Equine Veterinarians Australia (EVA), a special interest group of the Australian Veterinary Association, says the Hendra virus case confirmed in a horse near Casino, New South Wales, last week revealed unusual signs and aspects of the disease.

Ben Poole, BVSc, MANZCVS, EVA spokesman, said that this latest case in northeastern New South Wales makes dealing with Hendra even more complicated and concerning.

“The facts of the case would suggest the horse may have initially received a low infectious dose of the virus that eventually led to the horse succumbing to the disease, after an unusually protracted illness,” he said. “What’s different about this case is that the horse initially tested negative for Hendra virus after losing weight for two weeks and presenting with a sore mouth. It was given medication and the horse started recuperating while in quarantine on the farm.

“A week later the horse deteriorated rapidly and died a few days later,” he continued. “A nasal swab taken from the carcass a week after the horse died returned a positive test for Hendra virus. Further testing of tissue samples indicated that the horse had mounted an immune response to the virus.”

Poole said this demonstrates the difficulty of making an initial diagnosis of Hendra virus infection, and highlights the risk that Hendra virus poses to anyone including horse owners, veterinarians, and those who come in contact with horses displaying vague signs of illness.

“That’s why vaccination of horses against Hendra virus is important for managing the risks involved with the disease,” he said. “The summer timing of this case in the Northern Rivers is unusual and is probably due to food shortages and environmental stress on the bats in the area – so it’s really important to be vigilant all year round.”

Horse owners should contact their local veterinarian for more information about the Hendra virus vaccination.

Hendra virus has been known to yield numerous clinical signs in horses including lethargy, respiratory distress, frothy nasal discharge, elevated body temperature (above 40°C, or 104°F), and elevated heart rate; however, authorities caution that Hendra infection does not have specific signs.

The virus is transmitted to horses from flying foxes, a type of fruit bat that frequents Australia, but the exact method of transmission remains unclear.

The zoonotic disease is transmissible to humans and has killed four people since it was first discovered, including an equine veterinarian who contracted the virus after treating an affected foal in 2009.