As of 30 May 2012, a total of thirty-five outbreaks of Hendra virus have occurred, all involving infection of horses. As a result of these events, seventy-one horses have died or been euthanised, with a further four having died or been euthanised as a result of possibly hendra infection. Case fatality rate in humans is 60% and in horses 75%.
Four of these outbreaks have spread to humans as a result of direct contact with infected horses. On 26 July 2011 a dog living on the Mt Alford property was reported to have HeV antibodies, the first time an animal other than a flying fox, horse, or human has tested positive outside an experimental situation.
These events have all been on the east coast of Australia, with the most northern event at Cairns, Queensland and the event furthest south at Macksville, NSW. Until the event at Chinchilla, Queensland in July 2011, all outbreak sites had been within the distribution of at least two of the four mainland flying-foxes (fruit bats); Little red flying-fox, (Pteropus scapulatus), black flying-fox, (Pteropus alecto), grey-headed flying-fox, (Pteropus poliocephalus) and spectacled flying-fox, (Pteropus conspicillatus). Chinchilla is considered to be only within the range of little red flying-fox and is west of the Great Dividing Range. This is the furthest west the infection has ever been identified in horses.
The timing of incidents indicates a seasonal pattern of outbreaks, possibly related to the breeding cycle of the little red flying-foxes. These species typically give birth between April and May. As there is no evidence of transmission to humans directly from bats, it is thought that human infection only occurs via an intermediate host, a horse.
- August 1994, Mackay, Queensland: Death of two horses and one person, Mark Preston.
- September 1994, Hendra, Queensland: 20 horses died or were euthanised. Two people infected, with one death, Victor Rail who was a nationally prominent trainer of racing horses.
- January 1999, Trinity Beach, Cairns, Queensland: Death of one horse.
- October 2004, Gordonvale, Cairns, Queensland: Death of one horse. A veterinarian involved in autopsy of the horse was infected with Hendra virus, and suffered a mild illness.
- December 2004, Townsville, Queensland: Death of one horse.
- June 2006, Peachester, Sunshine Coast, Queensland: Death of one horse.
- October 2006, Murwillumbah, New South Wales: Death of one horse.
- July 2007, Peachester, Sunshine Coast, Queensland: Infection of one horse (euthanised)
- July 2007, Clifton Beach, Cairns, Queensland: Infection of one horse (euthanised).
- July 2008, Redlands, Brisbane, Queensland: Death of five horses; four died from the Henda virus, the remaining animal recovered but was euthanised because of a government policy that requires all animals with antibodies to be euthanised due to a potential threat to health. Two veterinary workers from the affected property were infected leading to the death of one, veterinary surgeon Ben Cuneen, on the 20th of August, 2008. The second veterinarian was hospitalized after pricking herself with a needle she had used to euthanize the horse that had recovered. A nurse exposed to the disease while assisting Cuneen in caring for the infected horses was also hospitalized. The Biosecurity Queensland website indicates that 8 horses died during this event (http://www.dpi.qld.gov.au/4790_11112.htm, access 31 July 2011) however a review of the event indicates that five horses are confirmed to have died from HeV and three of the horses "are regarded as improbable cases of Hendra virus infection ...".
- July 2008, Proserpine, Queensland; Death of four horses.
- July 2009, Cawarral, Queensland: Death of four horses. Queensland veterinary surgeon Alister Rodgers tested positive after treating the horses. On September 1, 2009 after two weeks in a coma, he became the fourth person to die from exposure to the virus.
- September 2009, Bowen, Queensland. Death of two horses.
- May 2010, Tewantin, Queensland: Death of one horse.
- 20 June 2011 - 31 July 2011, Mt Alford, (near Boonah) Queensland: Death of three horses (all confirmed to have died of Hendra) and sero-conversion of a dog. The first horse death on this property occurred on 20 June 2011, although it was not until after the second death on 1 July 2011 that samples taken from the first animal were tested. The third horse was euthanised on 4 July 2011. On 26 July 2011 a dog from this property was reported to have tested positive for HeV antibodies. Reports indicate that this Australian Kelpie, a family companion, will be euthanised in line with government policy. Biosecurity Queensland suggest the dog most likely was exposed to HeV though one of the sick horses. Dusty was euthanised on 31 July 2011 following a second positive antibody test.
- 26 June 2011, Kerry, Queensland (the horse was moved after it became sick to another property at Beaudesert), Queensland: Death of one horse.
- 28 June 2011 Loganlea, Logan City, Queensland: death of one horse.
- 29 June 2011, Mcleans Ridges, Wollongbar, New South Wales: Death of one horse. The second horse on the property tested positive to Hendra and was euthanised on 12 July 2011.
- 3 July 2011, Macksville, New South Wales: Death of one horse.
- 4 July 2011, Park Ridge, Logan City, Queensland: Death of one horse.
- 11 July 2011, Kuranda, west of Cairns, Queensland: Death of one horse.
- 13 July 2011, Hervey Bay, Queensland: Death of one horse.
- 14 July 2011, Lismore, New South Wales: Death of one horse.
- 15 July 2011, Boondall, Queensland: Death of one horse.
- 22 July 2011, Chinchilla, Queensland:Death of one horse.
- 24 July 2011, Mullumbimby, New South Wales: Death of one horse.
- 13 August 2011, Mullumbimby, New South Wales: Death of one horse. A horse was found dead after being unwell the day before. HeV infection was confirmed on 17 August 2011.
- 15 August 2011 Ballina, New South Wales: Death of one horse.
- 17 August 2011, South Ballina, New South Wales: Death of two horses. The 2 horses were found dead in a field. Both tested positive to HeV. The exact date of death is not known however HeV infection was confirmed on 17 August 2011.
- 23 August 2011, Currumbin Valley, Gold Coast, Queensland: Death of one horse.
- 28 August 2011, North of Ballina, New South Wales:Death of one horse.
- 11 October 2011, Beechmere, Caboolture Queensland. One horse euthanised after testing positive. A horse died one week previous on the property may have died of HeV. On 15 October 2011 another horse on the property was euthanised following a positive HeV antibody test.
- 3 January 2012, Townsville, Queensland: a horse that died or was euthanised on 3 January 2012 returned a positive HeV test on 5 January 2012.
- 26 May 2012, Rockhampton, Queensland: one horse died. Other horses on the property are being quarantined.
- 28 May 2012, Ingham, Queensland: one horse died. Other horses on the property are being quarantined.
In the years 1994–2010, fourteen events were recorded. Between 20 June 2011 and 28 August 2011, a further seventeen events were identified, during which twenty-one horses died.
It's not clear why there has been a sudden increase in the number of spillover events between June and August 2011. Typically HeV spillover events are more common between May and October. This time is sometimes called "Hendra Season". This is a time when there are large numbers of fruit bats of all species congregated in SE Queensland as this area contains valuable winter foraging habitat. The weather (warm and humid) is favourable to the survival of henipavirus in the environment.
There have been suggestions that the flooding that affected SE Queensland and Northern NSW in December 2010 and January 2011 may be having an impact upon the health of the fruit bats. Urine sampling in flying-fox camps indicate that a larger proportion of flying-foxes than usual are shedding live virus. Biosecurity Queensland's ongoing surveillance usually shows 7% of the animals are shedding live virus. In June and July nearly 30% animals have been reported to be shedding live virus. Present advice is that these events are not being driven by any mutation in HeV itself.
Other suggestions include that an increase in testing has led to an increase in detection. As the actual mode of transmission between bats and horses has not been determined, it is not clear what, if any, factors can increase the chance of infection in horses.
Following the confirmation of a dog with HeV antibodies, on 27 July 2011, the Queensland and NSW governments will boost research funding into the Hendra virus by $6 million to be spent by 2014/2015. This money will be used for research into ecological drivers of infection in the bats and the mechanism of virus transmission between bats and other species. A further 6 million dollars was allocated by the federal government with the funds being split, half for human health investigations and half for animal health and biodiversity research.