Murray Valley Encephalitis down-under - Help from the chickens
Although the weather in Southwestern Ontario seems quite confused lately regarding whether it wants to be winter or spring, at least we're still a few months off from having to worry about mosquitoes and the viruses they carry once again. Warmer parts of the world, however, are in the midst of their mosquito season, and some chickens are lending a hand to give people in the area a "heads up" about what's around.
The Health Department of Western Australia has detected Murray Valley encephalitis virus (MVEV) in chicken flocks in East Kimberley. The department has also tested and found the virus in its sentinel chickens in Wyndham and Kununurra. These sentinel birds play an important role as an early warning system when viruses like MVEV are circulating in the area. Just like West Nile virus, MVEV typically circulates between birds and the mosquitoes that like to feed on them, but problems occur when the same mosquitoes start to bite people (or other susceptible animals such as horses), particularly when there are a lot of mosquitoes, like when the weather is very wet or when there's been flooding. Although most people who are infected with MVEV or WNV fight off the virus with no difficulty, or may simply develop short-term, non-specific signs of illness like mild fever and malaise, in some people these viruses can cause severe infection of the brain (encephalitis) and may even be fatal.
Knowing that MVEV has been found in these "guardian" chickens lets people know (via warnings issued by the health department) to take extra precautions against mosquito bites, such as:
- Staying indoors during peak mosquito activity - dusk and dawn
- Wearing protective clothing including long-sleeves and long pants
- Applying insect repellent
In North America, you can pretty much substitute West Nile for Murray Valley in a case like this. Sentinel chickens have been used to provide early warnings of circulating WNV here, before cases are detected in people or horses. Another means of early detection that is also used is testing pools of mosquitoes directly.
It just goes to show you can still be an important part of the country's defenses, even if you're a little chicken :p
Bat slaughter = Hendra virus control?
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Bob Katter, an Australian Member of Parliament and leader of the Australian Party, has proposed culling flying foxes (fruit bats) as a way to control Hendra virus, which is spread by these large Australian bats. He's not the first person to make such a proposal, but it's a knee-jerk reaction that in reality doesn't make a lot of sense.
It's not completely clear whether Mr. Katter is proposing a plan to completely eradicate the flying foxes altogether, or to simply let people kill any such bats they find on their property, but neither approach is likely to be effective in terms of decreasing the risk of Hendra virus transmission.
If people kill flying foxes on their property, they'll just be replaced in short order by bats from neighbouring areas.
Trying to eradicate the entire species is a bad idea for a variety of reasons:
- Tinkering with a complex ecosystem doesn't often turn out the way you want it to. Australians certainly know from past experiences that bad things can happen when new species are introduced (rabbits are just one example). The same might happen when a species is removed.
- Eradication of the species is probably impossible or at least very difficult. I don't know much about the reproductive rate of flying foxes, but if the species can reproduce at a reasonable rate, they can probably replace the culled animals unless people are really aggressive and seek out all remote breeding sites. The limitations of culling have been clearly shown in rabies control, where it doesn't do much because culled dogs are quickly replaced by new dogs.
- Eradicating flying foxes would be very expensive. What could that money do if put into research on vaccination, treatment, and other worthwhile ventures? What if efforts were focused on eliminating flying fox roosting sites in horse pastures? Overall, the impact would probably be much greater.
Why stop with flying foxes? Australia has lots of nasty critters, ranging from spiders to saltwater crocodiles. Should we kill all of those too? Dog bites kill more people than Hendra every year. Should we kill all dogs?
Hendra virus is not something to ignore. While infections in horses are rare, they are usually fatal and there's the risk of transmission to people. Human infections are very rare but often fatal. So, ways to reduce infection of horses as a means of reducing both human and horse disease are important, but the slaughter of flying foxes doesn't make a lot of sense.
Bad 2012 for Hendra virus in Australia
While you don't want to read too much into a single case, 2012 has started off in a bad way for Queensland horses. Hendra virus was identified in a Townsville area horses that died. This zoonotic viral disease is largely restricted to Queensland, Australia, but it has a high fatality rate in horses (and people). Hendra virus is spread by fruit bats and is an ever-present concern to Queensland horse owners and veterinarians, but a mid-summer infection is quite unusual (remember that it's currently mid-summer in Australia). Most cases tend to occur from July to September - this case is a reminder that seasonal trends are just that: trends, not absolute rules.
Fortunately, the attending veterinarian used proper precautions when handling the horse to limit the risk of zoonotic transmission of Hendra virus. However, there will presumably be an investigation to determine who had contact with the horse and their potential for exposure. There is currently no way to prevent or specifically treat Hendra virus infection. An experimental antiviral treatment has been tried in the past, but it's effectiveness if far from clear.
Last year was quite bad in terms of the number of Hendra cases that were detected in Australia. Let's hope this early 2012 case isn't a sign of things to come.
No Answer In Aussie Horse Deaths
Despite relatively intensive efforts, no cause has been identified for the deaths of 22 horses ona Kooralbyn farm in Queensland, Australia. Readily identifiable causes have been ruled out, leaving two main theories:
As mentioned in an earlier post, one possibility is botulism It can be very hard to diagnose botulism in horses, and the disease is often presumptively diagnosed by ruling out all other reasonable options.
The other possibility is tick paralysis, which unfortunately is equally difficult to diagnose definitively. Certain types of ticks can cause progressive and severe paralysis which may look similar to botulism in some ways. Scrub ticks (the name typically used for Ixodes holocyclus) were noted on one of the first affected horses, but there's no information about whether all of the other horses had ticks too, and if so whether they were ticks that can cause paralysis. Kooralbyn is in a region where these paralysis ticks can be found and spring (e.g. now in Australia) tends to be the peak time for paralysis cases, so it's a reasonable consideration.
It's frustrating but far from unusual not to be able to make a solid diagnosis in outbreaks. Beyond the frustration factor, it's also a concern because it makes it hard to take precautions to prevent it from happening again.
Image: Two Ixodes holocyclus ticks, one before and one after feeding (photo credit: Bjørn Christian Tørrissen, click for source)
Botulism Suspected In Aussie Outbreak
A couple of days ago, I reported about a deadly outbreak on a Queensland farm that had killed a significant number of horses. A definitive diagnosis has still not been made, but it is starting to look like botulism might be the cause. In my previous assessment, I said botulism was a potential cause of an outbreak like this, but that this particular disease has a pretty consistent clinical presentation so it was probably unlikely if no one was talking about it as a leading option. It looks like now they are, with the owner stating "I've been talking to vets all over Queensland and they're saying the symptoms are spot-on for botulism." It's unclear whether the first vet(s) didn't consider it or whether there wasn't much veterinary involvement at all initially. Regardless, botulism makes sense, particularly with the description of the type of illness that's now being provided.
Botulism testing is underway, but it's often hard to get a positive lab test for this disease in horses. Often, it's a presumptive diagnosis made based on the clinical appearance and lack of any other identifiable cause. Botulism outbreaks on horse farms can be devastating, as in this case. They are often associated with feeding improperly fermented silage or haylage, but there are a variety of ways horses can ingest feed (or water) contaminated with the toxins produced Clostridium botulinum.
The good thing that comes out of this, if botulism is diagnosed, is that there's not much risk to other horses in the region, or at least not any higher risk than is always present. Whenever a large number of horses die from an unknown cause, it's always a concern that a new disease might be involved, something that fortunately does not seem to be likely here.
Image: Poor tongue tone is one of the classic signs of botulism in horses, which results in difficulty eating and drinking (click image for source).
Queensland Horse Deaths Being Investigated
There's still no confirmed cause of death for 19 horses that died within a short period of time on a Kooralbyn, Queensland (Australia) farm. Sudden death and Queensland invariably conjures up thoughts of Hendra virus, considering the large number of Hendra cases that have occurred in the area this year, but that particular disease has already been ruled out.
Large numbers of horses dying on a farm around the same time obviously raises a lot of concern. Often, diagnosis is difficult and takes time. One problem is even deciding where to start. For an outbreak like this there are various considerations:
- The usual (infectious) suspects: Common things occur commonly, and strange things are often caused by atypical presentations of common diseases. Hendra's been ruled out but other infectious causes can't be ignored.
- Toxin-associated bacterial diseases: This mainly refers to botulism, which causes adult horses to get sick after eating feed contaminated with botulinum toxin. Poorly fermented feed or feed that has (accidentally) incorporated the remains of an animal that died of botulism can be the source. Botulism outbreaks are usually fairly characteristic clinically since animals with botulism have pretty consistent and remarkable clinical signs of illness. Presumably, it's low on the list here as I haven't seen it mentioned in any reports.
- Toxins: A toxic cause is pretty high on the list, and can be hard to trace. Potential culprits include toxic plants or inadvertent access to toxic chemicals (I remember an outbreak of dead horses I was involved with a few years ago in which the horses died of pesticide exposure... on an organic beef farm!). Malicious poisoning always has to be considered as well.
- New diseases: New diseases don't come along very often, but they can. Similarly, diseases that have been rare can sometimes peak out of nowhere, but something like this is much less likely than the categories above.
- Miscellaneous: For example, if all the horses died inside, electric shock would have to be considered. I assume that's not the case here.
Diagnosis of the cause in an outbreak like this requires a lot of effort, including careful consideration of any signs of illness that were identified before death, good post mortem examinations (necropsies) of dead animals, thorough investigation of the farm looking for toxic plants and other toxic substances, investigation of other farms in the area to see if there are any unexplained horse deaths, investigation of any unexplained deaths of other animals in the area (e.g. looking for abnormal numbers of dead birds on the farm or in the area), testing of samples from horses for various toxins and testing tissues for possible infectious causes. Not easy or cheap, but hopefully effective, and hopefully will ultimately help save other horses from the same fate.
Who's Better At Biosecurity?
There are a lot of recommendations out there for establishing or improving sound infection control practices on horse farms, many of which can be found on this very blog. Some refer to such practices as "biosecurity," but what's done on horse farms compared to the often very strict biosecurity protocols at facilities such as swine or poultry operations (e.g. all-in all-out management, closed barns, shower in) is very different, so we prefer to call it an infection control program, rather than "biosecurity." Regardless, one of the biggest challenges with regard to infection control, in almost any setting, is getting people to comply with all the various policies and recommendations. Unfortunately, it's not enough to just tell people what needs to be done (that'd be too easy!) - knowledge by itself usually won't change people's behaviour. They also need to be motivated to change their behaviour, for example by the potential for a positive reward (e.g. they get to take their horses to shows) or the potential to avoid a negative outcome (e.g. their horses don't get sick). Furthermore, individuals need to really believe they are capable (physically and mentally) of performing the required tasks - if they don't think they can do it or be effective at it, they're unlikely to try. In reality, getting people to change their behaviour to adopt sound infection control practices can be quite complex.
A study soon to be published in Preventative Veterinary Medicine (Schemann et al. in press) looked at some of the factors that affect horse owners' biosecurity practices and perceptions. The study was performed in Australia one year after the devastating equine influenza outbreak that occurred in 2007, using an online questionnaire to which 759 horse owners responded. Each owner's biosecurity compliance was rated as low (30%), medium (20%) or high (50%) based on how often they reported using 16 different infection control measures.
Factors that were associated with low compliance or poor biosecurity practices included people who:
- were younger in age
- had two or more children
- were not involved with horses commercially
- had no long-term business impact from the 2007 equine flu outbreak
- were not fearful of a future outbreak of equine flu in Australia
- thought their current hygiene and access control practices were not very effective in protecting their horses
Now, studies based on surveys of this kind always need to be taken with a grain of salt, as the study population itself was difficult to define and the information was all self-reported by owners, which can lead to confounding and misclassification bias. Nonetheless, the results are still interesting and on the whole are consistent with behaviour theory. Those whose income and livelihood were not dependent on the horse industry, and those who were not fearful of another outbreak, would be less motivated to put the effort into infection control measures. Furthermore, those who felt that what they were doing already wasn't really effective (for whatever reason) would be less motivated to try harder because they can't see the benefit. It's quite possible (as the authors speculate) that having two or more children results in less compliance with infection control simply due to the time constraints associated with having kids. Lack of time to properly perform infection control procedures is a major barrier to compliance, even in human hospitals, particularly with understaffing issues. The lower compliance among young people is also common to studies looking at protective behaviour in human health, possibly because young people have a sense of certain degree of invulnerability that results in riskier behaviour overall.
When it comes to infection control, the old adage "a chain is only as strong as its weakest link" is very important to remember. Although 50% of the horse owners in this study reported having high biosecurity compliance, the 30% with low compliance could ruin all their efforts should another outbreak occur, by contributing to the transmission and propagation of the disease on their own farms as well as to others. Hopefully this study will help the horse industry and government identify specific groups (i.e. young people, those not financially dependent on horses) at which educational and motivational campaigns can be targeted in the future.
Economic Impact Of Aussie Horse Flu
A huge equine influenza virus outbreak occurred in Australia in 2007 - a classic example of what can happen when a virus gets into an area where it's never been before. There were huge numbers of affected horses and a massive disruption to the industry due to quarantines and other control measures.
A special edition of the Australian Veterinary Journal (July 2011) includes a series of papers covering different aspects of this outbreak. In one paper (Smyth et al) the authors look at the economic consequences and tried to determine the financial costs of the outbreak. Such estimates are always tough to make and can never be 100% accurate, but they can give a general idea of the scope and impact of an outbreak. Not surprisingly, the costs were pretty astounding.
Australian Government
A series of measures were implemented to assist individuals and organization that were impacted. The total cost of those packages was over $263 million AusD.
State/Territory Governments
New South Wales and Queensland were most seriously affected, but all states and territories were impacted. These governments provided support in addition to the federal funds. For example, Queensland allocated over $27 million to various efforts, while New South Wales contributed more than $46 million.
Racing and Wagering Western Australia
This is the government body that regulates racing in Western Australia. The outbreak cost this agency around $500 000, a figure that does not include lost employee time and approximately $15 million in lost wagering revenue. Some of this was recovered through insurance, but it's now unlikely that they will be able to get further insurance to cover outbreaks.
Harness Racing Industry
It's always hard to figure out the true costs to an industry after a major disaster because the trickle down effect goes so far, affecting people who provide support and services (e.g. hay suppliers) to various businesses that are affected directly because people in those groups don't have money to spend. The total identifiable costs were calculated to be over $23 million, about half of which was to owners and trainers. The authors acknowledge the true costs were probably much higher.
Inquiry
A large inquiry was commissioned after the outbreak. This cost over $5 million.
Animal Health Australia
This group coordinated the emergency response and had to divert tremendous personnel time and resources. This included the vaccination program that distributed 670 000 doses of vaccine.
Households and businesses
Overall, it was estimated that horse associations lost $281 million, horse businesses $65 million and households $34 million.
Horse deaths
The value of horses that were reported to have died was close to $1 million, despite the fact that equine flu is uncommonly fatal. This number doesn't include intangible costs associated with losing a horse. However, reported deaths may be a minority and it was estimated that true horse death costs may have been $44 million. (However, I suspect the death rate estimate used for this value is high.)
Veterinary treatment
Estimated costs...$35.7 million.
Do the exact numbers matter? No. They simply show that an infectious disease outbreak can cost a lot. In many areas, horses receive little government attention because they are not food animals, despite the fact that the highly mobile horse population is probably at much higher risk of importing a new disease, and despite the fact that the economic impact of the industry is huge (and often overlooked by governments and groups that fund agricultural research).
If nothing else, this should serve as a reminder to government and industry groups that attention needs to be paid to infection control and emergency planning. While groups are often reluctant to put much or any time, effort and funds into these areas, the amount of money that would be spent is inconsequential compared to the potential impact of even a small outbreak.
Image source: www.dailyclipart.net
MRSA In Aussie Horses
In the early 2000s, we took a lot of bad publicity in Ontario (particularly at the Ontario Veterinary College) because of MRSA in horses. While MRSA had been found in horses before and there were anecdotal reports of MRSA infections and outbreaks in different areas, the fact that we intensively investigated the issue and published a lot of our findings made it look like we were the hotbed of MRSA internationally. We suspected at the time that MRSA was widespread in horses and that the limited reports were because few people were looking or publishing their observations. That suspicion has been supported by reports over the past few years of MRSA in horses in many countries, and it appears that MRSA is present in horses around the world.
A recent study from Australia (Axon et al, Australian Veterinary Journal 2011) provides more support for this conclusion. In the study, horses that were admitted to a veterinary hospital's intensive care unit over a 30 day period in 2008 were tested for MRSA carriage by culturing swabs from their noses. MRSA was isolated from 3.7% of horses, which is similar to the prevalence here based on data we've gathered over the years.
For the second part of the study, the authors looked at medical records from horses at the hospital from 2004-2009 and collected data on MRSA infections. During that time, MRSA was isolated from 75 horses.
- That number (75) surprises me a little, since it's much higher than what we see here. Even though we see approximately 2% of horses carrying MRSA when they arrive at the hospital, we have a very low MRSA infection rate in our patient population. A few of those 75 horses probably didn't really have MRSA infections, since nine horses only had positive nasal samples which is more likely to be from subclinical colonization rather than infection of the nasal passages. A few others had MRSA isolated from catheter sites, and it's hard to say whether those are truly infection or just contamination of the skin. So, the number of true infections might be lower, but it's still a significant issue. It would be interesting to know how many of those horses came in with MRSA infections versus how many picked up MRSA in hospital.
Wound infections were most common, accounting for 43 (57%) of the cases. Five horses were euthanized because of the MRSA infection, all of which had joint infections that did not respond to intensive treatment.
One farm accounted for 18 MRSA-positive results in the second part of the study, as well as two positive horses in the surveillance part of the study. This farm would seem to have a pretty big MRSA problem, which we've seen occasionally on a few biohazardous breeding farms that we've found over the years. MRSA can be controlled on farms like that but it takes effort. We've had some farms address the issue properly and eliminate MRSA, while others essentially ignored the problem and continued to have widespread MRSA for years.
Not surprisingly, most of the MRSA isolates in the Australian study belonged to sequence type 8 (ST8), the group of MRSA that we find in horses here in Ontario and internationally. This is a recognized human strain that seems to have become adapted to horses. It's also found in a disproportionately high percentage of horse owners and horse vets, likely indicating movement of teh strain between horses and people.
Overall, the results of this study are not surprising, but are very useful in that they support the notion that MRSA is present in horses around the world, and the situation with MRSA in horses is probably quite similar in many different countries.
More information about MRSA in horses can be found in on the Worms & Germs Resources - Horses page.
Hendra-exposed dog euthanized
Dusty, the dog who tested positive for Hendra virus exposure on a Queensland farm, has been euthanized. The owners confirmed through their Member of Parliament that their pet had been euthanized voluntarily, rather than waiting for Biosecurity Queensland to compel them to do so.
Based on publicly available information, this seems like an illogical and unnecessary response, as well as an unethical approach by the government because it did not explain the implications of a positive result when they ask for voluntary testing of the dog.
The family said Dusty was euthanized because "most recent blood tests confirmed that he carried Hendra virus antibodies, which meant he was able to shed the virus to other animals." However, that's false. If government officials told them that, that's incredibly frustrating, disappointing and concerning. Antibodies have nothing to do with being infectious. I carry antibodies in my blood to a wide range of viral diseases that I've had over the course of my life. That doesn't mean that I still have the viruses in m. The presence of antibodies simply means the body has been exposed and mounted an immune response.
All information that I've seen so far indicates that there's no evidence that the dog was shedding virus and therefore no evidence that it posed a potential infectious risk. Furthermore, an experimental study from 1994 showed that infected dogs did not shed the virus. So, unless there are new data that aren't being released, euthanasia is a completely unnecessary and illogical response, probably based more on fear of liability than any evidence or reasonable assessment of risk. It would have been better to quarantine and monitor the dog, to prevent unnecessary euthanasia and to learn more about this virus in dogs.
If evidence indicating a true risk of transmission of Hendra virus from pets exists, this information needs to be released so that other pet owners in Queensland know what the situation is. If not, more common sense needs to be used when dealing with this disease in such animals.
This Worms & Germs blog entry was originally posted on equIDblog on 01-Aug-11.
More on dogs and Hendra virus
Neil Fearon and his family have lost three horses to Hendra virus, and are concerned about one other. They are now dealing with the implications of their dog, a Kelpie named Dusty, having tested positive for Hendra virus antibodies in its blood. As I mentioned in yesterday's post, the presence of antibodies in the blood of this dog, detected during voluntary testing as part of the outbreak response, only indicates that the dog was exposed to the virus. Viral shedding was not identified, suggesting that the exposure was a prior event and that an active infection was not present. Despite this, government authorities are requiring that the Hendra antibody-positive dog be euthanized.
Poor communication and mixed messages are often the cause of problems during outbreak management, and this seems to be the case here. Based on the news reports, there are some pretty concerning issues.
Testing of the dog was voluntary and the owner was not notified that euthanasia would be required if the dog tested positive.
- This is rather unethical. People need to understand the implications of outbreak control measures. It's not fair to have such an aggressive response to a voluntary test without proper notification.
Mixed messages are being given about the risk the dog poses to the family.
- Authorities want to euthanize the dog, indicating they must believe there is some risk. However, the owner is very concerned about his 11-year-old son who has slept with the dog in his bed for the last few weeks. Yet, ABC news indicates authorities reassured Mr. Fearon that the risks are minimal. If the risks are minimal from that type of prolonged, close contact during the period when the dog may have been actively infected, it's hard to justify euthanasia after the fact on the basis of the dog posing a risk to people or animals (especially when the virus is endemic in the bat population in the area).
- Why euthanasia is being required seems to be unclear. While fear of Hendra virus shedding makes the most sense, Queensland's chief vet has stated that the dog will be euthanized as a precaution because "As a result of that infection, it may make it aggressive." It seems rather strange to euthanize a dog because of concern that an infection (which may not be active) might cause aggression, with no evidence that disease will occur or that it can cause aggression in dogs. Quarantine and observation would make more sense. There are a lot more dogs that are prone to aggression wandering around Australia.
This type of action drives things underground.
- When overly-aggressive actions are used, and people either don't agree with them or don't understand them, faith in the system decreases. What's the likelihood that people are going to allow their pets to be tested now? I assume it's a lot lower now that they've seen what will happen. So, the ability to determine exposure of other species and the potential risks from other species will be impacted.
Hendra virus is not something with which to play around. It's a very serious disease and one must err on the side of caution. How far you err on the side of caution is the question, and it's a hard thing to determine. It's easy to be very strict when setting rules, and fear of liability or fear of making a subjective decision often override logical thought and discussion.
As a somewhat informed outsider, I have a hard time supporting mandatory euthanasia for a dog that has evidence of previous infection but no evidence of active viral shedding. Yes, no test for virus shedding is 100%, but a pretty high level of assurance can be obtained and the dog can be quarantined for further testing. There's no indication from laboratory studies that I know of that dogs (or other non-bat species) can become longterm carriers of the virus. The owners should be involved in the decision making process and be given enough information to understand the implications of keeping the dog, the risks that might be present, and what they can do to reduce the risks. Government authorities need to clearly state their concerns and the evidence supporting them. With that, it's easier to make a logical plan that protects the public but is also appropriate for the animal and its owners. If the risk is deemed to be real and/or the owners are not willing to accept some degree of risk, then euthanasia is reasonable.
"Kill the dog" is an easy knee-jerk response. I simply don't see the evidence supporting it. Is it possible that authorities have a true reason to be concerned? Sure, but if so, that indicates another communication problem. If there is really evidence that this dog is a concern, this needs to be clearly communicated so people understand what's happening and why such drastic actions are being taken.
This Worms & Germs blog entry was originally posted on equIDblog on 27-Jul-11.
Hendra virus in a dog
Adding a new twist to the already very concerning situation in Australia, Hendra virus infection has now also been identified in a dog. It's been a bad year for Hendra virus in Australia, with larger numbers of cases of this highly fatal disease in horses in a geographic range that seems to be expanding. Spread by flying foxes (fruit bats), Hendra virus predominantly infects horses, but can be transmitted to people working with infectedhorses.
The Australian Animal Health Laboratory in Geelong has now announced diagnosis of Hendra virus infection in a dog. The dog is from a quarantined farm in Queensland where the virus has been identified in a horse. The dog was healthy and was tested as part of a standard policy to test dogs and cats on infected farms. It's great to see this approach being used, since it helps identify other potential sources proactively - something that is often overlooked in outbreak investigations that focus only on the main species that are already known to be involved.
In this case, the dog had antibodies against the virus in its blood. That means that it was exposed to the virus and mounted an immune response. It doesn't indicate whether it was exposed recently or in the past. Two tests for the virus itself were negative, suggesting that the dog's immune system eliminated the virus (or that the virus isn't really capable of surviving for long in a dog). This is a good news/bad news scenario.
Bad news:
- Dogs can be infected. It increases the range of known susceptible species.
- If dogs can be infected and shed live virus, then they could be a source of infection for other individuals, including people.
- The dog wasn't sick. This might sound like strange "bad news," but healthy carriers of infectious diseases are harder to spot and control than ones that are sick.
Good news:
- The dog wasn't shedding the virus. That's critical since if dogs can be infected but not infectious (i.e. if they can carry the virus but not transmit it), then they are of limited concern.
- They have been testing farm dogs and cats as a routine measure, and this was the first positive. Infection of pets therefore must be relatively uncommon even on farms where the virus is active.
- The dog wasn't sick. While it's only one case and doesn't guarantee dogs won't be affected clinically, this might suggest that dogs just occasionally get exposed with no disease. Since it's highly fatal in other species, that's a good thing.
What should be done based on this?
- Probably not much more than should have been done before this finding, but it's a good reminder about the potential involvement of other species.
- Dogs and cats should be kept away from fruit bat roosting sites.
- Dogs and cats should be kept away from infected horses.
- If a farm is quarantined because of Hendra virus, dogs and cats should be tested and quarantined. Quarantining the animal while testing is underway helps reduce the risk of an infectious dog or cat (should that occur) transmiting the virus to people on the farm, or wandering away and exposing other people or animals.
- Animals of any type in areas where Hendra virus is active that get sick with signs that could possibly be consistent with Hendra virus infection should be tested.
This should also be taken as yet another reminder that infectious diseases are unpredictable. Considering the potential involvement of different species in a proactive manner as was done here is critical.
Image: Bay Horse and White Dog by George Stubbs (1724-1806)
This Worms & Germs blog entry was originally posted on equIDblog on 26-Jul-11.
Bat cull for Hendra virus prevention?
As Australia faces a particularly bad year for Hendra virus, with possible expansion of the range of this serious disease, there have been calls for a mass cull of flying foxes (fruit bats). These bats are the reservoir of the virus but also a protected species. The virus lives in the bats and is spread mainly through their urine. Horses that are exposed to bat urine or feces (e.g. grazing under a tree where bats are roosting) can become infected and then serve as a source of human infection. Being a highly fatal disease for which there is no available vaccine, looking at ways to reduce exposure to the virus is critical. When you have a wildlife-associated disease, questions about trying to eliminate the wildlife source often arise. Any discussion of culling wildlife leads to intense debate, and this situation is no different. Some people support culling bats in areas around people and horses, while others are opposed on various grounds, including a lack of evidence that it will be effective.
Can fruit bat numbers really be decreased? A lot of bats would have to be killed to have a significant impact on the population. Bats can reproduce quickly and migrate readily, therefore a single cull may have only a limited and short-term effect. A good understanding of the dynamics of the bat population is required to determine how many would need to be killed in a given area to have any significant impact. As Biosecurity Queensland's chief veterinarian RIck Symons stated "Culling is against government policy. I believe in terms of biosecurity it's counterproductive, because it does stress flying foxes and they're more likely to excrete (the virus). It could be filled by another bat colony the next day and if you're moving them on, you're moving it on to somebody else and it's somebody else's problem, so that is not the solution."
Will a cull actually achieve anything? Even if effective at reducing bat numbers (probably just in the short term), culls don't necessarily have an impact on disease rates. All bats would not be eliminated, and it's unclear whether there is a critical mass of bats that is required to transmit infection or whether a small number of bats distributed across the same region would be as likely to result in infections. Small or temporary decreases in bat numbers may have no effect.
What unintended consequences might occur if a cull is effective at reducing bat numbers? Removing an animal from any ecosystem has an effect, and it's important to be confident that that effect isn't accompanied by problems of its own. I don't know enough about fruit bat ecology to say much here, but if this species is greatly reduced, are there other species that will come and occupy that ecological niche, and might they be associated with problems of their own? Careful scientific study can help to figure this out in theory, but you can never be certain.
Are other control measures, such as removing roosting sites from pastures and other bat avoidance measures, being adequately used? Culls should only be considered when other measures have failed, but it can be difficult to ensure or enforce compliance with these other measures. Certainly, people in endemic areas should remove trees in which bats roost from pastures. However, not all Hendra cases are associated with identifiable roosting sites. For example, one affected Queensland farm does not have any fruit bats residing on the property, but it lies along a common flight path for the bats.
It's easy to talk about avoiding a cull when you're not in the heart of the Hendra epidemic, and I understand the reasoning behind the calls for a cull. Hendra is a devastating disease that's a threat to both horse and human health, and it's unpredictable - and that's scarey for a lot of folks. People that have been exposed face an incredibly stressful period while they wait and see if they've been infected with a virus that kills in ~50% of cases. A vaccine is probably still a couple of years away, leaving a period of continued risk and stress. With such a serious disease, considering culling is reasonable. However, it can't be a knee-jerk reaction to public outcry. It needs to be based on sound science to ensure that if it's used, it will be effective. The impact on this protected species also can't be ignored.
This Worms & Germs blog entry was originally posted on equIDblog on 19-Jul-11.
Murray Valley encephalitis suspected in Aussie man and horses
Yesterday, I wrote an equIDblog post about an outbreak of unexplained neurological disease in horses in the Murray River region of Australia. Today, a ProMed report indicates that Murray Valley encephalitis is now being considered as a possible cause of death in a man from the area.
Murray Valley encephalitis (MVE) is one of the possible causes of the equine neurological disease outbreak, and it's quite likely that if it caused disease in one species in the region, it did the same to another. This rare mosquito-borne disease hasn't been seen in decades in the region, but it's possible that high mosquito numbers following heavy rainfall and flooding have increased the risk of transmission.
While this virus poses a risk to both humans and horses, humans and horses pose no risk to each other. Both acquire the disease the same way - from mosquitoes - and neither can pass it on to the other. This is also true of other insect-borne viruses such as West Nile virus and Eastern Equine Encephalitis (EEE) virus.
This is a good example of why human and animal disease surveillance need to be linked, and why governments need to put resources into testing of animals beyond food animals. Rapidly identifying a disease in horses or other animal species can help determine whether there is any risk to humans, and hopefully lead to preventive measures being taken earlier.
Prevention of this disease is focused predominantly on mosquito avoidance. It's impossible to completely prevent mosquito exposure, but some basic practices can help reduce the risk. Click here for some practical tips on protecting yourself and your horses from mosquitoes.
Image: Location of the Murray River in Australia (click for source)
This Worms & Germs blog entry was originally posted on equIDblog on 13-Mar-11.
