FLYING-FOXES, HORSES AND HENDRA
HORSING AROUND WITH REALITY

With the death of another person from Hendra virus infection the media are again promulgating superstitions and uncritically reporting that flying-foxes are responsible for spreading Hendra virus to horses and humans. The reports that more viruses are being found in bats have not helped either. While it is true that many new viruses have been found in bats around the world in recent years, it remains unknown whether these viruses are all harmful to man. Also, the fact that similar extensive searches performed in other groups of mammals (for example rodents) have similarly led to discovery of potentially harmful viruses, such as Hantavirus, has not been mentioned.

FLYING-FOXES HAVE ANTI-BODIES TO HENDRA VIRUS YET VIRUS HAS NOT BEEN ISOLATED FROM A FREE LIVING FLYING-FOX IN AUSTRALIA.

When first searching for the source of Hendra virus after the initial outbreak in Brisbane, the Queensland DPI considered that flying-foxes would be too difficult to sample. And they would have been, except for the co-operation of the large number of wildlife carers who allowed flying-foxes in their care to be tested for Hendra antibodies. This is how the DPI found the antibodies and it was an alert carer who first collected a flying-fox foetus infected with Hendra. Through the flying-fox carer network thousands of flying-foxes were tested for Hendra virus.

It is our understanding that extensive testing by the CSIRO Animal Health Laboratories failed to show any mechanism for the transfer of Hendra Virus from flying-foxes to horses. Every type of flying-fox excretory product (urine, faeces, oral saliva, placentae) from infected flying-foxes and even the virus itself was tested on horses without a successful transfer occurring. Experimentally they were able to transfer the virus to guinea pigs and a cat. This suggests that the virus, if at all present, is released at very low levels.

It has been subsequently shown (experimentally) that infected flying-foxes can shed small amounts of Hendra virus in their urine, but the survival time of the virus in urine is likely to be very short. Most micturation (urinating) by flying-foxes is done at the roost before fly out and then afterwards during the day. Urine bathing is an important part of grooming while at the roost during the day. In any case, the transmission of Hendra from flying-foxes via urine to horses was tested experimentally with negative results.

No other mammal group or species has been surveyed for Hendra virus to the same extent as flying-foxes. There was a small sample of native mammals (possums and bandicoots) tested at the initial outbreak site at Hendra but to our knowledge no significant testing of possible mammalian hosts to Hendra (other than flying-foxes) has occurred. These mammals include rats, mice, cats, brush-tailed possums as well as other possibilities such as ticks, carpet snakes and birds that regularly frequent horse yards. Due to the cyclic nature and low incidence of Hendra found in flying-foxes, large samples of animals inhabiting horse stables would need to be done if the virus is to be detected.

There have been studies overseas that show 35% of horses will eat meat. We are also trying to source a scientific paper that confirms horses will also eat rodents, dead or alive.

Nearly all recent cases of Hendra have occurred in horses being supplementary fed on stored food and kept in yards were there is scant natural food on the ground. On a recent visit to some horse yards where flying foxes have been regularly roosting in overhead trees for over 30 years the owner said “ those flying-foxes have been pissing and shitting all over my horses and their food for years, and none of my horses has ever become ill”.

The clinical manifestation of Hendra in infected horses has been changing. Initially it was recognizable by the production of blood-stained mucous discharged from the nose. Then the symptoms suggested some form of neurological disorder and the latest horse was thought to be suffering from snake-bite. This may suggest that either the virus is mutating or that the method of contracting the virus could be varying. Whatever the case, Hendra virus is a serious occupational risk for veterinarians and people attending sick horses. Appropriate health warnings should be distributed to all horse owners. Exposure to any body fluids and possibly inhaling airborne mucous from sick and infected horses can transfer the virus to humans. But it is important to emphasize that humans do not get Hendra virus directly from flying-foxes.

The current singular focus on finding the mechanism of transmission from infected flying-foxes directly to horses, while seemingly a reasonable pursuit, may be hampering progress. It would be important to focus on the horses and how and where they could become infected. Horses are where the deaths occur and where Hendra gets transferred to humans. All possible routes via any animal that interacts with horses, working outwards from the horse, should be investigated appropriately (i.e. sampled in a manner that is appropriate to locating the virus, given the low incidence of the virus). This route of inquiry is more likely to reveal the real circumstances causing the virus to transfer to horses. The investigation would take a considerable amount of time and funding. Also – has the immune competency of any of the horses that contracted Hendra been investigated? Why have the majority of horses that have contracted Hendra been thoroughbreds and kept in yards and fed supplementary food? If there is a direct transfer of the virus from flying-foxes to horses, why don’t more stock horses out in paddocks feeding under fig trees get the virus?

The appearance on TV and in other media of researchers entering flying-fox colonies in full cover “space-suits” is sending a seriously disturbing message to the community. While the clothing maybe a requirement for health and safety reasons it scares anybody who lives near a flying-fox colony. With the media continually reporting that flying-foxes are the source of Hendra virus which kills horses and humans, the public are becoming hostile to one of the most important native animals in our forests.

It’s time that knowledge about Hendra virus (and the related Nipah virus) is reported properly. We know very little about the virus, its hosts and how it is transmitted to horses. Most money has been spent on laboratory work by the CSIRO in classifying and describing the virus. This has been to the detriment of important field research in sampling for all possible hosts and methods of transmission. The current laboratory tests to reveal Hendra antibodies still require further improvement. Flying-foxes are the only animals that have been thoroughly tested for the presence of Hendra virus. The help from flying-fox carers in locating Hendra virus saved enormous amounts of time and money for the public health authorities. If sampling of fauna for Hendra virus had been left to the small number of government officials alone – they may have still been searching for it today. It appears that funding is being cut from the group who is presently doing most of the field work on Hendra virus. Because of the low human incidence rate (seven people, with four deaths, in sixteen years) health authorities may regard Hendra virus as a low risk and are unlikely to provide any significant funds for research. What has the equine industry done in the way of providing funds for Hendra research? We have still so much to learn about this new virus.

BAT CARE BRISBANE INC.
www.bats.org.au
info@bats.org.au

Updated 07/09/09

The University of Queensland has established the Alister Rodgers Memorial Hendra Virus Research Assistance Fund to work towards a solution to the problems of Hendra virus. Donations to the Alister Rodgers Memorial Hendra Virus Research Assistance Fund can be made by contacting the University Advancement Office at the University of Queensland, on (07) 3346 3900 or by specifying the fund online at https://www.uq.edu.au/secure/donations/appeal.html