Equis ISSN 2398-2977

Hendra virus

Synonym(s): Equine Morbillivirus

Contributor(s): Melissa Kennedy, Graham Munroe, Vetstream Ltd

Introduction

Classification

Taxonomy

  • Family: Paramyxoviridae.
  • Subfamily: Paramyxovirinae.
  • Genus: Henipavirus.
  • Species: Hendra virus.

Etymology

  • Named for suburb of Brisbane, Australia, where first occurred in 1994.

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Clinical Effects

Epidemiology

Habitat

  • Reservoir is fruit bats/flying foxes (Pteropus spp) - most are subclinically infected, excreting live virus in their urine, saliva and feces for approximately 1 week post-infection.
  • Virus has also been isolated from uterine fluid and fetal tissues of infected fruit bats.

Transmission

  • Experimentally, respiratory transmission is very inefficient and respiratory spread between horses is unlikely.
  • Virus titers are high in the kidney of infected animals.
  • Urine may be an important source.
  • Virus is also found in saliva and nasal mucosa of horses.
  • Aborted bat fetus or reproductive fluids may be a source.
  • Vertical transmission in fruit bats occurs.
  • No human to human spread; direct physical contact with the secretions or body fluids (such as nasal discharge or blood) from an infected or dead horse appears to be necessary for human infection.
  • The most likely route of infection in horses is ingestion of pasture or feed contaminated with the urine, feces, saliva or birthing products from infected flying foxes.
  • Horse-to-horse transmission occurs between stabled horses or paddock-mates, presumably via contamination of fomites.
  • To date, there is no evidence of human-to-human, human-to-horse or flying fox-to-human transmission of Hendra virus.
  • Other species do not seem to be affected, however, experimentally, cats, guinea pigs and pigs can be infected. At least two cases in dogs have been detected by seroconversion: disease was not evident or mild.

Pathological effects

  • Macrophages, monocytes in lung and lesions in fruit bats coincide with peak antibody titer.
  • Subpleural edema.
  • Consolidation of lungs.
  • Petechial hemorrhages.
  • Histologically acute interstitial pneumonia, capillary endothelium is damaged → edema, fibrinous exudate and hemorrhage. The underlying pathology is a vasculitis of small vessels in multiple organs.
  • Syncytial cells also observed.
  • Vascular lesions in many organs.
  • Can cause CNS edema → encephalitis.

Other Host Effects

  • Can cause severe disease in horses, cats, guinea pigs Hendra virus disease.
  • In humans, serious influenza-like illness with respiratory signs, fever and myalgia - fatal encephalitis in one person.
  • Incubation in horses of ~10-14 days.
  • Actue course of 1-3 days; horses may be found dead.
  • Anorexia, depression and fever.
  • Rapid labored respiration.
  • Sweating with congested mucous membranes.
  • Copious yellow frothy nasal discharge Nose: nasal discharge seen terminally.
  • Neurologic signs and meningitis may occur.

Control

Control via animal

  • Avoidance of contact with fruit bats.
  • Flying foxes are a protected species so culling is inappropriate.
  • Quarantine suspected equine cases and apply strict quarantine management practices to protect handlers and other equines.

Control via chemotherapies

  • The virus is very susceptible to disinfectants.

Control via environment

  • Minimize contact with fruit bats and their excretions.
  • Feed and water troughs should be placed under cover and away from trees where fruit bats might feed or roost.
  • Horse feed that might attract fruit bats (such as apples, carrots or anything sweet) should be avoided.
  • The virus can easilly be killed by heat or desiccation.

Vaccination

  • At the current time there are no specific drugs or antiviral therapy.
  • A subunit vaccine Hendra virus vaccine is available and can be given to horses as young as 4 months; a booster 3 weeks after primary inoculation is required, as are yearly revaccinations. Immunity is protective.

Other countermeasures

  • When examining potentially infected horses, an initial risk assessment should be conducted to avoid unnecessary exposure, and to instigate appropriate infection control procedures as described in Guidelines for Veterinarians Handling Potential Hendra Virs Infection in Horses (see Sources).

Vaccination

  • A subunit vaccine Hendra virus vaccine is available and can be given to horses as young as 4 months; a booster 3 weeks after primary inoculation is required, as are yearly revaccinations. Immunity is protective.

Diagnosis

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Hess I M R et al (2011) Hendra virus: what do we know? NSW Public Health Bull 22 (6), 118-122 PubMed.
  • Barclay A J & Paton D J (2000) Hendra (equine morbillivirus). Vet J 160 (3), 169-176 PubMed.
  • Westbury H (2000) Hendra virus - a highly lethal zoonotic agent. Vet J 160 (3), 165-166 PubMed.
  • Halpin K, Young P L, Field H & MacKenzie J S (1999) Newly discovered viruses of flying foxes. Vet Microbiol 68 (1-2), 83-87 PubMed.
  • Williamson M Met al (1998) Transmission studies of Hendra virus (equine morbillivirus) in fruit bats, horses and cats. Aust Vet J 76 (12), 813-818 PubMed.

Other sources of information

  • Biosecurity Queensland (2011) Guidelines for Veterinarians Handling Potential Hendra Virus Infection in Horses. Version 4.1. Department of Employment, Economic Development and Innovation, Queensland Government. Website: www.dpi.qld.gov.au/4790_13371.htm.
  • Primary Industries and Fisheries, Queensland Government (2011) Hendra Virus. Website: www.dpi.qld.gov.au/4790_2900.htm.

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