Hendra virus has posed a number of challenges for horse owners, equine veterinarians, government agencies, equine industries and the general public since it was first identified in 1994.
Since then, outbreaks have continued to occur sporadically in coastal Queensland as far west as Chinchilla and from the Queensland border to as far south as Kempsey on the Mid-North Coast of NSW.
In disease outbreaks so far recorded, the virus has not been shown to be highly contagious, however, it is highly lethal.
Protection against Hendra
In 2012, a safe, effective horse vaccine became available and it is the single most effective way of reducing the risk of Hendra virus infection and provides a work health and safety as well as a public health benefit.
Hendra virus (HeV) is an emerging virus disease that was first identified in a large outbreak of a highly lethal disease in racehorses in 1994 in two adjoining Brisbane racing stables where 13 horses either died or were humanely euthanised, and 7 horses recovered and were subsequently euthanised. A trainer died from multi-organ failure and his stable hand became ill but recovered.
HeV is a single-stranded, negative-sense RNA virus within the family Paramyxoviridae and the genus Henipavirus. There are two other known members of this genus - Nipah virus (NiV) which, like Hendra, is also highly pathogenic, and Cedar virus (CedV) which does not appear to be highly pathogenic.
Four species of Australian flying foxes are the natural reservoir of HeV and the virus does not appear to cause clinical disease in them. HeV and NiV have also been detected in flying foxes in Papua New Guinea.
Hendra virus is regarded as an endemic disease in flying foxes in Australia. All known cases in horses have occurred in coastal areas of Queensland and NSW and research indicates that all infections have occurred within the range of the black flying fox (Pteropus alecto) and the spectacled flying fox (Pteropus conspiculatus) species. The virus transmission dynamics in these 2 species and in the other 2 species, the grey-headed (Pteropus poliocephalus) and little red (Pteropus scapulatus), are complex and incompletely understood, so the transmission risk to horses from the latter 2 species is still undetermined.
The clinical signs of Hendra virus in horses are mainly respiratory and/or neurological usually with a rapid progression to death and with a 79% mortality rate. Some horses diagnosed with Hendra have recovered from the disease, and to date, they have all been euthanased.
Research has now established there is no evidence that recovered horses or humans shed infectious virus and the previous policy regarding euthanasia of seropositive recovered horses has recently been reviewed in 2016 by Australia’s Animal Health Committee and compulsory euthanasia is no longer mandatory. Management of seropositive non-vaccinated horses is at the discretion of State Chief Veterinary Officers.
Hendra virus is a rare disease in humans. There have been seven known cases, with four deaths, a case fatality rate of 57%. The human cases have all occurred by close contact with the secretions or body fluids of infected horses which act as amplifiers of the virus. One person became infected from a horse in the late incubation stage before it showed clinical signs.
There has been no evidence of direct flying fox-to-human transmission, or of human-to-human transmission as has occurred overseas with the closely related Nipah virus. Horse to horse transmission is more likely to occur when horses are in close contact with each other.
There are 2 recorded incidents in 2011 and 2013 where dogs have become infected, plausibly by contact with blood or excretions from infected horses on the properties. The clinical signs in dogs are mild and likely to go unnoticed, however, dogs can represent a transmission risk to humans from saliva soon after they become infected.
How is Hendra virus spread?
A recent study confirmed that flying fox urine is the most significant route of HeV excretion in wild-caught black flying foxes. Transmission pathways facilitating spillover to horses via urinary contamination of pasture, feed and water sources is highly plausible. Routine observation of the abundance of flying-fox urine, faeces, and food debris underneath trees in which they are feeding suggests that horses have a high likelihood of direct physical contamination with a potentially infectious material at these sites. As horses are more likely to be resting than grazing or browsing when flying-foxes are most actively foraging, direct inoculation of infectious flying-fox urine with the mucosal surfaces of horses is another plausible transmission pathway in addition to ingestion of contaminated material.
The AVA believes that the Hendra vaccine is the single most effective way of reducing the risk of Hendra virus infection in horses and therefore of preventing disease transmission to people.
What animals are at risk of contracting Hendra virus?
Hendra virus infections have been confirmed in flying foxes, horses, and dogs.
Other animals known to be susceptible include cats, ferrets, pigs, guinea pigs, hamsters, and non-human primates.
Horses suspected of being infected with HeV should be isolated from all other animals to avoid spreading disease. People should not kiss horses on the muzzle, and personal protective equipment should be worn when dealing with sick horses. Good personal hygiene should always be practiced around horses, dogs, and other animals - it's not a good idea to let dogs lick people's faces at any time, and washing of hands after touching any animal should always be practised. Children of any age should always be supervised by an adult around dogs.
The story so far
From 1994 to August 2017, there have been 60 known outbreaks of Hendra resulting in the death of 102 horses, with a 79% mortality rate. Survivors were euthanased according to the former national policy.
In this period Queensland has recorded 40 outbreaks and NSW 20 outbreaks.
From 2011 to August 2017 there have been 46 outbreaks resulting in the death of 54 horses with Queensland recording 27 outbreaks and NSW recording 19 outbreaks. By way of comparison NSW only recorded 1 outbreak from 1994 – 2010.
There have been seven confirmed cases in people, all of whom had significant contact with horse body fluids. Of those who tested positive for Hendra, four died of the disease, including two veterinarians, Dr. Ben Cunneen in 2008, and Dr. Alister Rodgers in 2009.
Monoclonal antibody m102.4 has been offered on compassionate grounds and used as a post-exposure therapy to treat 10 Australians since 2009. All of the patients were heavily exposed to infected horses. Unfortunately, in 2009, it was unsuccessful due to an advanced progression of the disease in that patient. The other human cases were a mother and daughter from Tewantin in 2010, a Rockhampton woman in 2012, and 6 people from NSW and Queensland in 2014. Two laboratory workers, one in the USA and one in Australia, have also been treated with the monoclonal antibody.
Following on from the release of the vaccine in late 2012 there has been a steady decline in the number of Hendra virus outbreaks in horses in both States, with all 19 cases have occurred in unvaccinated horses.
Hendra in 2016 / 2017
Following on from full registration being granted by the APVMA for Equivac® HeV in August 2015, there have been five recorded disease outbreaks of Hendra virus. One in NSW at Kyogle in December 2016 and one in Queensland at Tambourine Mountain in May 2017, two in Lismore in July 2017, and one in Murwillumbah in August 2017.
In other significant developments in 2016 the Equivac® HeV vaccine was approved for use in pregnant mares in January 2016 and the 12-month duration of immunity, following 2 initial doses and a booster at 6 months, was approved by the APVMA in May 2016.
In June, the Queensland Chief Medical Officer announced successful results of the safety studies of the m102.4 monoclonal antibody Phase 1 human clinical trial conducted at the Queensland Institute of Medical Research
On 25 February 2016, the Queensland Legislative Assembly agreed to a motion that the Agriculture and Environment Committee inquire into and report on the Equivac ® HeV vaccine and its use by veterinary surgeons in Queensland. The Agriculture and Environment Committee called for submissions and 300 were received. Public hearings were held throughout Queensland 4-7 July, and AVA provided a detailed submission and appeared before the Committee in Parliament House on 6 July. The Government released its responses to the Committee's eleven recommendations on 21 April 2017. The Government announced that currently it does not support mandatory vaccination for every horse in Queensland but supports the right and discretion of equestrian event organisers to require vaccination as a condition of entry for equestrian events on the basis of their own informed risk assessment.
From 2015 to 2017 the Queensland Workplace Health and Safety Authority prosecuted three veterinarians over their handling of positive Hendra virus cases. These cases have now been heard in court. In all three cases, no conviction was recorded against the veterinarians. They are free to continue practising.
The Hendra vaccine
The Equivac® HeV vaccine became available to horse owners on 1 November 2012. It is an animal medicine, fully registered by the Australian Pesticides and Veterinary Medicines Authority (APVMA.) The vaccine has been declared as safe and effective (Source: Qld Parliament Report into the Hendra Vaccine; October 2016.) The vaccine was initially released to high-risk areas in Australia and then to all horse owners soon afterward.
The vaccine was the result of scientific and collaborative efforts between the Uniformed Services University of the Health Sciences in Maryland USA, the Henry M Jackson for the Advancement of Military Medicine in Maryland USA, Pfizer Animal Health (now Zoetis), and CSIRO's Australian Animal Health Laboratory.
A timeline from 1994 to 2012 (the year the Hendra virus vaccine was released) has been developed to provide a summary of the research that has improved our knowledge of the deadly disease and contributed to the development of the vaccine.
A review by Professor C Broder, Dr. D Weir and Dr. P Reid of the development of active and passive Hendra virus and Nipah virus animal vaccines has recently been published June 2016 in the internationally renowned journal Vaccine. Available online here.
The current scheduling protocol for healthy microchipped horses over four months of age is two initial vaccinations administered three to six weeks apart, followed by a booster at 6 months, followed by annual boosters, with all vaccinations recorded in a central database register. The vaccine should not be used in sick or immunocompromised animals. As no animal or human vaccines are regarded as 100% effective in all individuals, appropriate PPE, good personal hygiene and biosecurity practices should always be used when dealing with sick, vaccinated or unvaccinated horses.
The vaccine is only available to veterinarians. The reasoning behind this is based on the fact that because Hendra is such a lethal disease, the vaccine needs, therefore, to be handled, stored and administered by veterinary professionals, to ensure adherence to correct administration protocols in order to protect animal and human health, in line with the best international standards for preventive medical care. In addition, the record of horse vaccination is entered into a central database which can be used to used by veterinarians to check the horse's current vaccination status.
No vaccinated horses have ever contracted Hendra virus, whilst 20 laboratories confirmed HeV infections in horses have occurred in Queensland and NSW since vaccine release in November 2012.
The vaccine is the single most effective way of reducing the risk of Hendra virus infection and provides a work health and safety as well as a public health benefit and there is a high level of confidence in the vaccine held by veterinarians and by both Queensland and NSW State Governments and the Australian Government through the Animal Health Committee. This has been evidenced in outbreak situations since the vaccine became available.
From 2013-2015 there were seven horse deaths in NSW. Of the seven NSW properties affected there were 19 horses in contact with the HeV positive cases which had not been vaccinated. These 19 in contact with horses were then vaccinated and subsequently did not become infected. In an outbreak in Queensland on the Atherton Tablelands in July 2015 where one horse died from HeV, there were also six vaccinated horses and three unvaccinated horses on a property. These six vaccinated horses were regarded by QDAF’s Biosecurity Queensland as “low interest” horses and subsequently released early from quarantine in line with national Animal Health Committee policy.
Information for the community
The AVA concurs with the advice to the public published in October 2014 by the Queensland Government Department of Health in the Hendra virus Infection Prevention Advice.
This document states:
“The vaccine is the single most effective way of reducing the risk of Hendra virus infection in horses and provides a work health and safety and public health benefit by the vaccine's ability to not only protect horses from infection but also to break the cycle of virus transmission from horses to humans. Widespread uptake of the horse vaccine has the potential to significantly reduce the number and risk of human exposures.”
Vaccination of horses is regarded as the highest order of risk management.
In addition to vaccination, there are a number of strategies that can be employed by horse owners to reduce the risk of transmission of the virus.
- Place all feed and water containers under cover.
- Bring horses into covered enclosures or enclosed paddocks with no trees at night to reduce potential contact with foraging flying foxes.
- Remove horses from paddocks where trees attract flying foxes or fence off trees to prevent horses grazing underneath.
- When planting trees on your property do not plant trees that attract flying foxes in or near horse paddocks. These include trees with soft fruits for example, figs and stone fruits such as peaches, loquats, and mangos.
- Seek veterinary advice before bringing any sick horses on to your property.
- If you have a horse that you suspect of having Hendra, do not move any other horse off the property until given the all clear by the proper authorities.
- Keep any sick horses isolated from people and other animals.
- Plan a quarantine area on your property where sick horses can be isolated.
- Remember to thoroughly wash your hands after and between handling individual horses to prevent the potential spread of Hendra virus infection.
How do I know if my horse has contracted Hendra?
Clinical signs of Hendra virus infection are varied, vague and similar to many common equine ailments that veterinarians encounter on a daily basis. The Queensland government’s Guidelines for veterinarians handling potential Hendra virus infection in horses states that Hendra virus infection should be considered if a horse may have had contact with flying foxes and any one or combination of the following signs are present:
- Acute illness
- Increased temperature
- Increased heart rate
- Discomfort or shifting weight between legs
- Depression or rapid deterioration in health.
Horses with confirmed Hendra virus infection have also presented with respiratory, colic, or neurologic signs, weakness, inappetence or behaviour change.
Essentially this indicates that almost any unvaccinated sick horse with potential exposure to flying fox excretions, virus-contaminated objects or other horses may have a Hendra virus infection.
A horse can only be diagnosed with Hendra virus by submitting a range of samples to State Government and Australian Animal Health Laboratories (AAHL). It is not possible to diagnose Hendra purely from observation or an examination because the clinical signs of the disease may mimic other diseases.
Hendra video – a safer tomorrow
In 2013, a documentary was created to highlight the progress that had been made in relation to Hendra. The online documentary features former AVA President Dr. Ben Gardiner, Dr. Lin-fa Wang and Dr. Deborah Middleton from AAHL, former EVA Presidents Dr. Warwick Vale and Dr. James Gilkerson, Professor Christopher Broder from the Uniformed Services University in the US and Dr. Peter Reid.
Watch the documentary A safer tomorrow: our stand against Hendra virus below.
Videos provided by Zoetis Australia.
Hendra Virus - A Safer Tomorrow - Chapter 1/6
A Safer Tomorrow - Join us for the first chapter of A Safer Tomorrow for an introduction to the Hendra experts and current opinions surrounding this deadly virus.
Hendra Virus - A Safer Tomorrow - Chapter 2/6
The Flying Fox Challenge - It is well known that flying foxes (fruit bats) carry Hendra virus. But even if you don't see bats in your area, it doesn't mean your horses are not at risk of infection. Watch this chapter of A Safer Tomorrow to find out more.
Hendra Virus - A Safer Tomorrow - Chapter 3/6
The Debate Around Mandatory Vaccination - Is mandatory vaccination the answer to stopping the spread of the deadly Hendra virus? This chapter of A Safer Tomorrow delves into this hot topic.
Hendra Virus - A Safer Tomorrow - Chapter 4/6
The Consequences of Hendra Virus Infection Have you ever worried about what would happen if there was an outbreak of Hendra at an event? Watch as equine experts explore the potential impact in this chapter of A Safer Tomorrow.
Hendra Virus - A Safer Tomorrow - Chapter 5/6
Living with Hendra Virus - In this emotional chapter of A Safer Tomorrow, Dr Debra Middleton of the Australian Animal Health Laboratory (AAHL) meets Hendra survivor, Natalie Boehm, to discuss the real-world impact Hendra virus can have on lives, businesses and the wider horse community.
Hendra Virus - A Safer Tomorrow - Chapter 6/6
The future of Hendra Virus Research - This final chapter of A Safer Tomorrow asks "What's next for Hendra?" Experts discuss the importance of collaboration, research and vaccination in aiming for a brighter future for the horse communities living with Hendra.
Hendra in the news
Despite Hendra being found in horses only in Queensland and northern NSW so far, it has made news headlines right across the country. Here is just some of the coverage.
- ABC Rural, 25 September 2016 - Dr Nathan Anthony talks Hendra prosecutions
- The Horse, 15 January 2015 - Hendra virus protection adopted by equine veterinarians
- The Horse, 28 September 2014 - Australian vets: have horses vaccinated against Hendra
- Horsetalk, 22 January 2013 - The Hendra virus in South Australia no surprise to vets
- ABC News, 2 November 2012 - Breakthrough Hendra virus vaccine released for horses
- The Age, 1 November 2012 - Deadly human link ends with horse vaccine for Hendra virus
- Canberra Times, 1 November 2012 - Deadly human link ends with horse vaccine for Hendra virus
- ABC News, 17 July 2011 - Caution as Hendra cases continue to climb
- Courier Mail, 8 July 2011 - Vets want financial help to fight Hendra
- Sydney Morning Herald, 23 May 2010 - Two more wait on Hendra virus results
Some of the AVA's recent reporting on Hendra
- 16 May 2016 - Equine vets welcome new annual booster vaccine for Hendra virus
- 28 April 2016 - Queensland Hendra vaccine inquiry
- 22 April 2016 - Veterinary submission to Hendra vaccine inquiry sets out a way forward
- 29 March 2016 - WHS case in relation to Hendra virus risks while treating horses
- 14 December 2015 - Work health ads safety concerns over Hendra virus
- 5 August 2015 - Hendra vaccine registration welcomed by equine vets
- 2 February 2015 - Vets criticise hate campaign against the Hendra vaccine
- 23 September 2014 - Vets urge horse owners to get their horses vaccinated
- 26 June 2014 - Attila the Hen and Hendra virus research
- 22 January 2013 - Hendra virus in South Australia - no surprise to vets
- 23 November 2012 - Hendra vaccine now available in the Northern Territory
- 1 November 2012 - Vaccine arrives to boost the fight against deadly Hendra virus
- 6 June 2012 - Veterinarians reassure dog owners over Hendra
- 14 July 2011 - Culling flying foxes won’t fix Hendra