Hendra Researchers Gain New Insight into Flying Fox Colonies

Hendra Researchers Gain New Insight into Flying Fox Colonies

"The level of hendra virus excretion was found to be higher in black and spectacled flying-foxes, suggesting these species may be a more important source of infection for horses than the little red or grey-headed flying foxes," Field said.

Photo: Justin Welbergen

Researchers from the Queensland Centre for Emerging Infectious Diseases (QCEID) in Australia have made significant progress into understanding the effect of dispersal on flying fox colonies, the animals known to transmit hendra virus to horses.

Biosecurity Queensland´s principal scientist Hume Field, BVSc, MSc, PhD, MACVS, said the 12-month research project assessed the impact of colony dispersal on stress and hendra virus infection levels in affected flying foxes.

"A key finding of the project (was) there was no association between the disturbance to a colony from dispersal and an increase in the excretion of hendra virus," Field said.

"Researchers measured the stress hormones and virus levels in flying foxes by collecting and testing urine before, during and after the dispersal of a colony," he explained. "Transmitters were also attached to flying foxes to track their movements by satellite, and showed that flying foxes did not stay in the one colony, but regularly moved from colony to colony. Of the 13 colonies monitored (10 in Queensland, 3 in New South Wales) 10 were dispersed or disturbed as a result of the submission of a Damage Mitigation Permit."

In Queensland, colony dispersal can only occur after a comprehensive assessment is completed by the Department of Environment and Heritage Protection and under a Damage Mitigation Permit.

Field said the study provided scientific evidence that disturbed colonies typically had measurable, short-lived stress of a similar level to that seen with natural stress events such as mating.

"Research also highlighted that hendra virus excretion was much less in little red flying foxes and in grey-headed flying foxes," Field said. "The level of hendra virus excretion was found to be higher in black and spectacled flying-foxes, suggesting these species may be a more important source of infection for horses than the little red or grey-headed flying foxes."

Field said QCEID was commissioned by National Hendra virus Research Program in 2011 to investigate any association between colony dispersal, stress, and hendra virus excretion. The National Hendra Virus Research Program is funded by the Commonwealth of Australia, the State of New South Wales, and the State of Queensland.

"Studies will continue to clarify the role of flying fox species, the role of environmental factors, and the role of horse behavior in the transmission of hendra virus from flying foxes to horses," Field said.

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 disease is zoonotic, meaning it can be transmitted from horses to humans, and as proved deadly for several humans exposed to sick horses in the past.

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, 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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