Well, hello, everyone. Thank you so much, for joining us for this webinar. My name is Julia Montgomery, and I'm a large animal internal medicine specialist and a professor at the Western College of Veterinary Medicine at the University of Saskatchewan in Canada.
So today, I'm gonna go through a review of equine respiratory diseases. This is obviously a very broad topic, however, it is also a very important topic. For anybody, for anybody that works with horses.
So my main objectives would be to review some of the important things to consider when dealing with infectious and non-infectious respiratory diseases, some strategies and recommendations for outbreak management. To also share some helpful resources and focus on some of the relevant research updates, and then I have a couple of cases at the end that we can go through. So to start us off, I will talk a little bit about respiratory viruses.
There are obviously a number of equine respiratory viruses, including herpes viruses, influenza, and a few other ones. I'm going to focus. On equine herpes virus and especially EHV one, since that has some major implications for facilities, especially when we are dealing with outbreaks, since it affects other body systems other than the respiratory system.
Just as a reminder, that's kind of why I put this image up here. There are many, many equine herpes viruses that present in different ways and affect different body systems. So as far as the respiratory system is concerned, the main focus will be EHV1 and EHV-4, but just as a Reminder, there is another type of herpes virus, EHV5, a gamma gamma herpes virus that is associated with a condition known as equine multinodular pulmonary fibrosis, which is a more chronic condition and presents differently than the alpha herpes viruses EHV1 and 4.
So both EHV 1 and 4 affect the respiratory system. One of the things to remember is that the clinical findings associated with respiratory viruses, regardless of the type of virus, are clinically indistinguishable, and this is gonna be my pitch for diagnostic testing. This is some something where there might be sometimes pushback from clients, to spend money on diagnostic testing.
Because most of the time if we're dealing with respiratory viruses, in most cases, the course of the disease is fairly mild and there's not really a lot of specific treatment. However, it is important to know, from a disease outbreak perspective, that what what virus you are dealing with and it's also possible that you might be dealing with coinfections, so several virus is at the same time. The reason why EHV one is of particular concern to veterinarians as well as our clients is that it can affect other body systems, specifically the one that we worry about the most is that it can affect the neuro nervous system and cause neurologic disease, and it can also cause abortion, especially late term abortion and neonatal death.
Since these viruses are associated with outbreaks, they tend to be seasonal, more common in the spring and summer when horses are moving around more for the show season. So another thing that is special about herpes viruses, and I just wanted to put in here as a reminder for everyone is that it can do this thing called latency. So, for all herpes viruses, this is true.
Once an animal has herpes, it has herpes forever, and it can be reactivated, especially in times of stress and result in virus shedding, and that can be a source. Of outbreaks in facilities. So that's just something to keep in mind when it comes specifically to herpes virus.
And obviously there are a number of different stressors for horses and transport and going to shows, it's one of them. So as I already mentioned, respiratory viruses and horses most of the time lead to mild or subclinical infections, and the reason why that is important to remember is that early clinical signs may be missed, and sometimes facilities may not be aware that They are dealing with an outbreak once more severe clinical signs show up. So, for example, secondary bacterial pneumonia or in the case of herpes virus, equine herpes virus one neurologic symptoms.
So one of the things that might be a useful Recommendations for facilities that want to be more proactive in preventing viral disease outbreaks would be to engage in a practise of regular temperature monitoring, which may be useful for screening as well as early detection of a viral infection. And another reminder that clinically these viruses are indistinguishable from each other, which is why diagnostic testing is so important. So how do we diagnose these guys?
So probably the most, the simplest and most useful testing would be PCR the other the main advantage of that being that it's a sample that's easy to obtain. All of us are familiar with that. Since the COVID pandemic, for sure, so that should be an easy one to explain to any horse owner, and also that for PCRs we have the option of running respiratory panels, which means you can test for a number of different infectious ideologies at the same time.
When it comes to EHB one, abortion, or early neonatal death, there would also be the possibility to inspect tissues associated with those animals. So obviously, in an ideal world, we like to prevent these disease outbreaks, however, that is really in many cases just not possible just because the viruses are around everywhere, and even with vaccination, which helps to control disease severity and improve herd immunity, we will probably never be able to get rid of herpes viruses or influenza. There are, however, some biosecurity measures that facilities can do, such as making sure that not co-house brood mares and show horses if at all possible, and sort of minimise traffic, between these groups.
And vaccination in at-risk animals is certainly an important preventive strategy. So I'd like to remind everyone that when it comes to all of the common equine respiratory diseases, we have some really nice resources available to us that are open access and available for free. So the ACVIM has put out a number of consensus statements including one on EHV one, so I've included the reference here, .
This is an open access source published in the Journal of Veterinary Internal Medicine. And even though it is, a few years old now, it still is quite helpful, sort of as a prescriptive resource on how to manage outbreaks, when to sample, who to sample, how to, Separate the different groups and control control traffic on facilities and those kind of things. So this would be the resource that I would recommend for anyone that has to deal with a herpes virus outbreak.
The other thing that comes up time and time again when we talk about diagnostic testing, and something that also some horse owners will have heard of is that there are a number of different strains, including one that often is referred to as the neurologic strain or neuropathogenic strain, which sometimes leads to the Impression that the other strains cannot cause neurologic disease, however, that is not true. So any EHP one strain can be associated with neurologic disease and horses. The other thing to keep in mind is that there is A newer variant that has been discovered first in Europe and more recently in North America, that may not show up on all type specific assays depending on the diagnostic lab you use.
So one of the things that's important when dealing with diagnostic testing, and that's true for all of the diseases that we go through today, is to have a good idea of what kind of testing your diagnostic lab does, and to be consistent in the diagnostic lab that you use. So this is a recent report that's also open access that sort of goes through an outbreak that was caused by this newer EHV1 genotype that traditionally did not show up on our commonly used PCR essays. So for those of you very interested in this topic, this is another resource that you might be able to look into.
So some of the main findings from this paper, just to summarise them, this paper also supports the regular monitoring of temperature for screening and early detection, so something proactive that facilities can do and as I already said, it highlights the importance of kind of having an idea of which genotypes your lab that you are using will be testing for. It also showed that there might be some benefit of using antivirals such as well cyclovir in early stages of the outbreak. This is, as you probably know, a little bit of a topic of contention, how How useful this drug is in horses since we know it has maybe not the best bioavailability, but there does seem to be some evidence that it might be useful in these outbreaks.
Obviously keeping in mind that it is fairly pricey, but especially when dealing with EHV1 and the concern for potential neurologic disease, this may be something to consider for some facilities. And here is another resource that I wanted to share about this discussion around the neuropathogenic strain. So another recent study that has looked at samples from another, a number of animals, and even though we sort of refer to one strain as more neuropath.
Genic than another, this supports the fact that really any EHV one strain can cause neurologic disease. So that would be an important communication piece for facilities where you're managing outbreaks. And if you're interested in sort of delving a little bit more into pros and cons of different diagnostic testing, this is a fairly recent resource that we've used this quite nicely, and it also is a reminder that even though we test for influenza, EHV1, EHV4, and also equine arteritis virus on most panels, there are other equine respiratory viruses that are not usually part of diagnostic testing in most commercial labs.
So that is just something to keep in mind for interpretation of your results. The other thing that this paper does it nicely reviews some of the advantages and challenges of PCR testing. So I already mentioned the advantage of having a panel available for testing, so that you are able to test for several pathogens at once because it certainly does happen that you might have coinfections, so that an outbreak may actually be caused by more than one infectious organism at the time.
There are, obviously also some disadvantages to PCR testing, the main one being that you don't always have information on viability of the infectious agent. This is where quantitative PCR can be helpful because it can provide a stronger disease association because it will give you a better idea of viral loads, which would be indicative of potentially actively replicating virus, specifically for EH31 and 4. So that kind of is the end of our equine viral disease review.
So I wanted to share a few brief updates on strangles. Obviously, as this picture also suggests, this is a very old disease that has been around or has been described, at least since the Middle Ages and probably has been around for longer. Everybody is very well familiar with it, but because it is still a very important disease, a disease that we deal with a lot, and that has some potentially severe complications associated with it, I just wanted to review a few important things about strangles.
So similar to EHV one, there is also a ACVIM consensus statement on how to manage strangles outbreaks. This is also published in the Journal of Veterinary Internal Medicine, has been recently updated in 2018. This is a free resource and a very helpful resource that will walk you through pros and cons of different diagnostic testing, which animals to treat with antimicrobials, which animals might be at risk of complications, and which animals might be at risk of complications after strangle's vaccination.
So it is a very helpful resource to to have on hand. This is just a reminder that unfortunately, when it comes to strangles, animals are infectious before they really have the typical clinical signs of strangles, and that is probably one of the reasons why it is still very successful organism. And even though many horses, especially younger horses, usually deal quite well with the infection and develop a very good immunity after they have gone through the acute infection.
The reason why we worry so much about this disease is kind of twofold one, because, Some horses can become carriers, carrying the bacteria in their guttural pouches and become shatters, and this is how they can introduce this into other groups. And the other reason is that there are some pretty severe strangles associated complications such as purpra hemorrhagica, and, myopathies. So I'm not gonna go through this table in detail.
This comes out of the consensus statement, but it is just a nice summary of the different types of samples that you can take and the pros and cons of those samples. So we probably all know that guttural pouch lavage is the most sensitive test, it's best for detecting carrier. Animals, but it's obviously also the most complicated sample to get and it requires special equipment, and some skill in obtaining those samples.
So that's the nice thing about this consensus statement that it does give you some other options. Although Garo pouch lava does remain the best testing, to detect carrier. Animals.
So depending on the guidelines of the facilities that you're dealing with, I know that in our practise area, there are now some boarding facilities that actually require a neg negative guttural pouch leva before a new, horse is admitted to the facility, for boarding. So that might be something to keep in mind. However, it can obviously be quite involved having to do a, a number of these if you are dealing with.
An outbreak and you like to declare this facility free or recovered after an outbreak and identify carriers. So for that reason, I wanted to share this resource also published in the Journal of Veterinary Internal Medicine which makes it open access, and it's a more recent study that has looked at maybe alternatives to gual pouch lavage that can be used to predict care. Your free status and recovery after an outbreak.
And this group has looked at repeated nasopharyngeal lavage sort of in lieu of guttural pouch lavage. So this would be a good resource for you to look at if you are managing an outbreak and are trying to support a facility and identifying any potential carriers. And then one of the more recent research findings that I wanted to share with you is this discovery of the link with myocene heavy chain myopathy.
We've known for a long time that one of the strangle's complications is a myopathy, but it has been discovered more recently that at least in quarter horse related breeds, this seems to be linked to a genetic mutation, and there is a genetic test available. So this myosine heavy chain myopathy is an immune-mediated myositis triggered by a recent respiratory disease or vaccination. The reason why it is important to keep that in mind, at least if you have quater horses or related breeds in your practise area, is that these are probably horses that should not, receive the strangles vaccine.
So that can. Sometimes be a challenge, if they are supposed to be housed at a facility that has that as a requirement, so they may require some kind of certificate from you that they could be exempt from such a vaccination. So the diagnostic test for this is available through the University of California Davis diagnostic lab, just a reminder that this is A mutation that can affect both homozygous and heterozygous animals, so it is a dominant mode of inheritance, and the clinic most obvious clinical findings would be very acute muscle atrophy, especially along the top line and acute in this case means literally within days, fairly noticeable difference, as well as elevation and muscle enzymes.
So the treatment for these guys is corticosteroids since it's an immune-mediated disease, but the reason I'm mentioning it here, even though it's technically not a respiratory disease, is that it is important for these cases that they should not receive the strangles vaccine. All right, so switching gears a little bit, however, staying within the realm of bacterial infections, just a few comments on hotococcus equine pneumonia and folds. So just in general, when we're talking about folds, the ideology when it comes to Infectious respiratory disease, should be ranked based on age.
So if you have any clinical findings that are consistent with pneumonia and neonates, so in about the first two weeks of life, this would be a manifestation of sepsis until proven otherwise. In older falls, we would be looking more likely for another primary, disease aetiology. And just a reminder that folds just as adults can get pneumonia associated with streptococcus eI subspecies zooid epidemicus as well.
However, one of the kind of foal specials ishotococcus equine pneumonia, which is something that we do not recognise in adults, at least immunocompetent adults. So just like one and strangled, there is a consensus statement talking about Rhotococcus equine pneumonia unfolds as well, published in the Journal of Veterinary Internal Medicine and Open Access. This is Focused on management of affected farms since we do recognise this particular disease seems to be endemic on certain farms.
And kind of going through some different control and prevention strategies on how to manage these outbreaks on farm. And screening of folds. So that is always one of the challenges, especially on endemic farms, where every that have a large number of folds, this can become quite Time consuming and costly if you have a number of folds to screen, which is why a lot of research has kind of gone into different ways of screening these folds and deciding which folds to treat, because the other challenge that is starting to develop is that we are starting to see some resistance and some of the antimicrobials used in this disease, so we're trying to really limit.
The number of folds that are treated by identifying those that really require treatment. So a lot of research has gone into that, and there are certainly more recent studies as well. But one of the nice things about the consensus statement is that you have a group of experts kind of review.
The literature and looking at the level of evidence for the different recommendations instead of providing a neat little summary. So if you're limited in time to go through the primary literature, this is certainly a good starting point, keeping in mind that there will be some newer studies out there. Another thing that's nice about fools kind of compared to adult horses is that .
They're a little bit easier to image in the field if you have sort of portable imaging equipment, specifically for X-rays. So we are somewhat limited, when it comes to X-raying the lungs of adult horses, and usually this will require transport to a to a clinic or a referral centre that has a more powerful X-ray unit, but certainly folds, it will be possible to take fairly decent lung radiographs. With a portable X-ray unit.
So lung radiographs would be a good way to find abscesses in these folds. At one of the screening tools that's used a lot and which is obviously very easy to use and portable as well as ultrasound, an ultrasound can certainly be helpful if you have lung. Abscesses that are superficial and close to the pleural surface of the lung.
However, if you have abscesses deeper in the lung, they may get missed on ultrasound screening just because, ultrasound will not penetrate through air. So that's just something to keep in mind, but certainly ultrasound is used a lot for screening and can potentially be useful. So these guys, we treat them with antimicrobials, in a perfect world, we like to treat any pneumonia based on culture and sensitivity testing, since even though, if you have a fall in the right age, age range, so 2 to 4 months about thereabouts, and with especially an on-farm history of hotococcus epi.
There are still other, . Potential causes of bacterial pneumonia. So there are a couple of options, what do you do before you have the results of that culture and sensitivity testing?
If the signal meant the presence of abscesses, and especially the on farm history suggest hotococcus equi treat with a macrolide plus or minus refampin and otherwise he would use a broad spectrum cover ridge similar to adults. So one of the things that has been studied quite a bit is sort of decisions between which macrolide antibiotic to choose. As I'm sure you well know, there are some concerns about risks for the mare when treating folds with Macrolides, since there is some association, especially between the use of erythromycin and colitis that develops in the mare, .
Or as the, as far as efficacy goes, the main consideration would be which of these has actually reaches the highest concentration in the lung. And so based on the studies that have been, have been completed, this would be cleythromycin. Which has been shown to reach the highest concentration of bronchoalveovage fluid.
One of the reasons why azithromycin may be a good recommendation in some cases is that it does require less frequent treatment intervals, which may be more practical for some owners, especially since falls sometimes need to be treated for several weeks. So I got this table out of the consensus statement as well, and it gives you just some supporting data on what I just said with regard to Concentration in the lung for chlorothromycin when compared to the other macrolide antimicrobials, certainly not something that you need to worry about in great detail, but for those of you that are interested, this resource does come out of the consensus statement on hotococcus equine. So next, I would like to review some important aspects of equine asthma, which is a non-infectious chronic lung disease of horses, that is ubiquitous and that we deal with on a fairly regular basis.
So if you are an equine or a ma animal practitioner, this would certainly be, what I like to call a bread and butter disease. So when it comes to the equine asthma syndrome, there is also an ACVIM consensus statement. The revised version was published in the Journal of Veterinary Internal Medicine in 2016, and it's called the inflammatory Airway Disease Consensus, a revised consensus statement.
Since that was really the consensus statement that proposed the change in nomenclature from what we used to call inflammatory airway disease and recurrent airway obstruction to what we now refer to as the equine asthma syndrome. Another review that was published a couple of years after the consensus statement that I would like to point out is reference on the bottom of the slide here, published in the Journal of Veterinary Internal Medicine which makes it open access, and it's a nice review that compares some of the features of. The equine asthma syndrome, to the human asthma syndrome.
So one of the reasons, why this change in terminology has happened is because over the years we've recognised that there are a lot of similarities between equine asthma and human asthma, namely that we are dealing more with the. Syndrome that has multiple phenotypes that present with different clinical severity, with different inflammatory cell types such as eosinophils, mast cells, and neutrophils, and that there are probably also different triggers involved. So we do recognise that.
Allergic airway inflammation and hypersensitivity to certain environmental triggers is likely the most common one, but there are Other triggers that we think about that can cause for sure asthma exacerbation such as viral respiratory disease, potentially bacterial pneumonia. There's likely a genetic component in some families and different age of onset. So that is something that's recognised in humans and it's very likely also the case in horses and sort of an area of ongoing research.
So what we used to call inflammatory airway disease, we now call mild to moderate equine asthma, what we used to call recurrent airway obstruction, we now refer to as severe equine asthma. And the other thing that I wanted to point out on the slide is just a reminder for everyone that if you want to diagnose mass cells on a cytology slide of a bronchoalvulva, this does require a special stain, so just make sure that your diagnostic lab, that you use is aware of that. So in the consensus statement, there's this nice table that lists some of the similarities and differences between mild to moderate equine asthma and severe equine asthma.
One of the things that's important to keep in mind is that Horses of any age can be affected by mild to moderate equine asthma, what we used to call inflammatory airway disease. Even though in the, in the earlier literature, this was often highlighted as a disease of younger horses, it really can affect horses of any age. The biggest difference between mild to moderate and severe equine asthma clinically is that only horses with severe equine asthma have very obvious clinical signs associated with respiratory difficulty and it increased respiratory effort at rest.
And so, for mild to moderate equine asthma, probably the most common presenting complaint will be poor performance rather than very obvious respiratory symptoms. The other thing to be aware is that severe equine asthma is pretty reliably inducible, by causing exacerbations of horses, through exposing them to triggers such as a dusty environment and mouldy hay. So that's also used in experimental studies.
So why should we be aware of that? Because it is something to keep in mind when you're looking, or reading different studies in the literature. So, when we are studying severe equine asthma, we have the option of using this experimental model, which is known as the mouldy hay challenge.
So horses that have been previously diagnosed with asthma that are in Miss get exposed to poor air quality and mouldy hay, which very reliably causes exacerbation. That means in these studies also we know the exposure to the trigger, we know when it happened, and usually these studies reflect the beginning of exacerbation, and our, the population is quite a bit more homogeneous. Whereas any study that looks at mild to moderate equine asthma, which is not inducible or naturally occurring asthma, often the trigger that caused the exacerbation, the onset of disease and the duration is less well known, so that just makes the findings quite a bit more variable.
So it makes this scenario a little bit hard to study, but it certainly also makes it more real world, but it is just something to keep in mind, when interpreting findings from these studies. When it comes to diagnosis and sample collection, the most important thing, and that is also highlighted in the consensus statement, is that it is important to be consistent with the sampling technique that you use, to consistently use the same lab and have an understanding, . What kind of process this lab use.
If you are not familiar with the diagnostic lab or if it's a new lab that you're using, make sure that you request that they do a differential cell count as well because that is really what we use for a cytological diagnosis. Another thing that I would like to highlight is that there are some discrepancies in cut-off values reported for cytological diagnosis on bronchoalve lavage. So generally we think of greater than 5% neutrophils, greater than 1% einophils, and greater than 2% mass cells.
Indicative of lower airway inflammation, but there is this grey area that has been highlighted in a number of studies. So that's why it is really important to interpret your cytological findings together with the history and clinical findings in these courses. .
It's not recommended to do a bronchoalvalava in a perfectly healthy horse with normal performance because there are a number of studies that have shown that just based on BAL cytology, you might document airway inflammation in these horses. So it's not recommended to do that. There really needs to be a clinical indication for collecting these samples.
So mild to moderate equine asthma is a little bit more vague and can sometimes be more difficult to diagnose, because many of these horses will not have very obvious respiratory symptoms. Poor performance is a common presenting complaint, and even though it is a common disease in younger horses and especially race horses, we do see it in horses of all ages. So there's one study here that has looked at raising thoroughbreds that I wanted to share for those of you that are interested in looking at some of this in more detail and again, published in the Journal of Veterinary Internal Medicine, which makes it Open access.
And what this study has found is increased mass cells and a big part of the population that they studied, so highlighting the importance to make sure that your lab specifically stains from mast cells, . And that both mast cells and neutrophils increased in the bronchova were associated with poor performance in these forces. So one of the important things to highlight when it comes to management, and this really cannot be overstated, is that the number one treatment and the only treatment that will lead to long-term success are environmental modifications, and that is really challenging because it heavily relies on owner compliance.
But it is an important communication piece when talking to horse owners, because steroids alone will not long term control airway inflammation if the environmental triggers are not managed. So there are a number of things that we can do to help these horses. I always like to give different recommendations or options just because obviously every facility.
Has a different reality of what they can, work with. So we like to try and keep these horses on hay if we can, obviously because that would be the most natural diet for them, aside from grazing. So good quality square bale hail hay if possible, if environmental temperatures allow, wet hay is a potential option to Keep the dust content in the hay down.
Another thing that would be a more controlled, way to, to address dust and mould steamed hay, using hay steamers. So I included a reference here that is open access that sort of discusses that a little bit more in detail. Depending on where you are, and if this is an option for you, hailage would be another possibility, or some horses that are exquisitively sensitive and really can't tolerate any kind of hay may have to be switched to hay cubes or pellets.
There is another option that was, researched by our colleagues from the University of Montreal in Canada, which is, a proprietary oil mixture that will get mixed with the hay to kind of bring down the dust. So I've included the link here, so it's called neutrophone. The other thing when it comes to feeding horses is that if whenever possible to feed them off or near the ground, which will result in lowering of the head, so that helps just with the natural airway clearance.
And the most important part in communication with the owner is that it will take time for these changes to take effect, and The less well controlled the environment is, the longer it will take. And I really cannot overstate the importance of owner compliance, to the extent that this has actually been documented in the literature. So I've kind of highlighted the statement here in the abstract, from this recent study out of Portugal that basically said that successful implementation, .
Of, of the environmental recommendations was really the most important outcome in addition to addition to pharmacological management. So if If the environment is not controlled, it will take a long time for these forces to get better, and then especially in the case of severe asthma, they will likely suffer further exacerbations down the road. One additional dietary recommendation that you could add, especially to owners that like to have something else to do, and really like to give supplements.
This is a dietary supplement that has some scientific evidence behind it. I've included the reference here from the Journal of Veterinary Internal Medicine, and this is certainly something that could be added to the management of these forces. And then just a quick note on what if you can't control the environment, because as we all know, there are certain environmental triggers such as poor air quality because of forest fires, or dust in the air because of harvest activity, that we can't do anything about.
So in these cases, it's important that horses during episodes of poor air quality are not exercised and these horses likely will have to be treated, if they are And exacerbation until air quality improves. And this was shown by a group out of Calgary, that has sampled a number of horses during a time where Alberta was experiencing very bad forest fires, and Calgary had very poor air quality because of that. And basically, in summary, what they found in the study is that once air quality got better, the horses got better.
So I've mentioned on these, on the previous slide, what we like to call here prairie fog, which is basically dust associated with harvest activity. So you can see in the bottom picture, this is a perfectly clear day. This is not fog or haze.
This is the dust just from the combines. That are harvesting and you can imagine that a horse or a human suffering from chronic lower airway disease will not be happy on a day like that, but there's very little we can do to remove horses from this environment, so in this case, they might just have to be treated until air quality improves. OK, so to wrap up for today, I have a couple of case examples that I would like to go through, to, to kind of bring some of these concepts together in a case.
So the first case was a 17 year old Arabian ma that presented to our clinic with a one month history of respiratory difficulty. She was treated on and off with cetiphir, as well as dexamethasone and lambuterol. This showed some mild improvement, but she did not really, her clinical signs did not resolve.
And by the time she presented to us, her presenting complaint was respiratory distress, so she had suddenly significantly worsened. And so like any case that presents with respiratory distress, one of the first things we will do is take an arterial blood gas, just to determine whether this horse would benefit from intranasal oxygen. So this is her initial arterial blood gas, .
At the top, and then the second one is the sample we took a couple of hours after we started her oxygen therapy. And as you can see, the CO2 is quite low, so it was 70 at a time of presentation. So this was a horse that definitely we put on oxygen right away.
So even though clinically she looked very much like a horse and asthma exacerbation, so she had nostril flaring and an increased abdominal effort at breathing. We, sort of went through and did our full diagnostic workup. So one of the things that we always like to do is do a complete blood count, to rule in or rule out bacterial pneumonia, and that is important because, You obviously don't want to start a horse on high doses of corticosteroids if you're dealing with a bacterial pneumonia, and certainly, we have seen a number of cases that can kind of suffer from both concurrently, or where the pneumonia is likely what caused the asthma exacerbation.
So this horse was a good example of that. So she had a leukopenia, so a low total white blood cell count, she also had a neutropenia and a left shift, so increased band neutrophils, and a fairly high fibrinogen. So certainly evidence of systemic inflammation.
We also went ahead as part of our workup and did a tracheal wash, cytology and culture. So just a reminder that a tracheal wash is, a great diagnostic test to rule in or rule out bacterial pneumonia. However, for the diagnosis of equine.
Asthma, it is really important to do a broncho alveolar lavage, because it is not it is not uncommon to find high numbers of non-degenerate neutrophils in the tracheal wash of normal horses. So a cytology of a tracheala wash is really only helpful for Distinguishing between bacterial pneumonia. Or, absence of a bacterial infection.
So, this horse, so what's kind of important in the cytological description, it had both degenerate and non-degenerate neutrophils, so degenerate neutrophils or activated neutrophils are something we often see with a bacterial airway infection. And the other thing that was important about this is that some of those bacteria that were seen on the slides were present within the neutrophils, so not just potentially contamination, but actually a true infection. And then below that you see the results of the culture, which sort of show us some of the more common species that we see in horses with pneumonia, which is streptococcus and actinibacillus.
On lung radiographs, this horse, actually only had a diffused bronchoinitial pattern, which is something that is more consistent with equine asthma. So based on that, we diagnosed this man with equine asthma exacerbated by bacterial pneumonia. So this makes, these guys are a little bit more challenging to treat initially, as I already mentioned, since we don't really like to give Corticosteroids and repeatedly to animals with bacterial pneumonia.
So we initially treated her for her pneumonia and then started Also nebulization with saline, which is just a nice treatment to sort of help calm down their airways as well as the bronchodilator, salbutamol with a 1 metre dose inhaler, and then we did a recheck CBC, . On day 3, which showed significant improvements, so at that point I felt a lot more brave to start this horse on corticosteroids, and address her asthma exacerbation. So the second case that I wanted to share with you was an 11 year old quarter horse gelding.
His presenting complaint was chronic respiratory disease and severe weight loss, and when I say severe, I mean that this horse literally. Within the course of a month went from looking like a really healthy horse with a 5 to 6 out of 9 body condition score to a horse that almost looked like a welfare case with a 2 out of 9 body condition score. This horse had previously been treated with 3 different antimicrobials, dexamethasone and clanbuterol.
There was no response to the antimicrobial treatment and a slight improvement, when the horse was treated with dexamethasone and the bronchodilator. So on physical examination, his body condition score was 2 out of 9. He presented in severe respiratory distress, and he was also tachycardic.
So, I would like to share his arterial blood gas on admission as well. And as you can see, he had a severely low CO2 at 50.9.
So this horse was also started on intranasal oxygen. And his diagnostic plan. Included a CBC which showed only a hyperfibrino anaemia, so there was no otherwise no evidence of systemic inflammation.
The biochemistry was overall unremarkable. The thoracic ultrasound showed some abnormal or regular lung surface over all the lung fields, and the thoracic radiographs were probably the most interesting part in this horse, which showed severe interstitial pneumonia with suspect nodular lesions. So similar to the previous case, we sort of repeated the blood gas a number of hours after we started the oxygen, just kind of to see how well he would respond and his PO2 didn't really significant.
Increase. So just as a reminder, I'm including here the initial blood gas for comparison, so it only went from 50 to about 61, giving us an indication that gas exchange was not really great in this force, even on a 100% oxygen. So, so this guy is a little bit interesting and, and I sort of included him here just as a reminder that equine multinodular pulmonary fibrosis, which is not a super common diagnosis, should still be something to keep in mind as a differential specifically to horses that And like what might look like severe equine asthma.
So we know the common saying, if you hear hoofbeats, think horses, not zebras, and that certainly is true. So most horses that look like severe equine asthma will have severe equine asthma. But if you have a horse that either in addition to the respiratory symptoms, has This history of very severe weight loss or a horse that has been treated for severe equine asthma and is really not responding to the treatment even though environmental management is appropriate.
These are the kind of cases where I would consider looking further and also adding equine multinodular pulmonary fibrosis to your list of differentials. So this disease is associated with the herpes virus, specifically EHV 5, which is a gamma herpes virus. The challenge with This particular disease is that causality is not that easy to prove since equine herpes virus 5 in carrier status is common in many horses and does not necessarily mean that these horses do have EMPF or ever down the road will develop it.
However, there is a group that has shown that the link between the two is quite likely. So what are some common clinical findings in these horses? So it generally affects middle aged to older horses.
A really common clinical finding or part of the history is this rapid and severe weight loss, and because they have poor gas exchange, because of the changes in their lungs, they often will present with pretty severe respiratory symptoms. So we can make a suspect diagnosis based on the history and clinical findings, the lung radiographs that frequently will show this interstitial pattern and nodular changes, and by ruling out equine asthma, . A definitive diagnosis is a little bit more challenging partly because many horses will carry EHV 5, so serology, is really not super helpful.
The gold standard would be a lung biopsy and immunohistochemistry. However, this is obviously very invasive and, and especially in a horse that is severe respiratory distress, not. Really a great idea.
So, there are some researchers that have looked at potential alternatives, and it appears that doing, a PCR for EA35, on bronchoalveolarvage fluid, together with, suggestive clinical signed, findings certainly is a reasonable, diagnostic approach in lieu of performing a lung biopsy. So I guess that concludes the webinar for today and I hope that it was helpful and that you enjoyed some of the resources and if you have any follow-up questions, you are more than welcome to send me an email.
