Emergence Hendra virus (originally called "Equine morbillivirus") was discovered in September 1994 when it caused the deaths of thirteen
horses, and a trainer at a training complex at 10 Williams Avenue,
Hendra, a suburb of
Brisbane in
Queensland, Australia. The
index case, a mare called Drama Series, brought in from a paddock in
Cannon Hill, was housed with 19 other horses after falling ill, and died two days later. Subsequently, all of the horses became ill, with 13 dying. The remaining six animals were subsequently euthanised as a way of preventing relapsing infection and possible further transmission. A second
outbreak occurred in August 1994 (chronologically preceding the first outbreak) in
Mackay north of Brisbane resulting in the deaths of two horses and their owner. The owner assisted in
necropsies of the horses, and within three weeks was admitted to hospital suffering from
meningitis. He recovered, but 14 months later developed
neurologic signs and died. This outbreak was diagnosed retrospectively by the presence of Hendra virus in the brain of the patient.
Outbreak in Australia As of June 2014, a total of fifty outbreaks of Hendra virus have occurred in Australia, all involving infection of horses. Since 1994, Hendra virus has been the cause of death in over 100 horses. Most cases have been the result of spillover infection from flying-foxes. Others have been the result of direct transmission from infected horses. 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
Scone, New South Wales. 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. Initially this was thought to possibly be related to the breeding cycle of the little red flying foxes. These species typically give birth between April and May. Subsequently, however, the Spectacled flying fox and the Black flying fox have been identified as the species more likely to be involved in infection spillovers. Timing of outbreaks also appears more likely during the cooler months when it is possible the temperature and humidity are more favourable to the longer term survival of the virus in the environment. There is no evidence of transmission to humans directly from bats, and, as such it appears that human infection only occurs via an intermediate host, a horse. Despite this in 2014 the
NSW Government approved the destruction of flying fox colonies.
Events of June–August 2011 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 is not clear why there was 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", which is a time when there are large numbers of fruit bats of all species congregated in SE Queensland's valuable winter foraging habitat. The weather (warm and humid) is favourable to the survival of henipavirus in the environment. 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. == References ==