Fatal encephalitis due to Nipah virus among pig-farmers in Malaysia

Unhealthy landscapes: Policy recommendations on land use change and infectious disease emergence

Anthropogenic land use changes drive a range of infectious disease outbreaks and emergence events and modify the transmission of endemic infections. These drivers include agricultural encroachment, deforestation, road construction, dam building, irrigation, wetland modification, mining, the concentration or expansion of urban environments, coastal zone degradation, and other activities. These changes in turn cause a cascade of factors that exacerbate infectious disease emergence, such as forest fragmentation, disease introduction, pollution, poverty, and human migration. The Working Group on Land Use Change and Disease Emergence grew out of a special colloquium that convened international experts in infectious diseases, ecology, and environmental health to assess the current state of knowledge and to develop recommendations for addressing these environmental health challenges. The group established a systems model approach and priority lists of infectious diseases affected by ecologic degradation. Policy-relevant levels of the model include specific health risk factors, landscape or habitat change, and institutional (economic and behavioral) levels. The group recommended creating Centers of Excellence in Ecology and Health Research and Training, based at regional universities and/or research institutes with close links to the surrounding communities. The centers' objectives would be 3-fold: a) to provide information to local communities about the links between environmental change and public health; b) to facilitate fully interdisciplinary research from a variety of natural, social, and health sciences and train professionals who can conduct interdisciplinary research; and c) to engage in science-based communication and assessment for policy making toward sustainable health and ecosystems.

Novel viral encephalitides associated with bats (Chiroptera)--host management strategies

Several novel viruses recently described in bats of the genus Pteropus (sub-order Megachiroptera) in Australia and southeast Asia cause encephalitic disease in animals and humans. These viruses include Hendra virus and Nipah virus (genus Henipavirus, family Paramyxoviridae) and Australian bat lyssavirus (ABLV; genus Lyssavirus, family Rhabdoviridae). Broadly, strategies for disease prevention and control in the spillover host are directed at minimising direct or indirect contact with the natural host, improving farm-gate and on-farm biosecurity, and better disease recognition and diagnosis. Additional strategies for ABLV include the use of rabies vaccine for effective pre- and post-exposure prophylaxis in humans. Effective management strategies in the natural host are predicated on an understanding of the ecology of the disease in the natural host, and the identification and avoidance of factors putatively associated with emergence, such as habitat loss, land use change and demographic shifts. A possible future management strategy for ABLV in reservoir populations is immunisation using bait or plant-derived vaccination.

Emerging encephalitogenic viruses: lyssaviruses and henipaviruses transmitted by frugivorous bats

Three newly recognized encephalitogenic zoonotic viruses spread from fruit bats of the genus Pteropus (order Chiroptera, suborder Megachiroptera) have been recognised over the past decade. These are: Hendra virus, formerly named equine morbillivirus, which was responsible for an outbreak of disease in horses and humans in Brisbane, Australia, in 1994; Australian bat lyssavirus, the cause of a severe acute encephalitis, in 1996; and Nipah virus, the cause of a major outbreak of encephalitis and pulmonary disease in domestic pigs and people in peninsula Malaysia in 1999. Hendra and Nipah viruses have been shown to be the first two members of a new genus, Henipavirus, in the family Paramyxoviridae, subfamily Paramyxovirinae, whereas Australian bat lyssavirus is closely related antigenically to classical rabies virus in the genus Lyssavirus, family Rhabdoviridae, although it can be distinguished on genetic grounds. Hendra and Nipah viruses have neurological and pneumonic tropisms. The first humans and equids with Hendra virus infections died from acute respiratory disease, whereas the second human patient died from an encephalitis. With Nipah virus, the predominant clinical syndrome in humans was encephalitic rather than respiratory, whereas in pigs, the infection was characterised by acute fever with respiratory involvement with or without neurological signs. Two human infections with Australian bat lyssavirus have been reported, the clinical signs of which were consistent with classical rabies infection and included a diffuse, non-suppurative encephalitis. Many important questions remain to be answered regarding modes of transmission, pathogenesis, and geographic range of these viruses.

Mapping of domains responsible for nucleocapsid protein–phosphoprotein interaction of henipaviruses

Hendra virus (HeV) and Nipah virus (NiV) are members of a new genus, Henipavirus, in the family Paramyxoviridae. Each virus encodes a phosphoprotein (P) that is significantly larger than its counterparts in other known paramyxoviruses. The interaction of this unusually large P with its nucleocapsid protein (N) was investigated in this study by using recombinant full-length and truncated proteins expressed in bacteria and a modified protein-blotting protein-overlay assay. Results from our group demonstrated that the N and P of both viruses were able to form not only homologous, but also heterologous, N–P complexes, i.e. HeV N was able to interact with NiV P and vice versa. Deletion analysis of the N and P revealed that there were at least two independent N-binding sites on P and they resided at the N and C termini, respectively. Similarly, more than one P-binding site was present on N and one of these was mapped to a 29 amino acid (aa) C-terminal region, which on its own was sufficient to interact with the extreme C-terminal 165 aa region of P.

A target site for template-based design of measles virus entry inhibitors

Measles virus (MV) constitutes a principal cause of worldwide mortality, accounting for almost 1 million deaths annually. Although a live-attenuated vaccine protects against MV, vaccination efficiency of young infants is low because of interference by maternal antibodies. Parental concerns about vaccination safety further contribute to waning herd immunity in developed countries, resulting in recent MV outbreaks. The development of novel antivirals that close the vaccination gap in infants and silence viral outbreaks is thus highly desirable. We previously identified a microdomain in the MV fusion protein (F protein) that is structurally conserved in the paramyxovirus family and constitutes a promising target site for rationally designed antivirals. Here we report the template-based development of a small-molecule MV inhibitor, providing proof-of-concept for our approach. This lead compound specifically inhibits fusion and spread of live MV and MV glycoprotein-induced membrane fusion. The inhibitor induces negligible cytotoxicity and does not interfere with receptor binding or F protein biosynthesis or transport but prevents F protein-induced lipid mixing. Mutations in the postulated target site alter viral sensitivity to inhibition. In silico docking of the compound in this microdomain suggests a binding model that is experimentally corroborated by a structure-activity analysis of the compound and the inhibition profile of mutated F proteins. A second-generation compound designed on the basis of the interaction model shows a 200-fold increase in antiviral activity, creating the basis for novel MV therapeutics. This template-based design approach for MV may be applicable to other clinically relevant members of the paramyxovirus family.

Basis for fusion inhibition by peptides: analysis of the heptad repeat regions of the fusion proteins from Nipah and Hendra viruses, newly emergent zoonotic paramyxoviruses

Nipah virus (NiV) and Hendra virus (HeV) are novel zoonotic members of the Paramyxoviridae family and are the prototypes for a newly designated genus, Genus Henipavirus. Recent studies have shown that paramyxovirus might adopt a similar mechanism of virus fusion-entry. Under this mechanism, the two highly conserved heptad repeat (HR) regions, HR1 and HR2, in the fusion (F) protein, seem to show characteristic structure in the fusion core: the formation of a 6-helix coiled-coil bundle. The three HR1s form the alpha-helix coiled-coil surrounded by three HR2s. In this study, the two HR regions of NiV or HeV were expressed in an Escherichia coli system as a single chain and the results do show that HR1 and HR2 interact with each other in both NiV and HeV and form typical 6-helix coiled-coil bundles. This provides the molecular basis of HR2 inhibition to NiV and HeV fusion as observed in an earlier report.

Production and characterization of monoclonal antibodies against formalin-inactivated Nipah virus isolated from the lungs of a pig

Eight clones of monoclonal antibodies (Mabs) to Nipah virus (NV) were produced against formalin-inactivated NV antigens. They reacted positive by indirect immunofluorescent antibody test, and one of them also demonstrated virus neutralizing activity. They were classified into six different types based on their biological properties. These Mabs will be useful for immunodiagnosis of NV infections in animals and further research studies involving the genomes and proteins of NV.

Full-length genome sequence of Mossman virus, a novel paramyxovirus isolated from rodents in Australia

Mossman virus (MoV) was isolated on two occasions from wild rats trapped in Queensland, Australia, during the early 1970s. Together with Nariva virus and J-virus MoV belongs to a group of novel paramyxoviruses isolated from rodents during the last 40 years, none of which had been characterized at the molecular level until now. cDNA subtraction strategies used to isolate virus-specific cDNA derived from both MoV-infected cells and crude MoV pellets were pivotal steps in rapid characterization of the complete genome sequence. Analysis of the full-length genome and its encoded proteins confirmed that MoV is a novel member of the subfamily Paramyxovirinae which cannot be assigned to an existing genus. MoV appears to be more closely related to another unclassified paramyxovirus Tupaia paramyxovirus (TPMV), isolated from the tree shrew Tupaia belangeri. Together with Salem virus (SalV), a further unclassified paramyxovirus that was isolated from a horse, MoV and TPMV make up a new collection of paramyxoviruses situated evolutionally between the genus Morbillivirus and the newly established genus Henipavirus.

Solubility, immunogenicity and physical properties of the nucleocapsid protein of Nipah virus produced inEscherichia coli

The nucleocapsid (N) protein of Nipah virus (NiV) can be produced in three Escherichia coli strains [TOP10, BL21(DE3) and SG935] under the control of trc promoter. However, most of the product existed in the form of insoluble inclusion bodies. There was no improvement in the solubility of the product when this protein was placed under the control of T7 promoter. However, the solubility of the N protein was significantly improved by lowering the growth temperature of E. coli BL21(DE3) cell cultures. Solubility analysis of N- and C-terminally deleted mutants revealed that the full-length N protein has the highest solubility. The soluble N protein could be purified efficiently by sucrose gradient centrifugation and nickel affinity chromatography. Electron microscopic analysis of the purified product revealed that the N protein assembled into herringbone-like particles of different lengths. The C-terminal end of the N protein contains the major antigenic region when probed with antisera from humans and pigs infected naturally.

Toward novel vaccines and therapies based on negative-strand RNA viruses

The study of negative-strand RNA viruses has suggested new strategies to produce more attenuated viruses. Reverse genetics has allowed the implementation of the strategies, and new or improved monovalent vaccines are being developed. In addition, recombinant viruses expressing foreign proteins or epitopes have been produced with the aim of developing multivalent vaccines capable of stimulating humoral and cellular immune responses against more than one pathogen. Finally, recombinant viruses that selectively enter cells expressing tumor markers or the HIV envelope protein have been engineered and shown to lyse target cells. Preclinical and clinical trials of improved and multivalent vaccines and therapeutic (oncolytic) viruses are ongoing.

A golden hamster model for human acute Nipah virus infection

A predominantly pig-to-human zoonotic infection caused by the novel Nipah virus emerged recently to cause severe morbidity and mortality in both animals and man. Human autopsy studies showed the pathogenesis to be related to systemic vasculitis that led to widespread thrombotic occlusion and microinfarction in most major organs especially in the central nervous system. There was also evidence of extravascular parenchymal infection, particularly near damaged vessels (Wong KT, Shieh WJ, Kumar S, Norain K, Abdullah W, Guarner J, Goldsmith CS, Chua KB, Lam SK, Tan CT, Goh KJ, Chong HT, Jusoh R, Rollin PE, Ksiazek TG, Zaki SR, Nipah Virus Pathology Working Group: Nipah virus infection: Pathology and pathogenesis of an emerging paramyxoviral zoonosis. Am J Pathol 2002, 161:2153-2167). We describe here a golden hamster (Mesocricetus auratus) model that appears to reproduce the pathology and pathogenesis of acute human Nipah infection. Hamsters infected by intranasal or intraperitoneal routes died within 9 to 29 days or 5 to 9 days, respectively. Pathological lesions were most severe and extensive in the hamster brain. Vasculitis, thrombosis, and more rarely, multinucleated endothelial syncytia, were found in blood vessels of multiple organs. Viral antigen and RNA were localized in both vascular and extravascular tissues including neurons, lung, kidney, and spleen, as demonstrated by immunohistochemistry and in situ hybridization, respectively. Paramyxoviral-type nucleocapsids were identified in neurons and in vessel walls. At the terminal stage of infection, virus and/or viral RNA could be recovered from most solid organs and urine, but not from serum. The golden hamster is proposed as a suitable model for further studies including pathogenesis studies, anti-viral drug testing, and vaccine development against acute Nipah infection.

Exogenous porcine viruses

Porcine organs, cells and tissues provide a viable source of transplants in humans, though there is some concern of public health risk from adaptation of swine infectious agents in humans. Limited information is available on the public health risk of many exogenous swine viruses, and reliable and rapid diagnostic tests are available for only a few of these. The ability of several porcine viruses to cause transplacental fetal infection (parvoviruses, circoviruses, and arteriviruses), emergence or recognition of several new porcine viruses during the last two decades (porcine circovirus, arterivirus, paramyxoviruses, herpesviruses, and porcine respiratory coronavirus) and the immunosuppressed state of the transplant recipients increases the xenozoonoses risk of humans to porcine viruses through transplantation. Much of this risk can be eliminated with vigilance and sustained monitoring along with a better understanding of pathogenesis and development of better diagnostic tests. In this review we present information on selected exogenous viruses, highlighting their characteristics, pathogenesis of viral infections in swine, methods for their detection, and the potential xenozoonoses risk they present. Emphasis has been given in this review to swine influenza virus, paramyxovirus (Nipah virus, Menagle virus, LaPiedad paramyxovirus, porcine paramyxovirus), arterivirus (porcine reproductive and respiratory syndrome virus) and circovirus as either they represent new swine viruses or present the greatest risk. We have also presented information on porcine parvovirus, Japanese encephalitis virus, encephalomyocarditis virus, herpesviruses (pseudorabies virus, porcine lymphotropic herpesvirus, porcine cytomegalovirus), coronaviruses (TGEV, PRCV, HEV, PEDV) and adenovirus. The potential of swine viruses to infect humans needs to be assessed in vitro and in vivo and rapid and more reliable diagnostic methods need to be developed to assure safe supply of porcine tissues and cells for xenotransplantation.

Managing emerging diseases borne by fruit bats (flying foxes), with particular reference to henipaviruses and Australian bat lyssavirus

Since 1994, a number of novel viruses have been described from bats in Australia and Malaysia, particularly from fruit bats belonging to the genus Pteropus (flying foxes), and it is probable that related viruses will be found in other countries across the geographical range of other members of the genus. These viruses include Hendra and Nipah viruses, members of a new genus, Henipaviruses, within the family Paramyxoviridae; Menangle and Tioman viruses, new members of the Rubulavirus genus within the Paramyxoviridae; and Australian bat lyssavirus (ABLV), a member of the Lyssavirus genus in the family Rhabdoviridae. All but Tioman virus are known to be associated with human and/or livestock diseases. The isolation, disease associations and biological properties of the viruses are described, and are used as the basis for developing management strategies for disease prevention or control. These strategies are directed largely at disease minimization through good farm management practices, reducing the potential for exposure to flying foxes, and better disease recognition and diagnosis, and for ABLV specifically, the use of rabies vaccine for pre- and post-exposure prophylaxis. Finally, an intriguing and long-term strategy is that of wildlife immunization through plant-derived vaccination.

Xenotransplantation and pig endogenous retroviruses

Xenotransplantation, in particular transplantation of pig cells, tissues and organs into human patients, may alleviate the current shortage of suitable allografts available for human transplantation. This overview addresses the physiological, immunological and virological factors considered with regard to xenotransplantation. Among the issues reviewed are the merits of using pigs as xenograft source species, the compatibility of pig and human organ physiology and the immunological hindrances with regard to the various types of rejection and attempts at abrogating rejection. Advances in the prevention of pig organ rejection by creating genetically modified pigs that are more suited to the human microenvironment are also discussed. Finally, with regard to virology, possible zoonotic infections emanating from pigs are reviewed, with special emphasis on the pig endogenous retrovirus (PERV). An in depth account of PERV studies, comprising their discovery as well as recent knowledge of the virus, is given. To date, all retrospective studies on patients with pig xenografts have shown no evidence of PERV transmission, however, many factors make us interpret these results with caution. Although the lack of PERV infection in xenograft recipients up to now is encouraging, more basic research and controlled animal studies that mimic the pig to human xenotransplantation setting more closely are required for safety assessment.

Newer viral encephalitides

BACKGROUND

Viral encephalitis occurs in epidemic settings or is sporadic. New encephalitis patterns reflect the roles that biologic reservoirs and vectors play in determining virus-human interactions. "New" viral encephalitis can also result from human host modifications that increase susceptibility to neuroinvasive viral infection.

REVIEW SUMMARY

Three human viruses, Nipah virus, Human Herpesvirus-6, and West Nile virus, present examples of how "new" viral encephalitides emerge in a specific geographic region or clinical setting. Nipah virus encephalitis emerged after the molecular evolution of a new zoonotic viral genus within the Paramyxovirinae family. Human herpesvirus-6 encephalitis has emerged in the immune suppressed human host harboring this ubiquitous but typically benign herpesvirus. West Nile virus encephalitis has emerged in the Western hemisphere after apparent abrupt translocation of this mosquito-borne virus to a distant geographic region with immunologically naive avian and human hosts.

CONCLUSION

While the clinical features of these viral encephalitides are somewhat distinct, they each emerged as the result of human-derived factors that altered the biologic dynamic between humans and their viral pathogens.

Canine distemper, a re-emerging morbillivirus with complex neuropathogenic mechanisms

Paramyxoviruses are responsible for a wide variety of diseases both in humans and in animals. Common to many paramyxoviruses is the fact that they can cause neurological symptoms in their final host. Newly discovered paramyxoviruses, such as the Hendra and Nipah viruses, show the same pattern of pathogenesis as that of the paramyxoviruses already known. Canine distemper virus (CDV) is a well-studied member of the genus Morbillivirus. Study of the neuropathogenesis of CDV might give insight into disease mechanisms and suggest approaches for the prevention of other recently discovered paramyxovirus infections.

A novel approach for collecting samples from fruit bats for isolation of infectious agents

During the outbreak of Nipah virus encephalitis involving pigs and humans in peninsular Malaysia in 1998/1999, a conventional approach was initially undertaken to collect specimens from fruit bats by mist-netting and shooting, as an integral part of wildlife surveillance of the natural reservoir host of Nipah virus. This study describes a novel method of collecting fruit bats' urine samples using plastic sheets for isolation of Nipah virus. This novel approach resulted in the isolation of several other known and unidentified infectious agents besides Nipah virus.

Emerging viral infections of the nervous system

New viral infections of the nervous system have been appearing with great regularity. Some result from the evolution of new agents and others from the entry of viruses into new hosts or environments. The emergence of neurovirulent enteroviruses causing a paralytic poliomyelitis syndrome and rhomboencephalitis represent the evolution of new human viruses. Most emerging viral infections represent movement of an agent into new geographic areas or across species barriers. The transport of neurovirulent strains of West Nile virus into the Western Hemisphere and the penetration of Nipah virus, a newly recognized paramyxovirus, across species barriers from bat to pig to man are examples that are highlighted in this review. The burgeoning human population and the speed and frequency of travel favor the evolution, preservation, and spread of new viral agents.

Nipah virus outbreak in Malaysia

Nipah virus, a novel paramyxovirus, closely related to Hendra virus emerged in northern part of Peninsular Malaysia in 1998. The virus caused an outbreak of severe febrile encephalitis in humans with a high mortality rate, whereas, in pigs, encephalitis and respiratory diseases but with a relatively low mortality rate. The outbreak subsequently spread to various regions of the country and Singapore in the south due to the movement of infected pigs. Nipah virus caused systemic infections in humans, pigs and other mammals. Histopathological and radiological findings were characteristic of the disease. Fruitbats of Pteropid species were identified as the natural reservoir hosts. Evidence suggested that climatic and anthropogenic driven ecological changes coupled with the location of piggeries in orchard and the design of pigsties allowed the spill-over of this novel paramyxovirus from its reservoir host into the domestic pigs and ultimately to humans and other animals.

Are environmental factors important in primary systemic vasculitis? A case-control study

OBJECTIVE

To investigate the association between primary systemic vasculitis (PSV) and environmental risk factors.

METHODS

Seventy-five PSV cases and 273 controls (220 nonvasculitis, 19 secondary vasculitis, and 34 asthma controls) were interviewed using a structured questionnaire. Factors investigated were social class, occupational and residential history, smoking, pets, allergies, vaccinations, medications, hepatitis, tuberculosis, and farm exposure in the year before symptom onset (index year). The Standard Occupational Classification 2000 and job-exposure matrices were used to assess occupational silica, solvent, and metal exposure. Stepwise multiple logistic regression was used to calculate the odds ratio (OR) and 95% confidence interval (95% CI) adjusted for potential confounders. Total PSV, subgroups (47 Wegener's granulomatosis [WG], 12 microscopic polyangiitis, 16 Churg-Strauss syndrome [CSS]), and antineutrophil cytoplasmic antibody (ANCA)-positive cases were compared with control groups.

RESULTS

Farming in the index year was significantly associated with PSV (OR 2.3 [95% CI 1.2-4.6]), with WG (2.7 [1.2-5.8]), with MPA (6.3 [1.9-21.6]), and with perinuclear ANCA (pANCA) (4.3 [1.5-12.7]). Farming during working lifetime was associated with PSV (2.2 [1.2-3.8]) and with WG (2.7 [1.3-5.7]). Significant associations were found for high occupational silica exposure in the index year (with PSV 3.0 [1.0-8.4], with CSS 5.6 [1.3-23.5], and with ANCA 4.9 [1.3-18.6]), high occupational solvent exposure in the index year (with PSV 3.4 [0.9-12.5], with WG 4.8 [1.2-19.8], and with classic ANCA [cANCA] 3.9 [1.6-9.5]), high occupational solvent exposure during working lifetime (with PSV 2.7 [1.1-6.6], with WG 3.4 [1.3-8.9], and with cANCA 3.3 [1.0-10.8]), drug allergy (with PSV 3.6 [1.8-7.0], with WG 4.0 [1.8-8.7], and with cANCA 4.7 [1.9-11.7]), and allergy overall (with PSV 2.2 [1.2-3.9], with WG 2.7 [1.4-5.7]). No other significant associations were found.

CONCLUSION

A significant association between farming and PSV has been identified for the first time. Results also support previously reported associations with silica, solvents, and allergy.

Elucidation of Nipah virus morphogenesis and replication using ultrastructural and molecular approaches

Nipah virus, which was first recognized during an outbreak of encephalitis with high mortality in Peninsular Malaysia during 1998-1999, is most closely related to Hendra virus, another emergent paramyxovirus first recognized in Australia in 1994. We have studied the morphologic features of Nipah virus in infected Vero E6 cells and human brain by using standard and immunogold electron microscopy and ultrastructural in situ hybridization. Nipah virions are enveloped particles composed of a tangle of filamentous nucleocapsids and measured as large as 1900 nm in diameter. The nucleocapsids measured up to 1.67 microm in length and had the herringbone structure characteristic for paramyxoviruses. Cellular infection was associated with multinucleation, intracytoplasmic nucleocapsid inclusions (NCIs), and long cytoplasmic tubules. Previously undescribed for other members of the family Paramyxoviridae, infected cells also contained an inclusion formed of reticular structures. Ultrastructural ISH studies suggest these inclusions play an important role in the transcription process.

Sites of phosphorylation of P and V proteins from Hendra and Nipah viruses: newly emerged members of Paramyxoviridae

Hendra (HeV) and Nipah (NiV) viruses are newly emerged, zoonotic viruses and their genomes have nucleotide and predicted amino acid homologies placing them in the subfamily Paramyxoviridae. The polymerase-associated phosphoproteins (P proteins) of paramyxoviruses have been shown, by direct and indirect methods, to be highly phosphorylated. In this study, a comprehensive comparison of in vivo phosphorylation of HeV and NiV P proteins, derived from virus particles, was achieved by a direct approach using electrospray ionization ion trap mass spectrometry (ESI-IT-MS). Phosphorylation sites for the P proteins were determined at Ser-224 and Thr-239 in HeV and at Ser-240 and Ser-472 in NiV. These phosphorylation patterns do not appear to be consistent with those reported for other paramyxoviruses. Protein V, a product of a frame shift in the P protein gene, was identified by specific antibodies in HeV preparations but not in NiV. HeV V protein was found to contain phosphoserine but not phosphothreonine. In addition, P proteins from both viruses were found to be modified by N-terminal acetylation.

Nipah virus--a potential agent of bioterrorism?

Nipah virus, a newly emerging deadly paramyxovirus isolated during a large outbreak of viral encephalitis in Malaysia, has many of the physical attributes to serve as a potential agent of bioterrorism. The outbreak caused widespread panic and fear because of its high mortality and the inability to control the disease initially. There were considerable social disruptions and tremendous economic loss to an important pig-rearing industry. This highly virulent virus, believed to be introduced into pig farms by fruit bats, spread easily among pigs and was transmitted to humans who came into close contact with infected animals. From pigs, the virus was also transmitted to other animals such as dogs, cats, and horses. The Nipah virus has the potential to be considered an agent of bioterrorism.

Fruit bats as a natural reservoir of zoonotic viruses

As a natural reservoir of manifold zoonotic viruses, fruit bats have been involved in at least three emerging zoonoses in recent years. This paper aims to introduce the epidemiological characteristics of these diseases emerged in the Australasian region between 1994 and 1999, transmission pathways of the newly discovered viruses and the relationship between the changed entironment of fruit bats and occurrences of these emerging diseases and provide a clue for the epidemiological investigations of SARS.

Nipah virus infection: pathology and pathogenesis of an emerging paramyxoviral zoonosis

In 1998, an outbreak of acute encephalitis with high mortality rates among pig handlers in Malaysia led to the discovery of a novel paramyxovirus named Nipah virus. A multidisciplinary investigation that included epidemiology, microbiology, molecular biology, and pathology was pivotal in the discovery of this new human infection. Clinical and autopsy findings were derived from a series of 32 fatal human cases of Nipah virus infection. Diagnosis was established in all cases by a combination of immunohistochemistry (IHC) and serology. Routine histological stains, IHC, and electron microscopy were used to examine autopsy tissues. The main histopathological findings included a systemic vasculitis with extensive thrombosis and parenchymal necrosis, particularly in the central nervous system. Endothelial cell damage, necrosis, and syncytial giant cell formation were seen in affected vessels. Characteristic viral inclusions were seen by light and electron microscopy. IHC analysis showed widespread presence of Nipah virus antigens in endothelial and smooth muscle cells of blood vessels. Abundant viral antigens were also seen in various parenchymal cells, particularly in neurons. Infection of endothelial cells and neurons as well as vasculitis and thrombosis seem to be critical to the pathogenesis of this new human disease.

Paramyxovirus strategies for evading the interferon response

Two genera, the Respirovirus (Sendai virus (SeV) and human parainfluenza virus (hPIV3) and the Rubulavirus (simian virus (SV) 5, SV41, mumps virus and hPIV2), of the three in the subfamily Paramyxovirinae inhibit interferon (IFN) signalling to circumvent the IFN response. The viral protein responsible for the inhibition is the C protein for respirovirus SeV and the V protein for the rubulaviruses, both of which are multifunctional accessory proteins expressed from the P gene. SeV suppresses IFN-stimulated tyrosine phosphorylation of signal transducers and activators of transcription (STATs) at an early phase of infection and further inhibits the downstream signalling without degrading any of the signalling components in most cell lines. On the contrary, the Rubulavirus V protein targets Stat1 or Stat2 for degradation. Proteasome-mediated degradation appears to be involved in most cases. Studies on the molecular mechanisms by which paramyxoviruses evade the IFN response will offer important information for modulating the JAK-STAT pathway, designing novel antiviral drugs and recombinant live vaccines, and improving paramyxovirus expression vectors for gene therapy.

Menangle and Nipah virus infections of pigs

Viruses belonging to the family Paramyxoviridae generally have not been recognized as a significant cause of disease in pigs until recently. Between 1997 and 1999, there were large outbreaks of disease in pigs in Australia and Malaysia due to infection with viruses that have been shown to be new members of the Paramyxoviridae family. This article reviews current knowledge of Menangle and Nipah virus infections in pigs, the only major species of domestic animals to experience serious disease after infection with these viruses.

Antibodies to Nipah-like virus in bats (Pteropus lylei), Cambodia

Serum specimens from fruit bats were obtained at restaurants in Cambodia. We detected antibodies cross-reactive to Nipah virus by enzyme immunoassay in 11 (11.5%) of 96 Lyle's flying foxes (Pteropus lylei). Our study suggests that viruses closely related to Nipah or Hendra viruses are more widespread in Southeast Asia than previously documented.

Paramyxovirus accessory proteins as interferon antagonists

A new role of the Paramyxovirus accessory proteins has been uncovered. The P gene of the subfamily Paramyxovirinae encodes accessory proteins including the V and/or C protein by means of pseudotemplated nucleotide addition (RNA editing) or by overlapping open reading frame. The Respirovirus (Sendai virus and human parainfluenza virus (hPIV)3) and Rubulavirus (simian virus (SV)5, SV41, mumps virus and hPIV2) circumvent the interferon (IFN) response by inhibiting IFN signaling. The responsible genes were mapped to the C gene for SeV and the V gene for rubulaviruses. On the other hand, wild type measles viruses isolated from clinical specimens suppress production of IFN, although responsible viral factors remain to be identified. Both human and bovine respiratory syncytial viruses (RSVs) counteract the antiviral effect of IFN with inhibiting neither IFN signaling nor IFN production. Bovine RSV NS1 and NS2 proteins cooperatively antagonize the antiviral effect of IFN. Studies on the molecular mechanism by which viruses circumvent the host IFN response will not only illustrate co-evolution of virus strategies of immune evasion but also provide basic information useful for engineering novel antiviral drugs as well as recombinant live vaccine.

Isolation of Salem virus, a novel equine paramyxovirus, and assessment of its etiologic role in a disease outbreak

Salem virus (SalV) is a recently identified equine virus belonging to the family Paramyxoviridae. The only known isolate was obtained from a horse that was involved in a disease outbreak of undetermined nature and the circumstances of its isolation suggested an etiologic role. However, the experimental infection of a colostrum-deprived foal failed to reproduce the disease; only mild neutropenia and temperature elevation were recorded. An additional attempt to establish an etiological relationship with the disease was made by conducting a retrospective evaluation of the serological profiles of animals involved in the outbreak. Animals reported as being affected by the disease according to a comprehensive United States Department of Agriculture (USDA) database were found to be 48% (n=27) positive for antibodies to SalV, but the percent positive for all horses, affected and unaffected, was actually higher at 56% (n=62). For 15 affected horses for which paired acute and convalescent serum specimens were available, no unequivocal seroconversions to SalV were identified. Furthermore, the horse from which SalV was isolated was not listed as one of the animals affected by the disease. In total, the evidence suggests that SalV was not the etiological agent of the disease and that its isolation was fortuitous.

Relapsed and late-onset Nipah encephalitis

An outbreak of infection with the Nipah virus, a novel paramyxovirus, occurred among pig farmers between September 1998 and June 1999 in Malaysia, involving 265 patients with 105 fatalities. This is a follow-up study 24 months after the outbreak. Twelve survivors (7.5%) of acute encephalitis had recurrent neurological disease (relapsed encephalitis). Of those who initially had acute nonencephalitic or asymptomatic infection, 10 patients (3.4%) had late-onset encephalitis. The mean interval between the first neurological episode and the time of initial infection was 8.4 months. Three patients had a second neurological episode. The onset of the relapsed or late-onset encephalitis was usually acute. Common clinical features were fever, headache, seizures, and focal neurological signs. Four of the 22 relapsed and late-onset encephalitis patients (18%) died. Magnetic resonance imaging typically showed patchy areas of confluent cortical lesions. Serial single-photon emission computed tomography showed the evolution of focal hyperperfusion to hypoperfusion in the corresponding areas. Necropsy of 2 patients showed changes of focal encephalitis with positive immunolocalization for Nipah virus antigens but no evidence of perivenous demyelination. We concluded that a unique relapsing and remitting encephalitis or late-onset encephalitis may result as a complication of persistent Nipah virus infection in the central nervous system.

Nipah virus encephalitis outbreak in Malaysia

Emerging infectious diseases involving zoonosis have become important global health problems. The 1998 outbreak of severe febrile encephalitis among pig farmers in Malaysia caused by a newly emergent paramyxovirus, Nipah virus, is a good example. This disease has the potential to spread to other countries through infected animals and can cause considerable economic loss. The clinical presentation includes segmental myoclonus, areflexia, hypertension, and tachycardia, and histologic evidence includes endothelial damage and vasculitis of the brain and other major organs. Magnetic resonance imaging has demonstrated the presence of discrete high-signal-intensity lesions disseminated throughout the brain. Nipah virus causes syncytial formation in Vero cells and is antigenically related to Hendra virus. The Island flying fox (Pteropus hypomelanus; the fruit bat) is a likely reservoir of this virus. The outbreak in Malaysia was controlled through the culling of >1 million pigs.

Functional properties of the fusion and attachment glycoproteins of Nipah virus

Nipah virus (NV) and Hendra virus (HV) are recently emergent, related viruses that can cause severe disease in humans and animals. The goal of this study was to investigate the immunogenic and functional properties of the fusion (F) and attachment (G) glycoproteins of NV. Vaccination of mice with recombinant vaccinia viruses (rVVs) expressing either the F (rVV/NV-F) or G (rVV/NV-G) proteins of NV induced neutralizing antibody responses to NV, with higher titers produced after vaccination with rVV/NV-G. When the homologous pairs of F and G proteins from either HV or NV were coexpressed in a transient expression system, fusion was detected in less than 12 h. An equivalent amount of fusion was observed when the heterologous pairs of F and G proteins from HV and NV were coexpressed. Membrane fusion was inhibited by antiserum from mice vaccinated with rVV/NV-G and rVV/NV-F. Therefore, as with other paramyxoviruses, the membrane glycoproteins of NV are the targets of neutralizing antibodies and membrane fusion mediated by NV requires the presence of both the F and the G proteins. Data from these biological assays support the taxonomic grouping of both HV and NV in the new genus, Henipavirus, within the family Paramyxoviridae.

Viral encephalitis: familiar infections and emerging pathogens

Significant advances have been made in our understanding of the natural history and pathogenesis of viral encephalitides. The development of PCR has greatly increased our ability to diagnose viral infections of the central nervous system, particularly for herpes and enteroviral infections. Advancing knowledge has led to the recognition that some encephalitides can be reliably prevented by vaccination (eg, Japanese encephalitis and rabies). For other pathogens such as the arboviruses, the focus has been on prevention by vector control. Finally, effective therapy has been established for a very limited number of viral infections (eg, acyclovir for herpes simplex encephalitis). Other potentially useful treatments, such as pleconaril for enteroviral meningoencephalitis are under clinical evaluation. We review current understanding of viral encephalitides with particular reference to emerging viral infections and the availability of existing treatment regimens.

Isolation of Nipah virus from Malaysian Island flying-foxes

In late 1998, Nipah virus emerged in peninsular Malaysia and caused fatal disease in domestic pigs and humans and substantial economic loss to the local pig industry. Surveillance of wildlife species during the outbreak showed neutralizing antibodies to Nipah virus mainly in Island flying-foxes (Pteropus hypomelanus) and Malayan flying-foxes (Pteropus vampyrus) but no virus reactive with anti-Nipah virus antibodies was isolated. We adopted a novel approach of collecting urine from these Island flying-foxes and swabs of their partially eaten fruits. Three viral isolates (two from urine and one from a partially eaten fruit swab) that caused Nipah virus-like syncytial cytopathic effect in Vero cells and stained strongly with Nipah- and Hendra-specific antibodies were isolated. Molecular sequencing and analysis of the 11,200-nucleotide fragment representing the beginning of the nucleocapsid gene to the end of the glycoprotein gene of one isolate confirmed the isolate to be Nipah virus with a sequence deviation of five to six nucleotides from Nipah virus isolated from humans. The isolation of Nipah virus from the Island flying-fox corroborates the serological evidence that it is one of the natural hosts of the virus.

Nipah encephalitis outbreak in Malaysia, clinical features in patients from Seremban

BACKGROUND

An outbreak of viral encephalitis occurred among pig industry workers in Malaysia in September 1998 to April 1999. The encephalitis was attributed to a new paramyxovirus, Nipah virus. This is a description of the clinical features of 103 patients treated in the Seremban Hospital with characterization of the prognostic factors.

METHODS

Clinical case records and laboratory investigations were reviewed. The case definition was: patients from the outbreak area, direct contact or in close proximity with pigs, clinical or CSF features of encephalitis.

RESULTS

The mean age was 38 years, 89% were male, 58% were ethnic Chinese, 78% were pig farm owners or hired workers. The mean incubation period was 10 days. The patients typically presented with nonspecific systemic symptoms of fever, headache, myalgia and sore throat. Seizures and focal neurological signs were seen in 16% and 5% respectively. In the more severe cases, this was followed by drowsiness and deteriorating consciousness requiring ventilation in 61%. Autonomic disturbances and myoclonic jerks were common features. The mortality was high at 41%. Systolic hypertension, tachycardia and high fever were associated with poor outcome. On the other hand, 40% recovered fully. As for the other 19%, the residual neurological signs were mostly mild.

CONCLUSION

Nipah virus caused an encephalitis illness with short incubation period and high mortality. The prognosis for the survivors was good.

Experimental Nipah virus infection in pigs and cats

A human isolate of Nipah virus from an outbreak of febrile encephalitis in Malaysia that coincided with a field outbreak of disease in pigs was used to infect eight 6-week-old pigs orally or subcutaneously and two cats oronasally. In pigs, the virus induced a respiratory and neurological syndrome consistent with that observed in the Malaysian pigs. Not all the pigs showed clinical signs, but Nipah virus was recovered from the nose and oropharynx of both clinically and sub-clinically infected animals. Natural infection of in-contact pigs, which was readily demonstrated, appeared to be acute and self-limiting. Subclinical infections occurred in both inoculated and in-contact pigs. Respiratory and neurological disease was also produced in the cats, with recovery of virus from urine as well as from the oropharynx. The clinical and pathological syndrome induced by Nipah virus in cats was comparable with that associated with Hendra virus infection in this species, except that in fatal infection with Nipah virus there was extensive inflammation of the respiratory epithelium, associated with the presence of viral antigen. Viral shedding via the nasopharynx, as observed in pigs and cats in the present study, was not a regular feature of earlier reports of experimental Hendra virus infection in cats and horses. The findings indicate the possibility of field transmission of Nipah virus between pigs via respiratory and oropharyngeal secretions.

Nipah virus encephalitis: serial MR study of an emerging disease

PURPOSE

To report the serial magnetic resonance (MR) imaging findings of the Nipah virus.

MATERIALS AND METHODS

Twelve patients underwent serial MR imaging. Eight patients were examined at the outbreak; 11, at 1 month; and seven, at 6 months. Contrast material-enhanced MR images, diffusion-weighted images, and single-voxel proton MR spectroscopic images were reviewed. Clinical and neurologic assessment, as well as analysis of the size, location, and appearance of brain lesions on MR images, were performed.

RESULTS

During the outbreak, all eight patients had multiple small foci of high signal intensity within the white matter on T2-weighted images. In six patients, cortical and brain stem lesions were also detected, and five patients had diffusion-weighted MR imaging-depicted hyperintensities. One month after the outbreak, five patients had widespread tiny foci of high signal intensity on T1-weighted images, particularly in the cerebral cortex. Diffusion-weighted images showed decreased prominence or disappearance of lesions over time. There was no evidence of progression or relapse of the lesions at 6-month follow-up. MR spectroscopy depicted reduction in N-acetylaspartate-to-creatine ratio and elevation of choline-to-creatine ratios.

CONCLUSION

The Nipah virus has findings unlike other viral encephalitides: small lesions that are primarily within the white matter, with transient punctate cortical hyperintensities on T1-weighted images.

Functional expression and membrane fusion tropism of the envelope glycoproteins of Hendra virus

Hendra virus (HeV) is an emerging paramyxovirus first isolated from cases of severe respiratory disease that fatally affected both horses and humans. Understanding the mechanisms of host cell infection and cross-species transmission is an important step in addressing the risk posed by such emerging pathogens. We have initiated studies to characterize the biological properties of the HeV envelope glycoproteins. Recombinant vaccinia viruses encoding the HeV F and G open reading frames were generated and glycoprotein expression was verified by metabolic labeling and detection using specific antisera. Glycoprotein function and cellular tropism were examined with a quantitative assay for HeV-mediated membrane fusion. Fusion specificity was verified through specific inhibition by anti-HeV antiserum and a peptide corresponding to one of the alpha-helical heptad repeats of F. HeV requires both F and G to mediate fusion. Permissive target cells have been identified, including cell lines derived from cat, bat, horse, human, monkey, mouse, and rabbit. Fusion negative cell types have also been identified. Protease treatments of the target cells abolished fusion activity, suggesting that the virus is employing a cell-surface protein as its receptor.

Nipah virus infection among abattoir workers in Malaysia, 1998-1999

BACKGROUND

An outbreak of encephalitis primarily affecting pig farmers occurred during 1998-1999 in Malaysia and was linked to a new paramyxovirus, Nipah virus, which infected pigs, humans, dogs, and cats. Because five abattoir workers were also affected, a survey was conducted to assess the risk of Nipah infection among abattoir workers.

METHODS

Workers from all 143 registered abattoirs in 11 of 13 states in Malaysia were invited to participate in this cross-sectional study. Participants were interviewed to ascertain information on illness and activities performed at the abattoir. A serum sample was obtained to test for Nipah virus antibody.

RESULTS

Seven (1.6 %) of 435 abattoir workers who slaughtered pigs versus zero (0%) of 233 workers who slaughtered ruminants showed antibody to Nipah virus (P = 0.05). All antibody-positive workers were from abattoirs in the three states that reported outbreak cases among pig farmers. Workers in these three states were more likely than those in other states to have Nipah antibody (7/144 [4.86%] versus 0/291 [0%], P < 0.001) and report symptoms suggestive of Nipah disease in pigs admitted to the abattoirs (P = 0.001).

CONCLUSIONS

Nipah infection was not widespread among abattoir workers in Malaysia and was linked to exposure to pigs. Since it may be difficult to identify Nipah-infected pigs capable of transmitting virus by clinical symptoms, using personal protective equipment, conducting surveillance for Nipah infection on pig farms which supply abattoirs, and avoiding handling and processing of potentially infected pigs are presently the best strategies to prevent transmission of Nipah virus in abattoirs.

Complete nucleotide sequences of Nipah virus isolates from Malaysia

We have completely sequenced the genomes of two Nipah virus (NiV) isolates, one from the throat secretion and the other from the cerebrospinal fluid (CSF) of the sole surviving encephalitic patient with positive CSF virus isolation in Malaysia. The two genomes have 18246 nucleotides each and differ by only 4 nucleotides. The NiV genome is 12 nucleotides longer than the Hendra virus (HeV) genome and both genomes have identical leader and trailer sequence lengths and hexamer-phasing positions for all their genes. Both NiV and HeV are also very closely related with respect to their genomic end sequences, gene start and stop signals, P gene-editing signals and deduced amino acid sequences of nucleocapsid protein, phosphoprotein, matrix protein, fusion protein, glycoprotein and RNA polymerase. The existing evidence demonstrates a clear need for the creation of a new genus within the subfamily Paramyxovirinae to accommodate the close similarities between NiV and HeV and their significant differences from other members of the subfamily.

Molecular characterization of the polymerase gene and genomic termini of Nipah virus

In 1998, Nipah virus (NV) emerged in peninsular Malaysia, causing fatal encephalitis in humans and a respiratory disease in swine. NV is most closely related to Hendra virus (HV), a paramyxovirus that was identified in Australia in 1994, and it has been proposed that HV and NV represent a new genus within the family Paramyxoviridae. This report describes the analysis of the sequences of the polymerase gene (L) and genomic termini of NV as well as a comparison of the full-length, genomic sequences of HV and NV. The L gene of NV is predicted to be 2244 amino acids in size and contains the six domains found within the L proteins of all nonsegmented, negative-stranded (NNS) RNA viruses. However, the GDNQ motif found in most NNS RNA viruses was replaced by GDNE in both NV and HV. The 3' and 5' termini of the NV genome are nearly identical to the genomic termini of HV and share sequence homology with the genomic termini of other members of the subfamily Paramyxovirinae. At 18,246 nucleotides, the genome of NV is 12 nucleotides longer than the genome of HV and they have the largest genomes within the family Paramyxoviridae. The comparison of the structures of the genomes of HV and NV is now complete and this information will help to establish the taxonomic position of these novel viruses within the family Paramyxoviridae.

The Leeuwenhoek Lecture 2001. Animal origins of human infectious disease

Since time immemorial animals have been a major source of human infectious disease. Certain infections like rabies are recognized as zoonoses caused in each case by direct animal-to-human transmission. Others like measles became independently sustained with the human population so that the causative virus has diverged from its animal progenitor. Recent examples of direct zoonoses are variant Creutzfeldt-Jakob disease arising from bovine spongiform encephalopathy, and the H5N1 avian influenza outbreak in Hong Kong. Epidemics of recent animal origin are the 1918-1919 influenza pandemic, and acquired immune deficiency syndrome caused by human immunodeficiency virus (HIV). Some retroviruses jump into and out of the chromosomal DNA of the host germline, so that they oscillate between being inherited Mendelian traits or infectious agents in different species. Will new procedures like animal-to-human transplants unleash further infections? Do microbes become more virulent upon cross-species transfer? Are animal microbes a threat as biological weapons? Will the vast reservoir of immunodeficient hosts due to the HIV pandemic provide conditions permissive for sporadic zoonoses to take off as human-to-human transmissible diseases? Do human infections now pose a threat to endangered primates? These questions are addressed in this lecture.