Simian alphaherpesviruses and their relation to the human herpes simplex viruses

Questioning the Extreme Neurovirulence of Monkey B Virus (Macacine alphaherpesvirus 1)

Monkey B virus (Macacine alphaherpesvirus 1; BV) occurs naturally in macaques of the genus Macaca, which includes rhesus and long-tailed (cynomolgus) monkeys that are widely used in biomedical research. BV is closely related to the human herpes simplex viruses (HSV), and BV infections in its natural macaque host are quite similar to HSV infections in humans. Zoonotic BV is extremely rare, having been diagnosed in only a handful of North American facilities with the last documented case occurring in 1998. However, BV is notorious for its neurovirulence since zoonotic infections are serious, usually involving the central nervous system, and are frequently fatal. Little is known about factors underlying the extreme neurovirulence of BV in humans. Here we review what is actually known about the molecular biology of BV and viral factors affecting its neurovirulence. Based on what is known about related herpesviruses, areas for future research that may elucidate mechanisms underlying the neurovirulence of this intriguing virus are also reviewed.

Understanding Primate Herpesviruses

Viruses related to the herpes simplex viruses of humans are present in all nonhuman primate (NHP) species tested and cross species transmission has been documented. The herpesvirus present in macaques, Herpes B virus (BV) rarely causes disease in its natural macaque host. However, when transmitted to a nonnative host, BV has occasionally caused severe and even fatal disease if not treated immediately. Here we present a comprehensive review of the taxonomy, molecular biology, physiology, epidemiology, diagnosis and treatment of BV. We also summarizes what is known about related herpesviruses of other NHP species and the zoonotic potential of these viruses.

B Virus (Macacine Herpesvirus 1) Divergence: Variations in Glycoprotein D from Clinical and Laboratory Isolates Diversify Virus Entry Strategies

B virus (Macacine herpesvirus 1) can cause deadly zoonotic disease in humans. Molecular mechanisms of B virus cell entry are poorly understood for both macaques and humans. Here we investigated the abilities of clinical B virus isolates to use entry receptors of herpes simplex viruses (HSV). We showed that resistant B78H1 cells became susceptible to B virus clinical strains upon expression of either human nectin-2 or nectin-1. Antibody against glycoprotein D (gD) protected these nectin-bearing cells from B virus infection, and a gD-negative recombinant B virus failed to enter these cells, indicating that the nectin-mediated B virus entry depends on gD. We observed that the infectivity of B virus isolates with a single amino acid substitution (D122N) in the IgV-core of the gD ectodomain was impaired on nectin-1-bearing cells. Computational homology-based modeling of the B virus gD-nectin-1 complex revealed conformational differences between the structures of the gD-122N and gD-122D variants that affected the gD-nectin-1 protein-protein interface and binding affinity. Unlike HSV, B virus clinical strains were unable to use herpesvirus entry mediator (HVEM) as a receptor, regardless of conservation of the gD amino acid residues essential for HSV-1 entry via HVEM. Based on the model of the B virus gD-HVEM interface, we predict that residues R7, R11, and G15 are largely responsible for the inability of B virus to utilize HVEM for entry. The ability of B virus to enter cells of a human host by using a combination of receptors distinct from those for HSV-1 or HSV-2 suggests a possible mechanism of enhanced neuropathogenicity associated with zoonotic infections.

IMPORTANCE

B virus causes brainstem destruction in infected humans in the absence of timely diagnosis and intervention. Nectins are cell adhesion molecules that are widely expressed in human tissues, including neurons and neuronal synapses. Here we report that human nectin-2 is a target receptor for B virus entry, in addition to the reported receptor human nectin-1. Similar to a B virus lab strain, B virus clinical strains can effectively use both nectin-1 and nectin-2 as cellular receptors for entry into human cells, but unlike HSV-1 and HSV-2, none of the clinical strains uses an HVEM-mediated entry pathway. Ultimately, these differences between B virus and HSV-1 and -2 may provide insight into the neuropathogenicity of B virus during zoonotic infections.

Optimized Expression, Purification of Herpes B Virus gD Protein in Escherichia coli, and Production of Its Monoclonal Antibodies

BACKGROUND

Herpes B virus (BV) is a zoonotic disease caused by double-stranded enveloped DNA virus with cercopithecidae as its natural host. The mortality rate of infected people could be up to 70% with fatal encephalitis and encephalomyelitis. Up to now, there are no effective treatments for BV infection. Among the various proteins encoded by monkey B virus, gD, a conserved structural protein, harbors important application value for serological diagnosis of frequent variations of the monkey B virus.

OBJECTIVES

This study aimed to expressed the gD protein of BV in Escherichia coli by a recombinant vector, and prepare specific monoclonal antibodies against gD of BV to pave the way for effective and quick diagnosis reagent research.

MATERIALS AND METHODS

The gD gene of BV was optimized by OptimWiz to improve codon usage bias and synthesis, and the recombinant plasmid, pET32a/gD, was constructed and expressed in E. coli Rosetta (DE3). The expressed fusion protein, His-gD, was purified and the BALB/c mice were immunized by this protein. Spleen cells from the immunized mice and SP2/0 myeloma cells were fused together, and the monoclonal cell strains were obtained by indirect enzyme-linked immunosorbent assay (ELISA) screening, followed by preparation of monoclonal antibody ascetic fluid.

RESULTS

The optimized gD protein was highly expressed in E. coli and successfully purified. Five monoclonal antibodies (mAbs) against BV were obtained and named as 4E3, 3F8, 3E7, 1H3 and 4B6, and with ascetic fluid titers of 2 × 10(6), 2 × 10(5), 2 × 10(5), 2 × 10(3) and 2 × 10(2), respectively. The 1H3 and 4E3 belonged to the IgG2b subclass, while 3E7, 3F8 and 4B6 belonged to the IgG1 subclass.

CONCLUSIONS

The cell lines obtained in this work secreted potent, stable and specific anti-BV mAbs, which were suitable for the development of herpes B virus diagnosis reagents.

Xenozoonoses

Immunological and technical advances have led to tremendous increases in the number of people potentially able to benefit from allotransplantation. Ironically, it is the success of the field that has led to a renewed interest in xenotransplantation during the past several decades. To a large part, this has occurred because of the great scarcity of human organ and tissue donors. However, it has expanded to include the use of cells from animals into humans such as porcine islet cells for diabetes or extracorporeal perfusion of human blood through animal organs or cells. Similar to allotransplantation, issues regarding transmission of infections from the graft to the human recipient were brought up for consideration with these procedures in the 1990s (Michaels and Simmons, 1994; Chapman et al., 1995; Hammel et al., 1998; Fishman et al., 1998). A risk for infection exists with the use of any biologic agent regardless of whether it is from a human or an animal source. Accordingly, transmission of infections from human organs, tissues, or cells is a well-recognized cause of disease after allotransplantation (Ison and Grossi, 2013; Green and Michaels, 2012). As the human graft shortage continues, newer cellular therapies are explored. Thus, attention continues to be given to the potential use of xenogeneic organs, tissues, or cells for human maladies through xenotransplantation. The potential for novel zoonotic infections to emerge because of xenotransplantation (xenozoonoses or xenosis) led to a debate on whether the field should be permitted to progress. This chapter reviews the issues of xenotransplantation related to infections from animals to humans. Lessons learned from infections with prior nonhuman primate xenotransplantation and human allotransplantation are used to help inform about risks with newer xenogeneic procedures. In addition, information on known zoonoses is reviewed to better develop constructs to decrease the hazard of infection with these novel procedures.

Evolutionary origins of human herpes simplex viruses 1 and 2

Herpesviruses have been infecting and codiverging with their vertebrate hosts for hundreds of millions of years. The primate simplex viruses exemplify this pattern of virus-host codivergence, at a minimum, as far back as the most recent common ancestor of New World monkeys, Old World monkeys, and apes. Humans are the only primate species known to be infected with two distinct herpes simplex viruses: HSV-1 and HSV-2. Human herpes simplex viruses are ubiquitous, with over two-thirds of the human population infected by at least one virus. Here, we investigated whether the additional human simplex virus is the result of ancient viral lineage duplication or cross-species transmission. We found that standard phylogenetic models of nucleotide substitution are inadequate for distinguishing among these competing hypotheses; the extent of synonymous substitutions causes a substantial underestimation of the lengths of some of the branches in the phylogeny, consistent with observations in other viruses (e.g., avian influenza, Ebola, and coronaviruses). To more accurately estimate ancient viral divergence times, we applied a branch-site random effects likelihood model of molecular evolution that allows the strength of natural selection to vary across both the viral phylogeny and the gene alignment. This selection-informed model favored a scenario in which HSV-1 is the result of ancient codivergence and HSV-2 arose from a cross-species transmission event from the ancestor of modern chimpanzees to an extinct Homo precursor of modern humans, around 1.6 Ma. These results provide a new framework for understanding human herpes simplex virus evolution and demonstrate the importance of using selection-informed models of sequence evolution when investigating viral origin hypotheses.

Structure and sequence of the saimiriine herpesvirus 1 genome

We report here the complete genome sequence of the squirrel monkey α-herpesvirus saimiriine herpesvirus 1 (HVS1). Unlike the simplexviruses of other primate species, only the unique short region of the HVS1 genome is bounded by inverted repeats. While all Old World simian simplexviruses characterized to date lack the herpes simplex virus RL1 (γ34.5) gene, HVS1 has an RL1 gene. HVS1 lacks several genes that are present in other primate simplexviruses (US8.5, US10-12, UL43/43.5 and UL49A). Although the overall genome structure appears more like that of varicelloviruses, the encoded HVS1 proteins are most closely related to homologous proteins of the primate simplexviruses. Phylogenetic analyses confirm that HVS1 is a simplexvirus. Limited comparison of two HVS1 strains revealed a very low degree of sequence variation more typical of varicelloviruses. HVS1 is thus unique among the primate α-herpesviruses in that its genome has properties of both simplexviruses and varicelloviruses.

Simian herpesviruses and their risk to humans

A high level of genetic and physiological homology with humans has rendered non-human primates (NHP) an essential animal model for biomedical research. As such NHP offer a unique opportunity to study host-pathogen interactions in a species that closely mimics human biology but can yet be maintained under tight laboratory conditions. Indeed, studies using NHP have been critical to our understanding of pathogenesis as well as the development of vaccines and therapeutics. This further facilitated by the fact that NHPs are susceptible to a variety of pathogens that bear significant homology to human pathogens. Unfortunately, these same viruses pose a potential health issue to humans. In this review we discuss the simian herpesviruses and their potential to cause disease in researchers that come into close contact with them.

Prevalence of antibody reaction with cercopithecine herpesvirus 1 antigen in Macaca cyclopis, Macaca fascicularis, and Papio anubis in Taiwan

BACKGROUND AND METHODS

A total of 284 non-human primate sera were collected between December 2004 and September 2005 and tested by a commercially available dot immunobinding assay for the antibodies to cercopithecine herpesvirus 1, an alphaherpesvirus with high mortality for infected humans.

RESULTS

Seropositive rates were 58% among non-human primates from animal shelters and 38% among those from zoos and academic institutes. Positive reactors were found in three species, the Formosan macaque (Macaca cyclopis; 57%), the cynomolgus macaque (Macaca fascicularis; 11%) and the olive baboon (Papio anubis; 68%).

CONCLUSIONS

Our results showed that natural infection by cercopithecine herpesvirus 1 in Formosan macaques was highly prevalent, and to a certain extent reflected the situation of the wild populations in Taiwan. The findings raised the issues of zoonotic public health and the occupational health of primate workers. High positive rate in olive baboons was also found, although, it cannot be ruled out that the positivity was due to cross-reactivity between cercopithecine herpesvirus 1 and other herpesviruses.

Discrimination of antibody to herpes B virus from antibody to herpes simplex virus types 1 and 2 in human and macaque sera

The antigenic cross-reactive characteristics of herpes B virus and herpes simplex virus (HSV) type 1 (HSV-1) and HSV-2 are responsible for false-positive diagnoses by serological assays in humans and macaques. In the present study, we developed a fluorometric indirect enzyme-linked immunosorbent assay (ELISA) with recombinant herpes B virus glycoprotein D (gD) and HSV-1 and HSV-2 gG (gG-1 and gG-2, respectively) to discriminate between the three primate herpesvirus infections. The secreted form of gD, gDdTM, was used to detect antibody to herpes B virus gD. Sera positive for herpes B virus, HSV-1, and HSV-2 showed specific reactions to gD, gG-1, and gG-2, respectively. Sera collected from humans and rhesus macaques were investigated for the presence of antibodies to the recombinant proteins of the three herpesviruses. The results suggested that the approach is able to discriminate between herpes B virus and HSV infections. The ELISA was also found to be able to detect infections with multiple primate herpesviruses and may have the potential to identify a subsequent infection in individuals that have already been infected with another herpesvirus. In addition, we found evidence of a greater cross-reactivity of herpes B virus with HSV-1 than with HSV-2. It is suggested that the ELISA with the recombinant antigens is useful not only for the serodiagnosis of primate herpesvirus infections but also for elucidation of the seroprevalence of herpesviruses in humans and primates.

Primary mouse dermal fibroblast cell cultures as an in vitro model system for the differential pathogenicity of cross-species herpesvirus papio 2 infections

Infection of mice with herpesvirus papio 2 (HVP2) parallels zoonotic monkey B virus infections. A major benefit of the HVP2/mouse model is the existence of two HVP2 subtypes: HVP2nv rapidly invades and destroys the CNS while HVP2ap produces no clinical signs and mild histopathological lesions. However, in the natural baboon host, no difference in pathogenicity of HVP2 subtypes is evident. Primary dermal fibroblast cells were evaluated as a model system for defining virus-host interactions that influence the outcome of a cross-species infection. No differences in plaque formation or virus replication were observed between HVP2 subtypes in primary baboon dermal fibroblast cultures. In contrast, when primary mouse dermal fibroblasts (PMDF) were infected, HVP2nv replicated to higher titers and was more efficient at shutting down host-cell protein synthesis compared to HVP2ap. HVP2ap-infected PMDF cells produced more IFN-beta compared to HVP2nv, and IFN-beta pretreatment of PMDF cultures inhibited HVP2ap replication but did not affect HVP2nv. The differential pathogenicity of HVP2 subtypes in mice and the lack of such differences in the natural baboon host are recapitulated in the primary dermal fibroblast cell culture system. This model may prove useful in examining early, local, host responses that influence the outcome of cross-species infections.

Isolation and characterization of a chimpanzee alphaherpesvirus

Although both beta- and gammaherpesviruses indigenous to great-ape species have been isolated, to date all alphaherpesviruses isolated from apes have proven to be human viruses [herpes simplex virus types 1 (HSV1) and 2 (HSV2) or varicella-zoster virus]. If the alphaherpesviruses have co-evolved with their host species, some if not all ape species should harbour their own alphaherpesviruses. Here, the isolation and characterization of an alphaherpesvirus from a chimpanzee (ChHV) are described. Sequencing of a number of genes throughout the ChHV genome indicates that it is collinear with that of HSV. Phylogenetic analyses place ChHV in a clade with HSV1 and HSV2, the alphaherpesviruses of Old World monkeys comprising a separate clade. Analysis of reactivity patterns of HSV2-immune human sera and ChHV-immune chimpanzee sera by competition ELISA support this relationship. Phylogenetic analyses also place ChHV rather than HSV1 as the closest relative of HSV2.

Prevalence of enzootic simian viruses among urban performance monkeys in Indonesia

Animal reservoirs are the most important sources of emerging infectious diseases that threaten human populations. Global travel and tourism bring ever-increasing numbers of humans into contact with animals, increasing the likelihood of cross species transmission of infectious agents. Non-human primates come into contact with humans in a variety of contexts and may harbor infectious agents with zoonotic potential. We investigated the prevalence of infection with enzootic simian viruses among 20 urban performance monkeys (Macaca fascicularis) in Jakarta, Indonesia. This report documents for the first time evidence of infection with four simian viruses in urban performance monkeys. Simian foamy virus was detected by PCR in 52.9% of the macaques. Antibodies to simian retrovirus were detected in 10.5% of the macaques. Antibodies to Cercopithecine Herpesvirus 1, were detected in 5.3% of the macaques. Similarly, antibodies to simian T-cell lymphotropic virus were detected in 5.3% of the macaques. No evidence of infection with simian immunodeficiency virus was detected in these macaques. These results suggest that urban performance monkeys are a reservoir for enzootic simian viruses known to be capable of infecting humans.

Temporal progression of viral replication and gross and histological lesions in Balb/c mice inoculated epidermally with Saimiriine herpesvirus 1 (SaHV-1)

Saimiriine herpesvirus 1 (SaHV-1), an alphaherpesvirus enzootic in squirrel monkeys, is genetically related to monkey B virus and human herpes simplex virus (HSV). To study the temporal progression of viral spread and associated lesions, Balb/c mice were inoculated epidermally by scarification with a green fluorescent protein (GFP)-expressing recombinant strain of SaHV-1 and killed sequentially. Pinpoint ulcerative lesions in the inoculated epidermis progressed over a few days to unilateral or bilateral hindlimb paresis or paralysis, urinary and faecal incontinence, abdominal distension, hunched posture and eventual depression warranting euthanasia. Viral replication was present within epidermal keratinocytes, neurons of the dorsal root ganglia and thoracolumbar spinal cord, regional autonomic ganglia, lower urinary tract epithelium and colonic myenteric plexuses, as indicated by histological lesions and GFP expression. Almost all mice inoculated with 10(5) or 10(6) plaque-forming units (PFU) of SaHV-1 developed rapidly progressive disease. Two of eight mice given 10(4)PFU developed disease, but no mice receiving less than 10(4)PFU gave evidence of infection. Mice that showed no clinical signs also failed to develop an antiviral IgG response, indicating absence of active viral infection. For SaHV-1 inoculated epidermally, the ID(50), CNSD(50) and LD(50) values were identical (10(4.38)), indicating that successful infection by this route invariably resulted in lethal CNS (central nervous system) disease. Consistently severe disease in all infected animals, with regionally extensive distribution of viral replication, constituted a marked difference from the disease produced by intramuscular inoculation.

Production of herpes B virus recombinant glycoproteins and evaluation of their diagnostic potential

B virus (cercopithecine herpesvirus 1) is the only deadly alphaherpesvirus that is zoonotically transmissible from macaques to humans. The detection of humoral immune responses is the method of choice for the rapid identification of B virus-infected animals. We evaluated the diagnostic potential of recombinant B virus glycoproteins for the detection of immunoglobulin G (IgG) antibodies in monkey and human sera. Glycoproteins B, C, and E and secreted (sgG) and membrane-associated (mgG) segments of glycoprotein G (gG) were expressed in the baculovirus expression system, while gD was expressed in CHO cells. We developed recombinant protein-based IgG enzyme-linked immunosorbent assays (ELISAs) and compared their diagnostic efficacies by using B virus antibody-negative (n = 40) and -positive (n = 75) macaque sera identified by a whole antigen-based ELISA and Western blotting. The diagnostic sensitivities of the gB-, gC-, gD-, and mgG-ELISAs were 100, 97.3, 88.0, and 80.0%, respectively. The specificities of the gB-, gC-, and gD-ELISAs and of the mgG-ELISA were 100 and 97.5%, respectively. In contrast, the sensitivities and specificities of sgG- and gE-ELISAs were low, suggesting that sgG and gE are less effective diagnostic antigens. Sera from nonmacaque monkeys cross-reacted with gB, gC, and gD, and only baboon sera reacted weakly with mgG. Human herpes simplex virus type 1 (HSV-1)- and HSV-2-positive sera pools reacted with gB and gD, whereas sera from B virus-infected individuals reacted with all four antigens. These data indicate that gB, gC, gD, and mgG have a high diagnostic potential for B virus serodiagnosis in macaques, whereas mgG may be a valuable antigen for discrimination between antibodies induced by B virus and those induced by other, closely related alphaherpesviruses, including HSV-1 and -2.

Specific detection and identification of herpes B virus by a PCR-microplate hybridization assay

Herpes B virus DNA was specifically amplified by PCR, targeting the regions that did not cross-react with herpes simplex virus (HSV). The amplified products, which were shown to be highly genetic polymorphisms among herpes B virus isolates, were identified by microplate hybridization with probes generated by PCR. The products immobilized in microplate wells were hybridized with the biotin-labeled probes derived from the SMHV strain of herpes B virus. The amplified products derived from the SMHV and E2490 strains of herpes B virus were identified by microplate hybridization. PCR products amplified from the trigeminal ganglia of seropositive cynomolgus macaques were identified as herpes B virus DNA. The utility of the PCR-microplate hybridization assay for genetic detection and identification of the polymorphic region of herpes B virus was determined.

Nonhuman primate herpesviruses: importance for xenotransplantation

Herpesviruses are found throughout the animal kingdom. Members of this family share properties including a highly orchestrated system of transcription, destruction of the host cell by active viral replication and an ability to persist in the host in a latent form. Human herpesviruses have all been implicated in causing substantial disease after allotransplantation. Often transmission of these viruses has been through the donor organ or blood products. Analogous species of herpesviruses exist in nonhuman primates. Accordingly, concern regarding the risk of their transmission and disease exists with xenotransplant procedures. This chapter reviews herpesviruses of nonhuman primates and their potential implication for causing disease after xenotransplantation.

Fatal Herpes simplex infection in a group of common marmosets (Callithrix jacchus)

An outbreak of classical herpetic infection causing vesicoulcerative stomatitis in a family group (eight animals) of Callithrix jacchus is described. In all eight infected animals, human herpesvirus 1 (HHV-1) was identified as the causative agent. This was confirmed by histologic, immunohistologic, and molecular biologic investigations, as well as by virus isolation. The clinical picture, the macroscopic appearance, and the histologic results indicated a herpes infection as the cause of mortality. Alterations of the oral mucous membranes were erosive to ulcerative with typical intranuclear inclusions. Immunohistologic and molecular biologic techniques clearly identified the HHV-1 virus and excluded other possible primate herpesviruses such as B-virus, SA8, HVP-2, and Herpes tamarinus. The significance of this herpesvirus infection for colony management is discussed.

Cloning and expression of the complement receptor glycoprotein C from Herpesvirus simiae (herpes B virus): protection from complement-mediated cell lysis

Simian herpes B virus (SHBV) is the herpes simplex virus (HSV) homologue for the species MACACA: Unlike in its natural host, and unlike other animal herpesviruses, SHBV causes high mortality in accidentally infected humans. SHBV-infected cells, like those infected with HSV-1 and equine herpesvirus types 1 and 4, express complement C3 receptor activity. To study immunoregulatory functions involved in susceptibility/resistance against interspecies transmission, the SHBV glycoprotein C (gC(SHBV)) gene (encoding 467 aa) was isolated. Sequence analysis revealed amino acid identity with gC proteins from HSV-2 (46.9 %), HSV-1 (44.5 %) and pseudorabies virus (21.2 %). Highly conserved cysteine residues were also noted. Similar to gC(HSV-2), gC(SHBV) is less glycosylated than gC(HSV-1), resulting in a molecular mass of 65 kDa if expressed in replication-deficient vaccinia virus Ankara. Stable transfectants expressing full-length gC(SHBV) on the cell surface induced C3 receptor activity and were substantially protected from complement-mediated lysis; no protection was observed with control constructs. This suggests that expression of the gC homologues on infected cell surfaces might also contribute to the survival of infected cells in addition to decreased virion inactivation. Interestingly, soluble gC(SHBV) isolated from protein-free culture supernatants did not interfere with the binding of the alternative complement pathway activator properdin to C3b, which is similar to our findings with gC(HSV-2) and could be attributed to major differences in the amino-terminal portion of the protein with extended deletions in both gC(SHBV) and gC(HSV-2). Binding of recombinant gC(SHBV) to polysulphates was observed. This, together with the heparin-sensitivity of the gC(SHBV)-C3 interaction on the infected cell surface, suggests a role in adherence to heparan sulphate, similar to the gC proteins of other herpesviruses.

Sequence and genetic arrangement of the U(S) region of the monkey B virus (cercopithecine herpesvirus 1) genome and comparison with the U(S) regions of other primate herpesviruses

The sequence of the unique short (U(S)) region of monkey B virus (BV) was determined. The 13 genes identified are arranged in the same order and orientation as in herpes simplex virus (HSV). These results demonstrate that the BV U(S) region is entirely colinear with that of HSV type 1 (HSV-1), HSV-2, and simian agent 8 virus.

Characterization of gross and histological lesions in Balb/c mice experimentally infected with herpesvirus saimiri 1 (HVS1)

Accidental B virus (Herpesvirus simiae) infection of human beings working with macaques is frequently fatal. However, the pathogenic potential of other similar simian alphaherpesviruses, such as the squirrel monkey virus Herpesvirus saimiri (HVS1), is virtually unknown. As part of an effort to develop a murine model for infections with these agents, Balb/c mice were inoculated intramuscularly in the left hindlimb with 10 to 10(6) plaque forming units (PFU) of HVS1. After observation for clinical signs of infection for 21 days, mice were killed and specimens collected for serology and histopathology. Mice receiving 510(3) PFU of HVS1 exhibited severe, pruritic, ulcerative skin lesions near the site of inoculation and developed unilateral or bilateral hindlimb paralysis with severe muscle atrophy. Histological lesions were characterized by a necrotizing dermatitis and folliculitis. Spinal cord lesions consisted of a non-suppurative myelitis affecting primarily the ipsilateral dorsal horn of the thoracolumbar spinal cord with occasional extension to ventral and contralateral spinal cord regions. Immunohistochemical labelling confirmed the presence of viral antigen within the lesions, and anti-HVS1 IgG concentrations were related to the occurrence of disease. HVS1 infection in some mice extended from the ipsilateral dorsal horn and funiculus into the ventral and contralateral grey and white matter, resulting in bilateral hindlimb paralysis. Thoracolumbar spinal cord lesions resolved without continued spread of the virus to cranial nervous system structures, i.e., cervical spinal cord and brain.

Molecular evidence for distinct genotypes of monkey B virus (herpesvirus simiae) which are related to the macaque host species

Although monkey B virus (herpesvirus simiae; BV) is common in all macaque species, fatal human infections appear to be associated with exposure to rhesus macaques (Macaca mulatta), suggesting that BV isolates from rhesus monkeys may be more lethal to nonmacaques than are BV strains indigenous to other macaque species. To determine if significant differences that would support this supposition exist among BV isolates, we compared multiple BV strains isolated from rhesus, cynomolgus, pigtail, and Japanese macaques. Antigenic analyses indicated that while the isolates were very closely related to one another, there are some antigenic determinants that are specific to BV isolates from different macaque species. Restriction enzyme digest patterns of viral DNA revealed marked similarities between rhesus and Japanese macaque isolates, while pigtail and cynomolgus macaque isolates had distinctive cleavage patterns. To further compare genetic diversity among BV isolates, DNA sequences from two regions of the viral genome containing genes that are conserved (UL27 and US6) and variable (US4 and US5) among primate alphaherpesviruses, as well as from two noncoding intergenic regions, were determined. From these sequence data and a phylogenetic analysis of them it was evident that while all isolates were closely related strains of BV, there were three distinct genotypes. The three BV genotypes were directly related to the macaque species of origin and were composed of (i) isolates from rhesus and Japanese macaques, (ii) cynomolgus monkey isolates, and (iii) isolates from pigtail macaques. This study demonstrates the existence of different BV genotypes which are related to the macaque host species and thus provides a molecular basis for the possible existence of BV isolates which vary in their levels of pathogenicity for nonmacaque species.

Threat to Humans from Virus Infections of Non-human Primates

Several hundred distinct non human primate species are recognised, and they are likely to harbour a similar range of viruses to humans. Simians such as cynomolgus and rhesus macaques, African green monkeys, and marmosets are widely used for biomedical research, but despite this extensive close contact very few simian viruses have been shown to pose a threat of infection or illness to humans. Herpesvirus Simiae is the best recognised zoonotic hazard of simians. It is an alphaherpes virus of Asiatic macaques, which causes a mild or subclinical primary infection followed by latency in its natural host. It can be acquired by humans following a bite and causes an ascending meningoencephalitis. Less than 40 human cases have been described and the mortality rate in untreated human infections is 70%. The infection is treatable with acyclovir and extensive guidelines for managing simians and potential exposures have been developed. Ebola virus and Marburg virus have caused epizootics in cynomolgus macaques and vervet monkeys respectively, which have resulted in human infection and fatalities. However, non human primates are unlikely to be their natural host. More recently simian immunodeficiency virus and simian foamy virus have infected researchers, but infection has not been linked to illness. Simian viruses also pose a direct threat to humans through the use of primary monkey tissue cultures in laboratory work and vaccine manufacture, indeed a significant exposure of the human population occurred when cells contaminated with SV40 a polyomavirus of rhesus monkeys were used for polio vaccine production. New medical interventions such as xenotransplantation using primate organs pose a potential risk which requires careful assessment. Copyright 1997 by John Wiley & Sons Ltd.

Fatal disseminated cercopithecine herpesvirus 1 (herpes B infection in cynomolgus monkeys (Macaca fascicularis)

Two adult female cynomolgus monkeys (Macaca fascicularis) that had been housed together for 4 months died within 2 weeks of each other after brief illnesses. Monkey No. 1 presented with collapse, watery stool, and hypothermia and died overnight. Monkey No. 2 presented with dyspnea, nasal discharge, leukopenia, and hypoproteinemia and was euthanized after 2 days. Both animals had peritoneal effusions, massive necrosis of pharyngeal, esophageal, and gastric mucosa, and multifocal hepatic and pancreatic necrosis. Monkey No. 2 also had lingual ulcers and locally extensive necrosis of spleen, adrenal glands, and lymph nodes. Large numbers of eosinophilic intranuclear inclusion bodies were present in epithelial and syncytial cells adjoining the necrotic foci in Monkey No. 2 but were absent in Monkey No. 1. Monkey No. 1 seroconverted to cercopithecine herpesvirus 1 (CHV-1, commonly known as herpes B) in the month before death. CHV-1 was isolated from a sample of stomach from Monkey No. 2, and electron microscopy of liver from this animal demonstrated herpesvirus particles within hepatocytes. Both animals were seropositive for simian type D retrovirus, and the virus was cultured from the liver of Monkey No. 2. A diagnosis of disseminated CHV-1 infection was made, possibly occurring secondary to immunosuppression due to infection with simian type D retrovirus. Although a high percentage of cynomolgus monkeys are apparently infected with CHV-1, disseminated disease is rare. Because infection with CHV-1 in humans is associated with a high fatality rate, familiarity with the lesions of disseminated infection with this virus is important.

Detection and differentiation of primate alpha-herpesviruses by PCR

A rapid method for detection and differentiation of 5 primate alpha-herpesviruses (human herpes simplex virus types 1 and 2 [HSV1, HSV2], green monkey simian agent 8, baboon herpesvirus 2 [HVP2], and macaque B virus [BV]) was developed utilizing the polymerase chain reaction (PCR). PCR primers were located in conserved regions of the gene encoding the glycoprotein B, which flanks an intervening region that is highly divergent among the 5 viruses. Amplified PCR products from the 5 viruses were readily differentiated by their unique restriction enzyme digestion patterns. No variation in digestion patterns was noted among strains of HSV1, HSV2, or HVP2. One clinical isolate of BV exhibited variation in a single restriction site, but its overall restriction pattern remained typical of BV. This method (PCR/RFLP) allowed the presence of herpesvirus DNA in clinical swabs from primates to be readily detected and the virus unambiguously identified.

Herpesvirus papio 2, an SA8-like alpha-herpesvirus of baboons

Several SA8 isolates obtained from baboons were compared to the prototype SA8 herpesvirus of African green monkeys. SDS-PAGE and restriction enzyme analyses revealed definite differences between green monkey and baboon isolates. DNA and amino acid sequences of the gB, gD and gJ glycoprotein genes exhibited substantial differences in variable regions. For the gB and gD, the amount of amino acid substitutions between SA8 and the baboon viruses was comparable to levels observed between analogous genes of SA8 & B virus or HSV1 & HSV2. Although a high degree of antigenic cross-reactivity was apparent, virus-specific antigenic determinants were also readily detected. Phylogenetic analyses supported separation of the baboon isolates and SA8 as distinct viruses. Taken together these results suggest that although closely related to SA8, the baboon viruses represent a distinct simian alpha-herpesvirus which we propose be designated Herpesvirus papio 2.

Glycoprotein B of bovine herpesvirus type 4: its phylogenetic relationship to gB equivalents of the herpesviruses

In order to estimate the phylogenetic relationship of BHV-4 among the herpesviruses, we have cloned and sequenced its glycoprotein B (gB). The 2.6 kb open reading frame codes for a 874 amino acid long protein. The comparison of its deduced amino acid sequence with those of its counterparts in 19 distinct herpesviruses groups BHV-4 into the gamma-herpesvirinae. The calculation of an evolutionary tree emphasized that BHV-4 is more closely related to herpesvirus saimiri (HVS) than to Epstein-Barr virus (EBV). However, in contrast to EBV and HVS, the gB of BHV-4 contains a putative protease cleavage site and 20 potential N-glycosylation sites. The alignment of the amino acid sequences revealed that 10 cysteine and 7 proline residues, as well as the motifs SPF and GQLG, were completely conserved among the 20 investigated gBs.

Simian agent 8 (SA8): morphogenesis and ultrastructure

Electron microscopic studies on the morphogenesis of SA8 in primary rabbit brain cell cultures revealed that in early stages of infection, envelopment of nucleocapsids commonly occurred at the inner nuclear membrane. From the perinuclear space, enveloped virus particles moved into the cisternae of the endoplasmic reticulum (ER) in which they were transported, through the cytoplasm, to the plasma membrane. Alternatively, de-envelopment at the outer nuclear membrane and egress of naked capsids into the cytoplasm were frequently observed. Non-enveloped cytoplasmic capsids were also a consistent feature of cells in late stages of infection, when nuclear membranes became ruptured. In these cases, the envelopment of naked capsids took place by budding either into the cisternae of ER or into cytoplasmic vesicles and vacuoles, in which transport to and exocytosis at the cell membrane occurred. Budding at the cell membrane was rarely found. Capsids of enveloped particles were asymmetrically surrounded by an electron-dense layer which may be identical to the tegument. Because only enveloped cytoplasmic and free virions were tegumented we suggested that the tegumentation must occur during the envelopment (budding) into cytoplasmic vesicles and at the plasma membrane.

Gene mapping and sequence analysis of the unique short region of the simian herpesvirus SA 8 genome

A 10.5 kbp BamHI restriction fragment representing most of the unique short (Us) region of the genome of the simian alpha-herpesvirus SA8 was identified and cloned. Partial sequencing of this DNA fragment identified regions of sequence homology with eight open reading frames (ORFs) of HSV1 and/or HSV2. Sequence and size analysis of subcloned fragments of the SA8 Us region and comparison with homologous HSV Us sequences determined that the number, order, size, and orientation of SA8 Us ORFs are comparable to those of HSV. Based on the location of transcriptional control elements, transcription of SA8 Us genes appears to be organized into 3' co-terminal mRNA sets as in HSV, although the grouping of the gene sets is different. The SA8 US4 (gG) ORF is more similar to that of HSV2 than HSV1, both in size and predicted amino acid sequence. Complete sequences were determined for five SA8 genes which represent homologs of the HSV gD, gE, gI, US5, and US9 genes. The predicted polypeptides encoded by SA8 are similar to the corresponding HSV polypeptides. All SA8 Us genes were more closely related to those of HSV than to related gene homologs of other mammalian alpha-herpesviruses.

Polymerase chain reaction for detection of herpesvirus simiae (B virus) in clinical specimens

A polymerase chain reaction (PCR) was designed which is specific to Macaca fascicularis (cynomolgus monkey) isolates of B virus. The PCR primers produced the expected 188 basepair product from the Cyno 2 strain and seven other cynomolgus monkey isolates of B virus. Oligomer hybridization with a 31-mer oligonucleotide was used to confirm the origin of this product. The PCR failed to amplify DNA of Epstein-Barr virus, cytomegalovirus, varicella-zoster virus, and other alphaherpesviruses (herpes simplex virus types 1 and 2, four SA 8 isolates and three rhesus isolates of B virus). PCR testing of swabs obtained from four orally-infected cynomolgus monkeys confirmed the presence of B virus DNA in samples previously shown to be positive by culture. In addition, PCR detected B virus in several swabs from infected monkeys that were culture negative. Total DNA extracts from the trigeminal and sacral ganglia of these animals were tested by nested PCR and B virus DNA was detected in the trigeminal ganglia of 3 of the 4 orally-infected cynomolgus monkeys. Nested PCR did not detect B virus DNA in total DNA extracts obtained from the brains of the four monkeys.

Sequence analysis of herpes simplex virus gB gene homologs of two platyrrhine monkey alpha-herpesviruses

Homologs of the herpes simplex virus gB gene were identified in two alpha-herpesviruses of platyrrhine monkeys, Herpesvirus saimiri 1 (HVS 1) and H. ateles 1 (HVA 1). These genes were cloned and sequenced in their entirety. Analysis of the predicted amino acid sequences indicated that the gB glycoproteins of these two viruses are of similar size, have 10 Cys residues and 5 potential N-linked glycosylation sites which align exactly with those in other primate alpha-herpesvirus gB polypeptides, and have a similar distribution of predicted secondary structural features, all of which indicate a conserved structure of the gB polypeptide. Alignment of these two gB sequences with those of four other primate alpha-herpesviruses (SA 8, B virus, HSV 1 and HSV 2) revealed localized regions of extensive sequence divergence as well as highly conserved regions. On comparison of the six primate virus gB sequences, the gBs of the two platyrrhine monkey viruses form a subgroup separate from that of the four catarrhine virus gBs. The degree of relatedness of the HVA 1 and HVS 1 gB sequences to each other was equivalent to the degree of relatedness between the human and the cercopithecine monkey virus gB sequences.

Monoclonal antibodies for the identification of herpesvirus simiae (B virus)

To differentiate between B virus and HSV isolates from monkeys and man monoclonal antibodies (mabs) were produced to herpesvirus simiae (B virus) and herpes simplex type 1 and 2 (HSV-1 and HSV-2). Mabs were tested by indirect immunofluorescence (IFAT) for reactivity against herpesviruses from Asiatic monkeys (B virus), African monkeys (SA 8 virus), and man (HSV-1, HSV-2, varicella-zoster virus, cytomegalovirus, and Epstein-Barr virus). Mabs could be divided into groups A-E displaying specific reactivity for B virus (A); reactivity with both B virus and SA 8 but not HSV (B); reactivity with B virus, SA 8 virus and HSV strains (C); specific reactivity with HSV-1 (D); and specific reactivity with HSV-2 (E). Two of the B virus specific mabs were able to differentiate between cynomolgus and rhesus strains of B virus. None of the mabs reacted with human varicella-zoster virus, cytomegalovirus, or Epstein-Barr virus. A panel of mabs for the unequivocal identification of B virus isolates from monkey or man is proposed.

The simian herpesvirus SA8 homologue of the herpes simplex virus gB gene: mapping, sequencing, and comparison to the HSV gB

The genomic location and DNA sequence of the simian herpesvirus SA8 gene encoding a homologue of the HSV1 gB glycoprotein was determined. Using a cloned gB gene of herpes simplex virus type 1 (HSV1) as probe in Southern blot hybridizations, the SA8 gB gene was localized to a 10-kbp KpnI fragment mapping in the unique long part of the genome. A 2.8 kbp, 68.4% GC segment of this fragment was sequenced. It contained a 2649 nucleotide ORF possibly encoding a 98.4 kDa polypeptide. The predicted amino acid sequence of the SA8 gB polypeptide is 78.4% and 78.9% identical to the sequence of the HSV1 and HSV2 gBs, respectively, and was 88.4% similar or identical to both HSV gB sequences. Structural characteristics predicted for the SA8 gB polypeptide were very similar to those of HSV1 gB. These included a hydrophobic signal sequence of 29 amino acids, conservation of all 10 cysteine residues and 5 of 6 potential N-linked glycosylation sites present in the HSV1 gB, a triple hydrophobic transmembrane domain, and a highly charged cytoplasmic tail region. Both hierarchical cluster analysis and phylogenetic analysis of sequences for gB polypeptides of 12 different herpesviruses demonstrated that the gB glycoprotein of SA8 is most closely related to the HSV gB glycoproteins. Comparison of these closely related gB sequences identified four regions in which non-conservative amino acid substitutions were clustered. Localized regions of the gB polypeptide were identified which are likely to be associated with the conserved structure/function of the polypeptide.

Simian agent 8--a herpes simplex-like monkey virus

This review summarizes the most recent information on Simian Agent 8, a herpes simplex-like monkey virus. The agent has a broad host range and--besides the classical morphogenesis (budding at the internal nuclear membrane)--the virus gets enveloped at all cytoplasmic membranes including the plasma membrane; strikingly it carries a rather prominent tegument. Regarding its sequence arrangement SA8 can be grouped to the E-type genomes. It has a G + C-content of 69% and a total DNA-homology with HSV-1 of 31%. The glycoproteins gC and gE are largely type-specific; whereas gB and gD as well as ICP35, ICP8 and the major capsid protein represent well conserved proteins of the simplexviruses. The type-common epitopes of gB and gD induce cross-reacting antibodies, which are even involved in cross-neutralization.

Relatedness of glycoproteins expressed on the surface of simian herpes-virus virions and infected cells to specific HSV glycoproteins

The antigenic relatedness of the surface glycoprotein antigens of six herpesviruses indigenous to human and nonhuman primates was examined. Binding of anti-viral sera to viral antigens expressed on the surface of infected cells demonstrated that the surface antigens of herpes simplex virus type 1 (HSV 1), HSV 2, simian agent 8 (SA8), and Herpesvirus simiae (B virus) exhibit extensive cross-reactivity. Surface antigens of two viruses isolated from South American primates, H. saimiri 1 (HVS 1) and H. ateles 1 (HVA 1), were comparatively more virus-specific in their antigenic reactivity. Endpoint neutralization tests performed in the presence and absence of complement confirmed these results. Immunoprecipitation of viral proteins was used to identify those representing cross-reactive surface antigens. A glycoprotein of approximately 110,000-125,000 Daltons (110-125 k) was immunoprecipitated from cells infected with each of the six primate herpesvirus by antisera to each of the viruses. Using monospecific antisera, these glycoproteins were shown to be antigenically related to the gB glycoproteins of HSV. Although these glycoproteins were antigenically conserved among all six viruses, antibodies to the gB glycoproteins did not cross-neutralize heterologous viruses. A glycoprotein of approximately 60-70 k was precipitated from HSV 1, HSV 2, SA8, and B virus infected cells by antisera to each of these four viruses. These SA8 and B virus glycoproteins were shown to be antigenically related to the gD glycoproteins of HSV 1 and HSV 2 and to be involved in cross-neutralization among these viruses. Antisera to HVS 1 and HVA 1 did not recognize these gD glycoproteins nor was a glycoprotein of similar molecular weight precipitable from HVS 1 or HVA 1 infected cells by antisera to the other four viruses. Southern blot hybridizations using probes for HSV glycoprotein genes confirmed the conservation of the gB glycoproteins among all the simian viruses and of the gD gene in SA8 and B virus. A glycoprotein of approximately 75-80 k was, however, precipitated from HVS 1 and HVA 1 infected cells by antisera to either of these two viruses. In addition, at least one glycoprotein which appeared to be predominantly virus-specific in its reactivity was identified for five of the viruses.