Ratification Date: 05 Nov 2021
Vaccination of horses is the most effective way to help manage Hendra virus infection and provides a public health and work health and safety benefit by reducing the risk of Hendra virus transmission to humans and other susceptible animals.1,2 A registered vaccine is available to help prevent Hendra virus disease in horses. All vaccinations of horses against Hendra virus must be administered by veterinarians, and recorded in the central database, to ensure accurate information on vaccination status is available to veterinarians and other people in contact with sick horses.
Precautions must be taken by horse owners, handlers and veterinary staff to minimise the risk of Hendra virus infection in horses and people. Veterinarians and others operating businesses involving horses have a legal obligation under work health and safety laws to operate a safe working environment. This obligation can be enforced through the legal system.2,3
Hendra virus (HeV) is a serious, potentially fatal virus that is spread from flying foxes to horses, and from infected horses to humans. The clinical signs of Hendra virus in horses are varied and may include fever, elevated heart and respiratory rates, nasal discharge, ataxia, muscle twitching, recumbency, blindness or sudden death.4
Diagnosis of Hendra virus infection in horses is impossible without laboratory confirmation.
All known cases of human HeV disease have been associated with equine cases. The level of contact between bats and horses is not known and the risks posed by the HeV variant described in 2021 are not fully understood. The most effective means to minimise risk of HeV infection in horses and humans is to vaccinate all horses against Hendra virus.
Antibodies to HeV, and HeV nucleic acid, have been detected in all four mainland species of Australian Pteropid bats (Black, Spectacled, Grey Headed, and Little Red flying foxes), from various colonies around the east coast between Far North Queensland and Adelaide, and also in north-west of WA.5 The factors that are associated with HeV spillover from bats to horses are not fully understood. The identification in 2021 of a new variant of HeV, and the occurrence of a case in October 2021 diagnosed further south in NSW than any previous case, has increased the uncertainty around the geographical distribution of this disease in horses and the epidemiology of HeV infection in the natural host.
The currently accepted mode of transmission of HeV from bats to horses involves flying foxes shedding virus into the environment in which the horse lives.6 Vaccination of horses is the most effective way to help manage Hendra virus disease. Amino acid sequencing of the new HeV variant suggest that the immune response to HeV vaccination will provide equivalent protection for horses exposed to either variant. The Australian Centre for Disease Preparedness (ACDP, CSIRO) conducted studies that have shown that serum from vaccinated horses can neutralise the new genotype, suggesting the vaccine is effective against HeV-G2.7 Other preventive measures are those which aim to minimise contact between horses and flying foxes. Additional precautions to protect people include using personal protective equipment and implementing good hygiene and infection control practices when handling horses.
The most appropriate precautions in any given circumstance will depend on a range of factors including the geographical location, vaccination status of the horse, the presence of flying foxes, the nature of any presenting signs in the horse, and the risk of exposure to infectious bodily fluids.
A key consideration is that, in an infected horse, Hendra virus nucleic acid is detectable in respiratory secretions before the infected horse shows any signs of illness. This means that there is a low but nonetheless identified risk of apparently healthy horses infecting other horses or people with Hendra virus up to 3-5 days before the onset of illness.7
Mandatory vaccination can be achieved through government legislation or through mandatory programs implemented by industry. Both may be necessary to achieve the level of vaccination required to protect the community.
Because of the many variables that affect the potential risk of infection for people, veterinarians undertake a risk analysis to decide how best to protect themselves and others against Hendra virus. There are also government guidelines in several states on how to manage the risk of Hendra virus in veterinary practice. 8,9,10,11 The policy responses of veterinary practices will vary due to the range of factors that influence risk. As the examination of seemingly healthy horses still poses risk, some practices consider that the risk of examining unvaccinated horses is too high given the potentially fatal consequences of infection. Citizen juries have canvassed the views of well-informed people on HeV control. Participants acknowledged the challenge for private veterinarians, but the majority of jurors believed that veterinarians should not be obliged to attend unvaccinated horses.12
Section 19 (2) of the Queensland Workplace Health and Safety Act 2011 states that “A person conducting a business or undertaking must ensure, so far as is reasonably practicable, that the health and safety of other persons is not put at risk from work carried out as part of the conduct of the business or undertaking.” Similar legal requirements are in place in other states and territories and can be enforced by prosecution of any workers in contact with horses that may contract Hendra virus.13,3
Sick, unvaccinated horses must have Hendra virus infection ruled out by the collection of blood and nasal, oral and/or rectal swabs by the attending veterinarian. Until results of Hendra virus exclusion testing are received, horses should receive only such care that can be provided with minimal contact with the affected horse, and diagnostic procedures will similarly be limited. This is in order to comply with the requirements of workplace health and safety laws, and to minimise the risk of transmission of the disease to people. It may result in suffering that could have been avoided by current vaccination status of these animals against Hendra virus.
- Wang, J., et al. (2021). "A new Hendra virus genotype found in Australian
flying foxes." Virology journal 18(1): 1-13.
- Hume E Field,(2016) “Hendra virus ecology and transmission”, Current Opinion in Virology,16:120-125
- Agriculture Victoria Biosecurity Advisory 14th October 2021 https://agriculture.vic.gov.au/biosecurity/animal-diseases/vetsource/biosecurity-advisory/hendra-virus-further-genotype-detected-in-victorian-flying-foxes
- Biosecurity Queensland. Guidelines for veterinarians handling potential Hendra virus infection in horses. Brisbane, 2011. https://www.health.qld.gov.au/__data/assets/pdf_file/0026/428624/hev-inf-prev-adv.pdf Hendra Virus Protection Advice. Hendra Virus interagency technical working group report, October 2014.
- NSW Department of Primary Industries, General information on Hendra virus https://www.dpi.nsw.gov.au/animals-and-livestock/horses/health-and-disease/hendra-virus
- Annand, E. J., Reid, P. A., Johnson, J., Gilbert, G. L., Taylor, M., Walsh, M., ... & Degeling, C. (2020). Citizens' juries give verdict on whether private practice veterinarians should attend unvaccinated Hendra virus suspect horses. Australian Veterinary Journal, 98(7), 273-279.
- Workplace Health and Safety Queensland, https://www.worksafe.qld.gov.au/laws-and-compliance/work-health-and-safety-laws