The role of flying foxes in Hendra virus

Queensland has all four flying fox species that occur in Australia:

  • grey-headed (Pteropus poliocephalus)
  • black (P. alecto)
  • little red (P. scapulatus)
  • spectacled (P. conspicillatus).

Flying foxes are a natural reservoir for Hendra virus. Flying foxes do not show any signs of illness when infected with Hendra virus.

Infection is periodically present in flying fox populations across Australia. The exact route of transmission of Hendra virus from flying foxes to horses is not yet fully understood.

The virus has been detected in the blood, urine, faeces, placental material, aborted foetuses and birthing fluids of flying foxes.

Ongoing research is continually increasing our knowledge about this disease.

Accelerated Hendra virus research and the 2011 / 2012 incidents

Due to the funding provided by the National Hendra Virus Research Program , the Queensland Centre for Emerging Infectious Diseases (QCEID) has accelerated research into flying foxes and Hendra virus transmission in Queensland in 2011/2012.

After every Hendra virus incident, scientists from QCEID screen local flying fox colonies for Hendra virus and compare the genetic fingerprint with that from the horses.

QCEID scientists are also seeking to identify any environmental and ecological factors that might determine if and where Hendra virus cases will occur.

There are also investigations into why in 2011, Hendra virus cases mostly occurred in South East Queensland and northern New South Wales, yet in 2012, Hendra virus cases have so far occurred in Central and North Queensland. A key question is what factors can cause this year to year variation.

Other research outcomes:

  • From monitored flying fox colonies across QLD, the infection rate of Hendra virus is generally between 0-10%, but in any particular colony it fluctuates with the coming and going of individuals or groups of flying foxes.
  • QCEID scientists believe that factors in addition to the level of infection in flying foxes contribute to the likelihood of infection in horses. These include temperature (the virus survives longer at lower temperatures), rainfall (the virus survives longer in a moist environment), pasture status (horses love to browse whether they are hungry or not), and personality (some horses are inquisitive, some are dominant).

Control of flying foxes

Although Hendra virus infection occurs naturally in flying foxes, culling of specific colonies is not an effective Hendra virus risk management strategy, because flying foxes continually move from one colony to another. Any colony acts similar to a motel - most individuals only stay a day or two, some stay a week or two, a few stay a month or more.

Flying foxes are protected species, critical to our environment, as they pollinate our native trees and spread seeds. Without flying foxes, we wouldn't have our eucalypt forests, rainforests and melaleucas.

Any unauthorised attempt to disturb flying fox colonies is illegal. Disturbing flying fox colonies to reduce the risk of Hendra virus transmission to horses is likely to be ineffective because:

  • flying foxes are widespread in Australia and are highly mobile
  • there are more effective steps people can take to reduce the risk of Hendra virus infection in horses and in people
  • dispersing or culling flying foxes could worsen the problem. QCEID scientists are currently investigating whether dispersal and/or any associated stress may change Hendra virus excretion levels.

Flying foxes and trees

Flying foxes prefer nectar and pollen from eucalypts, melaleucas and banksias, however they are attracted to a broad range of flowering and fruiting trees, and vegetation, as food sources.

Some examples of the trees and vegetation on Queensland properties where Hendra virus in horses has occurred include:

  • a range of fig trees (including the Moreton Bay fig tree)
  • melaleucas (including paperbarks)
  • eucalypts
  • bottlebrushes
  • mandarin trees
  • Climbing asparagus vine
  • Cocos palm

Other trees that may attract flying foxes include flowering or fruiting trees with soft fruits and stonefruits (e.g. mangoes and papaws), palms, lilly-pillies and grevilleas.

Please note this is not an exhaustive list of trees that attract flying foxes. This will vary with the geographical area. You should identify the trees on your property that attract flying foxes to help you manage your horses.

See more information on living with flying foxes.

Tracking flying foxes

In an Australian first, Queensland scientists are fitting flying foxes with GPS data loggers to find out where they're going and what they're doing.

We can use the information from the GPS data loggers to determine whether a flying fox is feeding, sleeping or flying, and where it is flying to.

This information helps us build an understanding of flying fox movement between colonies, which in turn helps modelling when analysing the spread of Hendra virus among flying fox populations.

Flying foxes and Hendra virus videos

  • Watch a video of Dr Hume Field, Principal Scientist, Biosecurity Queensland fitting a flying fox with a GPS data logger for the first time in Australia.
  • Watch a video of the expert panel who came together on Friday 23 September 2011 to address the myths and clarify the facts around flying foxes and Hendra virus.

For more information about flying foxes, see the Department of Environment and Heritage Protection website or call on 1300 130 372.

Last updated 25 May 2015