Equid Blog : Horse Health & Diseases : University of Guelph : Ontario Veterinary College : Equine Infectious Diseases

Unfortunately, but not surprisingly, Hendra virus has resurfaced in Australia. Horses are the only known species that are naturally infected by this deadly virus, which is carried by flying foxes (bats). Death rates are high, and the infection can be transmitted to people, with fatal consequences. Four out the seven people that have ever been diagnosed with Hendra virus died.

In the latest equine case, nine people were exposed to the infected horse (that was euthanized on Monday), including a nine-year-old girl. All of these individuals are being monitored. No treatments are being given because there is no established way to treat or prevent the disease. Ribivirin, an antiviral drug, has been tried in some people that have been exposed to Hendra virus, but the drug is quite toxic and it's far from convincing that it works. So, for the moment, they are taking a wait-and-see approach. Fortunately, it seems like very close contact with secretions from infected horses is required for transmission, so hopefully the true risk of exposure for these individuals is low. It's going to be a tough couple of weeks for them, however, while they wait to see if any of them get sick.

This is a very tough situation to control and a major concern for people in Queensland.

• There is no clear way to prevent exposure of horses to this virus, since it has a wildlife reservoir.
• There is no vaccine available, although fundraising is underway to support vaccine research.
• There are no effective treatments.
• Measures to reduce the risk of transmission from horses are based on common sense, but have not been specifically investigated.
• Hendra virus is not always an obvious diagnosis when a horse first begins to show signs of illness, so people can be exposed before realizing they may be dealing with a deadly disease.

More information about Hendra virus is available in our archives.

Image: Australian Stock Horse (click for source)

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The latest edition of the journal Emerging Infectious Diseases contains a paper describing the 2008  Australian Hendra virus outbreak in horses and people.

In this outbreak, there were five horses infected and two humans infected. The horses predominantly had signs of neurological disease, not respiratory disease like some other reports describing this disease. Four horses died. One recovered but was euthanized for public health reasons.

Two people became infected after working with the sick horses, which represents 10% of the total veterinary staff that were exposed to the infected horses.  Both people started off with influenza-like illness, which seemed to improve initially, but then signs of severe neurological disease developed. They were treated with ribavirin, an antiviral drug, as part of an experimental treatment. One of them died after 40 days of illness, the other person survived.

The authors stressed that the effectiveness of ribavirin could not be determined, but they recommend it nonetheless because of the severity of Hendra virus infection and lack of other options. Ribavirin was also used in the 2009 outbreak, but it is clearly not 100% effective since one person died there also.

A number of concerning activities occurred that put people at risk of infection, including a "percutaneous blood exposure while euthanizing an infected horses" (they didn't explain exactly what this was, but it could have been a needlestick), low use of personal protective equipment, and contact with potentially infectious body fluids. This is unfortunately not surprising since the approach to infection control (particularly in terms of zoonotic infections) is often lax in equine medicine. That certainly has to change, particularly in areas where Hendra virus may be present.

Much more information about how to control this potentially devastating virus is needed. Fortunately, infections are uncommon and it is restricted to a fairly small geographic range in Queensland, Australia.

Image source: http://animalphotos.info/

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A proposed levy on horse owners to fund Hendra virus research has been met with opposition in Queensland. It has been suggested that a $25/horse levy in Queensland would provide needed funding for research into this rare but deadly disease, but this has been opposed by some vets and horse owners. One comment in response to the suggestion of a Hendra virus research levy is that the disease kills humans, so it should be publicly funded. However, Hendra only affects humans who have very close contact with horses, so that's a questionable argument. Also, medical research funding is certainly not overflowing, and the odds of a study such as this getting funded this way may be limited because it is so horse-oriented. I run into the same problem all the time with zoonotic disease research grants. Medical agencies don't want to fund it because it's too animal related, while animal agencies don't want to fund it because it deals more with human health.

Who should fund equine research? Should the government (i.e. all taxpayers) be solely responsible, or should some of the responsibility fall on horse owners, who stand to benefit the most from equine research? This is particularly true for a disease like Hendra that is very rare, currently restricted to one region, and only affects horses and people associated with horses. The rarity of the disease means that industry (e.g. vaccine companies) is probably not eager to fund research (because it would not be profitable). The focal nature of the problem geographically may limit interest from national or international groups. These factors could result in failure to do the necessary research to try to control this deadly disease.

This raises broader questions about funding for equine research. Many people and governments make lots of money from horses, directly or indirectly. You'd like to think that since so much money is made off the backs of horses (both figuratively and in some cases literally), that some of the profits would be put back into helping ensure the health and welfare of these animals. A fraction of a percent of the money generated by horses would be a tremendous asset for equine research, and help make great strides in improving the health and welfare of horses.  Unfortunately, such funding is rarely available, and equine researchers are often very limited in terms of the research that can be done with the available dollars. As a researcher, I know the difficulties of finding enough research funding to pay laboratory personnel and grad students, plus perform high quality research. The limited funding that is available is one reason that equine research is now only a fraction of my overall research program. The equine industry as a whole needs to think about its role in research, even if it's from a self-serving standpoint whereby research is funded to help boost performance and profits.

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Another horse farm in Queensland is under quarantine for Hendra virus. This follows the high-profile outbreak on another Queensland farm this past summer that resulted in the death of a veterinarian. Ongoing identification of affected farms is quite concerning for a disease that is typically very rare and sporadic. It's hard to say what this means.

Does it mean that Hendra virus is spreading and becoming more common? It's certainly a possibility. Even though we've known about this virus for a while and it's only caused rare outbreaks until now, established infectious diseases sometimes change their patterns for no clear reason.

Does this mean that Hendra virus is just being recognized more now? This is certainly a possibility too. Not all apparent changes in disease patterns are truly changes in disease patterns. Improved awareness, diagnostic tests or increased efforts to diagnose a disease can all lead to the impression that a disease is becoming more common when in fact it's just the same. I don't know whether that's the case in Queensland, but Hendra is certainly getting a lot more attention now.  I suspect that many horses that would not have been tested in the past are now being tested.

How do we answer these (and other) questions? Research and surveillance. We need to know a lot more about this virus. We need to make sure that horses with signs that might be indicative of Hendra virus get tested. Since veterinary medicine is a user-pay system and diagnostic testing often gets skipped (especially when a horse has already died), some form of subsidized testing might be required. Unfortunately, a lot of it comes down to money. Money is needed to do research, provide diagnostic testing, perform surveillance and educate everyone involved. Money for these types of efforts is getting harder to find, although it's usually much easier during a high-profile outbreak.

Image: Grey-headed Flying-fox (Pteropus poliocephalus) (source: www.environment.gov.au, photographer: Andrew Smith)

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An Australian horse group, the Queensland Horse Council, is calling for the equine industry to change its culture in terms of biosecurity. I agree completely, however, as I've said before, I think the term "infection control" is really what we are talking about here. Biosecurity involves keeping pathogens off a farm, as is done with tight controls on pig farms. Infection control also tries to do this, but realizes it's not completely possible with how we manage horses, and therefore also focuses on controlling the impact and spread of infectious diseases on the farm.

This is obviously in response to the recent Hendra virus outbreak in Australia. It usually takes a remarkable (and sometimes tragic) event to get people talking about infection control. It becomes a hot topic, people call for improved efforts and resources, and everyone gets on board... for a few weeks. After a short period of time without problems, people tend to revert to their usual behaviour, and infection control often gets marginalized again. The key, therefore, is establishing a sustained effort. That's the hardest part of infection control, be it in a hospital or on a farm.

Queensland Horse Council (QHC) president Debbie Dekker is quoted in the Sydney Morning Herald as saying "We are a pretty gung-ho lot and biosecurity is treated like some sort of wussy thing. Everyone needs to tighten up their biosecurity practices."

Well said.

"We still have a lot of people who don't know about Hendra virus so we need to get the information out to horse owners."

Communication and education are key. Just telling people they need to do something is not going to be very effective. Infection control practices usually involve some degree of effort or change in normal practices. If people don't understand why they should change, they are less likely to do so.

Sporadic infectious diseases and outbreaks will continue to happen (in horses, people and others). We can never completely eliminate the risk. We can, however, reduce some of the risks. While nothing can change what has happened with the most recent Hendra virus outbreak, we should at least make sure some good comes out of it, and that it leads to improved infection control awareness in Queensland and beyond.

Thanks to Dr. Doug Powell of Barfblog for the headline.

Image source: www.qldhorsecouncil.com

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In the wake of the death of Dr. Alister Rodgers from Hendra virus, there have been increasing calls for the Australian government to put significant resources into Hendra virus research. Various areas need to be investigated, including how this virus is maintained in the bat population, how it is transmitted from bats to horses, ways to treat infection and ways to prevent infection. Vaccination is an obvious topic, and creation of a vaccine appears to be possible. However, as I wrote the other day, there's a question about whether a company would put millions of dollars into development of a Hendra virus vaccine for people, given that the disease is very rare, is currently limited to one region, and only appears to be a risk for people in close contact with sick horses.

One thing that needs to be considered is whether it may be better to develop a vaccine for horses rather than people. Think about it:

• All reported human Hendra virus infections have come from people in close contact with sick horses.
• Human vaccines are very expensive to develop, test, get approved and market.
• Vaccines for animals are much cheaper to make because testing and regulatory requirements are not as strict. (This can lead to marketing of vaccines for animals with limited evidence of effectiveness, but the upside is that vaccines can get to market quicker and with less expense.)
• People are often more willing to get their horses vaccinated than to get vaccinated themselves.

So, even though it might sound strange, development of a Hendra virus vaccine for horses may be a more effective way to protect people.

If this approach is taken, a key step would be continued research into the epidemiology of Hendra virus infection to investigate other routes of human exposure. If people can get infected by other routes, vaccination of horses obviously wouldn't address the entire problem. However, based on what we know currently, vaccination of horses might be the most effective, timely and economic response to this pressing problem.

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Unfortunately, Dr. Alister Rodgers, who had been hospitalized with Hendra virus infection acquired from a sick horse, died yesterday in a hospital in Brisbane, Australia. He was infected last month while treating an infected horse on a farm that was subsequently identified as having multiple horses infected with the virus. Despite experimental ribavirin treatment, he developed the infection three weeks later. He is the second veterinarian from Queensland to die from Hendra virus infection in a little over a year. Four of the seven people known to have been infected by this virus since it first emerged in 1994 have died.

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Hendra virus, as you've probably seen here and elsewhere, is back in the news as the cause of another outbreak in horses in Australia with subsequent transmission to people. This bat-borne disease is very rare but devastating, with high mortality rates in both horses and people. Currently, a veterinarian is in critical condition in the ICU of a Brisbane hospital fighting this virus, while other exposed horse farm personnel are waiting to see whether they get sick too. Last year, another veterinarian died. Because of the severity of disease, vaccination gets discussed. Development of a Hendra virus vaccine is possible and a prototype vaccine has been produced. However, the question is will such a vaccine ever get used?

Vaccines are very expensive to develop, test and market. Given the nature of the pharmaceutical industry, there usually has to be a reasonable expectation that the costs will be recovered through sale of the vaccine. Some treatments for rare diseases that have no chance at making money are produced by pharmaceutical companies as a service to society, but not every money-losing product can be made. The problem with Hendra virus, in terms of vaccination, is that it is such a rare disease. Only 7 people have been diagnosed with the infection. It's tough for companies to justify spending millions on a vaccine for such a rare disease if they don't think people will use it. Vaccines for rare diseases can be profitable if a lot of people get vaccinated (e.g. rabies). However, given the sporadic nature of Hendra virus, the limited geographic range where it occurs and the fact that it seems only people with close contact with horses are at risk, the market would be very small. Unless things change with respect to how common this disease is (and we all hope not to see any more of such a terrible disease), I doubt we'll ever see this vaccine on the market.

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A veterinarian, one of four people in Australia that were under close observation due to exposure to horses with Hendra virus infection, has developed signs of infection. Dr. Alister Rodgers is now in hospital in critical condition. He had close contact with a sick infected horse three weeks ago - Hendra virus was not considered initially, it was thought that the dying horse had been bitten by a venomous snake. Dr. Rogers didn't wear gloves or a mask when examining the horse because he had left them in his car.

Dr. Rodgers received experimental treatment for five days to try to prevent or reduce the severity of infection. He had returned home from hospital following the treatment only one day before he became ill. It has now been confirmed that he is infected. Only six people have been previously diagnosed with this rare disease; three have died. There were hopes that all of the exposed individuals would escape unscathed given initial tests showing no sign of infection and the experimental therapy, but it's clear now that early detection of infection is not easy.

Image: Coloured electron micrograph of Hendra virus (source: www.csiro.au/science/Hendra-Virus.html)

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Four people exposed to horses infected with Hendra virus in Australia are taking an experimental drug to try to prevent or reduce the severity of infection. All are currently healthy, but it is unknown whether the virus is incubating in them and whether disease may develop.  People can be infected with this virus through close contact with infected horses, as was the case with these four individuals. While human infections are rare, 50% of infected people die. Therefore, it's understandable that they would choose to try an experimental treatment.

These people will be treated for five days with intravenous ribavirin, an antiviral drug. There is evidence that ribavirin can kill Hendra virus in the laboratory, but it's not known if it actually does anything in infected people. It has some potential adverse effects, but given the severity of disease and high risk that these people have been exposed, it's certainly a reasonable decision. This treatment was also used in the Hendra virus outbreak in 2008. One person died, one survived after a long stay in ICU, and one did not get sick.  It's not known whether the drug did anything to help. The death of the treated person doesn't necessarily mean the treatment is not useful for some people or for certain stages of infection. Hopefully, ribavirin has a better chance of working when infection is only developing, before these people get sick.

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Hendra virus, a virus that can kill horses and people, has resurfaced in Queensland, Australia. This bat-borne disease has caused periodic fatalities in horses and people that work with horses. The latest outbreak is thought to have killed up to three horses and resulted in the potential exposure of at least 30 people. The likelihood of these people getting sick depends on how close their contact was with the sick horses. Close contact with secretions from infected horses seems to be required to transmit disease. One person reported being snorted on by an infected, dying horse and being "covered" in blood, which is certainly concerning. An outbreak last year killed a veterinarian and hospitalized a veterinary nurse.

The farm in question is under quarantine and people that have been exposed are being monitored. There is no treatment for potentially exposed individuals, so they are in the unenviable position of having to wait and see if they get sick.

A virus like this is very hard to control. It's lives in fruit bats and only occasionally crosses into horses. The sporadic nature of disease makes it hard to control and predict when cases will occur. The key is early identification so that there is minimal exposure to other horses and people. People also need to take routine infection control precautions. One veterinarian handled an infected horse without using gloves or a face mask, as recommended, because he had left them in the car. Exposure to a potentially fatal infectious disease is not worth the few minutes of time saved by not following recommended precautions.

Photo credit: M. Anderson, 2009.

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This summer, a small outbreak of the potentially deadly Hendra virus was identified in a group of horses near Brisbane, Australia. This virus has caused periodic cases of illness and death in horses, and can be transmitted to people working closely with infected horses. In the latest outbreak, 3 horses died, making this the worst outbreak since 1994 when 14 horses and 2 people died.  A human case was also identified. This person worked at a veterinary clinic that treated infected horses. This individual was admitted to hospital overnight but was discharged, so  presumably was not very ill.

While Hendra virus (genus Henipavirus) is only found in Australia, it is a good reminder for everyone about the strange nature of some infectious diseases. The natural reservoir of the virus is the fruit bat. It is believed that horses become exposed when infected fruit bats give birth and contaminate horse pastures with uterine fluids. Horses develop respiratory disease ranging from mild to fatal. Human cases have been reported in people working closely with infected horses. A horse trainer and veterinarian's assistant died in the 1994 outbreak. Close contact is required for transmission to people.

Picture: Locations of previous Henipavirus outbreaks (red stars – Hendra virus; blue stars – Nipah virus) and distribution of Henipavirus flying fox reservoirs (red shading – Hendra virus; blue shading – Nipah virus)

It's very difficult to take specific measures to protect horses, people or other animals from sporadic, rare diseases such as Hendravirus infection. However, common sense infection control measures can reduce the risks associated with any animal contact.

• Wash your hands after contact with any animal.
• Avoid contact with sick animals - consider sick animals to be potentially infectious until proven otherwise.
• Remember that  new animal diseases are regularly being identified, and that they might be able to infect people.
• People that work in veterinary clinics must be diligent and use good infection control practices because they are at higher risk of exposure to various diseases.

This equIDblog entry was originally posted on the Worms & Germs blog on 15-Jul-08.

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