Hendra virus


Hendra virus, scientific name Hendra henipavirus, is a bat-borne virus that is associated with a highly fatal infection in horses and humans. Numerous disease outbreaks in Australia among horses have been caused by Hendra virus. The Hendra virus belongs to the genus Henipavirus, which also contains the Nipah virus, which has also caused disease outbreaks. Hendra virus is the type species of Henipavirus.

Pathology

es experimentally infected with the Hendra virus develop a viraemia and shed the virus in their urine, faeces and saliva for approximately one week. There is no other indication of an illness in them. Symptoms of Hendra virus infection of humans may be respiratory, including hemorrhage and edema of the lungs, or in some cases viral meningitis. In horses, infection usually causes pulmonary oedema, congestion and / or neurological signs.
Ephrin B2 has been identified as the main receptor for the henipaviruses.
Viruses of this genus can only be studied in a BSL4 compliant laboratory.

Transmission

es have been identified as the reservoir host of Hendra virus. A seroprevalence of 47% is found in the flying foxes, suggesting an endemic infection of the bat population throughout Australia. Horses become infected with Hendra after exposure to bodily fluid from an infected flying fox. This often happens in the form of urine, feces, or masticated fruit covered in the flying fox's saliva when horses are allowed to graze below roosting sites. The seven human cases have all been infected only after contact with sick horses. As a result, veterinarians are particularly at risk for contracting the disease.

Prevention, detection and treatment

Three main approaches are currently followed to reduce the risk to humans.

Emergence

Hendra virus 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. The trainer, Victory Rail, and the stable foreman, Ray Unwin, were involved in nursing the index case, and both fell ill with an influenza-like illness within one week of the first horse's death. The stable hand recovered but Rail died of respiratory and kidney failure. The source of the virus was most likely frothy nasal discharge from the index case.
A second outbreak occurred in August 1994 in Mackay 1,000 km 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.

Australian outbreaks

As of June 2014, a total of fifty outbreaks of Hendra virus have occurred in Australia, all involving infection of horses. As a result of these events, eighty-three horses have died or been euthanised. A further four died or were euthanised as a result of possible 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 Kempsey, 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 ; Little red flying fox, ', black flying fox, ', grey-headed flying fox, ' and spectacled flying fox, '. 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 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 is favourable to the survival of henipavirus in the environment.
It is possible flooding in SE Queensland and Northern NSW in December 2010 and January 2011 may have affected 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.