Nipah virus infection, an emerging paramyxoviral zoonosis

Pathogenicity and virulence of henipaviruses

Paramyxoviruses are a family of single-stranded negative-sense RNA viruses, many of which are responsible for a range of respiratory and neurological diseases in humans and animals. Among the most notable are the henipaviruses, which include the deadly Nipah (NiV) and Hendra (HeV) viruses, the causative agents of outbreaks of severe disease and high case fatality rates in humans and animals. NiV and HeV are maintained in fruit bat reservoirs primarily in the family Pteropus and spillover into humans directly or by an intermediate amplifying host such as swine or horses. Recently, non-chiropteran associated Langya (LayV), Gamak (GAKV), and Mojiang (MojV) viruses have been discovered with confirmed or suspected ability to cause disease in humans or animals. These viruses are less genetically related to HeV and NiV yet share many features with their better-known counterparts. Recent advances in surveillance of wild animal reservoir viruses have revealed a high number of henipaviral genome sequences distributed across most continents, and mammalian orders previously unknown to harbour henipaviruses. In this review, we summarize the current knowledge on the range of pathogenesis observed for the henipaviruses as well as their replication cycle, epidemiology, genomics, and host responses. We focus on the most pathogenic viruses, including NiV, HeV, LayV, and GAKV, as well as the experimentally non-pathogenic CedV. We also highlight the emerging threats posed by these and potentially other closely related viruses.

Henipavirus Immune Evasion and Pathogenesis Mechanisms: Lessons Learnt from Natural Infection and Animal Models

Nipah henipavirus (NiV) and Hendra henipavirus (HeV) are zoonotic emerging paramyxoviruses causing severe disease outbreaks in humans and livestock, mostly in Australia, India, Malaysia, Singapore and Bangladesh. Both are bat-borne viruses and in humans, their mortality rates can reach 60% in the case of HeV and 92% for NiV, thus being two of the deadliest viruses known for humans. Several factors, including a large cellular tropism and a wide zoonotic potential, con-tribute to their high pathogenicity. This review provides an overview of HeV and NiV pathogenicity mechanisms and provides a summary of their interactions with the immune systems of their different host species, including their natural hosts bats, spillover-hosts pigs, horses, and humans, as well as in experimental animal models. A better understanding of the interactions between henipaviruses and their hosts could facilitate the development of new therapeutic strategies and vaccine measures against these re-emerging viruses.

Nipah Virus Efficiently Replicates in Human Smooth Muscle Cells without Cytopathic Effect

Nipah virus (NiV) is a highly pathogenic zoonotic virus with a broad species tropism, originating in pteropid bats. Human outbreaks of NiV disease occur almost annually, often with high case-fatality rates. The specific events that lead to pathogenesis are not well defined, but the disease has both respiratory and encephalitic components, with relapsing encephalitis occurring in some cases more than a year after initial infection. Several cell types are targets of NiV, dictated by the expression of the ephrin-B2/3 ligand on the cell's outer membrane, which interact with the NiV surface proteins. Vascular endothelial cells (ECs) are major targets of infection. Cytopathic effects (CPE), characterized by syncytia formation and cell death, and an ensuing vasculitis, are a major feature of the disease. Smooth muscle cells (SMCs) of the tunica media that line small blood vessels are infected in humans and animal models of NiV disease, although pathology or histologic changes associated with antigen-positive SMCs have not been reported. To gain an understanding of the possible contributions that SMCs might have in the development of NiV disease, we investigated the susceptibility and potential cytopathogenic changes of human SMCs to NiV infection in vitro. SMCs were permissive for NiV infection and resulted in high titers and prolonged NiV production, despite a lack of cytopathogenicity, and in the absence of detectable ephrin-B2/3. These results indicate that SMC might be important contributors to disease by producing progeny NiV during an infection, without suffering cytopathogenic consequences.

Interactions of the Nipah Virus P, V, and W Proteins across the STAT Family of Transcription Factors

The Nipah virus (NiV) phosphoprotein (P) gene encodes four proteins. Three of these-P, V, and W-possess a common N-terminal domain but distinct C termini. These proteins interact with immune modulators. Previous studies demonstrated that P, V, and W bind STAT1 and STAT4 and that V also interacts with STAT2 but not with STAT3. The STAT1 and STAT2 interactions block interferon (IFN)-induced STAT tyrosine phosphorylation. To more fully characterize the interactions of P, V, and W with the STATs, we screened for interaction of each viral protein with STATs 1 to 6 by coimmunoprecipitation. We demonstrate that NiV P, V, and W interact with STAT4 through their common N-terminal domain and block STAT4 activity, based on a STAT4 response element reporter assay. Although none of the NiV proteins interact with STAT3 or STAT6, NiV V, but not P or W, interacts with STAT5 through its unique C terminus. Furthermore, the interaction of NiV V with STAT5 was not disrupted by overexpression of the N-terminal binding STAT1 or the C-terminal binding MDA5. NiV V also inhibits a STAT5 response element reporter assay. Residues 114 to 140 of the common N-terminal domain of the NiV P gene products were found to be sufficient to bind STAT1 and STAT4. Analysis of STAT1-STAT3 chimeras suggests that the P gene products target the STAT1 SH2 domain. When fused to GST, the 114-140 peptide is sufficient to decrease STAT1 phosphorylation in IFN-β-stimulated cells, suggesting that this peptide could potentially be fused to heterologous proteins to confer inhibition of STAT1- and STAT4-dependent responses.IMPORTANCE How Nipah virus (NiV) antagonizes innate immune responses is incompletely understood. The P gene of NiV encodes the P, V, and W proteins. These proteins have a common N-terminal sequence that is sufficient to bind to STAT1 and STAT2 and block IFN-induced signal transduction. This study sought to more fully understand how P, V, and W engage with the STAT family of transcription factors to influence their functions. The results identify a novel interaction of V with STAT5 and demonstrate V inhibition of STAT5 function. We also demonstrate that the common N-terminal residues 114 to 140 of P, V, and W are critical for inhibition of STAT1 and STAT4 function, map the interaction to the SH2 region of STAT1, and show that a fusion construct with this peptide significantly inhibits cytokine-induced STAT1 phosphorylation. These data clarify how these important virulence factors modulate innate antiviral defenses.

Neurological Damage by Coronaviruses: A Catastrophe in the Queue!

Neurological disorders caused by neuroviral infections are an obvious pathogenic manifestation. However, non-neurotropic viruses or peripheral viral infections pose a considerable challenge as their neuropathological manifestations do not emerge because of primary infection. Their secondary or bystander pathologies develop much later, like a syndrome, during and after the recovery of patients from the primary disease. Massive inflammation caused by peripheral viral infections can trigger multiple neurological anomalies. These neurological damages may range from a general cognitive and motor dysfunction up to a wide spectrum of CNS anomalies, such as Acute Necrotizing Hemorrhagic Encephalopathy, Guillain-Barré syndrome, Encephalitis, Meningitis, anxiety, and other audio-visual disabilities. Peripheral viruses like Measles virus, Enteroviruses, Influenza viruses (HIN1 series), SARS-CoV-1, MERS-CoV, and, recently, SARS-CoV-2 are reported to cause various neurological manifestations in patients and are proven to be neuropathogenic even in cellular and animal model systems. This review presents a comprehensive picture of CNS susceptibilities toward these peripheral viral infections and explains some common underlying themes of their neuropathology in the human brain.

A 'what-if' scenario: Nipah virus attacks pig trade chains in Thailand

Background

Nipah virus (NiV) is a fatal zoonotic agent that was first identified amongst pig farmers in Malaysia in 1998, in an outbreak that resulted in 105 fatal human cases. That epidemic arose from a chain of infection, initiating from bats to pigs, and which then spilled over from pigs to humans. In Thailand, bat-pig-human communities can be observed across the country, particularly in the central plain. The present study therefore aimed to identify high-risk areas for potential NiV outbreaks and to model how the virus is likely to spread. Multi-criteria decision analysis (MCDA) and weighted linear combination (WLC) were employed to produce the NiV risk map. The map was then overlaid with the nationwide pig movement network to identify the index subdistricts in which NiV may emerge. Subsequently, susceptible-exposed-infectious-removed (SEIR) modeling was used to simulate NiV spread within each subdistrict, and network modeling was used to illustrate how the virus disperses across subdistricts.

Results

Based on the MCDA and pig movement data, 14 index subdistricts with a high-risk of NiV emergence were identified. We found in our infectious network modeling that the infected subdistricts clustered in, or close to the central plain, within a range of 171 km from the source subdistricts. However, the virus may travel as far as 528.5 km (R₀ = 5).

Conclusions

In conclusion, the risk of NiV dissemination through pig movement networks in Thailand is low but not negligible. The risk areas identified in our study can help the veterinary authority to allocate financial and human resources to where preventive strategies, such as pig farm regionalization, are required and to contain outbreaks in a timely fashion once they occur.

Detailed Molecular Biochemistry for Novel Therapeutic Design Against Nipah and Hendra Virus: A Systematic Review

BACKGROUND

Nipah virus (NiV) and Hendra virus (HeV) of genus Henipavirus are the deadliest zoonotic viruses, which cause severe respiratory ailments and fatal encephalitis in humans and other susceptible animals. The fatality rate for these infections had been alarmingly high with no approved treatment available to date. Viral attachment and fusion with host cell membrane is essential for viral entry and is the most essential event of viral infection. Viral attachment is mediated by interaction of Henipavirus attachment glycoprotein (G) with the host cell receptor: Ephrin B2/B3, while viral fusion and endocytosis are mediated by the combined action of both viral glycoprotein (G) and fusion protein (F).

CONCLUSION

This review highlights the mechanism of viral attachment, fusion and also explains the basic mechanism and pathobiology of this infection in humans. The drugs and therapeutics used either experimentally or clinically against NiV and HeV infection have been documented and classified in detail. Some amino acid residues essential for the functionality of G and F proteins were also emphasized. Therapeutic designing to target and block these residues can serve as a promising approach in future drug development against NiV and HeV.

Navigating Research Toward the Re-emerging Nipah Virus- A New Piece to the Puzzle

BACKGROUND

The recent Nipah virus (NiV) outbreak in India has caused a state of chaos, with potential to become the next international pandemic. There is still a great deal to learn about NiV for the development of a potent treatment against it. The NiV non-structural proteins play important roles in the lifecycle of the virus, with the RNA-dependent RNA-polymerase (RdRp) being a vital component in viral replication. In this study, we not only provide a comprehensive overview of all the literature concerning NiV, we also propose a model of the NiV RdRp and screen for potential inhibitors of the viral enzyme.

METHODS

In this study, computational tools were utilized in the design of a NiV RdRp homology model. The active site of RdRp was then identified and potential inhibitors of the protein were discovered with the use of pharmacophore-based screening.

RESULTS

Ramachandran plot analysis revealed a favourable model. Upon binding of nucleoside analog, 4'- Azidocytidine, active site residues Trp1714 and Ser1713 took part in stabilizing hydrogen bonds, while Thr1716, Ser1478, Ser1476 and Glu1465 contributed to hydrophobic interactions. Pharmacophore based screening yielded 18 hits, of which ZINC00085930 demonstrated the most optimal binding energy (-8.1 kcal/mol), validating its use for further analysis as an inhibitor of NiV.

CONCLUSION

In this study we provide a critical guide, elucidating on the in silico requirements of the drug design and discovery process against NiV. This material lays a foundation for future research into the design and development of drugs that inhibit NiV.

Case fatality rate and risk factors for Nipah virus encephalitis: A systematic review and meta-analysis

BACKGROUND

A wide range of Nipah virus (NiV) encephalitis case fatality rates (CFR) have been reported. Data on the involvement of several potential risk factors in Nipah virus transmission remain controversial. We performed a systematic review and meta-analysis to estimate the pooled CFR of NiV encephalitis and to assess the risk factors for NiV infection.

METHODS

Articles published up to the 27^thof November 2018 in MedLine, Embase and Web of knowledge databases were considered for this study. We included cross-sectional, cohort, and case-control studies that have reported NiV CFR and/or risk factors. Data were pooled with random-effects model. This review was registered in the PROSPERO, CRD42018116242.

FINDINGS

This global review included 22 citations (25 studies) including 2156, 1682, and 474 suspected, probable, and confirmed cases of NiV encephalitis, respectively. We determined a pooled CFR for NiV encephalitis at 61.0% (95% CI, 45.7-75.4; I² = 96.8%). Climbing trees (OR = 1.4; 95% CI; 1.0-1.9), male gender (OR = 1.5; 95% CI; 1.1-2.0), travel outside their own sub-district (OR = 2.0; 95% CI; 1.4-2.9), and exposure to date palm sap (DPS) (OR = 5.7; 95% CI; 3.8-8.6) or pigs (OR = 7.6; 95% CI; 1.2-45.4) were significantly associated with NiV infection.

CONCLUSION

Findings from this study suggest that NiV Encephalitis is associated with a high CFR and that male gender, travel outside their sub-district, climbing trees, and exposure to pigs and DPS are associated with an increased risk of NiV encephalitis.

Analysis of codon usage patterns and influencing factors in Nipah virus

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Nipah virus (NiV) genes are AT-rich.

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Codon usage bias of NiV genes is low.

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Patterns of codon usage bias differ across the genomes of NiV.

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Both mutation pressure and natural selection influenced codon usage bias of NiV genes.

Codon usage bias (CUB) is the unequal usage of synonymous codons of an amino acid in which some codons are used more often than others and is widely used in understanding molecular biology, genetics, and functional regulation of gene expression. Nipah virus (NiV) is an emerging zoonotic paramyxovirus that causes fatal disease in both humans and animals. NiV was first identified during an outbreak of a disease in Malaysia in 1998 and then occurred periodically since 2001 in India, Bangladesh, and the Philippines. We used bioinformatics tools to analyze the codon usage patterns in a genome-wide manner among 11 genomes of NiV as no work was reported yet. The compositional properties revealed that the overall GC and AT contents were 41.96 and 58.04%, respectively i.e. Nipah virus genes were AT-rich. Correlation analysis between overall nucleotide composition and its 3^rd codon position suggested that both mutation pressure and natural selection might influence the CUB across Nipah genomes. Neutrality plot revealed natural selection might have played a major role while mutation pressure had a minor role in shaping the codon usage bias in NiV genomes.

Exploring the Human-Nipah Virus Protein-Protein Interactome

Nipah virus is an emerging, highly pathogenic, zoonotic virus of the Paramyxoviridae family. Human transmission occurs by close contact with infected animals, the consumption of contaminated food, or, occasionally, via other infected individuals. Currently, we lack therapeutic or prophylactic treatments for Nipah virus. To develop these agents we must now improve our understanding of the host-virus interactions that underpin a productive infection. This aim led us to perform the present work, in which we identified 101 human-Nipah virus protein-protein interactions (PPIs), most of which (88) are novel. This data set provides a comprehensive view of the host complexes that are manipulated by viral proteins. Host targets include the PRP19 complex and the microRNA (miRNA) processing machinery. Furthermore, we explored the biologic consequences of the interaction with the PRP19 complex and found that the Nipah virus W protein is capable of altering p53 control and gene expression. We anticipate that these data will help in guiding the development of novel interventional strategies to counter this emerging viral threat.IMPORTANCE Nipah virus is a recently discovered virus that infects a wide range of mammals, including humans. Since its discovery there have been yearly outbreaks, and in some of them the mortality rate has reached 100% of the confirmed cases. However, the study of Nipah virus has been largely neglected, and currently we lack treatments for this infection. To develop these agents we must now improve our understanding of the host-virus interactions that underpin a productive infection. In the present work, we identified 101 human-Nipah virus protein-protein interactions using an affinity purification approach coupled with mass spectrometry. Additionally, we explored the cellular consequences of some of these interactions. Globally, this data set offers a comprehensive and detailed view of the host machinery's contribution to the Nipah virus's life cycle. Furthermore, our data present a large number of putative drug targets that could be exploited for the treatment of this infection.

Contribution of Human Lung Parenchyma and Leukocyte Influx to Oxidative Stress and Immune System-Mediated Pathology following Nipah Virus Infection

Nipah virus (NiV) is a zoonotic emerging paramyxovirus that can cause fatal respiratory illness or encephalitis in humans. Despite many efforts, the molecular mechanisms of NiV-induced acute lung injury (ALI) remain unclear. We previously showed that NiV replicates to high titers in human lung grafts in NOD-SCID/γ mice, resulting in a robust inflammatory response. Interestingly, these mice can undergo human immune system reconstitution by the bone marrow, liver, and thymus (BLT) reconstitution method, in addition to lung tissue engraftment, giving altogether a realistic model to study human respiratory viral infections. Here, we characterized NiV Bangladesh strain (NiV-B) infection of human lung grafts from human immune system-reconstituted mice in order to identify the overall effect of immune cells on NiV pathogenesis of the lung. We show that NiV-B replicated to high titers in human lung grafts and caused similar cytopathic effects irrespective of the presence of human leukocytes in mice. However, the human immune system interfered with virus spread across lung grafts, responded to infection by leukocyte migration to small airways and alveoli of the lung grafts, and accelerated oxidative stress in lung grafts. In addition, the presence of human leukocytes increased the expression of cytokines and chemokines that regulate inflammatory influx to sites of infection and tissue damage. These results advance our understanding of how the immune system limits NiV dissemination and contributes to ALI and inform efforts to identify therapeutic targets.IMPORTANCE Nipah virus (NiV) is an emerging paramyxovirus that can cause a lethal respiratory and neurological disease in humans. Only limited data are available on NiV pathogenesis in the human lung, and the relative contribution of the innate immune response and NiV to acute lung injury (ALI) is still unknown. Using human lung grafts in a human immune system-reconstituted mouse model, we showed that the NiV Bangladesh strain induced cytopathic lesions in lung grafts similar to those described in patients irrespective of the donor origin or the presence of leukocytes. However, the human immune system interfered with virus spread, responded to infection by leukocyte infiltration in the small airways and alveolar area, induced oxidative stress, and triggered the production of cytokines and chemokines that regulate inflammatory influx by leukocytes in response to infection. Understanding how leukocytes interact with NiV and cause ALI in human lung xenografts is crucial for identifying therapeutic targets.

Henipavirus Encephalitis: Recent Developments and Advances

The genus Henipavirus within the family Paramyxoviridae includes the Hendra virus (HeV) and Nipah virus (NiV) which were discovered in the 1990s in Australia and Malaysia, respectively, after emerging to cause severe and often fatal outbreaks in humans and animals. While HeV is confined to Australia, more recent NiV outbreaks have been reported in Bangladesh, India and the Philippines. The clinical manifestations of both henipaviruses in humans appear similar, with a predominance of an acute encephalitic syndrome. Likewise, the pathological features are similar and characterized by disseminated, multi-organ vasculopathy comprising endothelial infection/ulceration, vasculitis, vasculitis-induced thrombosis/occlusion, parenchymal ischemia/microinfarction, and parenchymal cell infection in the central nervous system (CNS), lung, kidney and other major organs. This unique dual pathogenetic mechanism of vasculitis-induced microinfarction and neuronal infection causes severe tissue damage in the CNS. Both viruses can also cause relapsing encephalitis months and years after the acute infection. Many animal models studied to date have largely confirmed the pathology of henipavirus infection, and provided the means to test new therapeutic agents and vaccines. As the bat is the natural host of henipaviruses and has worldwide distribution, spillover events into human populations are expected to occur in the future.

Henipavirus pathogenesis and antiviral approaches

Hendra virus and Nipah virus are closely related, recently emerged zoonotic paramyxoviruses, belonging to the Henipavirus genus. Both viruses induce generalized vasculitis affecting particularly the respiratory tract and CNS. The exceptionally broad species tropism of Henipavirus, the high case fatality rate and person-to-person transmission associated with Nipah virus outbreaks emphasize the necessity of effective antiviral strategies for these intriguing threatening pathogens. Current therapeutic approaches, validated in animal models, target early steps in viral infection; they include the use of neutralizing virus-specific antibodies and blocking membrane fusion with peptides that bind the viral fusion protein. A better understanding of Henipavirus pathogenesis is critical for the further advancement of antiviral treatment, and we summarize here the recent progress in the field.

Transmission routes for nipah virus from Malaysia and Bangladesh

Human infections with Nipah virus in Malaysia and Bangladesh are associated with markedly different patterns of transmission and pathogenicity. To compare the 2 strains, we conducted an in vivo study in which 2 groups of ferrets were oronasally exposed to either the Malaysia or Bangladesh strain of Nipah virus. Viral shedding and tissue tropism were compared between the 2 groups. Over the course of infection, significantly higher levels of viral RNA were recovered from oral secretions of ferrets infected with the Bangladesh strain. Higher levels of oral shedding of the Bangladesh strain of Nipah virus might be a key factor in onward transmission in outbreaks among humans.

Henipaviruses: an updated review focusing on the pteropid reservoir and features of transmission

The henipaviruses, Hendra virus and Nipah virus, are pathogens that have emerged from flying foxes in Australia and South-east Asia to infect both livestock and humans, often fatally. Since the emergence of Hendra virus in Australia in 1994 and the identification of Australian flying foxes as hosts to this virus, our appreciation of bats as reservoir hosts of henipaviruses has expanded globally to include much of Asia and areas of Africa. Despite this, little is currently known of the mechanisms by which bats harbour viruses capable of causing such severe disease in other terrestrial mammals. Pteropid bat ecology, henipavirus virology, therapeutic developments and features of henipavirus infection, pathology and disease in humans and other mammals are reviewed elsewhere in detail. This review focuses on bats as reservoir hosts to henipaviruses and features of transmission of Hendra virus and Nipah virus following spillover from these reservoir hosts.

Clinical and pathological manifestations of human henipavirus infection

The clinicopathological features of human Nipah virus and Hendra virus infections appear to be similar. The clinical manifestations may be mild, but if severe, includes acute encephalitic and pulmonary syndromes with a high mortality. The pathological features in human acute henipavirus infections comprise vasculopathy (vasculitis, endothelial multinucleated syncytia, thrombosis), microinfarcts and parenchymal cell infection in the central nervous system, lung, kidney and other major organs. Viral inclusions, antigens, nucleocapsids and RNA are readily demonstrated in blood vessel wall and numerous types of parenchymal cells. Relapsing henipavirus encephalitis is a rare complication reported in less than 10% of survivors of the acute infection and appears to be distinct from the acute encephalitic syndrome. Pathological evidence suggests viral recrudescence confined to the central nervous system as the cause.

Henipaviruses in their natural animal hosts

Hendra virus (HeV) and Nipah virus (NiV) form a separate genus Henipavirus within the family Paramyxoviridae, and are classified as biosafety level 4 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 twentieth century, causing severe disease in humans, horses and swine, and infecting a number of other mammalian species. The current review summarizes our up to date understanding of pathology and pathogenesis in the natural reservoir species, the Pteropus bat, and in the equine and porcine spill over species.

Pathology of acute henipavirus infection in humans and animals

Zoonoses as causes of human infections have been increasingly reported, and many of these are viruses that cause central nervous system infections. This paper focuses on the henipaviruses (family Paramyxoviridae, genus henipavirus) that have recently emerged to cause severe encephalitis and systemic infection in humans and animals in the Asia-Pacific region. The pathological features in the human infections comprise vasculopathy (vasculitis, endothelial multinucleated syncytia, thrombosis, etc.) and parenchymal cell infection in the central nervous system, lung, kidney, and other major organs. Most animals naturally or experimentally infected show more or less similar features confirming the dual pathogenetic mechanism of vasculopathy-associated microinfarction and direct extravascular parenchymal cell infection as causes of tissue injury. The most promising animal models include the hamster, ferret, squirrel monkey, and African green monkey. With increasing evidence of infection in the natural hosts, the pteropid bats and, hence, probable future outbreaks in many more countries, a greater awareness of henipavirus infection in both humans and animals is imperative.

A review of Nipah and Hendra viruses with an historical aside

The emergence of Hendra and Nipah viruses in the 1990s has been followed by the further emergence of these viruses in the tropical Old World. The history and current knowledge of the disease, the viruses and their epidemiology is reviewed in this article. A historical aside summarizes the role that Dr. Brian W.J. Mahy played at critical junctures in the early stories of these viruses.

Emerging epidemic viral encephalitides with a special focus on henipaviruses

In the last few decades, there is an increasing emergence and re-emergence of viruses, such as West Nile virus, Enterovirus 71 and henipaviruses that cause epidemic viral encephalitis and other central nervous system (CNS) manifestations. The mortality and morbidity associated with these outbreaks are significant and frequently severe. While aspects of epidemiology, basic virology, etc., may be known, the pathology and pathogenesis are often less so, partly due to a lack of interest among pathologists or because many of these infections are considered "third world" diseases. In the study of epidemic viral encephalitis, the pathologist's role in unravelling the pathology and pathogenesis is critical. The novel henipavirus infection is a good example. The newly created genus Henipavirus within the family Paramyxoviridae consists of two viruses, viz., Hendra virus and Nipah virus. These two viruses emerged in Australia and Asia, respectively, to cause severe encephalitides in humans and animals. Studies show that the pathological features of the acute encephalitis caused by henipaviruses are similar and a unique dual pathogenetic mechanism of vasculitis-induced microinfarction and parenchymal cell infection in the CNS (mainly neurons) and other organs causes severe tissue damage. Both viruses can cause relapsing encephalitis months and years after the acute infection due to a true recurrent infection as evidenced by the presence of virus in infected cells. Future emerging viral encephalitides will no doubt continue to pose considerable challenges to the neuropathologist, and as the West Nile virus outbreak demonstrates, even economically advanced nations are not spared.

Emerging and re-emerging viruses in Malaysia, 1997-2007

Over the past decade, a number of unique zoonotic and non-zoonotic viruses have emerged in Malaysia. Several of these viruses have resulted in significant morbidity and mortality to those affected and they have imposed a tremendous public health and economic burden on the state. Amongst the most devastating was the outbreak of Nipah virus encephalitis in 1998, which resulted in 109 deaths. The culling of more than a million pigs, identified as the amplifying host, ultimately brought the outbreak under control. A year prior to this, and subsequently again in 2000 and 2003, large outbreaks of hand-foot-and-mouth disease due to enterovirus 71, with rare cases of fatal neurological complications, were reported in young children. Three other new viruses – Tioman virus (1999), Pulau virus (1999), and Melaka virus (2006) – whose origins have all been linked to bats, have been added to the growing list of novel viruses being discovered in Malaysia. The highly pathogenic H5N1 avian influenza has also been detected in Malaysia with outbreaks in poultry in 2004, 2006, and 2007. Fortunately, no human infections were reported. Finally, the HIV/AIDS epidemic has seen the emergence of an HIV-1 recombinant form (CRF33_01B) in HIV-infected individuals from various risk groups, with evidence of ongoing and rapid expansion.

Envelope-receptor interactions in Nipah virus pathobiology

abstract: Nipah (NiV) and Hendra (HeV) viruses are members of the newly defined Henipavirus genus of the Paramyxoviridae. Nipah virus (NiV) is an emergent paramyxovirus that causes fatal encephalitis in up to 70% of infected patients, and there is increasing evidence of human‐to‐human transmission. NiV is designated a priority pathogen in the NIAID Biodefense Research Agenda, and could be a devastating agent of agrobioterrorism if used against the pig farming industry. Endothelial syncytium is a pathognomonic feature of NiV infections, and is mediated by the fusion (F) and attachment (G) envelope glycoproteins. This review summarizes what is known about the pathophysiology of NiV infections, and documents the identification of the NiV receptor. EphrinB2, the NiV and HeV receptor, is expressed on endothelial cells and neurons, consistent with the known cellular tropism for NiV. We discuss how the identification of the henipahvirus receptor sheds light on the pathobiology of NiV infection, and how it will spur the rational development of effective therapeutics. In addition, ephrinB3, a related protein, can serve as an alternative receptor, and we suggest that differential usage of ephrinB2 versus B3 may explain the variant pathogenic profiles observed between NiV and HeV. Thus, identifying the NiV receptors opens the door for a more comprehensive analysis of the envelope–receptor interactions in NiV pathobiology. Finally, we also describe how galectin‐1 (an innate immune defense lectin) can interact with specific N‐glycans on the Nipah envelope fusion protein, underscoring the potential role that innate immune defense mechanisms may play against emerging pathogens.

Rapid identification of emerging infectious agents using PCR and electrospray ionization mass spectrometry

abstract: Newly emergent infectious diseases are a global public health problem. The population dense regions of Southeast Asia are the epicenter of many emerging diseases, as evidenced by the outbreak of Nipah, SARS, avian influenza (H5N1), Dengue, and enterovirus 71 in this region in the past decade. Rapid identification, epidemiologic surveillance, and mitigation of transmission are major challenges in ensuring public health safety. Here we describe a powerful new approach for infectious disease surveillance that is based on polymerase chain reaction (PCR) to amplify nucleic acid targets from large groupings of organisms, electrospray ionization mass spectrometry (ESI‐MS) for accurate mass measurements of the PCR products, and base composition signature analysis to identify organisms in a sample. This approach is capable of automated analysis of more than 1,500 PCR reactions a day. It is applicable to the surveillance of bacterial, viral, fungal, or protozoal pathogens and will facilitate rapid characterization of known and emerging pathogens.

Human neuronal cell protein responses to Nipah virus infection

BACKGROUND

Nipah virus (NiV), a recently discovered zoonotic virus infects and replicates in several human cell types. Its replication in human neuronal cells, however, is less efficient in comparison to other fully susceptible cells. In the present study, the SK-N-MC human neuronal cell protein response to NiV infection is examined using proteomic approaches.

RESULTS

Method for separation of the NiV-infected human neuronal cell proteins using two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) was established. At least 800 protein spots were resolved of which seven were unique, six were significantly up-regulated and eight were significantly down-regulated. Six of these altered proteins were identified using mass spectrometry (MS) and confirmed using MS/MS. The heterogenous nuclear ribonucleoprotein (hnRNP) F, guanine nucleotide binding protein (G protein), voltage-dependent anion channel 2 (VDAC2) and cytochrome bc1 were present in abundance in the NiV-infected SK-N-MC cells in contrast to hnRNPs H and H2 that were significantly down-regulated.

CONCLUSION

Several human neuronal cell proteins that are differentially expressed following NiV infection are identified. The proteins are associated with various cellular functions and their abundance reflects their significance in the cytopathologic responses to the infection and the regulation of NiV replication. The potential importance of the ratio of hnRNP F, and hnRNPs H and H2 in regulation of NiV replication, the association of the mitochondrial protein with the cytopathologic responses to the infection and induction of apoptosis are highlighted.

The need for continuing vigilance: addressing the threat for transmission of blood-borne infectious disease

As international travel and human encroachment into previously isolated areas have increased, so too has the potential for the emergence of new infectious diseases. Populations likely to be susceptible to new infectious diseases have also increased in size. The past three decades have seen outbreaks of diseases caused by parvoviruses, Nipah virus, circoviruses, and prions. Infectious pathogens such as these are formidable opponents; they can adapt to new hosts or cause variant diseases within new hosts. Many are also resistant to current inactivation techniques. In order to prevent or contain outbreaks, pathogens that emerge must be identified quickly and efficiently; research and ongoing global surveillance are therefore of primary importance. To effectively protect the blood supply and blood-based therapies, this research should include investigations into improved techniques for detection, screening, and viral inactivation, as well as into ways to reduce patient exposure to infectious pathogens via therapeutic agents. The proactive devotion of appropriate resources to infectious disease containment and prevention prior to an epidemic should be perceived as both essential public health policy and cost effective.

Quantitative estimation of Nipah virus replication kinetics in vitro

BACKGROUND

Nipah virus is a zoonotic virus isolated from an outbreak in Malaysia in 1998. The virus causes infections in humans, pigs, and several other domestic animals. It has also been isolated from fruit bats. The pathogenesis of Nipah virus infection is still not well described. In the present study, Nipah virus replication kinetics were estimated from infection of African green monkey kidney cells (Vero) using the one-step SYBR Green I-based quantitative real-time reverse transcriptase-polymerase chain reaction (qRT-PCR) assay.

RESULTS

The qRT-PCR had a dynamic range of at least seven orders of magnitude and can detect Nipah virus from as low as one PFU/microL. Following initiation of infection, it was estimated that Nipah virus RNA doubles at every approximately 40 minutes and attained peak intracellular virus RNA level of approximately 8.4 log PFU/microL at about 32 hours post-infection (PI). Significant extracellular Nipah virus RNA release occurred only after 8 hours PI and the level peaked at approximately 7.9 log PFU/microL at 64 hours PI. The estimated rate of Nipah virus RNA released into the cell culture medium was approximately 0.07 log PFU/muL per hour and less than 10% of the released Nipah virus RNA was infectious.

CONCLUSION

The SYBR Green I-based qRT-PCR assay enabled quantitative assessment of Nipah virus RNA synthesis in Vero cells. A low rate of Nipah virus extracellular RNA release and low infectious virus yield together with extensive syncytial formation during the infection support a cell-to-cell spread mechanism for Nipah virus infection.

Hendra and Nipah viruses: different and dangerous

Hendra virus and Nipah virus are highly pathogenic paramyxoviruses that have recently emerged from flying foxes to cause serious disease outbreaks in humans and livestock in Australia, Malaysia, Singapore and Bangladesh. Their unique genetic constitution, high virulence and wide host range set them apart from other paramyxoviruses. These features led to their classification into the new genus Henipavirus within the family Paramyxoviridae and to their designation as Biosafety Level 4 pathogens. This review provides an overview of henipaviruses and the types of infection they cause, and describes how studies on the structure and function of henipavirus proteins expressed from cloned genes have provided insights into the unique biological properties of these emerging human pathogens.

Nipah virus RNA synthesis in cultured pig and human cells

Nipah virus infection of porcine stable kidney cells (PS), human neuronal cells (SK-N-MC), human lung fibroblasts cells (MRC-5), and human monocytes (THP-1) were examined. Rapid progression of cytopathic effects (CPE) and cell death were noted in PS cell cultures treated with Nipah virus, followed by MRC-5, SK-N-MC, and THP-1 cell cultures, in descending order of rapidity. Significant increase in the intracellular Nipah virus RNA occurred beginning at 24 hr PI in all the infected cells. Whereas, the extracellular release of Nipah virus RNA increased significantly beginning at 48 and 72 hr PI for the infected MRC-5 cells and PS cells, respectively. No significant release of extracellular Nipah virus RNA was detected from the Nipah virus-infected SK-N-MC and THP-1 cells. At its peak, approximately 6.6 log PFU/microl of extracellular Nipah virus RNA was released from the Nipah virus-infected PS cells, with at least a 100-fold less virus RNA was recorded in the Nipah virus-infected SK-N-MC and THP-1. Approximately 15.2% (+/-0.1%) of the released virus from the infected PS cell cultures was infectious in contrast to approximately 5.5% (+/-0.7%) from the infected SK-N-MC cells. The findings suggest that there are no differences in the capacity to support Nipah virus replication between pigs and humans in fully susceptible PS and MRC-5 cells. However, there are differences between these cells and human neuronal cells and monocytes in the ability to support Nipah virus replication and virus release.

Invasion of the central nervous system in a porcine host by nipah virus

Nipah virus, a newly emerged zoonotic paramyxovirus, infects a number of species. Human infections were linked to direct contact with pigs, specifically with their body fluids. Clinical signs in human cases indicated primarily involvement of the central nervous system, while in pigs the respiratory system was considered the primary virus target, with only rare involvement of the central nervous system. Eleven 5-week-old piglets were infected intranasally, orally, and ocularly with 2.5 x 10(5) PFU of Nipah virus per animal and euthanized between 3 and 8 days postinoculation. Nipah virus caused neurological signs in two out of eleven inoculated pigs. The rest of the pigs remained clinically healthy. Virus was detected in the respiratory system (turbinates, nasopharynx, trachea, bronchus, and lung in titers up to 10(5.3) PFU/g) and in the lymphoreticular system (endothelial cells of blood and lymphatic vessels, submandibular and bronchiolar lymph nodes, tonsil, and spleen with titers up to 10(6) PFU/g). Virus presence was confirmed in the nervous system of both sick and apparently healthy animals (cranial nerves, trigeminal ganglion, brain, and cerebrospinal fluid, with titers up to 10(7.7) PFU/g of tissue). Nipah virus distribution was confirmed by immunohistochemistry. The study presents novel findings indicating that Nipah virus invaded the central nervous system of the porcine host via cranial nerves as well as by crossing the blood-brain barrier after initial virus replication in the upper respiratory tract.

Isolation and molecular identification of Nipah virus from pigs

Nipah viruses from pigs from a Malaysian 1998 outbreak were isolated and sequenced. At least two different Nipah virus strains, including a previously unreported strain, were identified. The findings highlight the possibility that the Malaysia outbreaks had two origins of Nipah virus infections.