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Issue 52 | May 2009
This artificially coloured
electron micrograph of Hendra
virus is from the first identified
case in Brisbane in 1994
CSIRO scientists have made a major breakthrough in better understanding how the deadly Hendra virus (HeV) can transmit from infected horses to people and other horses.
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Listen to the podcast [Windows Media audio 6m:20s] |
The Hendra virus was first recognised in Queensland in 1994, and since then, infection in horses has sporadically occurred with at least two outbreaks recorded in four of the past five years.
Of the 11 equine outbreaks, four have also led to infection of humans with three of the six known human cases being fatal, the most recent of these in August 2008.
In a project led by Dr Deborah Middleton, from CSIRO's Australian Animal Health Laboratory, a number of infected horses were studied to determine the early signs of infection and establish how best to manage infected horses and prevent further spread of the disease.
In this podcast Dr Middleton explains how the virus is transmitted from horse to horse and from horse to human, and also the methods for early detection that are being investigated.
Hi and welcome to CSIROpod, I'm Glen Paul.
Since the Hendra Virus or HEV was first recognised in Queensland in 1994, infection in horses has sporadically occurred with at least two outbreaks recorded in four of the past five years. Of the eleven equine outbreaks, four have also led to the infection of humans, with three of the six known human cases being fatal, the most recent of these in August 2008. Currently, there is limited available information to guide the management of infected horses to prevent further spread to people and other susceptible horses.
In a project led by Dr Deborah Middleton from the CSIRO Australian Animal Health Laboratory a number of infected horses were studied to determine the early signs of infection. Dr Middleton joins me on the line.
Can you tell me what methods have you looked at to allow for early detection of Hendra Virus in horses?
Well, we've been able to follow horses from the time of known exposure to the virus and we've been able to collect a number of biological samples from these animals, both during the incubation period and into the onset of early clinical disease. So this has included samples such as nasal swabs, oral swabs, blood, rectal swabs and also urine and fecal material from the floor of the stall, and those samples have been subjected to a range of laboratory tests which were used for early detection of both live virus and also viral gene products.
Right. And what is the best biological sample for early detection out of the ones that you've described there?
Well, we've actually found detectable viral genome or virus genetic material in blood as early as 24 hours before animals actually start to show signs of fever. Now clearly, such an animal is going to appear clinically healthy and isn't going to come to the attention of either an owner or a veterinarian as being an animal that's incubating Hendra Virus. So the earliest samples that are likely to be of practical use, that is samples which are going to be able to be collected after an animal has actually started to show the early signs of disease, would be any one of those samples that I've mentioned. So, once an animal actually develops fever and comes to the attention of a veterinarian or an owner then any of those samples will be able to be used to diagnose infection.
Ok, you mentioned symptoms there, have these been documented to a point where a vet could comfortably make a diagnosis in the field?
Uh, no, I think that one of the unfortunate things about this disease is that the early signs of infection are very non-specific. That is, they could be consistent with a wide variety of illnesses that affect horses. But I think we are able to generate a list of signs which should certainly raise the index of suspicion that the veterinarian may be dealing with a case of Hendra Virus infection. I think that is certainly one area where our project has been able to add value to the guidelines that are currently available.
Ok. Now what about transmitting the disease? We know bats are likely responsible for the initial infection, but what about between horse and horse? I recall with the Equine Flu Virus it was possible for someone to handle a horse, get a bit of virus on their clothing then travel and handle another horse some time later, and then infect that horse. Just how does that compare with Hendra? How infectious is Hendra from horse to horse?
Well our data would suggest that to get transmission from horse to horse, the most risky period is going to be fairly late in the course of infection. So it's going to be when the animal is perhaps very close to death that is going to be the time at which transmission might occur. And it's likely that it will need the sort of contact that you've described. That is, it's entirely possible that the infection could be transmitted via people who might just act as a mechanical vector if you like, or just carry the virus on their hands and transmit it from horse to horse. We don't have any good data to help us understand how transmissible it is directly from horse to horse.
Ok. So at that point then, towards the end of the horse's life, is that the time when the virus has developed to a level where it can be transmitted to humans or does that occur earlier?
Well, I think certainly our data would suggest that it is the time when the risk is highest. But the fact that we're able to recover genetic material from these animals very early in the infection, suggests that it is certainly possible that they may transmit virus quite early. But the risk of that happening would be lower. Obviously, if someone has very close contact with the horse or its secretions, that risk may be actually elevated. I think that the key to preventing transmissions to people is early suspicion that you're dealing with a case of Hendra Virus infection, and then you should initiate infection control procedures. This might be as simple as putting on protective gloves and a face shield, to prevent yourself from secretions, the animal sneezing or coughing on you, as soon as you have the least suspicion that you're dealing with a case of Hendra Virus infection. Then you can go ahead and collect your diagnostic samples but you're minimising the risk of exposure to yourself while you do that.
So, what about the future of the research? Do you see a time when there'd be some form of inoculation to become available for a horse?
Oh, absolutely. I think there are certainly a couple of very promising vaccines in the pipeline. The key to controlling infection in humans is control of the disease in horses. And the difficulty, if you like, is a commercial one. That is finding a commercial partner who sees, you know, a market for vaccines in horses. I guess my own view is that if I had a horse and if I could be protected from the possibility of getting Hendra Virus then I'd be very willing to have the animal immunised on a, you know, yearly basis or whatever it took.
Oh, absolutely. I could see a big market for a vaccine. Perhaps there's even someone listening to this podcast now who'd like to get on board with you.
Oh, that would be good.
Anyway, Dr Middleton, thank you very much for taking time out from your research to talk to us today.
No worries, Glen.
Dr Deborah Middleton from the CSIRO Australian Animal Health Laboratory.
For more information, visit www.csiro.au.
[End of Recording]
