequent infectivity of bovine gammaherpesvirus 4 in endometrial cells in primary culture: An in vitro model of viral co-infection

Bovine viral diarrhea virus (BVDV) and bovine gammaherpesvirus 4 (BoHV-4) infect the uterus of cattle, being responsible for huge economic losses. Most of the pathogenesis of BoHV-4 in the bovine reproductive tract has been elucidated by conducting tests on primary cultures. Thus, it is important to have optimal in vitro conditions, avoiding the presence of other pathogens that can alter the results. BVDV is one of the most frequent viral contaminants of cell cultures. Considering that non-cytopathic (NCP) BVDV biotype can generate persistently infected (PI) cattle, which are the major source for virus transmission in susceptible herds, it is important to check products derived from cattle that are intended to be used in research laboratories. The aim of this work was to evaluate how the natural infection of bovine endometrial cells (BEC) with a NCP BVDV strain (BEC + BVDV) affects BoHV-4 replication. We have demonstrated a delay in BoHV-4 gene expression and a decrease in viral load in the extracellular environment in BEC + BDVD cells compared to BEC (BVDV-free) cells. These results confirm that replication of BoHV-4 in BEC primary cultures is affected by previous infection with BVDV. This finding highlights the importance of ruling out BVDV infection in bovine primary cell cultures to avoid biological interference or misinterpretation of results at the time of performing in vitro studies with BoHV-4.

Isolation and molecular characterization of bovine herpesvirus 4 from cattle in mainland China

Bovine herpesvirus 4 (BoHV-4) is one of the most important of the known viral respiratory and reproductive pathogens of both young and adult cattle. However, BoHV-4 has not been isolated or detected in mainland China prior to this study. In 2019, BoHV-4 strain 512 was isolated from cattle in Heilongjiang Province, China, using MDBK cells, and characterized by PCR, nucleotide sequence analysis, and transmission electron microscopy. Two other unknown herpesvirus strains, BL6010 and J4034, which were isolated from cattle in 2009 in China and stored at -70℃, were also propagated in MDBK cells and identified as BoHV-4 by PCR. Phylogenetic analysis based on partial nucleotide sequences of the thymidine kinase (TK) gene and glycoprotein B (gB) gene for the three isolates indicated that these three Chinese strains belong to BoHV-4 genotype 1. A preliminary virus neutralization test revealed that 64% of the 70 bovine sera (45/70) collected from Inner Mongolia Autonomous Region, China, had anti-BoHV-4 antibodies and that natural BoHV-4 infection occurred in cattle in China. Here, we report for the first time the isolation and molecular characterization of BoHV-4 from cattle in mainland China.

Gene expression and in vitro replication of bovine gammaherpesvirus type 4

In vitro cell cultures are widely used models for dissecting cellular and molecular mechanisms that lead to certain physiological conditions and diseases. The pathogenesis of BoHV-4 in the bovine reproductive tract has been studied by conducting tests on primary cultures. However, many questions remain to be answered about the role of BoHV-4 in endometrial cells. The aim of this study was to compare the replication and gene expression of BoHV-4 in cell lines and bovine reproductive tract primary cells as an in vitro model for the study of this virus. We demonstrated that BoHV-4 strains differ in their in vitro growth kinetics and gene expression but have the same cell type preference. Our results demonstrate that BoHV-4 replicates preferentially in bovine endometrial cells (BEC). However, its replication capacity extends to various cell types, since all cells that were tested were permissive to BoHV-4 infection. The highest virus titers were obtained in BEC cells. Nevertheless, virus replication efficiency could not be fully predicted from the mRNA expression profiles. This implies that there are multiple cell-type-dependent factors and strain properties that determine the level of BoHV-4 replication. The results of this study provide relevant information about the in vitro behavior of two field isolates of BoHV-4 in different cell cultures. These findings may be useful for the design of future in vitro experiments to obtain reliable results not only about the pathogenic role of BoHV-4 in the bovine female reproductive tract but also in the development of efficient antiviral strategies.

Genetic characterization of bovine herpesvirus 4 (BoHV-4) isolates from Argentine cattle suggests a complex evolutionary scenario

Bovine herpevsirus 4 (BoHV-4) is a gammaherpesvirus that has been associated with different clinical conditions in cattle. In Argentina, BoHV-4 was detected in diverse bovine samples. The aim of this study was to analyze the genetic relationship of 48 field BoHV-4 strains isolated from cattle in Argentina. According to thymidine kinase (tk) gene sequences, BoHV-4 isolates belong to genotypes 1, 2 and 3. Phylogenetic analyses confirmed the presence of the three previously described viral genotypes. However, some of the studied isolates presented conflicting phylogenetic signals between the studied markers. This suggests a complex evolutionary background, that is a history of recombination, incomplete lineage sorting (deep coalescence) or a combination of these, which requires further study. These potential events make difficult the diagnosis of BoHV-4 from clinical samples of cattle and may pose a significant problem for the control of the virus in the herds.

Comparative analysis of replicative properties of phylogenetically divergent, Argentinean BoHV-4 strains in cell lines from different origins

Bovine gammaherpesvirus 4 (BoHV4) is a member of the family Herpesviridae. In Argentina, BoHV4 was isolated and characterized in 2007 from samples of aborted cows. Argentinean isolates are highly divergent and are classified as: Genotype 1(Movar-like), Genotype 2 (DN599-like) and Genotype 3 (a novel group). The aim of this study was to comparatively evaluate the biological characteristics of six Argentinean BoHV4 field isolates in cell lines from different origins. All strains induced productive infection in the cell lines used, with different degrees of permissiveness. A direct relationship among the times of appearance of cytopathic effect, the growth kinetics, the size of the lysis plaques and the virulent-like behaviour in vitro could not be established. However, although slight, there are differences in the biological behaviour of the BoHV4 fields isolates analyzed. This variability is independent of their genetic classification but would be conditioned by the nature of the infected cells.

Whole Genome Sequencing of a Canadian Bovine Gammaherpesvirus 4 Strain and the Possible Link between the Viral Infection and Respiratory and Reproductive Clinical Manifestations in Dairy Cattle

Bovine gammaherpesvirus 4 (BoHV-4) is a herpesvirus widespread in cattle populations, and with no clear disease association. Its genome contains a long unique coding region (LUR) flanked by polyrepetitive DNA and 79 open reading frames (ORFs), with unique 17 ORFs, named Bo1 to Bo17. In 2009, a BoHV-4 strain was isolated (FMV09-1180503: BoHV-4-FMV) from cattle with respiratory disease from Quebec, Canada, and its LUR was sequenced. Despite the overall high similarity, BoHV-4-FMV had the most divergent LUR sequence compared to the two known BoHV-4 reference strain genomes; most of the divergences were in the Bo genes and in the repeat regions. Our phylogenetic analysis based on DNA polymerase and thymidine kinase genes revealed that virus isolate was BoHV-4 gammaherpesvirus and clustered it together with European BoHV-4 strains. Because BoHV-4-FMV was isolated from animals presenting respiratory signs, we have updated the BoHV-4 Canadian cattle seroprevalence data and tried to find out whether there is a link between clinical manifestation and BoHV-4 seropositivity. An indirect immunofluorescence assay (IFA) was performed with nearly 200 randomized sera of dairy cattle from two Canadian provinces, Quebec (n = 100) and Ontario (n = 91). An additional set of sera obtained from Quebec, from the healthy (n = 48) cows or from the animals experiencing respiratory or reproductive problems (n = 75), was also analyzed by IFA. BoHV-4 seroprevalence in Canadian dairy cattle was 7.9% (Quebec: 6% and Ontario: 9.9%). Among animals from the Quebec-based farms, diseased animals showed higher BoHV-4 seropositivity than healthy animals (P < 0.05), with a significant 2.494 odds ratio of being seropositive in sick compared to healthy animals. Although there is no established direct link between BoHV-4 and specific diseases, these seroprevalence data suggest the possible involvement of BoHV-4 in dairy cattle diseases.