Five new or recently discovered (GBV-A) virus species are indigenous to New World monkeys and may constitute a separate genus of the Flaviviridae

Human Pegivirus Type 1: A Common Human Virus That Is Beneficial in Immune-Mediated Disease?

Two groups identified a novel human flavivirus in the mid-1990s. One group named the virus hepatitis G virus (HGV) and the other named it GB Virus type C (GBV-C). Sequence analyses found these two isolates to be the same virus, and subsequent studies found that the virus does not cause hepatitis despite sharing genome organization with hepatitis C virus. Although HGV/GBV-C infection is common and may cause persistent infection in humans, the virus does not appear to directly cause any other known disease state. Thus, the virus was renamed “human pegivirus 1” (HPgV-1) for “persistent G” virus. HPgV-1 is found primarily in lymphocytes and not hepatocytes, and several studies found HPgV-1 infection associated with prolonged survival in people living with HIV. Co-infection of human lymphocytes with HPgV-1 and HIV inhibits HIV replication. Although three viral proteins directly inhibit HIV replication in vitro, the major effects of HPgV-1 leading to reduced HIV-related mortality appear to result from a global reduction in immune activation. HPgV-1 specifically interferes with T cell receptor signaling (TCR) by reducing proximal activation of the lymphocyte specific Src kinase LCK. Although TCR signaling is reduced, T cell activation is not abolished and with sufficient stimulus, T cell functions are enabled. Consequently, HPgV-1 is not associated with immune suppression. The HPgV-1 immunomodulatory effects are associated with beneficial outcomes in other diseases including Ebola virus infection and possibly graft-versus-host-disease following stem cell transplantation. Better understanding of HPgV-1 immune escape and mechanisms of inflammation may identify novel therapies for immune-based diseases.

Clinical and molecular aspects of human pegiviruses in the interaction host and infectious agent

Background

Human pegivirus 1 (HPgV-1) is a Positive-sense single-stranded RNA (+ ssRNA) virus, discovered in 1995 as a Flaviviridae member, and the closest human virus linked to HCV. In comparison to HCV, HPgV-1 seems to be lymphotropic and connected to the viral group that infects T and B lymphocytes. HPgV-1 infection is not persuasively correlated to any known human disease; nevertheless, multiple studies have reported a connection between chronic HPgV-1 infection and improved survival in HPgV-1/HIV co-infected patients with a delayed and favorable impact on HIV infection development. While the process has not been thoroughly clarified, different mechanisms for these observations have been proposed. HPgV-1 is categorized into seven genotypes and various subtypes. Infection with HPgV-1 is relatively common globally. It can be transferred parenterally, sexually, and through vertical ways, and thereby its co-infection with HIV and HCV is common. In most cases, the clearance of HPgV-1 from the body can be achieved by developing E2 antibodies after infection.

Main body

In this review, we thoroughly discuss the current knowledge and recent advances in understanding distinct epidemiological, molecular, and clinical aspects of HPgV-1.

Conclusion

Due to the unique characteristics of the HPgV-1, so advanced research on HPgV-1, particularly in light of HIV co-infection and other diseases, should be conducted to explore the essential mechanisms of HIV clearance and other viruses and thereby suggest novel strategies for viral therapy in the future.

Review of human pegivirus: Prevalence, transmission, pathogenesis, and clinical implication

Human pegivirus (HPgV-1), previously known as GB virus C (GBV-C) or hepatitis G virus (HGV), is a single-stranded positive RNA virus belonging to the genus Pegivirus of the Flaviviridae family. It is transmitted by percutaneous injuries (PIs), contaminated blood and/or blood products, sexual contact, and vertical mother-to-child transmission. It is widely prevalent in general population, especially in high-risk groups. HPgV-1 viremia is typically cleared within the first 1–2 years of infection in most healthy individuals, but may persist for longer periods of time in immunocompromised individuals and/or those co-infected by other viruses. A large body of evidences indicate that HPgV-1 persistent infection has a beneficial clinical effect on many infectious diseases, such as acquired immunodeficiency syndrome (AIDS) and hepatitis C. The beneficial effects seem to be related to a significant reduction of immune activation, and/or the inhabitation of co-infected viruses (e.g. HIV-1). HPgV-1 has a broad cellular tropism for lymphoid and myeloid cells, and preferentially replicates in bone marrow and spleen without cytopathic effect, implying a therapeutic potential. The paper aims to summarize the natural history, prevalence and distribution characteristics, and pathogenesis of HPgV-1, and discuss its association with other human viral diseases, and potential use in therapy as a biovaccine or viral vector.

An Introduction to the Callithrix Genus and Overview of Recent Advances in Marmoset Research

We provide here a current overview of marmoset (Callithrix) evolution, hybridization, species biology, basic/biomedical research, and conservation initiatives. Composed of 2 subgroups, the aurita group (C aurita and C flaviceps) and the jacchus group (C geoffroyi, C jacchus, C kuhlii, and C penicillata), this relatively young primate radiation is endemic to the Brazilian Cerrado, Caatinga, and Atlantic Forest biomes. Significant impacts on Callithrix within these biomes resulting from anthropogenic activity include (1) population declines, particularly for the aurita group; (2) widespread geographic displacement, biological invasions, and range expansions of C jacchus and C penicillata; (3) anthropogenic hybridization; and (4) epizootic Yellow Fever and Zika viral outbreaks. A number of Brazilian legal and conservation initiatives are now in place to protect the threatened aurita group and increase research about them. Due to their small size and rapid life history, marmosets are prized biomedical models. As a result, there are increasingly sophisticated genomic Callithrix resources available and burgeoning marmoset functional, immuno-, and epigenomic research. In both the laboratory and the wild, marmosets have given us insight into cognition, social group dynamics, human disease, and pregnancy. Callithrix jacchus and C penicillata are emerging neotropical primate models for arbovirus disease, including Dengue and Zika. Wild marmoset populations are helping us understand sylvatic transmission and human spillover of Zika and Yellow Fever viruses. All of these factors are positioning marmosets as preeminent models to facilitate understanding of facets of evolution, hybridization, conservation, human disease, and emerging infectious diseases.

Discovery of a Novel Simian Pegivirus in Common Marmosets (Callithrix jacchus) with Lymphocytic Enterocolitis

From 2010 to 2015, 73 common marmosets (Callithrix jacchus) housed at the Wisconsin National Primate Research Center (WNPRC) were diagnosed postmortem with lymphocytic enterocolitis. We used unbiased deep-sequencing to screen the blood of deceased enterocolitis-positive marmosets for viruses. In five out of eight common marmosets with lymphocytic enterocolitis, we discovered a novel pegivirus not present in ten matched, clinically normal controls. The novel virus, which we named Southwest bike trail virus (SOBV), is most closely related (68% nucleotide identity) to a strain of simian pegivirus A isolated from a three-striped night monkey (Aotus trivirgatus). We screened 146 living WNPRC common marmosets for SOBV, finding an overall prevalence of 34% (50/146). Over four years, 85 of these 146 animals died or were euthanized. Histological examination revealed 27 SOBV-positive marmosets from this cohort had lymphocytic enterocolitis, compared to 42 SOBV-negative marmosets, indicating no association between SOBV and disease in this cohort (p = 0.0798). We also detected SOBV in two of 33 (6%) clinically normal marmosets screened during transfer from the New England Primate Research Center, suggesting SOBV could be exerting confounding influences on comparisons of common marmoset studies from multiple colonies.

Novel hepaci- and pegi-like viruses in native Australian wildlife and non-human primates

The Flaviviridae family of positive-sense RNA viruses contains important pathogens of humans and other animals, including Zika virus, dengue virus, and hepatitis C virus. The Flaviviridae are currently divided into four genera-Hepacivirus, Pegivirus, Pestivirus, and Flavivirus-each with a diverse host range. Members of the genus Hepacivirus are associated with an array of animal species, including humans, non-human primates, other mammalian species, as well as birds and fish, while the closely related pegiviruses have been identified in a variety of mammalian taxa, also including humans. Using a combination of total RNA and whole-genome sequencing we identified four novel hepaci-like viruses and one novel variant of a known hepacivirus in five species of Australian wildlife. The hosts infected comprised native Australian marsupials and birds, as well as a native gecko (Gehyra lauta). From these data we identified a distinct marsupial clade of hepaci-like viruses that also included an engorged Ixodes holocyclus tick collected while feeding on Australian long-nosed bandicoots (Perameles nasuta). Distinct lineages of hepaci-like viruses associated with geckos and birds were also identified. By mining the SRA database we similarly identified three new hepaci-like viruses from avian and primate hosts, as well as two novel pegi-like viruses associated with primates. The phylogenetic history of the hepaci- and pegi-like viruses as a whole, combined with co-phylogenetic analysis, provided support for virus-host co-divergence over the course of vertebrate evolution, although with frequent cross-species virus transmission. Overall, our work highlights the diversity of the Hepacivirus and Pegivirus genera as well as the uncertain phylogenetic distinction between.

PCR-based screening and phylogenetic analysis of rat pegivirus (RPgV) carried by rodents in China

Rodent-borne pegiviruses were initially identified in serum samples from desert wood-rats in 2013, and subsequently in serum samples from commensal rats in 2014. However, the prevalence and phylogenetic characteristics of rodent pegiviruses in China are poorly understood. In this study, we screened serum samples collected from wild rats in southern China between 2015 and 2016 for the presence of rat pegivirus (RPgV) by PCR. Among the 314 serum samples from murine rodents (Rattus norvegicus, Rattus tanezumi, and Rattus losea) and house shrews (Suncus murinus), 21.66% (68/314) tested positive for RPgV. Out of these, 23.81% (62/219) of samples from R. norvegicus tested positive, which was significantly higher than that for the other species: 7.69% (1/13), 5.88% (2/34), and 6.25% (3/48) for R. tanezumi, R. losea, and S. murinus, respectively (χ²=18.91, P<0.001). Phylogenetic analysis revealed clustering of viral sequences in the main rodent clade. Analysis of the 3 near-full-length genome sequences of RPgV obtained in this study showed that these viruses exhibited mean nucleic acid and amino acid identities of 94.1% and 98.5% with Chinese RPgV strains, and 90.3 and 97.1% with an RPgV strain from the USA, respectively. This study provides novel insights into the geographic distribution of rodent pegiviruses in China, and identifies potential animal hosts for future studies of these pegiviruses.

Equine pegiviruses cause persistent infection of bone marrow and are not associated with hepatitis

Pegiviruses frequently cause persistent infection (as defined by >6 months), but unlike most other Flaviviridae members, no apparent clinical disease. Human pegivirus (HPgV, previously GBV-C) is detectable in 1–4% of healthy individuals and another 5–13% are seropositive. Some evidence for infection of bone marrow and spleen exists. Equine pegivirus 1 (EPgV-1) is not linked to disease, whereas another pegivirus, Theiler’s disease-associated virus (TDAV), was identified in an outbreak of acute serum hepatitis (Theiler’s disease) in horses. Although no subsequent reports link TDAV to disease, any association with hepatitis has not been formally examined. Here, we characterized EPgV-1 and TDAV tropism, sequence diversity, persistence and association with liver disease in horses. Among more than 20 tissue types, we consistently detected high viral loads only in serum, bone marrow and spleen, and viral RNA replication was consistently identified in bone marrow. PBMCs and lymph nodes, but not liver, were sporadically positive. To exclude potential effects of co-infecting agents in experimental infections, we constructed full-length consensus cDNA clones; this was enabled by determination of the complete viral genomes, including a novel TDAV 3’ terminus. Clone derived RNA transcripts were used for direct intrasplenic inoculation of healthy horses. This led to productive infection detectable from week 2–3 and persisting beyond the 28 weeks of study. We did not observe any clinical signs of illness or elevation of circulating liver enzymes. The polyprotein consensus sequences did not change, suggesting that both clones were fully functional. To our knowledge, this is the first successful extrahepatic viral RNA launch and the first robust reverse genetics system for a pegivirus. In conclusion, equine pegiviruses are bone marrow tropic, cause persistent infection in horses, and are not associated with hepatitis. Based on these findings, it may be appropriate to rename the group of TDAV and related viruses as EPgV-2.

Transmissible hepatitis in horses (Theiler’s disease) has been known for 100 years without knowledge of causative infectious agents. Recently, two novel equine pegiviruses (EPgV) were discovered. Whereas EPgV-1 was not associated to disease, the other was identified in an outbreak of acute serum hepatitis and therefore named Theiler’s disease-associated virus (TDAV). This finding was surprising since human and monkey pegiviruses typically cause long-term infection without associated clinical disease. Whereas no subsequent reports link TDAV to disease, the original association to hepatitis has not been formally examined. Here, we studied EPgV-1 and TDAV and found that their natural history of infection in horses were remarkably similar. Examination of various tissues identified the bone marrow as the primary site of replication for both viruses with no evidence of replication in the liver. To exclude potential effects of other infectious agents, we developed molecular full-length clones for EPgV-1 and TDAV and were able to initiate infection in horses using derived synthetic viral genetic material. This demonstrated long-term infection, but no association with hepatitis. These findings call into question the connection between TDAV, liver infection, and hepatitis in horses.

Animal Models Used in Hepatitis C Virus Research

The narrow range of species permissive to infection by hepatitis C virus (HCV) presents a unique challenge to the development of useful animal models for studying HCV, as well as host immune responses and development of chronic infection and disease. Following earlier studies in chimpanzees, several unique approaches have been pursued to develop useful animal models for research while avoiding the important ethical concerns and costs inherent in research with chimpanzees. Genetically related hepatotropic viruses that infect animals are being used as surrogates for HCV in research studies; chimeras of these surrogate viruses harboring specific regions of the HCV genome are being developed to improve their utility for vaccine testing. Concurrently, genetically humanized mice are being developed and continually advanced using human factors known to be involved in virus entry and replication. Further, xenotransplantation of human hepatocytes into mice allows for the direct study of HCV infection in human liver tissue in a small animal model. The current advances in each of these approaches are discussed in the present review.

First description of Theiler's disease-associated virus infection and epidemiological investigation of equine pegivirus and equine hepacivirus coinfection in Brazil

Recent advances in the study of equine pegivirus (EPgV), Theiler's disease-associated virus (TDAV) and equine hepacivirus (EqHV) highlight their importance to veterinary and human health. To gain some insight into virus distribution, possible risk factors, presence of liver damage and genetic variability of these viruses in Brazil, we performed a cross-sectional study of EPgV and TDAV infections using a simultaneous detection assay, and assessed EqHV coinfection in different horse cohorts. Of the 500 serum samples screened, TDAV, EPgV and EPgV-EqHV were present in 1.6%, 14.2% and 18.3%, respectively. EPgV-positive horses were present in four Brazilian states: Espírito Santo, Mato Grosso do Sul, Minas Gerais and Rio de Janeiro. Serum biochemical alterations were present in 40.4% of EPgV-infected horses, two of them presenting current liver injury. Chance of infection was 2.7 times higher in horses ≤5 years old (p = 0.0008) and 4.9 times higher in horses raised under intensive production systems (p = 0.0009). EPgV-EqHV coinfection was 75% less likely in horses older than 5 years comparatively to those with ≤5 years old (p = 0.047). TDAV-positive animals were detected in different horse categories without biochemical alteration. Nucleotide sequences were highly conserved among isolates from this study and previous field and commercial product isolates (≥88% identity). Tree topology revealed the formation of two clades (pp = 1) for both EPgV and TDAV NS3 partial sequences. In conclusion, the widespread presence of EPgV-RNA suggests an enzootic infection with subclinical viremia in Brazil. Horse management can influence virus spread. This first report of TDAV-infected horses outside the USA reveals the existence of subclinical viremic horses in distant geographical regions. EPgV and TDAV have similar circulating isolates worldwide. These findings contribute to global efforts to understand the epidemiology and pathogenesis of these equine viruses.

Identification and genetic characterization of equine Pegivirus in China

In 2013, two new viruses, equine pegivirus (EPgV) and Theiler's disease-associated virus (TDAV), both belonging to the genus Pegivirus within the family Flaviviridae, were identified. To investigate the geographical distribution and genetic diversity of these two viruses in China, we screened EPgV and TDAV infection in imported race horses and Chinese work horses by using reverse-transcription polymerase chain reaction (RT-PCR). EPgV was detected in 10.8 % (8/74) of the total horses tested, with a prevalence of 5.8 and 22.7 % in the race horses and work horses, respectively. No TDAV infection was found. A near full-length genome sequence of EPgV was obtained that showed an identity of 89.5-90.6 % at the nucleotide level and 98.1-98.3 % at the amino acid level with an American strain, C0035, and another Chinese strain, LW/216, respectively. Phylogenetic analysis showed two different clusters of the sequences from the race horses and work horses, indicating a difference in virus origin. Our results demonstrated a higher positive rate of EPgV in the Chinese work horses than in the imported race horses, a moderate genetic diversity of EPgV strains worldwide and possibly no liver pathogenesis for EPgV infection.

Pegivirus avoids immune recognition but does not attenuate acute-phase disease in a macaque model of HIV infection

Human pegivirus (HPgV) protects HIV+ people from HIV-associated disease, but the mechanism of this protective effect remains poorly understood. We sequentially infected cynomolgus macaques with simian pegivirus (SPgV) and simian immunodeficiency virus (SIV) to model HIV+HPgV co-infection. SPgV had no effect on acute-phase SIV pathogenesis-as measured by SIV viral load, CD4+ T cell destruction, immune activation, or adaptive immune responses-suggesting that HPgV's protective effect is exerted primarily during the chronic phase of HIV infection. We also examined the immune response to SPgV in unprecedented detail, and found that this virus elicits virtually no activation of the immune system despite persistently high titers in the blood over long periods of time. Overall, this study expands our understanding of the pegiviruses-an understudied group of viruses with a high prevalence in the global human population-and suggests that the protective effect observed in HIV+HPgV co-infected people occurs primarily during the chronic phase of HIV infection.

Proposed update to the taxonomy of the genera Hepacivirus and Pegivirus within the Flaviviridae family

Proposals are described for the assignment of recently reported viruses, infecting rodents, bats and other mammalian species, to new species within the Hepacivirus and Pegivirus genera (family Flaviviridae). Assignments into 14 Hepacivirus species (Hepacivirus A–N) and 11 Pegivirus species (Pegivirus A–K) are based on phylogenetic relationships and sequence distances between conserved regions extracted from complete coding sequences for members of each proposed taxon. We propose that the species Hepatitis C virus is renamed Hepacivirus C in order to acknowledge its unique historical position and so as to minimize confusion. Despite the newly documented genetic diversity of hepaciviruses and pegiviruses, members of these genera remain phylogenetically distinct, and differ in hepatotropism and the possession of a basic core protein; pegiviruses in general lack these features. However, other characteristics that were originally used to support their division into separate genera are no longer definitive; there is overlap between the two genera in the type of internal ribosomal entry site and the presence of miR-122 sites in the 5′ UTR, the predicted number of N-linked glycosylation sites in the envelope E1 and E2 proteins, the presence of poly U tracts in the 3′ UTR and the propensity of viruses to establish a persistent infection. While all classified hepaciviruses and pegiviruses have mammalian hosts, the recent description of a hepaci-/pegi-like virus from a shark and the likely existence of further homologues in other non-mammalian species indicate that further species or genera remain to be defined in the future.

Arteriviruses, Pegiviruses, and Lentiviruses Are Common among Wild African Monkeys

Nonhuman primates (NHPs) are a historically important source of zoonotic viruses and are a gold-standard model for research on many human pathogens. However, with the exception of simian immunodeficiency virus (SIV) (family Retroviridae), the blood-borne viruses harbored by these animals in the wild remain incompletely characterized. Here, we report the discovery and characterization of two novel simian pegiviruses (family Flaviviridae) and two novel simian arteriviruses (family Arteriviridae) in wild African green monkeys from Zambia (malbroucks [Chlorocebus cynosuros]) and South Africa (vervet monkeys [Chlorocebus pygerythrus]). We examine several aspects of infection, including viral load, genetic diversity, evolution, and geographic distribution, as well as host factors such as age, sex, and plasma cytokines. In combination with previous efforts to characterize blood-borne RNA viruses in wild primates across sub-Saharan Africa, these discoveries demonstrate that in addition to SIV, simian pegiviruses and simian arteriviruses are widespread and prevalent among many African cercopithecoid (i.e., Old World) monkeys.

IMPORTANCE

Primates are an important source of viruses that infect humans and serve as an important laboratory model of human virus infection. Here, we discover two new viruses in African green monkeys from Zambia and South Africa. In combination with previous virus discovery efforts, this finding suggests that these virus types are widespread among African monkeys. Our analysis suggests that one of these virus types, the simian arteriviruses, may have the potential to jump between different primate species and cause disease. In contrast, the other virus type, the pegiviruses, are thought to reduce the disease caused by human immunodeficiency virus (HIV) in humans. However, we did not observe a similar protective effect in SIV-infected African monkeys coinfected with pegiviruses, possibly because SIV causes little to no disease in these hosts.

First report of equine Pegivirus in South America, Brazil

The human Pegivirus (HPgV, also known as GBV-C virus or hepatitis G virus) is a lymphotropic RNA-virus phylogenetically related to the Hepatitis C virus, which infects approximately 5% of the world's human population. Recently, two novel, presumably hepatotropic, pegiviruses, designated as equine Pegivirus (EPgV) and Theiler's Disease Associated Virus (TDAV), were discovered in horses with clinical and laboratory evidence of hepatic disease. To verify the occurrence of pegiviruses infection in horses from Pará State, northern Brazil, serum samples from 114 horses located in four cities (Acará, Belém, Dom Eliseu and Ananindeua) were submitted for the molecular analysis of EPgV by nested RT-PCR. The results of nucleotide sequencing and phylogenetic analysis of EPgV NS3 and NS5B genomic regions confirmed one positive sample among 114 tested samples (1/114; 0.8%). No evidence of TDAV infection was found, but despite the low prevalence and unknown clinical significance among the studied population, these results represent the first molecular detection of EPgV in horses in South America.

Modeling HCV disease in animals: virology, immunology and pathogenesis of HCV and GBV-B infections

Hepatitis C virus (HCV) infection has become a global public health burden costing billions of dollars in health care annually. Even with rapidly advancing scientific technologies this disease still poses a significant threat due to a lack of vaccines and affordable treatment options. The immune correlates of protection and predisposing factors toward chronicity remain major obstacles to development of HCV vaccines and immunotherapeutics due, at least in part, to lack of a tangible infection animal model. This review discusses the currently available animal models for HCV disease with a primary focus on GB virus B (GBV-B) infection of New World primates that recapitulates the dual Hepacivirus phenotypes of acute viral clearance and chronic pathologic disease. HCV and GBV-B are also closely phylogenetically related and advances in characterization of the immune systems of New World primates have already led to the use of this model for drug testing and vaccine trials. Herein, we discuss the benefits and caveats of the GBV-B infection model and discuss potential avenues for future development of novel vaccines and immunotherapies.

Discovery and characterization of distinct simian pegiviruses in three wild African Old World monkey species

Within the Flaviviridae, the recently designated genus Pegivirus has expanded greatly due to new discoveries in bats, horses, and rodents. Here we report the discovery and characterization of three simian pegiviruses (SPgV) that resemble human pegivirus (HPgV) and infect red colobus monkeys (Procolobus tephrosceles), red-tailed guenons (Cercopithecus ascanius) and an olive baboon (Papio anubis). We have designated these viruses SPgVkrc, SPgVkrtg and SPgVkbab, reflecting their host species' common names, which include reference to their location of origin in Kibale National Park, Uganda. SPgVkrc and SPgVkrtg were detected in 47% (28/60) of red colobus and 42% (5/12) red-tailed guenons, respectively, while SPgVkbab infection was observed in 1 of 23 olive baboons tested. Infections were not associated with any apparent disease, despite the generally high viral loads observed for each variant. These viruses were monophyletic and equally divergent from HPgV and pegiviruses previously identified in chimpanzees (SPgVcpz). Overall, the high degree of conservation of genetic features among the novel SPgVs, HPgV and SPgVcpz suggests conservation of function among these closely related viruses. Our study describes the first primate pegiviruses detected in Old World monkeys, expanding the known genetic diversity and host range of pegiviruses and providing insight into the natural history of this genus.

A novel hepacivirus with an unusually long and intrinsically disordered NS5A protein in a wild Old World primate

GB virus B (GBV-B; family Flaviviridae, genus Hepacivirus) has been studied in New World primates as a model for human hepatitis C virus infection, but the distribution of GBV-B and its relatives in nature has remained obscure. Here, we report the discovery of a novel and highly divergent GBV-B-like virus in an Old World monkey, the black-and-white colobus (Colobus guereza), in Uganda. The new virus, guereza hepacivirus (GHV), clusters phylogenetically with GBV-B and recently described hepaciviruses infecting African bats and North American rodents, and it shows evidence of ancient recombination with these other hepaciviruses. Direct sequencing of reverse-transcribed RNA from blood plasma from three of nine colobus monkeys yielded near-complete GHV genomes, comprising two distinct viral variants. The viruses contain an exceptionally long nonstructural 5A (NS5A) gene, approximately half of which codes for a protein with no discernible homology to known proteins. Computational structure-based analyses indicate that the amino terminus of the GHV NS5A protein may serve a zinc-binding function, similar to the NS5A of other viruses within the family Flaviviridae. However, the 521-amino-acid carboxy terminus is intrinsically disordered, reflecting an unusual degree of structural plasticity and polyfunctionality. These findings shed new light on the natural history and evolution of the hepaciviruses and on the extent of structural variation within the Flaviviridae.

Evidence for novel hepaciviruses in rodents

Hepatitis C virus (HCV) is among the most relevant causes of liver cirrhosis and hepatocellular carcinoma. Research is complicated by a lack of accessible small animal models. The systematic investigation of viruses of small mammals could guide efforts to establish such models, while providing insight into viral evolutionary biology. We have assembled the so-far largest collection of small-mammal samples from around the world, qualified to be screened for bloodborne viruses, including sera and organs from 4,770 rodents (41 species); and sera from 2,939 bats (51 species). Three highly divergent rodent hepacivirus clades were detected in 27 (1.8%) of 1,465 European bank voles (Myodes glareolus) and 10 (1.9%) of 518 South African four-striped mice (Rhabdomys pumilio). Bats showed anti-HCV immunoblot reactivities but no virus detection, although the genetic relatedness suggested by the serologic results should have enabled RNA detection using the broadly reactive PCR assays developed for this study. 210 horses and 858 cats and dogs were tested, yielding further horse-associated hepaciviruses but none in dogs or cats. The rodent viruses were equidistant to HCV, exceeding by far the diversity of HCV and the canine/equine hepaciviruses taken together. Five full genomes were sequenced, representing all viral lineages. Salient genome features and distance criteria supported classification of all viruses as hepaciviruses. Quantitative RT-PCR, RNA in-situ hybridisation, and histopathology suggested hepatic tropism with liver inflammation resembling hepatitis C. Recombinant serology for two distinct hepacivirus lineages in 97 bank voles identified seroprevalence rates of 8.3 and 12.4%, respectively. Antibodies in bank vole sera neither cross-reacted with HCV, nor the heterologous bank vole hepacivirus. Co-occurrence of RNA and antibodies was found in 3 of 57 PCR-positive bank vole sera (5.3%). Our data enable new hypotheses regarding HCV evolution and encourage efforts to develop rodent surrogate models for HCV.

Convergent evolution of escape from hepaciviral antagonism in primates

Escape from antagonism by hepatitis C and related viruses has repeatedly evolved in antiviral factor MAVS via convergent evolution, revealing an ancient history of previous viral encounters in primates.

The ability to mount an interferon response on sensing viral infection is a critical component of mammalian innate immunity. Several viruses directly antagonize viral sensing pathways to block activation of the host immune response. Here, we show that recurrent viral antagonism has shaped the evolution of the host protein MAVS—a crucial component of the viral-sensing pathway in primates. From sequencing and phylogenetic analyses of MAVS from 21 simian primates, we found that MAVS has evolved under strong positive selection. We focused on how this positive selection has shaped MAVS' susceptibility to Hepatitis C virus (HCV). We functionally tested MAVS proteins from diverse primate species for their ability to resist antagonism by HCV, which uses its protease NS3/4A to cleave human MAVS. We found that MAVS from multiple primates are resistant to inhibition by the HCV protease. This resistance maps to single changes within the protease cleavage site in MAVS, which protect MAVS from getting cleaved by the HCV protease. Remarkably, most of these changes have been independently acquired at a single residue 506 that evolved under positive selection. We show that “escape” mutations lower affinity of the NS3 protease for MAVS and allow it to better restrict HCV replication. We further show that NS3 proteases from all other primate hepaciviruses, including the highly divergent GBV-A and GBV-C viruses, are functionally similar to HCV. We conclude that convergent evolution at residue 506 in multiple primates has resulted in escape from antagonism by hepaciviruses. Our study provides a model whereby insights into the ancient history of viral infections in primates can be gained using extant host and virus genes. Our analyses also provide a means by which primates might clear infections by extant hepaciviruses like HCV.

Hepatitis C virus (HCV) causes chronic liver disease and is estimated to infect 170 million people worldwide. HCV is able to establish a persistent infection in part by inhibiting the innate immune response. It does so by using its protease, NS3, to cleave the host's antiviral factor MAVS, which normally activates the interferon response. Using an assay that measures MAVS activity, we found that multiple primate species contain a version of MAVS that is resistant to HCV antagonism. Surprisingly, most of these primates have independently converged on changes in the same amino acid residue of MAVS to escape cleavage by the HCV protease. We found that the HCV protease has lower binding affinity for these resistant MAVS variants, which consequently are more effective at restricting HCV infection. Using a combination of phylogenetic and functional analyses of proteases from other HCV-related viruses, we infer that ancestral primates were likely exposed to and adapted to HCV-like viruses. One consequence of this adaptation is that changes that have given rise to extant MAVS variants may now provide protection from modern-day viruses.

Evidence against GB virus C infection in dromedary camels

A recent publication described finding GB virus C (GBV-C) RNA in 4 of 22 dromedary camel sera, and sequence analysis found that these viruses were phylogenetically clustered within human GBV-C isolates. Since all other GB viruses to date form monophyletic groups according to their host species, the close relationship between the sequences generated from camel sera and human GBV-C isolates seemed implausible, leading us to conduct an independent analysis of the sequences. Our investigation found three lines of evidence arguing against GBV-C infection in dromedary camels. First, strong evidence of artifactual sequence generation was identified for some of the sequences. Secondly, the sequence diversity within individual camel sera was 10-152-fold greater than that described for GBV-C within a human host. Finally, GBV-C sequences generated from each camel shared near complete identity with human isolates previously described by the same laboratory. Taken together, these data strongly suggest laboratory contamination. We suggest that additional validation experiments are needed before it is possible to conclude that camels are permissive for GBV-C infection.

Diversity of murine norovirus in wild-rodent populations: species-specific associations suggest an ancient divergence

A survey of wild-rodent populations has revealed that murine norovirus (MNV) is present and diverse in wild-house mice Mus musculus. This virus is genetically similar to MNV infecting show mice and previously described variants circulating in laboratory mice. The detection of MNV in wild-mouse populations suggests that MNV infection of laboratory mice and show mice (from which laboratory mice are derived) derives from contact with or their origins from wild-mouse progenitors. The survey additionally identified frequent infection of wood mice (Apodemus sylvaticus) with genetically divergent variants of MNV. These viruses are distinct from previously described MNV variants, differing by 22-23 % over the complete genome sequence compared with a maximum of 13 % between M. musculus-derived strains. Comparison with other noroviruses reveals that the Apodemus MNV groups with MNV in genogroup V and shares the same overall genome organization, predicted lengths of proteins encoded by ORFs 1-3 and the existence of a conserved alternative reading frame in VP1 encoding a homologue of the MNV ORF4. Different Apodemus MNV isolates were as variable as MNV isolates and showed evidence for inter-isolate recombination. Our observation of species-specific associations of MNV variants in wild populations suggests that murine noroviruses have an ancient origin, a feature that they may share with other norovirus genogroups.

The GB viruses: a review and proposed classification of GBV-A, GBV-C (HGV), and GBV-D in genus Pegivirus within the family Flaviviridae

In 1967, it was reported that experimental inoculation of serum from a surgeon (G.B.) with acute hepatitis into tamarins resulted in hepatitis. In 1995, two new members of the family Flaviviridae, named GBV-A and GBV-B, were identified in tamarins that developed hepatitis following inoculation with the 11th GB passage. Neither virus infects humans, and a number of GBV-A variants were identified in wild New World monkeys that were captured. Subsequently, a related human virus was identified [named GBV-C or hepatitis G virus (HGV)], and recently a more distantly related virus (named GBV-D) was discovered in bats. Only GBV-B, a second species within the genus Hepacivirus (type species hepatitis C virus), has been shown to cause hepatitis; it causes acute hepatitis in experimentally infected tamarins. The other GB viruses have however not been assigned to a genus within the family Flaviviridae. Based on phylogenetic relationships, genome organization and pathogenic features of the GB viruses, we propose to classify GBV-A-like viruses, GBV-C and GBV-D as members of a fourth genus in the family Flaviviridae, named Pegivirus (pe, persistent; g, GB or G). We also propose renaming 'GB' viruses within the tentative genus Pegivirus to reflect their host origin.

Identification of GBV-D, a novel GB-like flavivirus from old world frugivorous bats (Pteropus giganteus) in Bangladesh

Bats are reservoirs for a wide range of zoonotic agents including lyssa-, henipah-, SARS-like corona-, Marburg-, Ebola-, and astroviruses. In an effort to survey for the presence of other infectious agents, known and unknown, we screened sera from 16 Pteropus giganteus bats from Faridpur, Bangladesh, using high-throughput pyrosequencing. Sequence analyses indicated the presence of a previously undescribed virus that has approximately 50% identity at the amino acid level to GB virus A and C (GBV-A and -C). Viral nucleic acid was present in 5 of 98 sera (5%) from a single colony of free-ranging bats. Infection was not associated with evidence of hepatitis or hepatic dysfunction. Phylogenetic analysis indicates that this first GBV-like flavivirus reported in bats constitutes a distinct species within the Flaviviridae family and is ancestral to the GBV-A and -C virus clades.

Bayesian coalescent analysis reveals a high rate of molecular evolution in GB virus C

GB virus C/hepatitis G (GBV-C) is an RNA virus of the family Flaviviridae. Despite replicating with an RNA-dependent RNA polymerase, some previous estimates of rates of evolutionary change in GBV-C suggest that it fixes mutations at the anomalously low rate of approximately 10(-7) nucleotide substitution per site, per year. However, these estimates were largely based on the assumption that GBV-C and its close relative GBV-A (New World monkey GB viruses) codiverged with their primate hosts over millions of years. Herein, we estimated the substitution rate of GBV-C using the largest set of dated GBV-C isolates compiled to date and a Bayesian coalescent approach that utilizes the year of sampling and so is independent of the assumption of codivergence. This revealed a rate of evolutionary change approximately four orders of magnitude higher than that estimated previously, in the range of 10(-2) to 10(-3) sub/site/year, and hence in line with those previously determined for RNA viruses in general and the Flaviviridae in particular. In addition, we tested the assumption of host-virus codivergence in GBV-A by performing a reconciliation analysis of host and virus phylogenies. Strikingly, we found no statistical evidence for host-virus codivergence in GBV-A, indicating that substitution rates in the GB viruses should not be estimated from host divergence times.

Immunity against the GBV-B hepatitis virus in tamarins can prevent productive infection following rechallenge and is long-lived

GB virus-B (GBV-B) is the virus most closely related to hepatitis C virus (HCV). Thus, we have used GBV-B infection of tamarins, which develop acute hepatitis following experimental infection, as a surrogate model to study protective immunity. As challenge virus, we first produced a GBV-B pool from an infected tamarin, which was not infected with the related GBV-A viruses. Its infectivity titer was 10(6.6) tamarin 50% infectious doses per ml. Next, two tamarins that were convalescent from recombinant GBV-B infection were re-challenged. In the original infection viremia persisted for 8 and 12 weeks, respectively, and both animals developed moderately severe hepatitis. Each tamarin was re-challenged four times with 10(4.3) tamarin 50% infectious doses of the GBV-B challenge virus. In one animal, each re-challenge produced 1-2 weeks of viremia; hepatitis was observed following the first re-challenge. In the other animal, however, only the first re-challenge produced viremia, lasting 1 week. During the primary infection, peak GBV-B titers were about 10(8) genome equivalents/ml in both animals; following re-challenges, peak titers ranged from 10(3) to 10(6) genome equivalents/ml. Analysis of the polyprotein sequence of viruses recovered from both animals following the first re-challenge demonstrated that these did not represent immune escape variants since mutations were not detected. Neutralization studies suggested that the immunity was not humoral in nature. We also demonstrated that the immunity was long-lived: 1 year after the fourth challenge, the animal with sterilizing immunity had low titer viremia for only 1 week following an additional challenge.

Hepatitis viruses in non-human primates

BACKGROUND

Previous epidemiological studies of rural human populations in Gabon reveal a high prevalence of human hepatitis A, B, C and D viruses. In order to investigate the prevalence of the blood-born hepatitis viruses in apes and monkeys living in the same area, we performed an epidemiological survey of HBV, HCV and HDV in wild-born non-human primates.

METHODS

We tested 441 wild-born non-human primates from Gabon and Congo and 132 imported monkeys for the presence of serological markers of HBV, HCV and HDV infections.

RESULTS

None of Cercopithecidae monkeys were reactive against HBV/HDV and HCV. In contrast, 29.2% of wild-born great apes (154 chimpanzees and 14 gorillas) were positive for HBV serological markers. Nine chimpanzees were in the replicative phase of HBV infection. None of these HBV infected chimpanzees exhibited symptoms or significant changes in serum clinical chemistry related to HBV infection.

CONCLUSIONS

The negativity to HCV-related viruses and the negativity of the Cercopithecidae species tested against HBV/HDV do not allow us to definitively rule out the presence of an animal counterpart of human hepatitis viruses in non-human primates.

Structurally Driven Selection of Human Hepatitis C Virus Mimotopes

A structural genomics approach is proposed for the development of new diagnostic kits. It combines molecular modelling, peptide synthesis and immunological tests. The preliminary step is the development of a reliable three-dimensional structure of an immunodominant protein of the target pathogenic organism using the various bioinformatic strategies that are now available to structural biologists. Once the protein structure is obtained, the most surface-exposed fragments with minimal sequence variability among the different strains reported in the genomic data bank are reproduced synthetically as linear peptides. These peptides are then tested for immunoreactivity with the plasma of infected patients to determine whether the synthetic molecules have antigenic activity and can therefore be used to detect infecting agents. This structurally driven selection of mimotopes was successfully performed for the human hepatitis C virus, as five peptides that specifically interact with the plasma of HCV-infected patients were identified solely on the basis of the three-dimensional structure predicted for the E2 homodimer of the 1a viral subtype. A similar approach could easily be extended to a large variety of immunogenic proteins from other pathogenic organisms.

In vivo analysis of the 3' untranslated region of GB virus B after in vitro mutagenesis of an infectious cDNA clone: persistent infection in a transfected tamarin

GB virus B (GBV-B), the virus most closely related to hepatitis C virus (HCV), infects tamarins and causes acute hepatitis. The 3' untranslated region (UTR) of an infectious GBV-B clone (pGBB) has a proximal short sequence followed by a poly(U) tract and a 3' terminal sequence. Our investigators previously demonstrated that the 3' terminal sequence was critical for in vivo infectivity. Here, we tested the effect of deleting the short sequence and/or the poly(U) tract from pGBB; infectivity of each mutant was tested by intrahepatic transfection of two tamarins with transcribed RNA. A mutant lacking both regions was not viable. However, mutants lacking either the short sequence or the poly(U) tract were viable. All four tamarins had a wild-type-like acute infection and developed acute hepatitis. Whereas we found that five tamarins transfected with the wild-type clone pGBB had acute resolving infection, one tamarin transfected with the poly(U) deletion mutant became persistently infected. This animal had viremia and hepatitis until its death at week 90. The genomes recovered at weeks 2, 7, 15, 20, 60, and 90 lacked the poly(U) stretch. Eight amino acid changes were identified at week 90. One change, in the putative p7 protein, was dominant at week 15. Thus, persistence of GBV-B, like persistence of HCV, was associated with the emergence of virus variants. Four tamarins inoculated with serum collected at weeks 2 and 90 from the tamarin with persistent infection had an acute resolving infection. Nonetheless, the demonstration that GBV-B can persist in tamarins strengthens its relevance as a surrogate model for the study of HCV.

Development of a GB virus B marmoset model and its validation with a novel series of hepatitis C virus NS3 protease inhibitors

GB virus B (GBV-B), a flavivirus closely related to HCV, has previously been shown to infect and replicate to high titers in tamarins (Saguinus sp.). This study describes the use of GBV-B infection and replication in the common marmoset (Callithrix jacchus) for the successful development and validation of a surrogate animal model for hepatitis C virus (HCV). Infection of marmosets with GBV-B produced a viremia that peaked at 10(8) to 10(9) genome copies/ml for a period of 40 to 60 days followed by viral clearance at 60 to 80 days postinfection. Passage of the initial tamarin-derived GBV-B in marmosets produced an infectious stock that gave a more reproducible and consistent infection in the marmoset. Titration of the virus stocks in vivo indicated that they contained 1 infectious unit for every 1,000 genome copies. Cultures of primary marmoset hepatocytes were also successfully infected with GBV-B, with high levels of virus detected in supernatants and cells for up to 14 days postinfection. Treatment of GBV-B-infected hepatocyte cultures with a novel class of HCV protease inhibitor (pyrrolidine 5,5 trans-lactams) reduced viral levels by more than 2 logs. Treatment of GBV-B-infected marmosets with one such inhibitor resulted in a 3-log drop in serum viral titer over 4 days of therapy. These studies provide the first demonstration of the in vivo efficacy of a small-molecule inhibitor for HCV in an animal model and illustrate the utility of GBV-B as a surrogate animal model system for HCV.

Mapping of a conformational epitope shared between E1 and E2 on the serum-derived human hepatitis C virus envelope

Monoclonal antibody D32.10 produced by immunizing mice with a hepatitis C virus (HCV)-enriched pellet obtained from plasmapheresis of a chronically HCV1b-infected patient binds HCV particles derived from serum of different HCV1a- and HCV1b-infected patients. Moreover, this monoclonal has been shown to recognize both HCV envelope proteins E1 and E2. In an attempt to provide novel insight into the membrane topology of HCV envelope glycoproteins E1 and E2, we localized the epitope recognized by D32.10 on the E1 and/or E2 sequence using Ph.D.-12 phage display peptide library technology. Mimotopes selected from the phage display dodecapeptide library by D32.10 shared partial similarities with 297RHWTTQGCNC306 of the HCV E1 glycoprotein and with both 613YRLWHYPCT621 and 480PDQRPYCWHYPPKPC494 of the HCV E2 glycoprotein. Immunoreactivity of D32.10 with overlapping peptides corresponding to these three HCV regions confirmed these localizations and suggested that the three regions identified are likely closely juxtaposed on the surface of serum-derived particles as predicted by the secondary model structure of HCV E2 derived from the tick-borne encephalitis virus E protein. This assertion was supported by the detection of specific antibodies directed against these three E1E2 regions in sera from HCV-infected patients.

Comparison of tamarins and marmosets as hosts for GBV-B infections and the effect of immunosuppression on duration of viremia

GBV-B virus is a close relative to hepatitis C virus (HCV) that causes hepatitis in tamarins, and thus, is an attractive surrogate model for HCV. In this study, we demonstrate that the host range of GBV-B extends to the common marmoset with an infection profile similar to that observed for tamarins. Marmoset hepatocytes were susceptible to in vitro infection with GBV-B. Virus was efficiently secreted into the medium, and approximately 25% of hepatocytes were positive for NS3 staining. In an attempt to induce persistent infections, tamarins were immunosuppressed with FK506 and inoculated with GBV-B. Although no chronic infections were induced, the duration of viremia was increased in most animals. In one animal, the duration of viremia was extended to 46 weeks, but viral clearance occurred 18 weeks after stopping FK506 therapy. The greater availability of marmosets in comparison to tamarins will greatly facilitate future research efforts with this model.

A primer of primate pathology: lesions and nonlesions

Nonhuman primates are important laboratory animals for biomedical, pharmacology, and toxicology research. To effectively use primates as models, their gross and histologic anatomy, physiology and natural history, as well as common health problems and the source from which the primate is obtained, must be known and understood by pathologists involved in study design and/or interpretation. The first very important lesson in the "primer" is: there is no such thing as a generic monkey. Brand names (ie, species and subspecies) are important. Several taxonomic groups of primates are used in research including: prosimians, such as galagos and lemurs; New World monkeys, particularily marmosets; Old World monkeys, especially macaques and baboons; and the chimpanzee, an African ape. Differences between taxa are exemplified by the glucocorticoid resistance of New World monkeys compared to Old World monkeys, which results in the requirement for Vitamin D3 and their high circulating levels of steroids such as cortisone and progesterone. Differences in ovarian histology between Old and New World monkeys probably relate to steroid receptor biology as well. There are also variations in disease manifestations, even among closely related primate species such as rhesus and cynomolgus macaques (cynos). For example type D retrovirus infection is accompanied by lymphomas in cynos, but not rhesus. The second important lesson in this "primer" is: "not test article related" does not always mean "normal." Lymphoid nodules in bone marrow or salivary gland, a common background finding in macaques, often signal the presence of type D retrovirus. Other histologic changes and normal anatomic variations may be confusing to individuals not routinely examining primate tissues. The objective of this paper is to familiarize pathologists with the use of primates in research as well as lesions and nonlesions (normal anatomy or physiology) of primates that may influence study design and confound interpretation.

Host range studies of GB virus-B hepatitis agent, the closest relative of hepatitis C virus, in New World monkeys and chimpanzees

GB virus-B (GBV-B) is a member of the Flaviviridae family of viruses. This RNA virus causes acute resolving hepatitis in experimentally infected tamarins, but its natural host remains unknown. GBV-B and a related virus, GBV-A, were recovered from serum containing the "GB agent," which was believed to have originated from a surgeon (initials: GB) with acute hepatitis. GBV-B has special interest because it is the virus related most closely to hepatitis C virus, which is an important cause of acute and chronic liver disease in humans. In the present study, we found that the host range of GBV-B includes owl monkeys. Tamarins and owl monkeys belong to two different families of New World monkeys. The natural history of GBV-B in the two owl monkeys studied was similar to that previously found for tamarins and was characterized by early appearance of viremia and viral clearance. However, the peak viral titers of GBV-B observed in owl monkeys (10(5) genome equivalents [GE] /ml) were lower than those observed in experimentally infected tamarins (10(7)-10(8) GE/ml) and acute hepatitis was observed in only one animal. If GBV-B were indeed a virus of humans, it would be expected to infect chimpanzees, a surrogate of humans, because all recognized human hepatitis viruses are transmissible to chimpanzees and cause hepatitis. However, in the present study, we failed to transmit GBV-B to a naive chimpanzee. In addition, a second naive chimpanzee transfected intrahepatically with RNA transcripts from an infectious clone of GBV-B did not become infected. Thus, chimpanzees are apparently not susceptible to GBV-B. Finally, we failed to detect GBV-B in acute-phase serum from surgeon GB. Our data suggest that GBV-B is not a human virus and that GBV-B, like GBV-A, is a virus of New World monkeys.

Reconstructing the origins of human hepatitis viruses

Infections with hepatitis B and C viruses (HBV, HCV) are widespread in human populations throughout the world, and are major causes of chronic liver disease and liver cancer. HBV, HCV and the related hepatitis G virus or GB virus C (referred to here as HGV/GBV-C) are capable of establishing persistent, frequently lifelong infections characterized by high levels of continuous replication. All three viruses show substantial genetic heterogeneity, which has allowed each to be classified into a number of distinct genotypes that have different geographical distributions and associations with different risk groups for infection. Information on their past transmission and epidemiology might be obtained by estimation of the time of divergence of the different genotypes of HCV, HBV and HGV/GBV-C using knowledge of their rates of sequence change. While information on the latter is limited to short observation periods and is therefore subject to considerable error and uncertainty, the relatively recent times of origin for genotype of each virus predicted by this method (HCV, 500-2000 years; HBV, 3000 years; HGV/GBV-C, 200 years) are quite incompatible with their epidemiological distributions in human populations. They also cannot easily be reconciled with the recent evidence for species-associated variants of HBV and HGV/GBV-C in a range of non-human primates. The apparent conservatism of viruses over long periods implied by their epidemiological distributions instead suggests that nucleotide sequence change may be subject to constraints peculiar to viruses with single-stranded genomes, or with overlapping reading frames that defy attempts to reconstruct evolution according to the principles of the 'molecular clock'. Large population sizes and intense selection pressures that optimize fitness may be additional factors that set virus evolution apart from that of their hosts.

GB virus B as a model for hepatitis C virus

GB viruses A and B (GBV-A and GBV-B) are members of the Flaviviridae family and are isolated from tamarins injected with serum from a human hepatitis patient. Along with a related human virus, GB virus C, or alternatively, hepatitis G virus (GBV-C/HGV), the three viruses represent the GB agents. Of the three viruses, GBV-B has been proposed as a potential surrogate model for the study of hepatitis C virus (HCV) infections of humans. GBV-B is phylogenetically most closely related to HCV and causes an acute, self-resolving hepatitis in tamarins as indicated by an increase in alanine aminotransferase and changes in liver histology. Similarities between GBV-B and HCV are found at the nucleotide sequence level with the two viruses sharing 28% amino acid homology over the lengths of their open reading frames. Short regions have even higher levels of homology that are functionally significant as shown by the ability of the GBV-B NS3 protease to cleave recombinant HCV polyprotein substrates. The shared protease substrate specificities suggest that GBV-B may be useful in testing antiviral compounds for activity against HCV. Although there are numerous similarities between GBV-B and HCV, there are important differences in that HCV frequently causes chronic infections in people, whereas GBV-B appears to cause only acute infections. The acute versus chronic course of infection may point to important differences between the two viruses that, along with the numerous similarities, will make GBV-B in tamarins a good surrogate model for HCV.

Viral hepatitis and primates: historical and molecular analysis of human and nonhuman primate hepatitis A, B, and the GB-related viruses

The hepatitis viruses have long been assumed to be highly host-specific, with infection of other nonhuman primates occurring due to inoculation with, or exposure to, human viruses. This paradigm has slowly changed over the last 10 years, as mounting data has revealed nonhuman primate equivalents of hepatitis A virus, hepatitis B virus, and the hepatitis C-related viruses GBV-C and GBV-A. This review summarizes the historical and molecular information for each of these groups and highlights the impact of these nonhuman primate hepatitis viruses on our understanding of the evolution of each of these viruses.

Rapid elimination of GB virus C (hepatitis G virus) in the mosquito Aedes aegypti

The transmissibility of the GB virus C (hepatitis G virus; HGV), a member of the Flaviviridae, by a typical flavivirus vector was investigated. Female mosquitoes of the species Aedes aegypti were fed with HGV-infected human blood and assayed 1, 24, 48, 72 and 96 h after the blood meal for viral RNA, human glyceraldehyde-3-phosphate dehydrogenase mRNA, human beta-actin DNA and A. aegypti actin mRNA by total nucleic acid extraction, reverse transcription and PCR. Viral RNA had already disappeared from nucleic acid extracts 1 h after the blood meal and was not detectable throughout the observation period. Aedes-specific mRNA served as an internal control and was detected in all nucleic acid extracts, whereas human mRNA had disappeared after 24 h, indicating digestion of human cells. From these results we conclude that GB virus C (HGV) cannot replicate in A. aegypti, which is a widespread and competent vector of several other flaviviruses.

The origin and evolution of hepatitis viruses in humans

The spread and origins of hepatitis C virus (HCV) in human populations have been the subject of extensive investigations, not least because of the importance this information would provide in predicting clinical outcomes and controlling spread of HCV in the future. However, in the absence of historical and archaeological records of infection, the evolution of HCV and other human hepatitis viruses can only be inferred indirectly from their epidemiology and by genetic analysis of contemporary virus populations. Some information on the history of the latter may be obtained by dating the time of divergence of various genotypes of HCV, hepatitis B virus (HBV) and the non-pathogenic hepatitis G virus (HGV)/GB virus-C (GBV-C). However, the relatively recent times predicted for the origin of these viruses fit poorly with their epidemiological distributions and the recent evidence for species-associated variants of HBV and HGV/GBV-C in a wide range of non-human primates. The apparent conservatism of viruses over long periods implied by these latter observations may be the result of constraints on sequence change peculiar to viruses with single-stranded genomes, or with overlapping reading frames. Large population sizes and intense selection pressures that optimize fitness may be the factors that set virus evolution apart from that of their hosts.

Evolutionarily conserved RNA secondary structures in coding and non-coding sequences at the 3' end of the hepatitis G virus/GB-virus C genome

Hepatitis G virus (HGV)/GB virus C (GBV-C) causes persistent, non-pathogenic infection in a large proportion of the human population. Epidemiological and genetic evidence indicates a long-term association between HGV/GBV-C and related viruses and a range of primate species, and the co-speciation of these viruses with their hosts during primate evolution. Using a combination of covariance scanning and analysis of variability at synonymous sites, we previously demonstrated that the coding regions of HGV/GBV-C may contain extensive secondary structure of undefined function (Simmonds & Smith, Journal of Virology 73, 5787-5794, 1999 ). In this study we have carried out a detailed comparison of the structure of the 3'untranslated region (3'UTR) of HGV/GBV-C with that of the upstream NS5B coding sequence. By investigation of free energies on folding, secondary structure predictive algorithms and analysis of covariance between HGV/GBV-C genotypes 1-4 and the more distantly related HGV/GBV-C chimpanzee variant, we obtained evidence for extensive RNA secondary structure formation in both regions. In particular, the NS5B region contained long stem-loop structures of up to 38 internally paired nucleotides which were evolutionarily conserved between human and chimpanzee HGV/GBV-C variants. The prediction of similar structures in the same region of hepatitis C virus may allow the functions of these structures to be determined with a more tractable experimental model.

Homologous recombination in GB virus C/hepatitis G virus

Analysis of 33 GB virus C/hepatitis G virus (GBV-C/HGV) full or nearly full genome sequences revealed several putative inter- and intrasubtype recombinants. The breakpoints of the recombinant regions were mapped using a maximum-likelihood method, and the statistical significance for each region was tested using Monte Carlo simulation. The results were highly significant and provided evidence for the existence of complex mosaic genomes showing as many as nine recombination events, with breakpoints in the 5' UTR and in all of the coding regions except the short NS4b gene. Recombination was confirmed by separate phylogenetic analysis of the various recombinant regions and by Sawyer's runs test. Taken together, these findings demonstrate for the first time that recombination is common in natural populations of GBV-C and that it takes place both within and between subtypes. The wide-ranging implications of such nonclonal history for reconstructing the spread and timescale of GBV-C evolution are discussed.

Development of a primary tamarin hepatocyte culture system for GB virus-B: a surrogate model for hepatitis C virus

GB virus-B (GBV-B) causes an acute hepatitis in tamarins characterized by increased alanine transaminase levels that quickly return to normal as the virus is cleared. Phylogenetically, GBV-B is the closest relative to hepatitis C virus (HCV), and thus GBV-B infection of tamarins represents a powerful surrogate model system for the study of HCV. In this study, the course of infection of GBV-B in tamarins was followed using a real-time 5' exonuclease (TaqMan) reverse transcription-PCR assay to determine the level of GBV-B in the serum. Peak viremia levels exceeded 10(9) genome equivalents/ml, followed by viral clearance within 14 to 16 weeks. Rechallenge of animals that had cleared infection resulted in viremia that was limited to 1 week, suggestive of a strong protective immune response. A robust tissue culture system for GBV-B was developed using primary cultures of tamarin hepatocytes. Hepatocytes obtained from a GBV-B-infected animal maintained high levels of cell-associated viral RNA and virion secretion for 42 days of culture. In vitro infection of normal hepatocytes resulted in rapid amplification of cell-associated viral RNA and secretion of up to 10(7) genome equivalents/ml of culture supernatant. In addition, infection could be monitored by immunofluorescence staining for GBV-B nonstructural NS3 protein. This model system overcomes many of the current obstacles to HCV research, including low levels of viral replication, lack of a small primate animal model, and lack of a reproducible tissue culture system.

Hepatitis C virus envelope protein E2 binds to CD81 of tamarins

Since recombinant envelope glycoprotein E2 of hepatitis C virus (HCV) binds to CD81 on human and chimpanzee cells, it has been suggested that CD81 may be a receptor for HCV. Humans and chimpanzees are the only species known to be susceptible to HCV infection. E2 has been reported not to bind to CD81 of the African green monkey, mouse, or rat, suggesting that binding of HCV to CD81 is species specific and may determine susceptibility to infection with HCV. We investigated the interaction between E2 of HCV and CD81 of tamarins, a group of small New World monkeys frequently used for the study of human viruses. Tamarins are not susceptible to HCV infection. Nonetheless, we found that three different forms of HCV E2 (intracellular, secreted, and cell surface-displayed) bound more efficiently to recombinant tamarin CD81 than to human CD81, as determined by ELISA and immunofluorescence. The affinity of the interaction was approximately 10-fold higher for tamarin than for human CD81. Binding of E2 to CD81 on cultured or primary tamarin cells was demonstrated by flow cytometry. In contrast to previous reports, there was also a low-affinity interaction between E2 and African green monkey CD81. Thus, the HCV E2 interaction with CD81 is not limited to humans and chimpanzees and does not predict susceptibility to HCV infection.

Phylogenetic analysis of GBV-C/hepatitis G virus

Comparison of 33 epidemiologically distinct GBV-C/hepatitis G virus complete genome sequences suggests the existence of four major phylogenetic groupings that are equally divergent from the chimpanzee isolate GBV-C(tro) and have distinct geographical distributions. These four groupings are not consistently reproduced by analysis of the virus 5'-noncoding region (5'-NCR), or of individual genes or subgenomic fragments with the exception of the E2 gene as a whole or of 200-600 nucleotide fragments from its 3' half. This region is upstream of a proposed anti-sense reading frame and contains conserved potential RNA secondary structures that may be capable of directing the internal initiation of translation. Phylogenetic analysis of this region from certain South African isolates is consistent with previous analysis of the 5'-NCR suggesting that these belong to a fifth group. The geographical distribution of virus variants is consistent with a long evolutionary history that may parallel that of pre-historic human migrations, implying that the long-term evolution of this RNA virus is extremely slow.