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Hendra virus infection is a serious emerging zoonosis, and human infection is acquired through contact with acutely infected horses.
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The natural reservoirs of Hendra virus are Australian mainland flying foxes, and horses are infected following exposure to flying fox secretions.
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The increasing number of equine outbreaks and associated human risk exposures exacerbate community concerns and heighten pressure to cull flying fox populations.
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Use of an inactivated Hendra virus subunit vaccine in horses
Veterinary Clinics of North America: Equine Practice
Hendra Virus
Section snippets
Key points
Emergence
Hendra virus (HeV) is a zoonotic paramyxovirus that emerged in 1994 in the Brisbane suburb of Hendra, Queensland, Australia.1 It was the first member to be characterized within a new viral genus Henipavirus in the order Mononegavirales and family Paramyxoviridae, wherein it forms a distinct clade with Nipah virus and Cedar virus.2, 3 HeV was initially isolated from equine lung tissue during investigation of an outbreak of severe febrile respiratory disease in horses that led to the natural
Zoonotic infection
There have been five HeV outbreaks in horses that have been associated with transmission of infection to people, and there is a strong epidemiologic connection between infection of people and direct contact with horses. Six of the seven affected humans have been exposed to the blood or secretions of terminally ill horses or have been contaminated with body fluids during postmortem examination of infected horses; three were veterinarians. In the seventh patient, a veterinary nurse, the high-risk
The viral reservoir
A serologic study conducted soon after the discovery of HeV did not show evidence of neutralizing antibody in the Queensland horse population suggesting that the virus was not being maintained within this species, and so the possibility of another source for the virus was investigated.10 In an initial survey, sera from 46 species including 34 species of fauna were sampled and none were positive for antibody against HeV, but extension of the work to fruit bats (flying foxes) revealed a
Hendra virus infection in horses
HeV infection of horses is believed to be acquired following direct exposure to the virus in flying fox secretions; however, the precise way in which this occurs is not known. The infection is sporadic, commonly involving only a single horse within a group. Occasional multihorse outbreaks where there is evidence of horse-to-horse transmission (most likely via contamination of surfaces or equipment by infectious fluids) have permitted an estimation of the field incubation period between 4 and
Community impact
The 18 equine HeV incidents of 2011 and the first reported field infection of a dog were associated with increased national coverage in the mass media, and those communications to the public sent the message that burgeoning infection risk to the community was attributable to expansion of flying fox populations into urban areas27 rather than to direct contact with infected horses. As a result, there was increasing pressure to instigate measures for the control or extermination of flying fox
A Hendra virus vaccine for horses
There is no straightforward means of preventing exposure of horses to HeV that is shed by flying foxes. Factors influencing interspecies transmission are likely complex, are poorly understood, and the interface between bats and horses cannot be eliminated within periurban and rural communities. Thus, a more direct approach has been introduced to protect the health of horses and to reduce the risk of human infection, namely vaccination of horses. The aim of suppression of HeV virus replication
Postexposure therapeutics for people
Exposure of humans to infectious doses of HeV from acutely affected horses may occur in the future. Not all horses will be vaccinated against HeV and outbreaks occur in temperate to tropical climates where continual compliance with certain items of personal protective equipment may be difficult to achieve. The emotional attachment of humans to their horses leads to regular close contact where use of personal protective equipment is usually impractical, and the occupational exposure limits by
Other susceptible animal hosts
Diverse species have proved susceptible to HeV infection under experimental conditions including cats, ferrets, hamsters, pigs, and guinea pigs. Each exhibits disease generally similar to that observed in horses, with ferrets and hamsters in particular used in efficacy assessment of antihenipavirus vaccines and therapeutics.37, 38, 39, 40 More recently, Dups and colleagues41 reported encephalitis in wild-type laboratory mice in the absence of significant systemic infection; this model holds
Summary
The incidence of emerging zoonotic diseases has been increasing for several decades42 and significant predictors of emergence, such as increasing human population growth and density, will persist in the foreseeable future. Thus, it is to be expected that further new and highly pathogenic infections will enter the human population, that companion or agricultural animals may be the immediate source, and that a wildlife species will prove to be the pathogen’s reservoir host. As for HeV, mitigating
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Cited by (0)
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Funding Sources: National Health and Medical Research Council grants 1022516, National Institutes of Health grants U01-A107795, Commonwealth of Australia, Queensland State Government, Intergovernmental Hendra Virus Taskforce.
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Conflict of Interest: Nil.