Hendra virus is a deadly virus infecting horses in Australia. Over 70 horses have died due to this virus since the disease was first recognised in 1994. The case fatality rate (the numbers of infected horses dying from Hendra Virus), is high at 75%. The most worrying concern with Hendra virus however, is its ability to infect people. Seven cases of human infection have been recorded with four people dying. These people were infected by close association with infected horses.

It is known that Hendra virus is found in four species of flying foxes in Australia. 47% of a group of flying foxes that were sampled showed evidence of exposure to the virus. What we don’t know however is why the infection in horses were initially confined to Queensland and northern New South Wales, when flying foxes are prevalent further south. Hendra virus has been found in a bat in South Australia, which shows that the disease can also potentially occur in horses there.

The initial cases of Hendra virus infection presented with mainly respiratory signs and fever. These horses showed respiratory distress, then bloody, frothy nasal discharge and rapid deterioration, followed by death. The more recent cases however, have shown predominantly neurological signs with ataxia (incoordination), depression, head tilt, loss of vision and muscle twitching. These horses also showed fever and rapid deterioration. It is now considered that any abnormal clinical signs, even signs such as colic and head swelling can also be associated with the disease. We also now know that horses can carry and excrete the virus before they actually show signs of being sick!

Infection in horses is thought to be related to exposure to the birthing fluids and placental material of flying foxes, but have occurred throughout the year. Cases have typically been horses paddocked in areas that are attractive to flying foxes, with spread between horses occurring rarely. In a stable situation, where horses are in close proximity to each other, horse to horse transmission has occurred.

Recommendations for horse owners include stopping potential contact between horses and flying foxes. Horse owners should be discouraged from placing feed and water troughs under trees where bats are known to roost. Horse owners should be aware of the virus and should report any signs of disease in their horses to their local veterinarian.

The most recent innovation in our fight against this disease has been the release of a Hendra Virus Vaccine. As release of this vaccine occurred as quickly as possible, the vaccine is released on permit only. This means that it is not fully registered at this point of time, but has been proven to be safe and effective under experimental conditions. Since the vaccines release in November 2012, over 8000 horses have been vaccinated. There are minimal to no adverse effects reported with the vaccine, and trials are ongoing to confirm the length of time that the vaccine conveys protection. Early work suggests that this is at least six months, and it will hopefully protect for a full twelve month period. The vaccine must be given by a veterinarian trained in the use of the vaccine, and in addition the information regarding the vaccination must be logged on a National Register by your veterinarian within 48 hours of administration. The horse being vaccinated must also be microchipped so that it can be easily and permanently identified.

The vaccine’s safety in breeding animals has not been fully investigated, so at the present time, this needs to be considered and weighed up against the risk of disease. Horses that are likely to be exported from Australia are the only group that should not be vaccinated yet, until the test to differentiate between a vaccinated horse and a natural infected horse has become available, which should be completed soon. Other than these two groups of horses we are recommending that all horses be vaccinated against Hendra Virus. Until we can answer the question as to why the disease occurs in the areas that it does, when bats are infected almost entirely around the coastal areas of Australia, it is prudent to vaccinate all horses. Also bat populations are not stationary and do move in response to environmental conditions, so it is very hard to define ‘safe’ areas where the disease will not occur. It is far safer to vaccinate to ensure that your horse will be protected from this fatal disease. By protecting the horses, we are also protecting the people that own, handle, ride and treat these amazing athletes.

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