The horror of Hendra
Horse owners have been advised to stay vigilant despite the lifting of Hendra quarantine restrictions. SAMANTHA TAYLOR looks at the virus in Australia.
Lifting on quarantine
QUARANTINE restrictions on properties believed to be threatened by the deadly Hendra virus were lifted last week following final testing which yielded negative results. Despite the relaxing of these restrictions Queensland chief veterinary officer Rick Symons has warned horse owners to not become complacent and to continue to exercise caution where horses are concerned.
What is the Hendra virus?
The Hendra virus is a rare and potentially fatal disease, which primarily affects horses but can also infect humans and dogs. Hendra attacks organ cells, causing internal bleeding, inflammation and leaking of fluids. The Hendra virus bares a striking resemblance to a virus known as the Nipah virus also transmitted by bats in South East Asia which, since 1998 has been responsible for more than 250 deaths. The two viruses have been identified as belonging to the same subfamily of viruses, Henipavirus. The viruses in the Heniparvirus family are distinguished by a number of characteristics. These include the distinctive molecular make-up and the fact that the virus is not unique to any one species, with the ability to infect other animals and humans.
A history of Hendra
Since 1994 there has been 31 confirmed outbreaks resulting in the deaths of 64 horses, 4 humans and 1 dog. Each outbreak has occurred either in Queensland or NSW.
Seventeen of the outbreaks were in 2011. NSW acting chief veterinary officer Dr Sally Spence says this is the biggest Hendra outbreak seen to date and that there is no clear indication of what led to the increase.
What are the affects of the virus?
The incubation period of Hendra is believed to be between 5 and 16 days for both horses and humans, the virus generally presents with influenza like symptoms and can be mild or severe. Death in horses generally occurs within two days of infection due to acute encephalitis and fluid in the lungs. The virus has a mortality rate of more than 70%. While it is believed that some horses may survive the initial infection, for safety and prevention purposes it is mandatory that horses that test positive be put down. Identified symptoms range from an increase in temperature and heart rate, respiratory distress and nasal discharge to neurological signs such as loss of balance or vision.
How is the virus transmitted?
Extensive testing has indicated that the natural reservoir of the Hendra virus is the Flying Fox, a member of the bat family. Hendra does not appear to have the same affect on the host animals as it does in horses, humans and dogs. Scientists believe that the virus is transferred via urine and other bodily fluids between species of flying foxes during roosting and grooming times. It has then been assumed that horses, through exposure to these fluids in their natural habitats contract the virus by ingesting food or water contaminated with the waste.
Who is at risk of contracting Hendra?
To date each case of Hendra has involved an infected horse, which, when safety and quarantine precautions have not been exercised has been transmitted to other horses and humans. The disease is not considered to be overly contagious, as it is not carried on the breath, however significant exposure to fluids such as blood and nasal discharge is believed to be the main form of transmission. It is believed that, once infected, horses can transmit the virus to other horses and humans, however humans cannot transmit back to horses or to other humans.
What actions has Australia taken in response to Hendra?
A team of scientists at the CSIRO research Hendra full time in an effort to better understand the complex virus and are working on the possibility of creating a vaccine. The Hendra Virus is handled at the highest bio-security threat level to prevent further infection and possible transmission. Since the first outbreak of the virus in 1994 scientist have been able to tell what species the virus comes from, how it is transmitted and what the affects of the virus are.
In response to the increased outbreaks in 2011 the Australian Government has injected $12 million into research about the increase in the number of outbreaks. Dr Spence has identified that research priorities are identifying why the infection spills over from flying foxes and how horses and other animals are exposed to it.
Eradication of the virus
John Smith from CSIRO believes that it will not be possible for the Hendra virus to be eradicated because of the difficulty in treating a species such as bats. The proposition of a bat cull has been discarded as an option. Smith has also said that the cost of the vaccination once available is unknown and that it will be unlikely that the government will enforce mandatory inoculation against Hendra.
How can it be prevented?
There are a number of preventative measures. Horses feed bins and water troughs should be placed under cover. Avoiding planting trees that attract flying foxes in or near horse paddocks can reduce the risk of infection. When dealing with any sick horses it is important to ensure hygiene practices are carried out in relation to any equipment contaminated with fluids from sick horses. Observing these safety methods can help prevent further spread.
What is the treatment?
Horses that test positive for Hendra virus antibodies are put down to prevent further transmission. Due to the complexity of the virus it is not yet fully understood how best to create a vaccine for Hendra.