Feline model of acute nipah virus infection and protection with a soluble glycoprotein-based subunit vaccine

Henipavirus: A Review of Laboratory Animal Pathology

The genus Henipavirus contains two members—Hendra virus (HeV) and Nipah virus (NiV)—and each can cause fatal disease in humans and animals. HeV and Niv are currently classified as biosafety level 4, and NiV is classified as a category C priority pathogen. The aim of this article is to discuss the pathology of laboratory animal models of henipavirus infection and to assess their suitability as animal models for the development and testing of human therapeutics and vaccines. There has been considerable progress in the development of animal models for henipavirus disease. Suitable animal models include the golden hamster, ferrets, cats, and pigs, which develop disease resembling that observed in humans. Guinea pigs are a less reliable model for henipavirus disease, but they do develop henipavirus-induced encephalitis. Because human efficacy studies with henipaviruses are not permitted, animal studies are critical for the development of antiviral therapeutics and vaccines. Current research indicates that passive immunotherapy using monoclonal antibodies is protective of ferrets against NiV infection and that passive immunotherapy using NiV antibodies protects hamsters from HeV. Recombinant vaccines have been used to protect cats and pigs against NiV infection. Ribavirin and 6-aza-uridine were able to delay but not prevent NiV-induced mortality in hamsters. Further research is needed to develop a model and therapy for late-onset henipavirus encephalitis.

A novel model of lethal Hendra virus infection in African green monkeys and the effectiveness of ribavirin treatment

The henipaviruses, Hendra virus (HeV) and Nipah virus (NiV), are emerging zoonotic paramyxoviruses that can cause severe and often lethal neurologic and/or respiratory disease in a wide variety of mammalian hosts, including humans. There are presently no licensed vaccines or treatment options approved for human or veterinarian use. Guinea pigs, hamsters, cats, and ferrets, have been evaluated as animal models of human HeV infection, but studies in nonhuman primates (NHP) have not been reported, and the development and approval of any vaccine or antiviral for human use will likely require efficacy studies in an NHP model. Here, we examined the pathogenesis of HeV in the African green monkey (AGM) following intratracheal inoculation. Exposure of AGMs to HeV produced a uniformly lethal infection, and the observed clinical signs and pathology were highly consistent with HeV-mediated disease seen in humans. Ribavirin has been used to treat patients infected with either HeV or NiV; however, its utility in improving outcome remains, at best, uncertain. We examined the antiviral effect of ribavirin in a cohort of nine AGMs before or after exposure to HeV. Ribavirin treatment delayed disease onset by 1 to 2 days, with no significant benefit for disease progression and outcome. Together our findings introduce a new disease model of acute HeV infection suitable for testing antiviral strategies and also demonstrate that, while ribavirin may have some antiviral activity against the henipaviruses, its use as an effective standalone therapy for HeV infection is questionable.

Experimental infection of squirrel monkeys with nipah virus

We infected squirrel monkeys (Saimiri sciureus) with Nipah virus to determine the monkeys’ suitability for use as primate models in preclinical testing of preventive and therapeutic treatments. Infection of squirrel monkeys through intravenous injection was followed by high death rates associated with acute neurologic and respiratory illness and viral RNA and antigen production.

Development of an acute and highly pathogenic nonhuman primate model of Nipah virus infection

Nipah virus (NiV) is an enigmatic emerging pathogen that causes severe and often fatal neurologic and/or respiratory disease in both animals and humans. Amongst people, case fatality rates range between 40 and 75 percent and there are no vaccines or treatments approved for human use. Guinea pigs, hamsters, cats, ferrets, pigs and most recently squirrel monkeys (New World monkey) have been evaluated as animal models of human NiV infection, and with the exception of the ferret, no model recapitulates all aspects of NiV-mediated disease seen in humans. To identify a more viable nonhuman primate (NHP) model, we examined the pathogenesis of NiV in African green monkeys (AGM). Exposure of eight monkeys to NiV produced a severe systemic infection in all eight animals with seven of the animals succumbing to infection. Viral RNA was detected in the plasma of challenged animals and occurred in two of three subjects as a peak between days 7 and 21, providing the first clear demonstration of plasma-associated viremia in NiV experimentally infected animals and suggested a progressive infection that seeded multiple organs simultaneously from the initial site of virus replication. Unlike the cat, hamster and squirrel monkey models of NiV infection, severe respiratory pathology, neurological disease and generalized vasculitis all manifested in NiV-infected AGMs, providing an accurate reflection of what is observed in NiV-infected humans. Our findings demonstrate the first consistent and highly pathogenic NHP model of NiV infection, providing a new and critical platform in the evaluation and licensure of either passive and active immunization or therapeutic strategies for human use.

Antiviral activity of gliotoxin, gentian violet and brilliant green against Nipah and Hendra virus in vitro

Background

Using a recently described monolayer assay amenable to high throughput screening format for the identification of potential Nipah virus and Hendra virus antivirals, we have partially screened a low molecular weight compound library (>8,000 compounds) directly against live virus infection and identified twenty eight promising lead molecules. Initial single blind screens were conducted with 10 μM compound in triplicate with a minimum efficacy of 90% required for lead selection. Lead compounds were then further characterised to determine the median efficacy (IC₅₀), cytotoxicity (CC₅₀) and the in vitro therapeutic index in live virus and pseudotype assay formats.

Results

While a number of leads were identified, the current work describes three commercially available compounds: brilliant green, gentian violet and gliotoxin, identified as having potent antiviral activity against Nipah and Hendra virus. Similar efficacy was observed against pseudotyped Nipah and Hendra virus, vesicular stomatitis virus and human parainfluenza virus type 3 while only gliotoxin inhibited an influenza A virus suggesting a non-specific, broad spectrum activity for this compound.

Conclusion

All three of these compounds have been used previously for various aspects of anti-bacterial and anti-fungal therapy and the current results suggest that while unsuitable for internal administration, they may be amenable to topical antiviral applications, or as disinfectants and provide excellent positive controls for future studies.

A neutralizing human monoclonal antibody protects against lethal disease in a new ferret model of acute nipah virus infection

Nipah virus is a broadly tropic and highly pathogenic zoonotic paramyxovirus in the genus Henipavirus whose natural reservoirs are several species of Pteropus fruit bats. Nipah virus has repeatedly caused outbreaks over the past decade associated with a severe and often fatal disease in humans and animals. Here, a new ferret model of Nipah virus pathogenesis is described where both respiratory and neurological disease are present in infected animals. Severe disease occurs with viral doses as low as 500 TCID₅₀ within 6 to 10 days following infection. The underlying pathology seen in the ferret closely resembles that seen in Nipah virus infected humans, characterized as a widespread multisystemic vasculitis, with virus replicating in highly vascular tissues including lung, spleen and brain, with recoverable virus from a variety of tissues. Using this ferret model a cross-reactive neutralizing human monoclonal antibody, m102.4, targeting the henipavirus G glycoprotein was evaluated in vivo as a potential therapeutic agent. All ferrets that received m102.4 ten hours following a high dose oral-nasal Nipah virus challenge were protected from disease while all controls died. This study is the first successful post-exposure passive antibody therapy for Nipah virus using a human monoclonal antibody.

Nipah virus and Hendra virus are closely related and highly pathogenic zoonoses whose primary natural reservoirs are several species of Pteropus fruit bats. Both Nipah and Hendra viruses can cause severe and often fatal disease in a variety of mammalian hosts, including humans. The henipaviruses are categorized as biosafety level 4 (BSL-4) agents, which has limited the development of animal models and the testing of potential therapeutics and vaccine countermeasures. We show here a new ferret model of Nipah virus pathogenesis in which the underlying pathology closely mirrors the illness seen in Nipah virus-infected humans, including both respiratory and neurological disease. We also show that m102.4, a cross-reactive neutralizing human monoclonal antibody that targets the viral attachment glycoprotein, completely protected ferrets from disease when given ten hours after a lethal Nipah virus challenge. This study is the first successful and viable post-exposure passive antibody therapy for Nipah virus using a human monoclonal antibody.

Chloroquine administration does not prevent Nipah virus infection and disease in ferrets

Hendra virus and Nipah virus, two zoonotic paramyxoviruses in the genus Henipavirus, have recently emerged and continue to cause sporadic disease outbreaks in humans and animals. Mortality rates of up to 75% have been reported in humans, but there are presently no clinically licensed therapeutics for treating henipavirus-induced disease. A recent report indicated that chloroquine, used in malaria therapy for over 70 years, prevented infection with Nipah virus in vitro. Chloroquine was assessed using a ferret model of lethal Nipah virus infection and found to be ineffective against Nipah virus infection in vivo.

Modified PAXgene method allows for isolation of high-integrity total RNA from microlitre volumes of mouse whole blood

Analysis of gene expression is often used to evaluate the effects of experimental manipulations in laboratory animals. Blood is a rich source of potential biomarkers, including gene expression information, which may be obtained from whole blood. When compared with the end of a study, when whole blood samples can be easily obtained for gene expression measurements, the limiting volumes of whole blood obtainable from animals during the course of an experiment requires a method for RNA isolation from a minimal volume of whole blood. The PAXgene Blood RNA Extraction System originally designed for isolation of total RNA from 2.5 mL of human whole blood, was modified and successfully used to isolate high-integrity total RNA from as little as 50 microL of mouse whole blood. Fifty microlitres of mouse whole blood yielded an average of 2.3 microg highly intact total RNA, of sufficient quality and quantity allowing for multiple gene expression determinations. The utility of this method was demonstrated by confirming the time- and dose-dependent upregulation of haem oxygenase-1 (Hmox1) mRNA in response to a single injection of cobalt protoporphyrin. The successful isolation of total RNA from small volumes of mouse whole blood can allow for serial sampling on the same animals, thereby reducing the number of animals required for experimentation.

Evaluation of vaccines for H5N1 influenza virus in ferrets reveals the potential for protective single-shot immunization

As part of influenza pandemic preparedness, policy decisions need to be made about how best to utilize vaccines once they are manufactured. Since H5N1 avian influenza virus has the potential to initiate the next human pandemic, isolates of this subtype have been used for the production and testing of prepandemic vaccines. Clinical trials of such vaccines indicate that two injections of preparations containing adjuvant will be required to induce protective immunity. However, this is a working assumption based on classical serological measures only. Examined here are the dose of viral hemagglutinin (HA) and the number of inoculations required for two different H5N1 vaccines to achieve protection in ferrets after lethal H5N1 challenge. Ferrets inoculated twice with 30 microg of A/Vietnam/1194/2004 HA vaccine with AlPO4, or with doses as low as 3.8 microg of HA with Iscomatrix (ISCOMATRIX, referred to as Iscomatrix herein, is a registered trademark of CSL Limited) adjuvant, were completely protected against death and disease after H5N1 challenge, and the protection lasted at least 15 months. Cross-clade protection was also observed with both vaccines. Significantly, complete protection against death could be achieved with only a single inoculation of H5N1 vaccine containing as little as 15 microg of HA with AlPO4 or 3.8 microg of HA with Iscomatrix adjuvant. Ferrets vaccinated with the single-injection Iscomatrix vaccines showed fewer clinical manifestations of infection than those given AlPO4 vaccines and remained highly active. Our data provide the first indication that in the event of a future influenza pandemic, effective mass vaccination may be achievable with a low-dose "single-shot" vaccine and provide not only increased survival but also significant reduction in disease severity.

Acute Hendra virus infection: Analysis of the pathogenesis and passive antibody protection in the hamster model

Hendra virus (HeV) and Nipah virus (NiV) are recently-emerged, closely related and highly pathogenic paramyxoviruses. We have analysed here the pathogenesis of the acute HeV infection using the new animal model, golden hamster (Mesocricetus auratus), which is highly susceptible to HeV infection. HeV-specific RNA and viral antigens were found in multiple organs and virus was isolated from different tissues. Dual pathogenic mechanism was observed: parenchymal infection in various organs, including the brain, with vasculitis and multinucleated syncytia in many blood vessels. Furthermore, monoclonal antibodies specific for the NiV fusion protein neutralized HeV in vitro and efficiently protected hamsters from HeV if given before infection. These results reveal the similarities between HeV and NiV pathogenesis, particularly in affecting both respiratory and neuronal system. They demonstrate that hamster presents a convenient novel animal model to study HeV infection, opening new perspectives to evaluate vaccine and therapeutic approaches against this emergent infectious disease.

Development of a neutralization assay for Nipah virus using pseudotype particles

Nipah virus (NiV) and Hendra virus (HeV) are zoonotic paramyxoviruses capable of causing severe disease in humans and animals. These viruses require biosafety level 4 (BSL-4) containment. Like other paramyxoviruses, the plaque reduction neutralization test (PRNT) can be used to detect antibodies to the surface glycoproteins, fusion (F) and attachment (G), and PRNT titers give an indication of protective immunity. Unfortunately, for NiV and HeV, the PRNT must be performed in BSL-4 containment and takes several days to complete. Thus, we have developed a neutralization assay using VSV pseudotype particles expressing the F and G proteins of NiV (pVSV-NiV-F/G) as target antigens. This rapid assay, which can be performed at BSL-2, was evaluated using serum samples from outbreak investigations and more than 300 serum samples from an experimental NiV vaccination study in swine. The results of the neutralization assays with pVSV-NiV-F/G as antigen showed a good correlation with those of standard PRNT. Therefore, this new method has the potential to be a rapid and cost-effective diagnostic method, especially in locations that lack high containment facilities, and will provide a valuable tool for basic research and vaccine development.

Characteristics of Nipah virus and Hendra virus replication in different cell lines and their suitability for antiviral screening

We have recently described the development and validation of a high throughput screening assay suitable for henipavirus antiviral identification. While we are confident this assay is robust and effective, we wished to investigate assay performance in a range of alternative cell lines to determine if assay sensitivity and specificity could be improved. We evaluated ten different cell lines for their susceptibility to Hendra and Nipah virus infection and their sensitivity of detection of the effects of the broad spectrum antiviral, ribavirin and nine novel antivirals identified using our initial screening approach. Cell lines were grouped into three categories with respect to viral replication. Virus replicated best in Vero and BSR cells, followed by Hep-2, HeLa, BHK-21 and M17 cells. The lowest levels of RNA replication and viral protein expression were observed in BAEC, MMEC, A549 and ECV304 cells. Eight cell lines appeared to be similarly effective at discriminating the antiviral effects of ribavirin (<2.7-fold difference). The two cells lines most sensitive to the effect of ribavirin (ECV304 and BAEC) also displayed the lowest levels of viral replication while Vero cells were the least sensitive suggesting excess viral replication may limit drug efficacy and cell lines which limit viral replication may result in enhanced antiviral efficacy. However, there was no consistent trend observed with the other nine antivirals tested. While improvements in antiviral sensitivity in other cell lines may indicate an important role in future HTS assays, the slightly lower sensitivity to antiviral detection in Vero cells has inherent advantages in reducing the number of partially effective lead molecules identified during initial screens. Comparison of a panel of 54 novel antiviral compounds identified during routine screening of an in-house compound library in Vero, BHK-21 and BSR cells suggests no clear advantage of screening in either cell type.

Ephrin-B2 expression critically influences Nipah virus infection independent of its cytoplasmic tail

Background

Cell entry and cell-to-cell spread of the highly pathogenic Nipah virus (NiV) requires binding of the NiV G protein to cellular ephrin receptors and subsequent NiV F-mediated fusion. Since expression levels of the main NiV entry receptor ephrin-B2 (EB2) are highly regulated in vivo to fulfill the physiological functions in axon guidance and angiogenesis, the goal of this study was to determine if changes in the EB2 expression influence NiV infection.

Results

Surprisingly, transfection of increasing EB2 plasmid concentrations reduced cell-to-cell fusion both in cells expressing the NiV glycoproteins and in cells infected with NiV. This effect was attributed to the downregulation of the NiV glycoproteins from the cell surface. In addition to the influence on cell-to-cell fusion, increased EB2 expression significantly reduced the total amount of NiV-infected cells, thus interfered with virus entry. To determine if the negative effect of elevated EB2 expression on virus entry is a result of an increased EB2 signaling, receptor function of a tail-truncated and therefore signaling-defective ΔcEB2 was tested. Interestingly, ΔcEB2 fully functioned as NiV entry and fusion receptor, and overexpression also interfered with virus replication.

Conclusion

Our findings clearly show that EB2 signaling does not account for the striking negative impact of elevated receptor expression on NiV infection, but rather that the ratio between the NiV envelope glycoproteins and surface receptors critically influence cell-to-cell fusion and virus entry.

Animal models of henipavirus infection: a review

Hendra virus (HeV) and Nipah virus (NiV) form a separate genus Henipavirus within the family Paramyxoviridae, and are classified as biosafety level four pathogens due to their high case fatality rate following human infection and because of the lack of effective vaccines or therapy. Both viruses emerged from their natural reservoir during the last decade of the 20th century, causing severe disease in humans, horses and swine, and infecting a number of other mammalian species. The current review summarises current published data relating to experimental infection of small and large animals, including the natural reservoir species, the Pteropus bat, with HeV or NiV. Susceptibility to infection and virus distribution in the individual species is discussed, along with the pathogenesis, pathological changes, and potential routes of transmission.

Preparation of recombinant viral glycoproteins for novel and therapeutic antibody discovery

Neutralizing antibodies are a critical component in the protection or recovery from viral infections. In the absence of available vaccines or antiviral drugs for many important human viral pathogens, the identification and characterization of new human monoclonal antibodies (hmAbs) that are able to neutralize viruses offers the possibility for effective pre- and/or post-exposure therapeutic modalities. Such hmAbs may also help in our understanding of the virus entry process, the mechanisms of virus neutralization, and in the eventual development of specific entry inhibitors, vaccines, and research tools. The majority of the more recently developed antiviral hmAbs have come from the use of antibody phage-display technologies using both naïve and immune libraries. Many of these agents are also enveloped viruses possessing important neutralizing determinants within their membrane-anchored envelope glycoproteins, and the use of recombinant, soluble versions of these viral glycoproteins is often critical in the isolation and development of antiviral hmAbs. This chapter will detail several methods that have been successfully employed to produce, purify, and characterize soluble and secreted versions of several viral envelope glycoproteins which have been successfully used as antigens to capture and isolate human phage-displayed monoclonal antibodies.

Inhibition of Henipavirus infection by RNA interference

Nipah virus (NiV) and Hendra virus (HeV) are recently emerged zoonotic paramyxoviruses exclusively grouped within a new genus, Henipavirus. These viruses cause fatal disease in a wide range of species, including humans. Both NiV and HeV have continued to re-emerge sporadically in Bangladesh and Australia, respectively. There are currently no therapeutics or vaccines available to treat Henipavirus infection and both are classified as BSL4 pathogens.

RNA interference (RNAi) is a process by which double-stranded RNA directs sequence-specific degradation of messenger RNA in animal and plant cells. Small interfering RNAs (siRNAs) mediate RNAi by inhibiting gene expression of homologous mRNA and our preliminary studies suggest RNAi may be a useful approach to developing novel therapies for these highly lethal pathogens. Eight NiV siRNA molecules (four L and four N gene specific), two HeV N gene specific, and two non-specific control siRNA molecules were designed and tested for their ability to inhibit a henipavirus minigenome replication system (which does not require the use of live virus) in addition to live virus infections in vitro. In the minigenome assay three out of the four siRNAs that targeted the L gene of NiV effectively inhibited replication. In contrast, only NiV N gene siRNAs were effective in reducing live NiV replication, suggesting inhibition of early, abundantly expressed gene transcripts may be more effective than later, less abundant transcripts. Additionally, some of the siRNAs effective against NiV infection were only partially effective inhibitors of HeV infection. An inverse correlation between the number of nucleotide mismatches and the efficacy of siRNA inhibition was observed. The demonstration that RNAi effectively inhibits henipavirus replication in vitro, is a novel approach and may provide an effective therapy for these highly lethal, zoonotic pathogens.

A recombinant subunit vaccine formulation protects against lethal Nipah virus challenge in cats

Nipah virus (NiV) and Hendra virus (HeV) are closely related deadly zoonotic paramyxoviruses that have emerged and re-emerged over the last 10 years. In this study, a subunit vaccine formulation containing only recombinant, soluble, attachment glycoprotein from HeV (sG_HeV) and CpG adjuvant was evaluated as a potential NiV vaccine in the cat model. Different amounts of sG_HeV were employed and sG-induced immunity was examined. Vaccinated animals demonstrated varying levels of NiV-specific Ig systemically and importantly, all vaccinated cats possessed antigen-specific IgA on the mucosa. Upon oronasal challenge with NiV (50,000 TCID₅₀), all vaccinated animals were protected from disease although virus was detected on day 21 post-challenge in one animal. The ability to elicit protective systemic and mucosal immunity in this animal model provides significant progress towards the development of a human subunit vaccine against henipaviruses.

Functional studies of host-specific ephrin-B ligands as Henipavirus receptors

Hendra virus (HeV) and Nipah virus (NiV) are closely related paramyxoviruses that infect and cause disease in a wide range of mammalian hosts. To determine whether host receptor molecules play a role in species-specific and/or virus-specific infection we have cloned and characterized ephrin-B2 and ephrin-B3 ligands from a range of species, including human, horse, pig, cat, dog, bats (Pteropus alecto and Pteropus vampyrus) and mouse. HeV and NiV were both able to infect cells expressing any of the ephrin-B2 and ephrin-B3 molecules. There did not appear to be significant differences in receptor function from different species or receptor usage by HeV and NiV. Soluble ephrin ligands, their receptors and G-specific human monoclonal antibodies differentially blocked henipavirus infections suggesting different receptor affinities, overlapping receptor binding domains of the henipavirus attachment glycoprotein (G) and that the functional domains of the ephrin ligands may be important for henipavirus binding.

Animal models of highly pathogenic RNA viral infections: encephalitis viruses

The highly pathogenic RNA viruses that cause encephalitis include a significant number of emerging or re-emerging viruses that are also considered potential bioweapons. Many of these viruses, including members of the family Flaviviridae, the genus Alphavirus in the family Togaviridae, and the genus Henipavirus in the family Paramyxoviridae, circulate widely in their endemic areas, where they are transmitted by mosquitoes or ticks. They use a variety of vertebrate hosts, ranging from birds to bats, in their natural life cycle. As was discovered in the United States, the introduction of a mosquito-borne encephalitis virus such as West Nile virus can cause significant health and societal concerns. There are no effective therapeutics for treating diseases caused by any of these viruses and there is limited, if any, vaccine availability for most. In this review we provide a brief summary of the current status of animal models used to study highly pathogenic encephalitic RNA viruses for the development of antiviral therapeutics and vaccines.

Tioman virus, a paramyxovirus of bat origin, causes mild disease in pigs and has a predilection for lymphoid tissues

Disease manifestation, pathology, and tissue tropism following infection with Tioman virus (TioPV), a newly isolated, bat-derived paramyxovirus, was investigated in subcutaneously (n = 12) and oronasally (n = 4) inoculated pigs. Pigs were either asymptomatic or developed pyrexia, but all of the animals produced neutralizing antibodies. The virus (viral antigen and/or genome) was detected in lymphocytes of the thymus, tonsils, spleen, lymph nodes and Peyer's patches (ileum), tonsillar epithelium, and thymic epithelioreticular cells. Virus was isolated from oral swabs but not from urine. Our findings suggest that the pig could act as an intermediate or amplifying host for TioPV and that oral secretion is a possible means of viral transmission.

Targeted strategies for henipavirus therapeutics

Hendra and Nipah viruses are related emergent paramyxoviruses that infect and cause disease in animals and humans. Disease manifests as a generalized vasculitis affecting multiple organs, but is the most severe in the respiratory and central nervous systems. The high case fatality and person-to-person transmission associated with the most recent NiV outbreaks, and the recent re-emergence of HeV, emphasize the importance and necessity of effective therapeutics for these novel agents. In recent years henipavirus research has revealed a more complete understanding of pathogenesis and, as a consequence, viable approaches towards vaccines and therapeutics have emerged. All strategies target early steps in viral replication including receptor binding and membrane fusion. Animal models have been developed, some of which may prove more valuable than others for evaluating the efficacy of therapeutic agents and regimes. Assessments of protective host immunity and drug pharmacokinetics will be crucial to the further advancement of therapeutic compounds.

Recent progress in henipavirus research

Following the discovery of two new paramyxoviruses in the 1990s, much effort has been placed on rapidly finding the reservoir hosts, characterising the genomes, identifying the viral receptors and formulating potential vaccines and therapeutic options for these viruses, Hendra and Nipah viruses caused zoonotic disease on a scale not seen before with other paramyxoviruses. Nipah virus particularly caused high morbidity and mortality in humans and high morbidity in pig populations in the first outbreak in Malaysia. Both viruses continue to pose a threat with sporadic outbreaks continuing into the 21st century. Experimental and surveillance studies identified that pteropus bats are the reservoir hosts. Research continues in an attempt to understand events that precipitated spillover of these viruses. Discovered on the cusp of the molecular technology revolution, much progress has been made in understanding these new viruses. This review endeavours to capture the depth and breadth of these recent advances.

Neutralization assays for differential henipavirus serology using Bio-Plex Protein Array Systems

Hendra virus (HeV) and Nipah virus (NiV) are related emerging paramyxoviruses classified in the genus Henipavirus. Both cause fatal disease in animals and humans and are classified as biosafety level 4 pathogens. Here we detail two new multiplexed microsphere assays, one for antibody detection and differentiation and another designed as a surrogate for virus neutralization. Both assays utilize recombinant soluble attachment glycoproteins (sG) whereas the latter incorporates the cellular receptor, recombinant ephrin-B2. Spectrally distinct sG(HeV)- and sG(NiV)-coupled microspheres preferentially bound antibodies from HeV- and NiV-seropositive animals, demonstrating a simple procedure to differentiate antibodies to these closely related viruses. Soluble ephrin-B2 bound sG-coupled microspheres in a dose-dependent fashion. Specificity of binding was further evaluated with henipavirus G-specific sera and MAbs. Sera from henipavirus-seropositive animals differentially blocked ephrin-B2 binding, suggesting that detection and differentiation of HeV and NiV neutralizing antibodies can be done simultaneously in the absence of live virus.

Pathobiology of henipavirus entry: insights into therapeutic strategies

The recently emerged paramyxoviruses, Nipah (NiV) and Hendra (HeV), designated as Biosafety Level 4 pathogens, can cause lethal respiratory and neurological disease in both animals and humans. NiV outbreaks have been associated with efficient transmission amongst livestock (pigs) and mortality rates exceeding 70%, with documented cases of human-to-human transmission. Without vaccines or effective therapeutics, NiV and HeV continue to present an impending threat to global health and economies. The current understanding of henipavirus pathobiology has led to the development of small animal models reflecting certain aspects of the human pathology. In this review, we discuss how these animal models have been critical in testing vaccination strategies and in eliciting neutralizing antibodies against the envelope glycoproteins. Additionally, the discovery of the viral receptor and development of pseudotyped-viral systems have allowed us to explore the multiple opportunities for therapeutic intervention existing within the individual steps of the henipavirus entry pathway. Current research shows promise for the future development of effective strategies to limit the impact of these biological threats.

Quantitative analysis of Nipah virus proteins released as virus-like particles reveals central role for the matrix protein

Background

Nipah virus (NiV) is an emerging paramyxovirus distinguished by its ability to cause fatal disease in both animal and human hosts. Together with Hendra virus (HeV), they comprise the genus Henipavirus in the Paramyxoviridae family. NiV and HeV are also restricted to Biosafety Level-4 containment and this has hampered progress towards examining details of their replication and morphogenesis. Here, we have established recombinant expression systems to study NiV particle assembly and budding through the formation of virus-like particles (VLPs).

Results

When expressed by recombinant Modified Vaccinia virus Ankara (rMVA) or plasmid transfection, individual NiV matrix (M), fusion (F) and attachment (G) proteins were all released into culture supernatants in a membrane-associated state as determined by sucrose density gradient flotation and immunoprecipitation. However, co-expression of F and G along with M revealed a shift in their distribution across the gradient, indicating association with M in VLPs. Protein release was also altered depending on the context of viral proteins being expressed, with F, G and nucleocapsid (N) protein reducing M release, and N release dependent on the co-expression of M. Immunoelectron microscopy and density analysis revealed VLPs that were similar to authentic virus. Differences in the budding dynamics of NiV proteins were also noted between rMVA and plasmid based strategies, suggesting that over-expression by poxvirus may not be appropriate for studying the details of recombinant virus particle assembly and release.

Conclusion

Taken together, the results indicate that NiV M, F, and G each possess some ability to bud from expressing cells, and that co-expression of these viral proteins results in a more organized budding process with M playing a central role. These findings will aid our understanding of paramyxovirus particle assembly in general and could help facilitate the development of a novel vaccine approach for henipaviruses.