Review
Hendra virus: an emerging paramyxovirus in Australia

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Summary

Hendra virus, first identified in 1994 in Queensland, is an emerging zoonotic pathogen gaining importance in Australia because a growing number of infections are reported in horses and people. The virus, a member of the family Paramyxoviridae (genus Henipavirus), is transmitted to horses by pteropid bats (fruit bats or flying foxes), with human infection a result of direct contact with infected horses. Case-fatality rate is high in both horses and people, and so far, more than 60 horses and four people have died from Hendra virus infection in Australia. Human infection is characterised by an acute encephalitic syndrome or relapsing encephalitis, for which no effective treatment is currently available. Recent identification of Hendra virus infection in a domestic animal outside the laboratory setting, and the large range of pteropid bats in Australia, underpins the potential of this virus to cause greater morbidity and mortality in both rural and urban populations and its importance to both veterinary and human health. Attempts at treatment with ribavirin and chloroquine have been unsuccessful. Education, hygiene, and infection control measures have hitherto been the mainstay of prevention, while access to monoclonal antibody treatment and development of an animal vaccine offer further opportunities for disease prevention and control.

Introduction

Hendra virus was discovered in 1994 in the Brisbane suburb of Hendra (Queensland, Australia) after an outbreak of disease affecting 21 horses in a racing stable. The horses developed high fever and acute respiratory signs, and the case-fatality rate was high. Two people who had close contact with infected horses developed acute respiratory disease, one of whom died. Initially characterised as equine morbilliform virus, the virus was isolated and identified from one infected horse.1 Since 1994, several sporadic cases of equine Hendra virus infection have been recognised; transmission to people has occurred with a high fatality rate.

Section snippets

Basic virology

Hendra virus is the type species of the Henipavirus genus of the family Paramyxoviridae, subfamily Paramyxovirinae.2, 3, 4, 5 Nipah virus is the second known member of this genus on the basis of genome organisation, protein size and structure, and cross-neutralisation of antisera.6, 7, 8, 9 The Hendra virus helical nucleocapsid is encased in an envelope and forms pleomorphic virus particles up to 1900 nm in length, which vary from spherical to filamentous. By electron microscopy, 95% of virions

Transmission

Little is known about the transmission of Hendra virus in nature, with research hampered by the mobility of the reservoir host (flying foxes) and the abundance of the spillover host (horses). Flying foxes (Pteropus spp) are the natural reservoir of Hendra virus. They are nomadic nocturnal foragers and are growing in abundance in urban and periurban locations, particularly in eastern Australia, where food resources are increasingly reliable.30 Flying foxes roost by day in colonies of up to tens

Clinical and radiological features

Human Hendra virus infection has been identified in seven people (table 2). In six patients, the initial presentation was a fairly non-specific influenza-like illness. In two of these patients (cases 1 and 4), the influenza-like illness was self-limited with complete recovery and no clinically apparent relapse over a long period of follow-up (>5 years).60, 62 The other four patients (cases 2, 3, 5, and 6) progressed to more severe illness. Only one individual (case 7) has presented with

Laboratory diagnosis

Laboratory diagnostic methods are very important, because clinical features of equine and human Hendra virus infection are non-specific, even with late-stage respiratory and neurological signs. Various laboratory methods have been described and include virus isolation, electron microscopy, immunohistochemistry, serology, and PCR.1, 65

The virus is designated a biosafety level (BSL) 4 agent. Although initial attempts to isolate species of Henipavirus can be done in a BSL3 laboratory, if a

Therapeutic research

No approved effective antiviral drugs are available for human or animal infections with Hendra virus. Research in this area includes testing of known drugs, screening for novel antivirals based on small molecules or peptides, and development of recombinant monoclonal antibodies for passive immunotherapy.

The broad-spectrum antiviral drug ribavarin78 can inhibit replication in vitro.79 However, when a high-dose intravenous regimen of ribavirin was given to two patients infected with Hendra virus,

Conclusion

Members of the Henipavirus genus have gained increasing prominence in the Asia-Pacific region in recent years. Continuing research into the pathogenesis, diagnosis, and treatment of Hendra virus, and development of both equine and human vaccines, are important for the control of Hendra virus infection and potentially other flying fox-borne zoonotic diseases.

Search strategy and selection criteria

We searched PubMed with the terms “Hendra virus”, “Hepadnavirus”, or “paramyxovirus”. Qualifying terms were added to narrow the search area for every section: “transmission”, “control measures”, “bats”, “distribution”, “genome organisation”, “structure”, “protein functions”, “Henipah classification”, and “Equine Morbillivirus”. We imposed no language restrictions. Although all dates were included for most searches (earliest accepted article was from 1994), we did restrict clinical and pathology

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