Hendra virus

What is Hendra virus?

It is an emerging disease that was first identified in 1994 and has only been found in Australia. It occurs naturally in flying fox populations, and it’s thought to be transferred to horses through contaminated urine, faeces or foetal fluids. Humans become infected through close contact with infected horses. There’s been no evidence of direct infection from flying foxes to humans or of human-to-human infection. Horses can infect other horses as well as humans.

It’s very similar to Nipah virus , another emerging disease originating from flying foxes in Malaysia. Nipah virus has been transferred to pigs and then to humans, and has killed around 200 people in Malaysia, India and Bangladesh. Nipah has also been transmitted from human to human in Bangladesh. Hendra is more distantly related to the measles virus.

The clinical signs of Hendra virus in horses are respiratory or neurological, and 70% of horses that have tested positive have died from the disease. Those that recovered have been euthanased. There have been seven known cases in humans, with four fatalities. The human cases have come from close handling of infected horses.

It has become clear that Hendra virus is now an endemic disease in Australia. All known cases in horses (more than 30) have occurred in Queensland or northern NSW (one case to date) from the Great Dividing Range east. However, it’s thought that there is a potential for disease wherever there are flying foxes given that antibodies to the virus have been detected in some proportion of all Australian flying fox populations.

Summary

There is a 50% mortality rate in humans for Hendra however Hendra is one of the world’s rarest diseases.
The natural host for Hendra virus is the flying fox.
It is not clear how horses become infected, but it may be by eating food contaminated by bat urine or birthing products.
Human infections have occurred as a result of direct exposure to body substances from infected or dead horses.
To date there has been no known transfer of Hendra from person to person or from flying foxes to other animals apart from horses.

Outbreaks

Visit our Hendra virus update page for information about 2011 outbreaks

Twelve known outbreaks of Hendra virus occurred between 1994 and 2010, all involving the infection of horses. Humans were infected in four of these outbreaks as a result of direct contact with infected horses.

August 1994, Mackay, Queensland: Death of two horses and one person. The person relapsed and died a year after infection.

September 1994, Brisbane, Queensland: 14 horses died from a total of 20 that were infected and the remaining six were euthanased. Two people infected with one death.

January 1999, Cairns, Queensland: Death of one horse.

October 2004, Cairns, Queensland: Death of one horse. A vet involved in an autopsy of the horse was infected with Hendra virus and suffered a mild illness.

December 2004, Townsville, Queensland: Death of one horse.

June 2006, Sunshine Coast, Queensland: Death of one horse.

October 2006, Murwillumbah, New South Wales: Death of one horse.

July 2007, Clifton Beach, Queensland: Infection of one horse (euthanased).

July 2008, Redlands, Brisbane, Queensland: Death of five horses; four died from the Henda virus, the remaining animal recovered but was euthanased as it posed a health threat. Two veterinary workers from the affected veterinary practice were infected leading to the death of one, veterinary surgeon Dr Ben Cunneen, on 20 August, 2008. The second veterinarian was hospitalised after pricking herself with a needle she had used to euthanase, the horse that had recovered. A nurse exposed to the disease while assisting Cunneen in caring for the infected horses was also hospitalised.

July 2008, Cannonvale, Queensland: Death of two horses.

August 2009, Cawarral, Queensland: Death of one horse; the death of three other horses is being investigated. 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.

May 2010, Tewantin, Southern Queensland: Death of one horse and 11 people tested for Hendra virus infection. Tests on humans and other horses on the property found to be negative for Hendra virus infection

The distribution of black and spectacled flying foxes covers the outbreak sites, and the timing of incidents indicates a seasonal pattern of outbreaks possibly related to the seasonality of flying fox birthing. As there is no evidence of transmission to humans directly from bats, it is thought that human infection only occurs via an intermediate host.

How is Hendra virus spread?

Our knowledge of how Hendra virus is spread is limited, however we know that Hendra virus is present in flying foxes without having any apparent clinical effect on them. It is also known that the virus can be shed at particular times with the fluid secretions of the flying fox, with saliva and urine.

Dr Hume Fields from Biosecurity Queensland says that they have recently found that very high concentrations of virus material are deposited directly under trees in what they call the ‘drip zone’ and almost no virus is deposited once they leave the perimeter of the trees. This area of the trees where the spats and the urine of feeding flying foxes will be dropped is potentially extremely high risk for horses.

For horses to contract Hendra, they must have direct contact with the source of the virus. Direct access to the source of the virus means either flying fox fluids or another infected horse that is excreting virus. Humans then need to be exposed to fluids from a horse excreting the virus to become infected.

Recent research has also shown that a horse is capable of excreting virus for a short period before actually displaying any clinical abnormalities.

Hendra awareness for horse owners

Guidelines on fencing off trees to protect horses

Work on a Hendra vaccine

At the AVA Annual Conference in Adelaide in May 2011, Dr Deborah Middleton announced that her team at the CSIRO Australian Animal Health Laboratory has developed an experimental horse vaccine against Hendra.

The vaccine works by neutralising antibodies in the glycoprotein G, which means that if a horse is exposed to Hendra virus the viral shedding is eliminated and replication in the tissues is prevented. The fact that the vaccine is generated from the glycoprotein G and not from inactivated virus is a great advantage as it also means that it is a very safe.

Dr Middleton intends to carry out further experiments that will help to determine the lowest dose of antigen that will enable the vaccination to be effective, while keeping the cost of the product down. In this way she hopes to ensure that the eventual vaccine is as cost effective as possible.

Once the level of antigen has been determined, Dr Middleton and the CSIRO team will try to determine the duration of immunity, with horses being kept in a paddock conditions before being challenged to determine their susceptibility to infection over time.

To ensure the speed of availability of vaccination to the community, a commercial partner became involved in the process at an early stage in order to ensure that further testing is not needed to obtain final registration of the product.

Dr Middleton says that the current target for full registration of the horse vaccination is 2013.

Reducing Hendra risk

Based on the current understanding of the spread of Hendra virus infection 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.
Try to bring horses into covered enclosures or enclosed paddocks with no trees at night to reduce potential contact with flying fox colonies.
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.

Hendra awareness for horse owners

Guidelines on fencing off trees to protect horses

Associated diseases

Menangle

The Menangle virus, another paramyxovirus, was first identified in 1997 after a piggery in Menangle (NSW) experienced a high number of stillbirths. Two workers at the piggery became ill with unexplained, flu-like symptoms, but subsequently recovered.

Investigations later found that the virus was transmitted from a nearby population of flying foxes, through pigs which act as a carrier of the virus. Bats appear to be an asymptomatic host, with infection caused through contact with body fluids for infected animals.

Menangle is one of three recently discovered zoonotic viruses in Australia that are carried by bats, the others are Hendra virus and Australian bat lyssavirus (ABLV or bat rabies).

Nipah virus

Nipah virus was identified in 1999 when it caused an outbreak of neurological and respiratory disease in pigs on farms in peninsular Malaysia, resulting in 105 human deaths and the culling of one million pigs.

It is believed that bats are the natural hosts of Nipah virus, meaning that they carry the virus by are not affected by it. Because around 90% of those infected in the 1998–1999 infection were pig farmers or had contact with pigs, pigs were tested and found to be infected with the virus.

Other outbreaks of Nipah occurred in 2004, 47 people in Bangladesh became infected with Nipah in two outbreaks, with 35 of them dying.

In humans, the infection presents as fever, headache and drowsiness. Cough, abdominal pain, nausea, vomiting, weakness, problems with swallowing and blurred vision are relatively common. About a quarter of the patients have seizures and about 60% become comatose and might need mechanical ventilation. In patients with severe disease, their conscious state may deteriorate and they may develop severe hypertension, fast heart rate, and very high temperature.

Nipah virus is also known to cause relapse encephalitis. In the initial Malaysian outbreak, a patient presented with relapse encephalitis some 53 months after his initial infection. There is no definitive treatment for Nipah encephalitis, apart from supportive measures, such as mechanical ventilation and prevention of secondary infection. Ribavirin, an antiviral drug, was tested in the Malaysian outbreak and the results were encouraging, though further studies are still needed.

In animals, especially in pigs, the virus causes porcine respiratory and neurologic syndrome also known as barking pig syndrome or one mile cough.

Hendra and Nipah viruses are the only members of the genus Henipavirus of the family Paramyxoviridae.