Hi everyone, and thank you very much for listening in to the lecture today. Today I'm gonna be talking about equine infectious diseases, their diagnosis and treatment, and particularly I'm gonna highlight some recent work and some interesting stuff about some of the diseases and and vaccination because I think that's fairly significant at the moment. So what are we going to cover today?

We're gonna have a little look at strangles, we're gonna talk about some of the testing modalities, the vaccination that's just come out, in the last few months. A little bit about treatment, but not really more about what's going on, with the risk of resistance, in, in the bacteria itself. Then we gonna have a little look at equine herpes virus.

We're gonna talk again about how to test an outbreak, how to release from an outbreak, so I think that's quite an important question that we often struggle with making sure that we get that right. How do we treat cases and should we vaccinate, which I think is a really contentious issue, and one that keeps, rearing its ugly head, and we've been doing some work with vet partners trying to decide what the advice should be there. Touch on equine influenza, looking at the vaccination rules, and a few other little bits of information, and finally Borrelia Borri Lyme disease, because I'm interested in it and I, I like to talk about it, so we're just gonna touch on that for a couple of slides.

Most importantly, throughout all of these diseases, I'm not gonna spend long talking about the clinical symptoms or anything like that because I don't think that that's particularly helpful at this stage. Most people know these symptoms off the top of their head without the slightest problem. But with strangles, when we're looking at strap equi, we're talking about a pretty where it's most likely to affect young horses between 1 and 5 years of age.

It's spread by aerosol from sick horses, and it can spread about 10 metres, in the aerosol form, or more likely it's going to be spread via direct or indirect contact with discharge. So whether that's from sick horses on to shared housing, water, feed, utensils, tack equipment, personnel, any of those things. And what we're finding is that there's quite a variable environmental survival, and actually it seems to be that in most situations it's relatively short, so I'm gonna highlight some research Andy did, a little while ago, about a decade ago now, showing actually how variable and how short it can be.

What it all means is that actually, as a disease, it should be eminently eradicatable, but that would require a united, committed response from everyone in the UK, and the problem obviously lies with the carrier horse that's silently going to shed the organism and therefore maintain strangles in the general equine population. So although I'm saying it could be fixed and gone, and the reality is I don't think it ever will be. What we know is that the incubation is about 2 to 10 days and therefore can be a bit tricky to to control in the early stages.

I think from a disease process, the actual strangles and the vast majority of cases aren't that significant. You know, most of them will get over strangles without a problem. They might have some abscesses, they might be a bit ill for a while, but actually they, they get on, and it's more of a problem from the yard, from going out and competing and all those sorts of things.

I think though there are a number of cases that will have significant complications that we've got to talk about, just so that everyone's aware of them. Firstly, metastatic or bastard strangles, depending on what term you want to use, where you get abscessations throughout the body, often affecting the mesenteric lymph nodes. What should be stated is that there is absolutely no evidence to say that antibiotic use increases the risk of metastatic strangles.

So I know that there's a dogma out there that says, we really shouldn't be using antibiotics because it leads to metastatic strangles, and that is not the case. We shouldn't be using antibiotics in the early cases because there's no indication, and only if we follow the ACIM guidelines and consensus statement, which is probably the best document to be following. What we can say is that actually we only use antibiotics in those cases that are clinically struggling, whether that is severe abscessation, dysphagia, or if we start looking at some of these more serious conditions.

In my experience, though, I think I've seen one case of bastard strangles, and more frequently do we see purpura hemorrhagica. So with a significant vasculopathy, severe edoema, sort of ventral and, limbedema, and decreation of the mucous membranes. These these often need pretty intensive care and you need to take them on steroids as soon as you possibly can because until you get the steroids on on, you're gonna get a very poor outcome.

Now it should be noted that strangles can be fatal. Although it's not common, it can occur, whether that is through pur or hemorrhagic metatic strangles, or just through the severity of the signs associated with, with the primary disease. And so this is a horse that, presented here at Lip Hook with all the stereotypical clinical signs.

So tachypnea is dysphagia, constant hypersalivation. And sadly this horse did die because the symptoms were so, so severe and we could never get it under control, and actually we ended up euthanizing it on welfare grounds. So, although in the vast majority of cases, it is mild and insignificant, it can be significant in some.

So what guidelines should we follow? The HBLB often do have a, a number of guidelines for us, and I think there are some important points in this, this most recent HBLB guidelines, but there are some that I think we really should question. So first of all, stopping movement on and off premises obviously is an essential part of the process.

Isolating suspected cases is, is correct, there's no question in that. Obtaining a complete outbreak history that's true of all disease processes, especially with infectious diseases, so that we can trace all cases, contacts, and infectious sources. And I think that's significant, particularly when we start talking about equine herpes virus and the outbreaks that have occurred, so that we can actually control the disease and make sure that it doesn't spread to a number of other premises.

Obviously confirming the diagnosis and we're going to go through the diagnostic testing in a moment. And they talk about 3 nasop pharyngeal swabs 5 to 7 days apart, in cases and in contacts, and I think there's plenty of evidence of, body of evidence to suggest that that's a nasopharyngeal swabs are not the most appropriate way to diagnose these cases. And therefore we should be maybe using some other techniques.

Informing the relevant breeder Association, I'm not really sure why that's in there, but whatever they can, they can say that. And then obviously the use of endoscopy to eliminate carriers. Why is it important?

I, I, I think that's a slightly facetious question, but, what's important is that the techniques for diagnosis of strangles will vary dependent on the state of the outbreak itself or the need for, for testing. There are 3 main groups that we should be talking about when we're considering the diagnosis of strangles so that we can choose the most appropriate tests. So first of all, we've got the early suspected cases and it's important in these ones to establish whether the strangles is the cause of the disease and therefore get a definitive diagnosis as quickly as we possibly can in control of the outbreak.

What's important to note is that we see in the UK about 30 to 600 reported outbreaks a year. And so we are seeing a lot around the UK and amongst all the practises. Once the outbreak is controlled, we're talking about then the apparent recovery, so recovery, so is the horse still contagious?

How are we going to give a free from infection, agreement? And also significantly 10% of infected horses can become carriers. So how are we going to establish whether these horses are free from disease as a carrier, let alone as an acute infectious disease?

And then also finally is screening horses, new horses as a a way to identify carriers. And this is definitely a more controversial topic, and I've got some recent researchers as of the last sort of year that might sort of highlight why we shouldn't be using serological information. So the diagnosis, we've got different ways of sampling.

So nasopharyngeal sampling is the, the most appropriate in your acute stage. So when we're talking about that outbreak on the yard, this is what we're aiming at. Not nasal swabs, we shouldn't be using those, and the reason for that is that there's a lot of commensal bacteria that could be causing other diseases, especially if you culture the strepre we could be overgrown and therefore give you a false negative.

If you're doing a PCR, then you might get a positive result, which is great. So positive gives you a definitive answer, and negative doesn't give you that definitive answer. Nasopharyngeal swabs will come on to a moment.

Actually, what we can see from some research is that nasopharyngeal lavage is the most appropriate in the acute stage. And what that entails is using something like a dog urinary catheter, instilling about 150 mLs of saline up the nostril into the nasophararyngeal region, and then collecting the discharge as it comes out of the nostrils. And that's got the highest sensitivity for for picking up strangles.

Next is a guttural pouch wash. This is only for the carrier status, so, you know, there is absolutely no point in using a guttural pouch wash when we consider doing, when considering an acute case. So please diverge those two tests, because nasopharyngeal swabs and nasopharyngeal lavage is very poor for carrier status, guttural pouch is pointless for, acute cases because the retropharyngeal lymph node has not abscessated out yet into the gutural pouch and therefore, probably no bacteria in there.

And serological testing, a single sample is pretty much pointless. I don't see any, any rationale for doing that in any setting. Paired titers are very useful, but we have to be aware of both false negatives and false false positives when we're talking about serological testing.

What's important though is if it looks like strangles, it probably is, so trust your clinical acumen and if you're fairly convinced that this disease is strangles and you're getting a negative result, retest, do a different approach and try and get that answer for yourself. As far as I've mentioned, . Nasal swabs pretty much pointless, so I wouldn't bother doing a nasal swab, unless there's a really good reason.

The horse is very difficult, or, you can't sedate or something along those lines. But a study, a prospective study a while ago looked at assessing the identification rate and found that nasopharyngeal lavage was the most consistent sampling technique. And when PCR was used as the isolation modality, and then combined with culture, they were able to determine that 53 out of 57 samples were positive.

And 3 horses were negative in all tests, in other words, 56 out of 57 were the correct diagnosis and 1 later became positive. So pretty high specificity and sensitivity. With PCR alone, so rather than doing PCR and culture, nasopharyngeal lavage managed to identify 48, nasopanal swabs 41, and nasal swabs, 45.

So you start, when you take away the, the parallel testing of using both sorry, PCR and culture, you see that the sensitivity and specificity massively increases, increases. So let's say native angela virus test, native ngeal swab, not so much. 3 samples as they recommend is about 60 to 90% accurate when you're talking about culture alone.

And if you use PCR you can get a greater than 90% accuracy. So it is quite good. The one big caveat I would say is that in a study looking at this, what they found was that there were some horses that were carriers that never shed bacteria.

So although you're going to get a lot of them with the nasopharyngeal lavage, sorry, swab and all lava, you're never going to get them all. There'll always be one that avoids, your testing. Going back to culture versus PTR, I think it's important just to discuss a little bit further into it.

So culture obviously is going to confirm your active infection. And it's gonna differentiate your bacteria, in other words, is there strep equi equi or strep equi epidemics or a different, infectious cause. So I think it's important, it is a, a very useful technique.

It is prone to false negatives, and that can be because there's overgrowth of other bacteria, or it could be that the neutrophils are suppressing any growth as well. So be aware that a negative doesn't always mean a complete negative and can take up to 48 hours. PCR on the other hand, confirms the presence of the bacteria, but doesn't confirm whether or not they're dead or alive.

It's very quick, so same day turnaround, very specific. It's only going to pick up strep que equi. Our test will confirm whether they strep zoo at the same time, but we'll pick up strep que equi separately.

So in some ways, there's a risk of a false positive incentive if these bacteria are dead. And interestingly, there was a recent study that was trying to sort of highlight this risk, and they looked at the risk of false positives, in endoscope. So, they infected the biopsy channel of, 18 different endoscopes with strep equi equi, and then disinfected via various different methods.

So, this is normal flushing, brushing, sort of keeping in med quis, or some, sorry, keeping in, cold sterilisation. And also, then doing gassing as well. And what they found was that on culture, only 1 out of 18 was still positive, which is also very concerning that the cleaning process was unable to kill the strep equity in every single setting, which is, you know, it should be able to do that.

But also that the PCR was positive in 13 out of 18 or 72% of those biopsy channels. So it can really highlight that all of those were probably negative in the sense of an infectious disease process, but positive on PCR. So, we always recommend that you do culture and PCR at the same time, and even if you're really worried, you could add a cytology onto the fluid because if you've got no neutrophils, then it's unlikely that you've got an active infection going on.

Oh, this data is from another study, that indicates the poor diagnostic quality of direct sampling. And this study evaluated each technique, so that was nasal, swabs, nasopharyngeal nasal lavage, individually rather than in combination. And as you can see, actually, the techniques, although better with PCR were still pretty poor throughout.

So when we look at culture versus PCR for nasal, 37 and 53% sensitivity with a nasopharyngeal swab, 37 and 72, so it's starting to get a bit better, and nasopharyngellivva 1984%. So, when we combine this with the the information from the Lindahl paper, the one before, we can see that if you get a culture in PCR, we, we can increase the, actually to 93%. So, and then if we take away those three cases that were completely negative throughout, you get 98%.

So again, this is another study that confirms we should be using two modality, laboratory techniques, so the culture and the PCR in parallel to get our most sensitive diagnostics. The problem is obviously that there is a cost associated with that, and often owners aren't willing to take that cost requirement on. This is some historic looking at ANT with a.

A carrier status infections. And I would like to point out that this is very much being superseded, and I'll put it in here for interest to show how the new data's coming out. And this was looking at carriers with just the A, with just the B or with a combination of the A and A and C, sorry, I've I've written the A and B, A and C.

What they found was that about 32% of positive tests, positive results, did not confirm carry stats. In other words, 32% of those who were coming out that were positive were false positives. So lots of horses were getting swabbed for or gut or pouch for no reason.

But what it's saying to me is that 30% of the case, That we're getting a large percentage of the cases, sorry, that actually need guttural pouch washes, nasopharyngeal washes, and actually you can't trust the results to make that decision. 90% of carriers will test negative, so you're gonna get a whole raft of of carrier horses coming through that aren't being tested positive on your ANC. And finally, about 4 negative tests were wrong.

It's unlikely that a negative on this day that a negative test is a carrier, but also a positive result doesn't actually tell you anything. It might be a carrier or it might not be. So what is the use?

And so some more recent information from Andy in 2020 looked specifically at the ANC and looked at whether or not these cases had guttural pouch. Endoscopies were formed, and if they did, whether or not they then had strep query in those guttural pouches. He then further then categorised the serological results with the optical densities of greater than 0.5, which is what the current guidelines per the test manufacturers is as a positive, or as a, a greater than 0.3 to try and increase the sensitivity and specificity of the disease.

But what he found was that there was actually no serological testing, sorry, serological testing had absolutely no correlation to carrier status. When we look at the ODU ratio of 0.5.

We can see that when that is positive, in other words, indicating that there is a carrier status in that horse, as they deem the information to be true, we can see that one of those cases had guttural pouch, empaima with or chondroids with, strep equi equi in it. In other words, 98% of the positive results were incorrect as false positives. 2% were diagnosed correctly.

If we then look at the other way round, we have about a 3% of false negatives. In other words, 8 horses were negative on the serological testing but were carrying strap equi equi. If we then increase or decrease, sorry, the OD ratio to about 0.3, therefore, trying to increase the sensitivity and specificity of this test, what we then get to a point is that 95% were diagnosed incorrectly, so 64 out of 67, were saying that that it was positive for strep re equi when in fact there was nothing there.

And 5 2.7 were false positives, so actually we don't really help that ratio out all that much. So, in our opinion.

There's actually no point in using serological testing for carrier status. It's absolutely, absolutely pointless. You may, flipping a coin is going to be more accurate than using the serological testing in carrier status.

So is there a place for serological testing in any stable settings? And I think there is, yes, you can use it in the face of an outbreak. And by that I mean use head serology to show a rising type.

And it's often worth spinning and freezing the samples so that you then run them at the same time. And what that does is it confirms exposure. It doesn't confirm anything else, it's not telling you anything at all with whether there is a correlation with carrier status.

So can you use it to give an all clear, and I think the answer is no, because unless you can categorically say all the horses were clear as strangles before the outbreak, and therefore done paired tighter, and everyone's negative, then that I could believe. But nobody can guarantee that a yard has no carrier status horses on it, or very few yards can do that. So I don't think we can use serological testing as a, a, a means, and only means to way, to give complete clarity on clearance from the infection.

But what serological testing should we use? So, I'm sure lots of you are aware that we use at Lihook, we use the SEM tighter, whereas other, laboratories are still currently using the ANC, and I think there's some, some proof that we can maybe really thinking about which ones we should use. The ANC, the, is looking at antibodies to antigen A and antibodies to antigen C, whilst the SEM is a protein that minus the terminal kind of not required information, but there you go.

So Andy has been doing this study. It's currently unpublished, and so he's happy to share this information. And hopefully it will be published.

We used two laboratories so that we didn't have any bias, no perceived bias that we are against the ANC, and what we did or what Andy did was looking at the inter and the and the intra assay variability of these tests. I'm just highlighting the inter-assay variability, and the intro was not very good either. What we're most interested in is the CD values, and just for information, for in a variability.

What we would classify as acceptable is 10 to 15%. In other words, the result can range between 10 and 15% when you do different tests in different places. Most tests, most laboratory-based tests are around 5%, and that's what we would really sort of be hoping for.

What we can see is that the SEM sitting about and what we're looking at, sorry, in this first row that's highlighted is a low level, so, a serologically low value, 0.1, 0.2 on the ANC or or sort of in the tens of the SEM.

And you can see immediately that these these numbers are pretty poor, particularly on the ANC with a 36% and 56% interSA variability, and it doesn't really look much better when we go all the way through the mediums and the highs. And what we're particularly concerned about is the highs are fine, you know, if they're high high then actually a little bit of variance is a problem. If they're low, if it's staying in the low, it's when you're in that middle area that oh we make a decision.

The disease process is actually a carrier or an active infection. And yet that that result is going to vary by up to 40% each time you make the test. So, in other words, from this information, we should not be using the ANC because the inter-assay variability is so poor and therefore you cannot rely on the results being consistent from one day to the next.

So, we would always recommend using the SEM tighter. And there was a lot of sort of talk when we first brought it out that we were getting a lot more false positives, on the SEM and we absolutely do get false positives. So I'm not claiming that the SEM is perfect.

It's, it's far from it, and I don't think we should be using it for carrier status. But we got no more false positives than the ANC did either. So, from that perspective, that that's a moot point.

More recently, we've been looking at the strangled vaccination. So there's a new vaccination that's just come out, Strangacker sounds very exciting, and I'm gonna sort of go through some points which sort of might highlight some concerns about the vaccination itself. So the primary course is at 0 day 0 and 4 weeks with a booster every single 2 months.

And that's by the SPC. Now they're saying verbally that that can be stretched out, but, you know, if we're following the rules, which we should be, if we're going to use a vaccination, they should be giving it every 2 months. This information on the right hand side the graph is following vaccination and then a challenge 6 weeks after the primary vaccination.

So vaccination day 044 weeks sorry, and then challenge at 6 weeks. And this is sort of what you'd be talking about and trying to do it in an outbreak situation, you know, if you had an outbreak on the yard or local yards, you'd be looking to vaccinate in that short term. And what we can see is that, although the pyrexia, the dark blue line in that graph, is lower than the placebo, we are still getting a pyrexia.

And I, I've sort of gone against what the paper said. The paper said that the pyrexia is classified as 39 for 2 to 3 days. I would say 38.5 is your, your pyrexia and once is still a pyrexia.

And so actually all of these horses are pretty much getting pyrexic episodes. And also on the right hand side, the, the, the, the other graph is saying how many abscesses these horses get. So there is a decrease in your abscesses from 2.5 to about 2 per horse, but it's not all that big a difference in, in my opinion.

Then the second telegraphs are after approximately 2 months, where these horses, although they are not as pyretic, they're still flirting around the pyrexic line of 38.5. You have got a reduction in the number of abscesses, but they're still present.

And so the aim of this vaccination is to reduce the frequency of yorexia. It probably reduces it a bit, to reduce the number of abscesses, it seems to, but significantly not to stop all shedding. And also these studies were only performed on a pretty small number of horses, so we don't have enough data, in my opinion, to be able to say for certain how efficacious this vaccine is.

Also from my point of view, if you have a really good look at the SEC. You can see that there's a significant number of complications that they state, and this is different to the the influenza vaccines which are nowhere near as bad on this front. So pyrexia in 1 to 10 horses, localised tissue reactions in 1 to 10, ocular discharge in 1 to 10, and then less commonly a a loss of appetite which would fit with the sort of consistent vaccination levels.

They are stating that they're not seeing these reactions in clinical situations, but whether that's just a lack of reporting or whether they really aren't, I don't know. There's no data on the safety of using the vaccine when the horses have previously seen it converted. So in, in America, they advise against it, but it is a different vaccine, and, Andrew Weller was saying that the, the current vaccine doesn't work on the, this, the SEM protein, which is the bit that causes the, the vasculitis.

So, there might be some, some safety there, but, they can't claim it as safety. And significantly, vaccinated horses still get the bacteria. But for me, to sort of summarise the vaccination, I'd say the frequency of boosters is a bit extreme every two months.

I can't see too many people wanting to do that, especially with the rate of complications. Significant range of advert reactions, although they say they're not seeing them in clinical cases, is it a lack of reporting? The lack of complete resolution to design, you know, these courses are still pyre, and there's absolutely no data on whether these are shedding or not out in the literature.

So, you know, the whole point would be how much they're reducing the shed of the vaccine of the bacteria as well. So really the, the vaccine is not gonna make a huge difference to your isolation protocol. So I, I struggle to, to see too much of a point there.

And finally, looking at the survival of trap qui equi, I'm sure some of you might have seen this data. But to discuss when we talk talk about how to isolate. So there's all sorts of things out there.

There's one that says there's brief survival, there's one that's 3 that say about 3 days. There's one that is greater than 1 year. So what are we meant to do with that information?

Andy, in his wisdom, did a study in about 2015 in his garden with a shed and various other things. So he looked for various items, wet buckets, soles of shoes, plain wood, stomach tubes, rafts, overalls, fence posts, all things that you'd hopefully come into contact with when you're out and about, in, in a clinical setting. I mean, he looked at it in both summer and winter thinking that desiccation would obviously take the bacteria out a little bit faster.

What we found is that, you know, the survival in winter, so the, the solid dots was pretty short, you know, there, there's some going on beyond about a week, whereas the survival in the winter, was pretty significant and carried on for quite a long time. And so through summer, the stomach was the most long lasting, probably because it's damp on the inside, whereas in winter the bucket was the most significant. So it is important to be aware of the, the longevity of survival so that we can advise appropriately whenever we're dealing with an outbreak, making sure all these things are cleaned, because remember that the bacteria is pretty wimpy when it comes to biosecurity, and so good cleaning will pretty much clear it away from anything.

We're we're going to talk about treatment per se, it's a couple of notes, because obviously we're always worried about resistance out there, and whether or not we're going to see that in any bacteria at all. There's very limited research or data out there showing any resistance, thankfully, it's always a worry. Interestingly, Andrew was presenting some data when he was talking about the vaccination, showing that there is some evidence genetically.

That the bacteria is now getting a betalatamase resistance, and therefore could lead to a penicillin resistance. But we're not seeing that clinically yet, so I don't think we need to change our our antibiotic choices or anything like that, but it's always a worry that it could be coming. One study which terrified me was that they showed vancomycin resistance.

I don't understand why in any world it was acceptable for them to be using vancomycin to treat strep que que. So please don't ever use it, don't even think about it. It shouldn't even be a, a name that you know, .

And therefore continuing to use penicillin, primarily as the option is correct. And then in some of the lesser cases or the longer standing cases moving to TMPOS TMPS or doxycycline, being aware that TMPS acidic environments is not going to have much of an effect. And also that doxy has a bioavailability issue, so there's, you know, it's highly variable, so you've got to choose pretty carefully.

So that's it on strangles for now. Hopefully that covered a few interesting topics. So we're gonna talk about equine herpes virus for a little bit.

I'm mostly gonna be talking, or alluding to the neurologic form rather than the abortion form. That's purely because it's more what I am involved in, and sort of, in my world, a lot more catastrophic than the abortion. Obviously, if you're in a high breeding area, the abortion would take a lot more precedent, and is, is more common.

So, a brief introduction, you've got to think about your stereotypical signs, often starting as a respiratory disease with pyrexia and cough, and then the sort of the more concerning options are the late term abortions, the neonatal foal deaths, chorioretinopathy associated with vasculopathy, and then significantly equine herpes myoencephalopathy EHM that's causing the neurologic diseases. And in those cases, the neurologic signs are ataxia, in all fallen, but worse in the hind limbs with paresis being the main clinical symptom, urinary incontinence or an inability to urinate, fever, and often multiple horses being infected throughout, the yard. Interestingly, latent infection is thought to be in around the 80 to 90% of the population, although not definitive, and the significance of that is hard to understand at the moment.

There are some risk factors that we're aware of that seem to highlight whether or not a horse is going to get EHV, so horses over 20 seem to be more likely to be affected, although any age can be, and, you know, we, we definitely saw some of the younger horses being affected. Highest in autumn, winter and spring, probably just due to what's going on in the world, high temperatures in the environment, new horses in the herd. Females greater than males, so this is from the Henninger paper that I'll come on to in a little bit when it comes to vaccinations.

The, the, the study was a very good one. It was a very observational study, so, but I would, I wouldn't take too much information on that, to be honest. And then the stress, the immune status cause a problem with this disease and then that's a very unknown, and actually we are looking at that at lippo as to whether or not recrudescence occurs when horses is transported, when horses are hospitalised.

And so hopefully that will come out. Now, some previous studies have shown no, but when we had the EHV outbreak here, we had one horse apparently re-rede and shed EHV for one day. It never had any clinical symptoms, it was a different viral strain to the one that was, being presented in, in the clinical cases.

How does EHB cause EHM? And so what we're talking about is primary respiratory, infection. It affects the epithelial cells and then it's trafficked into the submucosal tissues by intracellular transfer to monocytes and lymphocytes.

And these cells then spread throughout the body, to local blood vessels, respiratory tracts, lymph nodes, and then virus amplification occurs, within the lymph nodes. These infected lymphocytes and monocytes enter the lymphatics with systemic blood circulation, thus establishing our cell associated biremia that we can pick up on the buffy coat. This viremia disseminates the infectious virus to sites of secondary replication, so that can be the endothelium of small blood vessels, whether that's within the placenta or within the spinal cord, most importantly.

And at that stage, you then get a secondary viremia, and replication period. Where that those cells, where the virus has landed in the endothelial cells, you start to see a resultant vasculitis and thrombosis formation. And within the spinal cord, and the placenta this then interrupts the blood supply, the oxygen supply, the, the nutrition supply leading to to damage and cell death.

As a very brief point, the equine microcoillion is very susceptible to thrombus formation as it is supplied by a single arterio and venule. Thus, if that gets affected, we start to see unzipping of the epitheliochoreal equine placenta, and a red bag abortion. Whilst going on, this will also infect the foal, so we start to see the virus positive foetal liver, lungs and thymus that can be picked up at postmortem.

In equine herpes myocephalopathy, the same sort of thing applies, that there's a one single vessel coming into the spinal cord that then disseminates out into all of the different parts of the spine. And wherever the damage occurs, you're gonna get swelling of neurons and haemorrhage with the extent and localization of the neurological lesions, determining the nature and the severity of the neurological clinical symptoms. Interestingly, the spinal outflow to the caudal and sacral plexus is the most often affected, which is why we start to see the caudal clinical symptoms.

So affecting the pathogenesis, we know that the route to infection is a combination of infectious dose over time, so in other words how much virus these forces are exposed to, versus the innate and specific immunity. But importantly, specific immunity is not a binary setting and therefore it is prone to steady decline over time from vaccination or previous exposure, or increase depending on the state of vaccination. So, there's a whole raft of components within this life that are going to decide whether or not that.

Viral load that that horse is being exposed to is going to breach the dam of the innate immunity and lead to clinical symptoms, or whether or not the horse is going to be able to avoid it. But how far has it spread? And I think this is a significant conversation when we talk about isolation and trying to deal with an outbreak.

And I think limited information, punitive information, sorry, on how far the aerosolized form of EHV spreads. AAP recommends about 10 metre separation between each horse to guarantee that there's no spread. In 2009, Paula looked at this, and showed it could be detected about 14 metres away, but this was an artificial setting where he aerosolized the, the, the virus and then used a machine to detect it, at different settings away from the aerosolization.

So a little bit different to a horse coughing in droplet form. And there's a bit of a parallel, we know that in bovine herpes virus one, we know that less than 4.4 metres, very specific, increases the risk of infection significantly.

So we can probably assume the same is true for EHBs, given that it's the same sort of, same genus of virus. The most effective way to spread it, it's mere spreading, in other words, nose to nose contact, so by avoiding. You know, contact you can massively reduce the risk of heading in the risk of the outbreak getting out of control.

Obviously it can also be phone mics, so it's important to maintain strict biosecurity, and that can really alleviate the problems of an outbreak. So how are we gonna test for EHV and I think in the acute phase, it's pretty simple, from infection, from the day of infection, you have about a week to test, nasally for PCR to guarantee you're gonna get a positive result. The blood er using a buffy coat for PCR is a bit more hit and miss because you could be in that primary or secondary biouremic phase.

But if you miss that, there might still be an infection going on, you're just not getting a systemic viremia. So, nasal swabs rather than nasopharyngeal swabs are absolutely acceptable. So Nicolaster again looked at some research showing this and found that the sensitivity and specificity of both were equivalent and therefore, it's a lot easier to do a nasal swab than it is to do a nasopharyngeal.

You should be using about a 15 centimetre swab so you can get into the nose. Ideally using both nostrils. For one swab, you don't need to use two swabs.

And doing it for 5 to 10 seconds to make sure you get a good amount of of viral load in the endothelial cells in there. So when you compare, this is Kerala paper looking at the swabs, we can see that in nasal swabs when they were positive, about 9 out of 28 were negative on the nasopharyngeal swab, whereas actually the other way around, you had what appears numerically to be a more sensitive test. But when it came to size, at true sensitivity and specificity and, whether or not the P value was reached, it, it didn't have any difference, so.

Fine to use nasal swabs. As I mentioned, you could do a PTR on a buffing code, and I think it's always useful to do this in the early stages when you're trying to decide whether or not an outbreak is occurring. But I wouldn't use it as a primary diagnostic modality, because, as I said, the viremia can, can shift around, so useful in parallel, not on its own.

And serology, and it's very much like strangles in the sense of sero conversion is very, very useful. So if you do a paired tighter at the beginning and at the end, you can be fairly happy that you are showing whether or not that horse has been exposed. But again, individual samples are pretty much useless.

What's good to note is that you should be taking swabs on a regular basis, and not just doing it as a one-off if you're worried, because, they, they can shed intermittently or shed very low levels in the neurologic phases of the disease. And, one of the vets over in Valencia showed this with the French horses where they tested multiple times over multiple weeks and horses would intermittently shed a virus and then stop. This isolation is obviously the gold standard you can categorically say which virus it is and whether it's infecting the horse or not.

But it's also very difficult, time consuming, and if there's a low viral load to get it in an egg, it is quite difficult. So useful from the monitoring perspective, especially, you know, the HT used to do that, and, Richard Newton is still doing it in different setting, so it is a useful technique. CSF sampling can be used, you know, in the acute neurological case with anacromia, but it's fairly non-specific, and just again, probably a parallel test rather than an individual test.

How to remove restrictions, so we've decided we've diagnosed E3, we know we've got the disease, how are we gonna get that yard out of isolation so that everyone can move on with their life. Difficult to set the strict protocol for every single scenario, so I think you have to then decide how to do this depending on the context, the location, the horses involved, so don't take any of this as the definitive answer. In Valencia, interestingly, the French team, when they were starting to come back into France, decided to place all horses in isolation, and they required two negative swabs each a week apart to prove negativity.

And they had multiple horses go on testing positive for many, many weeks and as I said, shed intermittently. That was a strict critical. When we had a small outbreak here, well, we had one clinical case that came in into isolation.

Thankfully it didn't spread anywhere. We felt confident being able to use prepared serology, over 2 weeks with multiple swabs, so every 3 days we were taking swabs. And if all of that was negative, then we were happy for the horses to be moved out of the hospital and returned to normal life.

And thankfully that happened. So that was a very easy outbreak, thank God. If you're in the middle of the road, so the more common case where you're, you're in a yard where it's happening, I think paired serology is still very useful.

Negative swabs two weeks after the last cases of the positive would be a pretty good way to know if you're showing any samples, any cases that are still positive. Serious isolation can expedite this, so if you've got the facilities to be able to separate your horses very well, you might be able to, you know, expedite those that are, have never shown clinical symptoms. But again, based on what you think.

So should we be vaccinating for E8 and I'm specifically talking about equine herpes, myoencephalopathy, not for abortion, not for respiratory sciences or anything like that. It's a bit of a contentious issue, so I'll put the COVID up there because I think, you know, there's, there's plenty of contentious issues regarding that. What we know is that vaccination with EHV will, with any of the vaccines, sorry, will result in increased antibodies.

Therefore, it will stop serology being useful in an outbreak. So if you're vaccinated in the face of an outbreak, you will get serological conversion, therefore, you can't use that as a way and a means out. But you can still use nasopharyngeal swabbing, repeated nasopharyngeal swabbing to get yourself out of an an infectious status.

Importantly, there is no licence for reducing signs of neurological disease, only abortion. So, you know, there there is no SPC to say that this is the right thing to do and therefore we are going off licence if we're trying to use it for the reduction of EHM signs. But what you could use it for is to reduce the shedding of VHB dramatically, and we know that occurs that as soon as you're vaccinated, these horses that are vaccinated regularly do not shed as much virus as others do.

And there's no real evidence that it causes neurological disease. We'll come on to those papers in a moment because I think it's important. So.

From this point of view, it's likely it's gonna reduce the spread of disease. Questionable whether or not it causes worsening EHM. Therefore, surely herd immunity might be the right thing to help reduce the risk of these EHM outbreaks being catastrophic.

What we need though is about 70% of the population needs to be vaccinated to reach herd immunity. And we're struggling to get there anywhere near there, we don't even have that with influenza, and that's a very common vaccine. So does vaccination increase the risk of HM and, you know, use some anti-vaxxer pictures, sorry to anyone who, doesn't agree with COVID vaccinations.

There are only two studies in the equine literature that even begin to look at whether or not EHV vaccination is associated with EHM. And I think it's important to point out both of these have their flaws, and the authors don't try and claim anything different. They're both observational studies, so they're looking at outbreaks that occurred and retrospectively looking at the data as to whether or not they had vaccines.

And also they're very different settings to to what we normally deal with. So the Henneer paper was looking at a group of forces that are vaccinated, pretty much all of them were apart from about 3. And the other, the trout Dargats, was a different population to what we mostly deal with.

In the trial of Dagas, what they found was that they, in initial modelling of the statistics, if the the horse was vaccinated 5 weeks prior, within the 5 weeks prior to the outbreak, they were more likely to get EHM. But once they started to bring all the co-founding problems, the variables that were in that paper into it. Suddenly that disappeared.

So actually, when you start talking about age, you know, where, where they were in the barn, all those sorts of things, suddenly the, the vaccine status actually didn't play any role at all. So I would strongly feel that that that vaccine did not play a role, although I can't say it for certain. They did find that mares were more likely than male horses to be affected, but actually the confidence interval was pretty poor there as well.

In the Henneer paper, this was the one where they had tonnes of vaccinations, so the, the numbers were really small in the unvaccinated population, so it makes it quite difficult to make a true, comparison between the two. What they found was that the number of vaccines received in the previous year was associated with neurological diseases. In other words, greater than 2 vaccines in that year seemed to be associated with neurologic disease.

But again, it's small numbers. And I, I struggle to really draw too much of a conclusion from it for for a number of reasons. So in my mind, when you break these papers down, neither shows evidence that vaccination leads to EHM or an increased risk of EHM.

But neither do those papers show that they are not associated. In other words, I don't think we can draw any significant conclusions from either paper to guide us, and therefore we're left with sort of white paper, oh sorry, grey paper decisions. In other words.

Using a lot of advice from different people, different specialists, you know, that I, I'm no specialist in the HM, you talk about the Lutz Goerings, people like that who, who really do know their stuff on this. And they had a round table consensus, a roundtable discussion, for ECIM and the general feeling was that vaccinating to reduce the spread of the virus was was the right thing to do. And because they feel that there's no real evidence that increases the risk of EHM.

So. Their their feeling was, yes, we should vaccinate, their caveats were the serological testing, there's a delay in the immunological response. So if you're talking about an outbreak occurring today and then vaccinating all the horses around, questionable whether or not that's gonna have any effect, but we should be vaccinating in the long term, trying to stop it happening.

But some people, some people still feel it is contraindicated, so you know, it's definitely not a black and white status. From a treatment point of view, I'll just rattled through this. I don't think this is significant for today.

Symptomatic supportive care is obviously essential, so all the nursing, the, urinary catheters, getting them up and down, eye care, all those sorts of things are significant. Drug wise, and I think this is important to just briefly discuss, non-steroidals, there's a very limited evidence that they're, they're going to affect the disease progression, but if they're making the horse more comfortable, all the more reason to use them, you know, if they're lying down like they've got pressure sores or anything like that, all the better to use it. Corticosteroids seem to have their place, because they're probably gonna reduce the cellular response in EHM and therefore reduce the vasculitis, thrombosis, vascular injury.

The caveat that people do often state is that it may lead to immunosuppression and therefore worsening remia. But in the outbreak that we had, two years ago, we, we felt that it was the right thing to do. And so every course that showed neurologic signs start on corticosteroids.

Whether to use antivirals, acyclovir val acyclovir is, is the question. Acyclovir in studies has very poor bioavailability, 1 to 2.8%, pretty terrible, and in some studies, questionable serum levels were achieved.

But in the Henneer paper, they found that the repeated dosing, rather than a single pharmacokinetic dosing study, showed that the values in the serum were reached that would then lead to, some sort of antiviral effect. Vallecyclovir is, has a higher bioavailability, a higher serum level, so it would be a preferential choice in my opinion. Cost can be a bit prohibitive, but if you were to choose one, that's what I would lean on, as the antiviral.

And then low molecular weight heparin and aspirin to try and reduce the risk of thrombosis and vascular injury, is, is advisable as well. Bitcoin influenza, we're gonna sort of skip through some of these things. There's not a lot out there to really talk about a little bit on vaccinations really, so.

We saw an increase in EIA activity in 2019 that led to the closure of racing for quite a long time, and numerous cancelled shows and lockdowns, things like that. What we know is that it has a limited infectious period, only about 10 days. There is no carrier status, therefore, it relies on a chain of transmission to keep this virus going.

Therefore, prevention and control strategies aimed at breaking these chains is essential and can stop the disease pretty quickly. So as I thought all of us are aware, vaccination is fundamental to control, and as soon as we can get that under control, we can, we can stop the disease spreading too far, and biosecurity will minimise the risk of the impact. Clinical signs are harsh cough, anorexia, tachypnea, nasal discharge, lethargy, depression, and anorexia.

I think we're, we're all aware of those. So let's have a look at the outbreaks that have occurred. So, 2019 was an exceptional year.

We saw that there were 216 distinct fosite of infection with multiple horses being affected each yard in the first seven months of the year. With an anecdotal estimate of about 30 to 40% of the equine population being vaccinated against flu, it's no surprise that we're seeing that outbreak occurring, . And what they found was that it was all played one, which has not been in the UK for the 10 years prior to that period.

We then sort of look through the next years, 2020, with COVID, probably stopped, six distinct foci, and then in 2021, we're getting back to a more normal routine of about 36 cases, with 77% of them, showing that a horse recently had come in from, from Europe, causing the outbreak. Oh, sorry, that, that last point was that in that outbreak in 2019, what we saw was that all vaccine brands had positive cases when horses were vaccinated. So although the vaccine is good, it is not perfect at stopping disease.

What it's trying to do is reduce the severity, reduce the heading. Incubation period about 1 to 3 days in the vast majority of cases, serology is obviously useful to say whether they've been exposed and isolation of influenza via a nasopharyngeal swab should be done within 3 to 5 days of the outbreak. And we can do virus isolation again, which is important from the point of view of epidemiological study, but probably not important in the acute case.

And horses to sample which include those that are unvaccinated with flu symptoms specifically, any vaccinated with horses with respiratory signs because they, they could just be suppressing and therefore showing mild respiratory signs or any intact horses with a known flu virus. The classification of equine influenza is based on subtypes of the location and the year of the isolation. Hemoglotin, hemoglutinin and neuraminidase are essential to the pathogenesis of the virus, and you see these glycoproteins having antigenic drift, enabling the the virus to evade host immunity, and therefore a difficulty in keeping the vaccinations up to date.

These are the ones that are most commonly circulating around the world, and Florida Clade one was the one that was occurring in 2019. The current guidelines are a little bit difficult, so OIE, the guys who were guiding us on this said that in 2010 the recommendations were, sorry, in 2019, the recommendations were still the same as 2010, which is when they had their, their last significant discussion about it. They go on to state that it is necessary to, it is not necessary to include an H7N7 virus or an H3N8 virus in the Eurasian lineage, as they have not been detected in any recent surveillance, and therefore, vaccines should ideally involve clade 1 and clade 2.

What I would state, we're gonna move on to which vaccines have that, is that there is a lack of evidence as to which vaccine is better, i.e., having both plates, is it significantly better or not?

We don't know. . Therefore we could probably lean on the OIE if there's a problem with supply, as there is right now, then we could lean onto the one where there's the most clades in this as possible.

Interestingly, there was a recent study that showed that actually mixed vaccination, much like the COVID vaccinations, increases the antibody levels and therefore might be quite good to mix your vaccinations up. So within the UK there are 3 licenced products available for vaccination against EI and they're all quite difficult. As we can see from the table, only Equilis Proquenza and Protec flu have late 1, whilst late 2 is only available in the Protec, flu, which is the one that would be appropriate by the OIE guidelines, as the the most appropriate.

EIP, only fulfils the OA guidelines from 24 years ago, regarding the lineages that they are using. So questionable whether or not we should be using it, but what they say is they've got data that shows, significant antibody production that would actually help with protection against horses. So, I, I would take it with a pinch of salt personally, and I would lean on the other two, particularly on the Prote flu, and then, going on from there.

Recently, there's been some work about current vaccination guidelines, some new stuff coming out from the VHA particularly. So before January of 2022, we were looking at the historic route, which is a vaccination on day 0, 21 to 92 days later, 150 to 250 days, 15 days, and then not more than a year apart as the boosters. What they're now saying is the BHA is day 0, 21 to 60, 120 to 180, and then 6 monthly to maintain a level of immunity which we know is correct.

As an example, protecting guidelines though on their SPC is the, interval presented by BHA. So I would recommend that you follow the sort of the grey area between the two, between the, the BHA guidelines and the Prote guidelines to make sure you are fulfilling the SPC, and therefore fulfilling the licencing agreements of, of that vaccine. That means that if there are any reactions or there's a breakdown or the horse gets the flu, you're far more likely to have a positive response from the drug companies.

All other current bodies are sticking with the previous rules, so just be aware that it's best to check with any of the, whoever you're competing with, to make sure that they are using the correct guidelines whenever you start. Has there been any new research, and the answer is not really, I don't think there's nothing much changing. There's lots of reviews on different lineages.

There's stuff saying that there's been zoonotic about 30 cases around the world in the last sort of decade of, of strep equity equi affecting people. And then there's a little bit of research on whether you can give the HP and EI vaccinations at the same time and falls and the answer is yes. But yeah, really, when I did a search I didn't find anything significant in the flu, that's clinically relevant.

There's lots of research going on out there. In the final 5 minutes, I'm just gonna talk about Lyme disease and my dooride because as I say, I find it a very interesting disease. Is it important?

And the answer is we, and I know it doesn't seem to matter how much research and how much talk we do, we don't seem to be progressing with with this as a disease. I think there's a few reasons for that as well. Picks are most active in spring and summer, so, you know, if you're trying to diagnose it in winter, it's probably unlikely.

In Europe, 1 to 5% of tick bites in humans leads to an infection with Lyme disease. And in the UK about 2.5 to 5.1% of ticks are infected with Borrelia bidorferi.

So, you know, it is very much out there and there are some far more affected areas in the UK than there are elsewhere. It appears that human cases are on the increase, unknown whether there are any increases in the equine patients. Well, the transmission is a 2 year endic life cycle.

It's quite a long old life cycle, and you need the ticks to be latching onto the mammals, and they need to be staying on there for 24 hours to get the the Berelia to spread into the blood system. So if you're removing them quickly, you're probably not going to be in cases. With the clinical time, the bacteria often reside, on the thinner around synovial structures, and so you start to see stiffness and lameness, myalgia, hyperthesia, changes in behaviour, and you can get neurologic signs.

Now all of this is very much lifted from human literature and. Imposesed onto our horses, there's no studies to show if we infect with Borrelia, you get these clinical signs. So I, I would be cautious in overinterpreting abnormal behaviour, but it is possible.

In a limited number of cases we see this necrosupparative to non-supparative, prevascular. If you meningoaddicular neuritis, in other words, this is what's causing your neurologic sign. So it's limited.

I've never seen one in the UK, saw them in America, where you get the neuroborreliosis, and they start as ataxia, facial nerve paralysis and, finally, head tremors, which is very consistent with the human neurologic form. There are some other disease processes out there, so there's some evidence of uveitis causing it, but it's only in a couple of horses in a couple of studies, so really not a significant form of uveitis. Pseudo lymphoma, the picture from the right, which is from the study from, in May in 2011, which, resolved with, with treatment.

Neal bursitis in 2021 and they treated with safety if you will for 80 days and locally as well, and the mayor recovered very well. Often it seems to be it goes hand in hand with Anaplasma as well, so, always look for that as well. And this is why I think that it's over or under, you know, depending on who you are and what you're doing.

So this is some stuff from America showing that 50% of patients with Lyme disease, remember a tick bite of 50%, 50% don't have any rashes. The EISA test is poor. So they're saying actually it seems to be that most people don't know that they're gonna be affected, and most people would take 5 doctor appointments over nearly 2 years before being diagnosed.

Also, what confounds the problem is that 30 to 40% of patients in an endemic area have evidence of neurological disease. Only about 9% of those will have clinical symptoms. So can we trust testing?

And this was a study done in Bulgaria, I think it was, where it showed that serology had a poor specificity with an apparent ser prevalence of the test of 22%, but when they started being PCR and like microscopy and actual prevalence of 11%, another 60% were false positives. And over there, sorry, Belgium, not bother, in Belgium, 5% of antibiotic use networks is contributed to the Lyme disease, so it's really significant that we should be trying to avoid false positive, diagnostics. But how can we improve diagnostics?

So currently in the UK we use a C6 lizer, and what that is is is C6 involves antigenic variation of the bacteria and their survival, therefore survival in the host. But all it does is it confirms exposure, not active infection. And when you're talking about a a serro prevalent disease that is, is endemic, serial conversion doesn't really mean much.

There is a multiplex in Cornell, which starts to sort of separate some different proteins which are involved in various stages of the bacteria's life on the outside of it. And so by grading the different Os OSA in the hindgut Osy during transmission in F in the horse, you might be able to say whether or not there is an active infection. But it's also not that clear cut, and also quite a lot of money for us to send it over there.

But the ACVIM guidelines are don't test if you're in a prevalent area unless you have a really significant reason to do it. And if we do decide to do what you'd be treating with. In humans, they're actually very strict, so if you've a cutaneous form, they may only give you antibiotics for a couple of days.

If you've got lameness or neuroborreliosis, you go up to a couple of months. But actually the vast majority is a 70 day, treatment, followed by more antibiotics if required. So normally I recommend IV oxytetracycline.

You can do doxycycline, but there's always the question about low, lower bioavailability in a theoretical, therefore theoretical risk that it's not getting up to a high enough level. Millicycline is very good, it's very bioavailable. It's got better distribution to the CSF and Is.

So in reality, in a very difficult case, that would be my primary choice. Do they use metronidazole, in the really difficult cases, but I, I would be reticent to do that unless there was absolute definitive diagnosis of, say, neuroborreliosis. And if you're gonna do any of these go for a prolonged time monitor renal function.

I think what's also important is just talking about the risk of, of antibiotic use. We, we've had a hawk recently, that we, we struggle with oxy tetracycline, we've lost a couple of colitis, so be sure that you really want to diagnose these cases and treat them as such, if you're going down that route. So I think we've covered a good few things here, I hope that's been helpful.

Strangles diagnosis diagnosis is more complex than it really should be, but if we break it down into our acute chronic and carrier tasis, we can be a little bit more understanding of it. Diagnosis can be easy in EHB and I think vaccination may help, but it's a decision you have to make with you and with your owner. And influenza, we've got to stick with the vaccinations to keep that under control.

And finally for me, Lyme disease, don't overdiagnose it and care with the treatment because the risks may outweigh the potential benefits that that you're getting. Thank you very much for listening.