Distribution of Viral Antigens and Development of Lesions in Chicken Embryos Inoculated with Nipah Virus

Nipah Virus Disease: Epidemiological, Clinical, Diagnostic and Legislative Aspects of This Unpredictable Emerging Zoonosis

Nipah virus (NiV) infection is a viral disease caused by a Henipavirus, belonging to the Paramyxoviridae family, responsible for a zoonosis. The course of the disease can be very serious and lead to death. NiV natural hosts are fruit bats (also known as megabats) belonging to the Pteropodidae family, especially those of the Pteropus genus. Natural infection in domestic animals has been described in farming pigs, horses, domestic and feral dogs and cats. Natural NiV transmission is possible intra-species (pig-to-pig, human-to-human) and inter-species (flying bat-to-human, pig-to-human, horse-to-human). The infection can be spread by humans or animals in different ways. It is peculiar how the viral transmission modes among different hosts also change depending on the geographical area for different reasons, including different breeding methods, eating habits and the recently identified genetic traits/molecular features of main virus proteins related to virulence. Outbreaks have been described in Malaysia, Singapore, Bangladesh, India and the Philippines with, in some cases, severe respiratory and neurological disease and high mortality in both humans and pigs. Diagnosis can be made using different methods including serological, molecular, virological and immunohistochemical methods. The cornerstones for control of the disease are biosecurity (via the correct management of reservoir and intermediate/amplifying hosts) and potential vaccines which are still under development. However, the evaluation of the potential influence of climate and anthropogenic changes on the NiV reservoir bats and their habitat as well as on disease spread and inter-specific infections is of great importance. Bats, as natural reservoirs of the virus, are responsible for the viral spread and, therefore, for the outbreaks of the disease in humans and animals. Due to the worldwide distribution of bats, potential new reports and spillovers are not to be dismissed in the future.

Henipaviruses: an expanding global public health concern?

Nipah virus (NiV) and Hendra virus (HeV) are highly pathogenic zoonotic viruses of the genus Henipavirus, family Paramyxoviridae that cause severe disease outbreaks in humans and also can infect and cause lethal disease across a broad range of mammalian species. Another related Henipavirus has been very recently identified in China in febrile patients with pneumonia, the Langya virus (LayV) of probable animal origin in shrews. NiV and HeV were first identified as the causative agents of severe respiratory and encephalitic disease in the 1990s across Australia and Southern Asia with mortality rates reaching up to 90%. They are responsible for rare and sporadic outbreaks with no approved treatment modalities. NiV and HeV have wide cellular tropism that contributes to their high pathogenicity. From their natural hosts bats, different scenarios propitiate their spillover to pigs, horses, and humans. Henipavirus-associated respiratory disease arises from vasculitis and respiratory epithelial cell infection while the neuropathogenesis of Henipavirus infection is still not completely understood but appears to arise from dual mechanisms of vascular disease and direct parenchymal brain infection. This brief review offers an overview of direct and indirect mechanisms of HeV and NiV pathogenicity and their interaction with the human immune system, as well as the main viral strategies to subvert such responses.

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.

Drivers and Distribution of Henipavirus-Induced Syncytia: What Do We Know?

Syncytium formation, i.e., cell-cell fusion resulting in the formation of multinucleated cells, is a hallmark of infection by paramyxoviruses and other pathogenic viruses. This natural mechanism has historically been a diagnostic marker for paramyxovirus infection in vivo and is now widely used for the study of virus-induced membrane fusion in vitro. However, the role of syncytium formation in within-host dissemination and pathogenicity of viruses remains poorly understood. The diversity of henipaviruses and their wide host range and tissue tropism make them particularly appropriate models with which to characterize the drivers of syncytium formation and the implications for virus fitness and pathogenicity. Based on the henipavirus literature, we summarized current knowledge on the mechanisms driving syncytium formation, mostly acquired from in vitro studies, and on the in vivo distribution of syncytia. While these data suggest that syncytium formation widely occurs across henipaviruses, hosts, and tissues, we identified important data gaps that undermined our understanding of the role of syncytium formation in virus pathogenesis. Based on these observations, we propose solutions of varying complexity to fill these data gaps, from better practices in data archiving and publication for in vivo studies, to experimental approaches in vitro.

A single dose investigational subunit vaccine for human use against Nipah virus and Hendra virus

Nipah and Hendra viruses are highly pathogenic bat-borne paramyxoviruses recently included in the WHO Blueprint priority diseases list. A fully registered horse anti-Hendra virus subunit vaccine has been in use in Australia since 2012. Based on the same immunogen, the Hendra virus attachment glycoprotein ectodomain, a subunit vaccine formulation for use in people is now in a Phase I clinical trial. We report that a single dose vaccination regimen of this human vaccine formulation protects against otherwise lethal challenges of either Hendra or Nipah virus in a nonhuman primate model. The protection against the Nipah Bangladesh strain begins as soon as 7 days post immunization with low dose of 0.1 mg protein subunit. Our data suggest this human vaccine could be utilized as efficient emergency vaccine to disrupt potential spreading of Nipah disease in an outbreak setting.

Advances in diagnostics, vaccines and therapeutics for Nipah virus

Nipah virus is an emerging zoonotic paramyxovirus that causes severe and often fatal respiratory and neurological disease in humans. The virus was first discovered after an outbreak of encephalitis in pig farmers in Malaysia and Singapore with subsequent outbreaks in Bangladesh or India occurring almost annually. Due to the highly pathogenic nature of NiV, its pandemic potential, and the lack of licensed vaccines or therapeutics, there is a requirement for research and development into highly sensitive and specific diagnostic tools as well as antivirals and vaccines to help prevent and control future outbreak situations.

Domesticated animals as hosts of henipaviruses and filoviruses: A systematic review

Bat-borne viruses carry undeniable risks to the health of human beings and animals, and there is growing recognition of the need for a 'One Health' approach to understand their frequently complex spill-over routes. While domesticated animals can play central roles in major spill-over events of zoonotic bat-borne viruses, for example during the pig-amplified Malaysian Nipah virus outbreak of 1998-1999, the extent of their potential to act as bridging or amplifying species for these viruses has not been characterised systematically. This review aims to compile current knowledge on the role of domesticated animals as hosts of two types of bat-borne viruses, henipaviruses and filoviruses. A systematic literature search of these virus-host interactions in domesticated animals identified 72 relevant studies, which were categorised by year, location, design and type of evidence generated. The review then focusses on Africa as a case study, comparing research efforts in domesticated animals and bats with the distributions of documented human cases. Major gaps remain in our knowledge of the potential ability of domesticated animals to contract or spread these zoonoses. Closing these gaps will be necessary to fully evaluate and mitigate spill-over risks of these viruses, especially with global agricultural intensification.

Hendra virus and Nipah virus animal vaccines

Hendra virus (HeV) and Nipah virus (NiV) are zoonotic viruses that emerged in the mid to late 1990s causing disease outbreaks in livestock and people. HeV appeared in Queensland, Australia in 1994 causing a severe respiratory disease in horses along with a human case fatality. NiV emerged a few years later in Malaysia and Singapore in 1998-1999 causing a large outbreak of encephalitis with high mortality in people and also respiratory disease in pigs which served as amplifying hosts. The key pathological elements of HeV and NiV infection in several species of mammals, and also in people, are a severe systemic and often fatal neurologic and/or respiratory disease. In people, both HeV and NiV are also capable of causing relapsed encephalitis following recovery from an acute infection. The known reservoir hosts of HeV and NiV are several species of pteropid fruit bats. Spillovers of HeV into horses continue to occur in Australia and NiV has caused outbreaks in people in Bangladesh and India nearly annually since 2001, making HeV and NiV important transboundary biological threats. NiV in particular possesses several features that underscore its potential as a pandemic threat, including its ability to infect humans directly from natural reservoirs or indirectly from other susceptible animals, along with a capacity of limited human-to-human transmission. Several HeV and NiV animal challenge models have been developed which have facilitated an understanding of pathogenesis and allowed for the successful development of both active and passive immunization countermeasures.

Henipaviruses

The first henipaviruses, Hendra virus (HeV), and Nipah virus (NiV) were pathogenic zoonoses that emerged in the mid to late 1990s causing serious disease outbreaks in livestock and humans. HeV was recognized in Australia 1994 in horses exhibiting respiratory disease along with a human case fatality, and then NiV was identified during a large outbreak of human cases of encephalitis with high mortality in Malaysia and Singapore in 1998–1999 along with respiratory disease in pigs which served as amplifying hosts. The recently identified third henipavirus isolate, Cedar virus (CedPV), is not pathogenic in animals susceptible to HeV and NiV disease. Molecular detection of additional henipavirus species has been reported but no additional isolates of virus have been reported. Central pathological features of both HeV and NiV infection in humans and several susceptible animal species is a severe systemic and often fatal neurologic and/or respiratory disease. In people, both viruses can also manifest relapsed encephalitis following recovery from an acute infection, particularly NiV. The recognized natural reservoir hosts of HeV, NiV, and CedPV are pteropid bats, which do not show clinical illness when infected. With spillovers of HeV continuing to occur in Australia and NiV in Bangladesh and India, these henipaviruses continue to be important transboundary biological threats. NiV in particular possesses several features that highlight a pandemic potential, such as its ability to infect humans directly from natural reservoirs or indirectly from other susceptible animals along with a capacity of limited human-to-human transmission. Several henipavirus animal challenge models have been developed which has aided in understanding HeV and NiV pathogenesis as well as how they invade the central nervous system, and successful active and passive immunization strategies against HeV and NiV have been reported which target the viral envelope glycoproteins.

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.

Nipah virus infection: current scenario

The emergence of Nipah virus (NiV) infection into the pig population and subsequently into the human population is believed to be due to changes in ecological conditions. In Malaysia, A major NiV outbreak occurred in pigs and humans from September 1998 to April 1999 that resulted in infection of 265 and death of 105 persons. About 1.1 million pigs had to be destroyed to control the outbreak. The disease was recorded in the form of a major outbreak in India in 2001 and then a small incidence in 2007, both the outbreaks in West Bengal only in humans without any involvement of pigs. There were series of human Nipah incidences in Bangladesh from 2001 till 2013 almost every year with mortality exceeding 70 %. The disease transmission from pigs acting as an intermediate host during Malaysian and Singapore outbreaks has changed in NIV outbreaks in India and Bangladesh, transmitting the disease directly from bats to human followed by human to human. The drinking of raw date palm sap contaminated with fruit bat urine or saliva containing NiV is the only known cause of outbreak of the disease in Bangladesh outbreaks. The virus is now known to exist in various fruit bats of Pteropus as well as bats of other genera in a wider belt from Asia to Africa.

Henipavirus receptor usage and tropism

Nipah (NiV) and Hendra (HeV) viruses are the deadliest human pathogens within the Paramyxoviridae family, which include human and animal pathogens of global biomedical importance. NiV and HeV infections cause respiratory and encephalitic illness with high mortality rates in humans. Henipaviruses (HNV) are the only Paramyxoviruses classified as biosafety level 4 (BSL4) pathogens due to their extreme pathogenicity, potential for bioterrorism, and lack of licensed vaccines and therapeutics. HNV use ephrin-B2 and ephrin-B3, highly conserved proteins, as viral entry receptors. This likely accounts for their unusually broad species tropism, and also provides opportunities to study how receptor usage, cellular tropism, and end-organ pathology relates to the pathobiology of HNV infections. The clinical and pathologic manifestations of NiV and HeV virus infections are reviewed in the chapters by Wong et al. and Geisbert et al. in this issue. Here, we will review the biology of the HNV receptors, and how receptor usage relates to HNV cell tropism in vitro and in vivo.

Animal Models of Human Viral Diseases

As the threat of exposure to emerging and reemerging viruses within a naive population increases, it is vital that the basic mechanisms of pathogenesis and immune response be thoroughly investigated. By using animal models in this endeavor, the response to viruses can be studied in a more natural context to identify novel drug targets, and assess the efficacy and safety of new products. This is especially true in the advent of the Food and Drug Administration's animal rule. Although no one animal model is able to recapitulate all the aspects of human disease, understanding the current limitations allows for a more targeted experimental design. Important facets to be considered before an animal study are the route of challenge, species of animals, biomarkers of disease, and a humane endpoint. This chapter covers the current animal models for medically important human viruses, and demonstrates where the gaps in knowledge exist.

Recent progress in henipavirus research: molecular biology, genetic diversity, animal models

Nipah and Hendra virus are members of a newly identified genus of emerging paramyxoviruses, the henipaviruses. Both viruses have the ability to cause severe pulmonary infection and severe acute encephalitis. Following their discovery in the 1990s, outbreaks caused by these zoonotic paramyxoviruses have been associated with high public health and especially economic threat potential. Currently, only geographic groupings in Asia and Australia have been described for the henipaviruses. However, while few viral isolates are available and more detailed characterization is necessary, there has been recent evidence that divergent henipaviruses might be present on the African continent. This review endeavours to capture recent advances in the field of henipavirus research, with a focus on genome structure and replication mechanisms, reservoir hosts, genetic diversity, pathogenesis and animal models.

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.

Emerging zoonotic viruses: new lessons on receptor and entry mechanisms

Viruses enter the host cell by binding cellular receptors that allow appropriate delivery of the viral genome. Although the horizontal propagation of viruses feeds the continuous emergence of novel pathogenic viruses, the genetic variation of cellular receptors can represent a challenging barrier. The SARS coronavirus, henipaviruses and filoviruses are zoonotic RNA viruses that use bats as their reservoir. Their lethality for man has fostered extensive research both on the cellular receptors they use and their entry pathways. These studies have allowed new insights into the diversity of the molecular mechanisms underlying both virus entry and pathogenesis.

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.

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.