Study: Fruiting Trees a Major Equine Hendra Virus Risk

New research has confirmed the longstanding belief that the risk of hendra virus infection can be significantly reduced by keeping horses away from fruiting or flowering trees that flying foxes (the type of Australian fruit bat that transmits the disease to horses) feed in.

Biosecurity Queensland, Australia, researcher Hume Field, BVSc, MSc, PhD, MACVS, said scientists from the Queensland Centre for Emerging Infectious Diseases (QCEID) had undertaken two studies into the levels and distribution patterns of hendra virus excreted by flying foxes.

"The investigation has found that all flying fox urine and almost all feces and fruit debris, or spats, fall directly under the canopy of fruiting trees in which they are feeding," Field said. "Therefore it is clear that unstabled horses should be kept in open pastures and away from trees in flower or fruit."

Field said QCEID scientists had looked at the amount of excreta and food debris left by flying foxes and the pattern of distribution.

"In one study, plastic sheets were laid under a large, heavily fruiting weeping fig to capture excretions," he said. "The second study involved laying plastic sheeting from the base of a heavily fruiting, small-leaved fig to a non-fruiting, non-flowering tree nearly 50 meters away.

"We wanted to quantify the amount of food debris and excreta produced by feeding flying foxes, and see how far it extended beyond the perimeter of the trees," he continued. "Less than 1% of excretions and spats were found under the nearby non-fruiting, non-flowering tree. Significantly, no excreta at all was discovered in the paddock between the two trees.

"I want to emphasize that vigilance is our most important weapon against this disease," he stressed. "Horse owners need to ensure they are doing all they can to reduce the risk. In the meantime, biosecurity authorities will continue to conduct research and provide the latest advice."

Hendra virus has been known to yield numerous clinical signs in horses including 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 Australian Veterinary Association suggested that horse owners can reduce the risks of hendra virus in their horses by fencing off trees attractive to flying foxes (a type of fruit bat thought to spread hendra to horses), covering horse feed and water containers, and not feeding horses food that could appeal to flying foxes, such as fruit and vegetables.

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