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Hendra horrors: what does the future hold?

July 8, 2011

Seven horses have died and more than 30 people are now playing a waiting game to see whether they have contracted the deadly Hendra virus. Laurie Dixon reports on the way forward.

An adult Flying Fox.
© Andrew Breed/Aust DAFF
It is hard to comprehend that a sick horse could carry an infection that poses a deadly threat to its handlers.

That, however, is the growing reality for Australians living in the parts of Australia known to be at risk from the Hendra virus.

Seven cases have been diagnosed in little over a fortnight. In all, 31 people now face a six-week wait and regular testing to determine whether they have the deadly infection.

It is, by any measure, a bad start to the Hendra season, which coincides with the breeding season of flying foxes - the native fruit bats that provide a reservoir for the virus.

It has been suggested that disruption to normal feeding grounds resulting from devastating floods in the region earlier this year may be in some way be responsible for the surge in cases.

The virus is able to be passed on to horses, and is then capable of jumping to humans. Of the seven known cases of human infection, four have proved fatal.

While the risk of people contracting the virus is considered low - victims have all had major exposure to bodily fluids from sick horses - the reality is that horse owners need to ramp up their biosecurity in areas considered prone.

There have been sporadic outbreaks of Hendra involving horses in Queensland and northern New South Wales since the first cases in Brisbane in 1994.

An artificially coloured transmission electron micrograph of Hendra virus. © CSIRO
In that outbreak, trainer Vic Rail died from the virus, named after the suburb of Brisbane where the outbreak occurred.

The number of cases has increased in recent years, in no small part due to greater awareness around the virus. There seems little doubt that over the years it has claimed other horses who went undiagnosed.

The threat posed by the virus has made it the subject of intense research, with scientists finding that the clinical nature of the viral infection in horses has changed, and the genetic sequences of the virus are also changing.

While horses can survive the infection, current national policy dictates that the animals be euthanised.

People in at-risk areas are advised to cover any cuts or abrasions on exposed skin before handling horses and to wash their hands well with soap and water, especially after handling their horse's mouth or nose - for example, fitting or removing a bridle. They should also wash before eating, smoking or touching their eyes, nose or mouth after handling horses.

Authorities stress that people have become infected from handling infected horses both before and after they developed clinical signs, as well as during autopsies.

They urge great care over personal protective measures, in particular the avoidance of contact with blood and other body fluids, especially respiratory and nasal secretions, saliva, urine, and tissues.

Horse owners have been told not to kiss horses on the muzzle, especially if the horse is sick.

All those involved in investigating a suspected case of Hendra must wear full protective clothing, including impervious overalls, boots, gloves, a respirator mask and face shield.

Other precautions are urged to reduce the infection risk in areas with flying foxes.

Searching for a vaccine to the deadly Nipah and Hendra viruses - CSIRO's Dr Bruce Mungall © CSIRO
Feed and water containers should be placed under cover and away from trees, especially those bearing fruit.

Nor should feed be left out that might attract the bats, such as apples, carrots, or molasses.

Where possible, horses owners should remove their animals from paddocks where flowering trees have temporarily attracted flying foxes. If not possible, authorities suggest removing the horses around dusk and night-time, which are times of peak activity for the bats.

Is this what the future holds for horse owners in affected areas of Queensland and New South Wales?

For now, there is little option, but scientists hold the promise of a vaccine for horses that could be available as soon as 2012.

There have been no known cases of Hendra in people resulting from direct exposure to bats, although scientists certainly do not dismiss that as a possibility.

While flying foxes are the natural hosts for Hendra virus, at certain times of the year - particularly around the breeding season for the bats - there is an increase in the number of cases in horses.

Scientists believe horses most likely catch it through exposure to the bats' faeces, urine and/or birth cleanings.

Exactly why the virus is able to infect people once it has infected horses is not fully understood.

The 1994 outbreak at a Hendra stable was the first of more than 45 cases of Hendra virus in horses that have been detected on or east of the Great Dividing Range from Cairns to northern New South Wales.

However, scientists stress that the virus could potentially occur wherever there are flying foxes.

The virus can cause a range of clinical signs and should be considered where there is acute onset, fever and rapid progression to death associated with either respiratory or neurological signs.

Most cases in horses are fatal but, occasionally, a horse will survive the infection. The reported mortality rate in affected horses is greater than 70 per cent, but regulations require all infected horses to be euthanised.

Calls have been made to cull flying foxes to reduce the infection risk, but authorities have rejected the idea. They argue it is not an effective way to reduce Hendra virus risk as the bats are an important part of our natural environment, are widespread and highly mobile.

A cull would not be feasible and ran the risk of dispersing surviving bats to fresh locations, they argue.

The brightest hope is in the development of a vaccine. There is also an anti-viral treatment that is offered to those considered to have had high exposure to the virus. To date, no instances of high exposure have been reported in the latest spate of cases.

The Hendra and related Nipah virus are given the same respect in laboratories as the Ebola Virus and Marburg Haemorrhagic Fever Virus.

CSIRO's high bio-containment facility at the Australian Animal Health Laboratory was necessary to safely asses the effectiveness of the new experimental vaccine. © CSIRO
Australian scientists from the Commonwealth Scientific and Industrial Research Organisation announced in May that a new experimental vaccine helped to protect horses against the deadly Hendra virus.

Dr Deborah Middleton, from the organisation's Australian Animal Health Laboratory, said: "Our trials so far have shown that the vaccine prevents the infection of horses with Hendra virus."

A horse vaccine, she says, is crucial to breaking the cycle of Hendra virus transmission from flying foxes to horses and then to people.

Depending on further development, field trials and registration, the vaccine may be available as early as 2012.

Authorities have yet to outline what strategy would be used in the rollout of a vaccine once it is approved.

The development of the vaccine goes back more than 10 years to shortly after CSIRO scientists first isolated the virus following the first outbreak.

The development and source of the vaccine is the result of a close collaboration with Dr Christopher Broder of the Uniformed Services University of the Health Sciences - the US federal health sciences university.

Dr Barry Smyth, president of the Australian Veterinary Association, said at the time of the announcement: "It's important that veterinarians and horse owners continue with precautions that reduce the risk of spreading the virus and that they report suspected cases immediately."

Anyone looking for complacency around Hendra won't find it among vets. The last two fatalities from the virus were equine veterinarians who had treated infected horses.



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