The following information was originally found on the Australian Veterinary Association website.
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.
- 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
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.
The AVA believes that all horses should be vaccinated against the Hendra virus.
Hendra and dogs
With a family pet testing positive to Hendra virus for the first time, 2011 continues to be an extraordinary year for Hendra virus cases. It’s not known how the dog became infected, but it was most likely through close contact with one of the infected horses on the property.
Although the dog showed no signs of illness, it tested positive to antibodies to the Hendra virus, indicating that there had been contact with the virus. This is the first time outside laboratory conditions that Hendra virus infection has been found in an animal other than a horse, a flying fox or a human.
Dogs, cats and other animals that might have had contact with infected horses have been routinely tested for Hendra virus for several years, but none has ever tested positive before. This unusual occurrence will hopefully help scientists understand more about the virus and how it’s transmitted.
Hendra virus can re-emerge after being dormant, which may pose a risk to humans and other animals. For this reason, the only safe place for an animal that may have been infected (even if it has recovered) is in a high level biocontainment facility. There would be no contact with any other animal, no access to the open air, and the only contact with humans would be when they were wearing pressurised biosecurity protection suits. This would not be a humane way to care for the animal, so the national policy agreed by state and federal governments is to euthanase animals that recover from a Hendra virus infection.
Two dogs were exposed to Hendra virus in laboratory conditions during the 1990s, and one became infected. While this wasn’t a long term study, scientists concluded from their observations that it was unlikely that dogs would become infected under normal conditions.
Advice for dog owners
- There has not been a case of Hendra virus in a dog before, although many dogs have been tested on properties where horses have been infected. This is an extremely rare occurrence.
- Sick animals, especially horses, should be kept away from all other animals to avoid spreading disease.
- Good hygiene is always a good idea around dogs and other animals – it’s not a good idea to let dogs lick people’s faces at any time, and you should wash your hands after touching any animal.
- Children under ten years should always be supervised by an adult around dogs.
The Equivac® HeV vaccine was made available to horse owners 1 November 2012. It was initially released to high-risk areas and then to all horse owners soon after.
The vaccine was the result of a collaboration between Pfizer Animal Health (now Zoetis) and CSIRO’s Australian Animal Health Laboratory.
The AVA says that although the vaccine will significantly decrease the risk of exposure to the Hendra virus for horse owners, handlers and veterinarians, precautions still need to be taken.
Resources and guidleines on the Hendra vaccine are available for vets and horse owners.
Reducing Hendra risk
The AVA believes that all horses should be vaccinate against the Hendra virus.
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.
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 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.