Update on EHV-1

Just a brief update on my last post, as the USDA released the latest stats on the EHV-1 outbreak last night.

     The incidence of equine herpes myeloencephalopathy (EHM) - i.e. actual neurologic disease caused by EHV-1 - remained very low, and only 11 deaths were reported for the more than 2,000 horses exposed.

     Here's a summary of the relevant stats:

• 415 horses were exposed at the event (primary exposure)
• another 1,635 horses were exposed via contact with horses returning from the event (secondary exposure) or via contact with horses exposed to the horses... (tertiary exposure)

     Of the 2,050 horses who were exposed, only 75 horses (3.7%) were confirmed as having EHV-1 infection or disease:

• 47 horses (2.3%) were confirmed to have EHV-1 infection but no neurologic signs
• 28 horses (1.4%) were confirmed to have EHM (i.e. EHV-1 + neurologic signs)

     Of those 75 horses confirmed as having EHV-1 infection or disease,

• 58 horses (77%) were primary infections
• 17 horses (23%) were secondary or tertiary infections

     So, although the exposure rate was high, the disease rate was low. Also, prompt quarantine measures seem to have been very effective at limiting secondary and tertiary infections.

     Assuming that all of the 11 horses who died had confirmed EHM (i.e. none of the horses merely positive for EHV-1 died),

• 39% of horses with EHM died
• 14.7% of horses with EHV-1 infection or disease died
• 0.5% of all exposed horses died

     So, while the mortality rate in horses with neurologic disease caused by EHV-1 was relatively high, the overall mortality rate in this outbreak was very low.

      And for my clients in Washington state:

• only 35 horses in our state were exposed, all of them primary exposures; there have been no reported secondary exposures
• only 4 horses were confirmed to have EHV-1 infection (but no neurologic signs)
• only 3 horses were confirmed to have EHM
• no horses have died

     Furthermore, most of the confirmed cases were in eastern Washington (Spokane, Chelan, Asotin, and Whitman counties). Thurston is the only county in western WA that has had a confirmed case of EHV-1.

     I think the worst of this outbreak is over now. Lessons learned will likely take a while to be distilled. Hopefully we'll have learned something useful before the next outbreak...

More soon,

-Dr. Chris King-

Nature's Apprentice

www.animavet.com

More thoughts on EHV-1

For those with horses or with friends or family who have horses, I wanted to share some thoughts on this latest outbreak of neurologic disease in horses caused by equine herpes virus type 1 (EHV-1). For those who want more of a primer on neuro herpes and how to deal with it, here is a link to an article I wrote during the last outbreak in 2007: Neuro Herpes

It’s May 23^rd, 2011. We’re now more than 2 weeks into the latest outbreak of neurologic disease caused by equine herpes virus type 1 (EHV-1), and I wanted to share some additional thoughts on this disease.

First, a quick reminder:

• the virus is EHV-1
• the neurologic disease it occasionally causes is EHM, for Equine Herpes Myeloencephalopathy (= disease of the spinal cord and brain)

But it’s important to realize that EHV-1 and EHM are not the same thing, and these terms are not interchangeable. Most horses with EHV-1 do not have, and never will have, EHM.

There has been a lot of research on EHV-1 in the past decade, but still we have more questions than answers. One of the most pressing questions is why only a few horses with EHV-1 develop EHM. What are the factors involved in individual susceptibility to EHM?

Equine herpes primer

Equine herpes viruses, particularly EHV-1 and EHV-4, are very common in horses. In fact, it would not be too great a stretch to use the word “ubiquitous.” Most horses are first infected as young foals, picking up the virus from their mothers, other broodmares on the farm, or other foals. The virus establishes long-term residence in the young horse, remaining probably for life in most cases, being dormant most of the time and reactivating only during periods of stress.

This common characteristic of herpes viruses is called latency: the infection is latent or dormant most of the time and active only occasionally. If you get cold sores when you’re stressed or sick, then you’ll be very familiar with this dynamic, as cold sores are caused by a human herpes virus.

Population studies in horses suggest that at least 60% of horses, and with the more sensitive diagnostic methods, almost 90% of horses in some populations, have at least one strain of EHV-1 in residence. A recent statement by the American College of Veterinary Internal Medicine included this telling remark: “For practical purposes, clinicians should presume that the majority of horses are latently infected with EHV-1.”

And yet, despite the prevalence of this virus, neurologic disease caused by EHV-1 is very uncommon. The outbreaks of EHM get a lot of attention when they occur, but given the size of the horse population here in the US and how much horses are moved around the country these days for competitions, breeding, sale, family relocation, etc.—for such a common virus, these outbreaks of EHM are strikingly uncommon.

Also, during an outbreak, the incidence of EHM in exposed horses typically is less than 10%. For example, although we’re only midway through this latest outbreak, the incidence of EHM in the more than 1,000 horses exposed either at the show or by horses returning home from the show is currently less than 3%. We’re not done with this outbreak yet, but we’ve likely seen the bulk of the EHM cases already, so although that figure will probably increase before all is said and done, it is not likely to climb out of the single digits. As a point of comparison, the incidence of fetal loss during outbreaks of EHV-1 abortion in broodmares may be over 50%.

EHV-1 strains

A lot of attention has been paid to the different strains or genetic variants of EHV-1 and their disease potential. Here’s a brief summary of what we know:

·      there are several different strains or genetic variants of EHV-1, but they have vastly more characteristics in common than they have differences, which is why they’re all called EHV-1

·      all strains of EHV-1 are primarily respiratory viruses; they first invade and multiply in the cells lining the airways, which is also how they are usually spread from horse to horse—in nasal secretions, and less often in a cough or sneeze

·      although EHV-1 is ubiquitous in the horse population, we only occasionally see clusters of either abortion or neurologic disease; and seldom, if ever, do we see both at the same time

·      with regard to its ability to cause either abortion or neurologic disease, there is one primary genetic variant of EHV-1 that I’ll simplify to N and D strains

·      the N strain is by far the most common variant, accounting for at least 80%, and in some populations up to 95%, of all EHV-1 strains; it is also the one most strongly associated with abortion

·      the D strain is much less common, accounting for between 5% and 20% of all EHV-1 strains; it is the one most strongly associated with neurologic disease, being responsible for 75–85% of all cases of EHM

·      however, it is possible for the N strain to cause neurologic disease and the D strain to cause abortion

·      most horses have either the N or the D strain, but a few are co-infected with both strains

But here’s where it gets really interesting. There is some evidence that the N variant is the more recent adaptation this virus has made to the various selection pressures it has experienced over its generations. Evidently, the N variation provides some selective advantage over the D strain. For one, the N strain causes less harm to its host.

The vast majority of cases of EHV-1 infection are seen in young horses, especially yearlings and 2-year-olds just starting in training and competition. In these horses it causes its primary disease: rhinopneumonitis, or inflammation of the upper and lower airways (rhino = nose; pneumo = lungs). Hence its common name, “rhino.” It causes usually mild, flu-like symptoms, and unless it is complicated by some other infection (e.g. bacterial pneumonia), the recovery rate is 100%.

Similarly, in outbreaks of EHV-1 abortion in mares, the recovery rate is pretty much 100%. The incidence of fetal or neonatal death is high, but few, if any, mares die from EHV-1 infection during these outbreaks. And typically, the affected mares don’t even show obvious signs of illness, other than spontaneous premature delivery or abortion.

In contrast, horses with EHM can be quite ill. A high fever is common at some point during the disease, and the neurologic signs can be quite severe, in some cases progressing to an inability to stand. The mortality rate, whether from natural causes or euthanasia, is at least 25% in horses with neurologic signs.

The D strain appears to be quite old. For example, it has been identified in a sample collected from a horse in 1941. In fact, there is some evidence that it may be the original genotype of EHV-1. In other words, the virus probably began as the D variant, but at some point and for some reason, it mutated to the N variant.

This mutation is not stable, meaning that it is not consistently inherited in subsequent viral generations. But that just lends weight to the speculation that this mutation is a positive adaptation, made to ensure the on-going survival of the virus in its host. Internal parasites face the same issue: it is not a good long-term survival strategy to kill one’s host!

The fact that this mutation is relatively unstable suggests that the virus is keeping its options open. What further adaptations EHV-1 might make, both at this specific N/D gene site and at others, remain to be seen. In recent decades EHV-1 has had to contend with widespread and intensive vaccination practices. Immunostimulant use has also increased in young performance horses—primarily for the control of respiratory infections! So, to ensure its continued survival, this virus may have to adopt even more stealthier habits.

Vulnerability theory

Thus far, we’ve established that the less neuropathic N variant is the most common strain of EHV-1 now in circulation. That takes us partway in understanding why EHM outbreaks occur so infrequently and affect so few horses: the more neuropathic D strain is relatively uncommon.

But might there be more going on? And what is it about the D strain that makes it more likely to cause neurologic disease?

We don’t yet know, but the possibilities include higher circulating levels of virus (i.e. greater degree of viremia) with the D strain, so greater potential for damage; and differences between strains in their ability to attach to the cells lining the blood vessels (endothelial cells) of the spinal cord and brain.

Yes, but why the central nervous system with the D strain? (And why the uterus and placenta with the N strain?) Why not other organs or tissues?

That’s what really interests me: why certain cell types, tissues, organs, or body parts are affected and not others. Same for cancer as well as for infectious diseases, injuries, and pretty much any other medical condition. Why there? is the question I keep asking myself. What does it mean that it’s happening in one site or system and not another? And what does that mean for how we treat and prevent this disease?

I’m also fascinated by the concept that viruses are little more than genetic code. They primarily consist of relatively short strands of DNA or RNA—in other words, encoded information which directs the functions of a cell. For the most part, viruses are quite species-specific. They also tend to be quite organ- or tissue-specific. So, infection by a particular virus or a particular strain of a virus tells us something about the individual host’s vulnerability.

Here are some things to ponder about EHV-1, particular in regard to EHM:

·      EHV-1 primarily infects the cells lining the airways so that it can readily be spread from horse to horse, and thus preserve its existence over time. Life is geared toward survival of the individual and perpetuation of the species—i.e. continuation of that life form. When it comes to EHV-1, both its habits and its changes over time reflect this tenacity.

·      EHV-1 hides out in white blood cells, lymph nodes, and in the trigeminal nerve, which is one of the major nerves that supply the face, including the lining of the nasal passages. From any of these locations, it can quickly reactivate and move into the airways whenever the body’s defenses are compromised because of stress or illness. It is interesting that this virus evades the body’s immune system by hiding out inside the immune system. It could only do that if the body’s defenses were somehow compromised by stress, illness, or immaturity.

·      EHV-1 secondarily infects the linings of the blood vessels in a couple of key sites—the uterus and placenta (causing abortion) or the spinal cord and brain (causing EHM). But why disease primarily occurs only in these organs or tissues is still a mystery. It could well be that these are the most vulnerable organs or tissues in that individual at that time. That certainly appears to be the case in pregnant mares...

·      EHV-1 abortions occur mostly in the last trimester of pregnancy, when the fetus is growing rapidly and demands on the pregnant mare are increasing by the day. In other words, pregnancy, while a normal physiological process, is taxing on the system, much like strenuous exercise is both normal and taxing. There are also hormonal and immunological changes in the late-term pregnant mare that may further increase her vulnerability. Perhaps that’s why the pregnant mare is vulnerable to EHV-1 disease and the uterus is the target organ.

·      EHV-1 myeloencephalopathy (EHM) occurs mostly in young adult horses under the stress of training and competition. It occurs most often in busy boarding/training barns and at events such as the cutting horse show in Utah recently. Horses traveled from all over the country to attend that high-stakes event.

·      The central nervous system is the generator of the body’s locomotor processes. Whether movement originates with a conscious thought or an unconscious impulse, the directive is sent to the muscles which enact it via the nerves of the brain and spinal cord.

·      The main signs of neurologic involvement in horses with EHM are weakness and incoordination (ataxia). In other words, the horse has less control over how his body moves, and even whether it moves under his direction.

·      Metaphorically, this state represents a crisis of self-direction and control over how the horse responds to what’s going on around him.

·      It should therefore not surprise us that EHM occurs most often in stressed young performance horses who find themselves transported many hours or days to an event, confined in unfamiliar quarters, surrounded by strangers, and then required to perform at their peak – talk about lack of control!

Combine that with the small percentage of horses latently infected with a D strain of EHV-1, and we gain a better understanding of why outbreaks of EHM occasionally occur at these events and seldom, if ever, at home. From the data we have, it seems clear that horses can be latently infected with a D strain of EHV-1 for life and never develop EHM. It’s not just about the virus. It’s never just about the virus.

Back to the vulnerability theory, a viral infection shows us where we are most vulnerable. With EHM, it is the spinal cord and brainstem—the parts that are responsible for core functions of information processing and response; especially response. It is interesting that the herpes viruses of all types have a habit of latency, re-emerging during periods of stress (i.e. increased vulnerability) to show us where we need to shore up our boundaries and otherwise address our vulnerabilities.

So, what does this mean for the prevention of EHM? I would suggest that, in addition to good food, plenty of rest, loving social bonds, and all the other fundamentals of good health and well-being, we ought to be encouraging as much self-determination, self-direction, and control as possible for the individual horse under the specific circumstances. How you go about that will depend on your horse and your situation. But no matter how you accomplish it, if my theory is even partially correct, enabling your horse to feel a bit more in control of what happens to him will likely go a long way toward reducing his vulnerability to EHM.

Or, you could just vaccinate and cross your fingers J

Copyright 2011, Christine M. King. All rights reserved. 

Primary Resource: Lunn DP, Davis-Poynter N, Flaminio MJBF, et al. Equine herpesvirus-1 consensus statement. Journal of Veterinary Internal Medicine 2009; 23: 450–461.

More soon,

-Dr. Chris King-

Nature's Apprentice

www.animavet.com

Work when you need, play when you want; do both together

Having to close my practice last year was very hard to bear. But now that I'm over the worst of the disappointment, and I've realised that there IS no walking away from one's purpose, I feel strangely liberated. Because if there's no way I can succeed by doing everything the "right" way - the way conventional wisdom says it should be done - then I'm free to try it another way.
     Here's the way I'm doing it now - after having taken more lessons from my dog:

• when there is something that needs to be done, then do it
• throw yourself into it with total enthusiasm and absorption; give it your all
• and then when the job is done, stop; go rest - or play
• as much as possible, combine work and play, so that the work is enjoyable and the play is both fun and useful

In other words, blur the lines between work and play. That way, work ceases to be a chore, we can fit more play into our days, and our play contributes more to our health and well-being. When we get it right, we can end up spending an entire day in enjoyable endeavour (combined, of course, with plenty of rest :-). That's my aspiration every day now, thanks to Ms. Lilly's unstinting instruction.


Play is very important to animals. Have you noticed? And doesn't it stop you in your tracks when you see a mature and ordinarily "sensible" animal gambolling about like a little kid? Doesn't that make you laugh with delight! It does me.
     It delights me both personally and professionally. That's because play is an important indicator that health and well-being are being restored to a chronically unhealthy or depleted system. I've taken to calling it the play index. It might just as well be called the quality-of-life index (as others do), but as return of play is one of the most unique milestones in the return to health and well-being, I like to make play the sentinel event.
     Particularly in senior animals, I'm especially glad to see them begin to play again after what might have been years. It's a very good sign, and it means we've managed to turn back the clock a bit on what was seemingly an inexorable decline.


However you can contrive to do it, give your animals ample opportunity - both space and time - to romp and play every day. With pets such as dogs and cats, the quality of their play is often enhanced by you joining in. I can make Ms. Lilly's whole head crack open in a wide, tongue-lolling grin just by joining her in one of her goofy games. We both end up on the ground laughing at our shared silliness. I don't know of any medications - natural or otherwise - that do quite as much good for body and soul as a fun game played together.
     Horses usually enjoy playing with one another or with another animal they especially like. I'm not inclined to encourage humans to play with their horses unless each thoroughly understands the species differences of the other. "Equal but different" is the catch-phrase of importance here. Horses and humans have different perspectives on life, different responses, and certainly different physicality. Unless both horse and human have made concerted efforts to understand the other and are careful to accommodate the differences in one's playmate, play can be hazzardous to one's health and to the relationship. So, by all means encourage your horses to play, but play advisedly if you're joining in.


Just a final thought before closing this post. I really like adaptogenic herbs for improving health and well-being in working animals, seniors, and others dealing with chronic stress or illness. A few months ago I wrote a pair of articles on adaptogens in dogs - one on working dogs, the other on senior dogs - that are archived on my web site. The one about seniors includes a short section at the end on quality of life and play. Take a look if you're interested (those links are live). The same information applies to horses and other animals as well (including cats, but with all the usual caveats about palatability and the inadvisability of wrestling medications into unwilling cats... :-).


Enjoy!


-Dr. Chris King-
Nature's Apprentice
www.animavet.com

Rest when you’re tired, sleep when you’re sleepy, get up when you’re done.

Apologies for the delay between posts. I was resting... :-)


This topic is mostly for the humans, although it's a lesson I've learned from my dog. (Animals are such masters at taking good care of themselves!)
     For the past several months I've been trying to pay better attention to my body in all things, one of which is to rest when I'm tired. We don't get much encouragement for that in our culture. Quite the opposite, in fact. To rest in the middle of the day - even if just to sit and read a book - is considered lazy, one of the worst things to be in our culture. It's almost better to be a thief than a layabout! Better to be grinding yourself into the ground with constant work than to be perceived as idle or lazy. Naps and playtime are for children, is the message from our culture.
     But here's the thing I've noticed since giving myself permission to stop and rest when I'm tired during the day, go to bed right after dinner if I need, and stay in bed until I'm no longer tired of a morning: I'm shocked at just how exhausted I am!
     Years and years of systematic and culturally sanctioned neglect, coupled with the stresses of starting a new business, only to have the economy fall out from under me, have left me feeling utterly drained.
     Well, duh!, you might say. But really, have you been taking any better care of yourself than I have of me? Your circumstances may be different, but every one of us is labouring under the same strains of cultural expectations, let alone family and personal expectations. Every one of us is overdoing it, slogging away day after day, trying to make a living, trying to prove ourselves worthy, fretting over the fact that we're not doing enough (and can never do enough), and all of the other inane and insane things we humans think are important...
     What would happen if you just stopped? What if you listened to your body for a change, and did its bidding instead of the other way around?
     Why not try it for a day, for just one day? (But note: your life may irrevocably change as a result...) Make it a weekend day if need be, but don't schedule anything at all for the day. Do nothing but the essentials: eat when you're hungry, drink when you're thirsty, pee when your bladder's full, etc. Don't even shower if you can stand yourself unwashed for a day. Do nothing you absolutely don't have to, just for a day.
     When my practice was busy, I'd try my best to make at least one of my weekend days just such a "drop-out" day. I'd feed the dog, feed myself, but other than that I'd do only what I felt like doing. Most of the time it was nothing but rest. I guess I should have cottoned to the fact right there that I was chronically over-tired and under-rested. 
     Since the new year, I decided to damn the torpedos and give myself permission to rest when I'm tired. That doesn't necessarily mean I actually lie down and sleep during the day.  I've never been much of a napper; if I sleep during the day, I wake up feeling like I've been drugged, and I don't sleep as well that night. I used to envy those who can "power nap" (i.e. have a short sleep during the day and wake up refreshed), but I'm definitely not one of them. I seldom nap, although I may lie down and read or close my eyes and daydream for a while.
     By "rest" I simply mean stop what I've been so focused on doing when I register that I'm tired and go do something else. I may go make myself a cup of tea and sit down and stare out the window for awhile or pick up one of the books I'm perpetually reading and enjoy a few pages. Or I may take the dog for an impromptu walk, which utterly delights first her and then me.
     The funny thing is that when I go through the day like this, I'm actually more productive than if I just keep pushing on through, not letting myself rest until after 5 p.m. I'm more relaxed, creative, and inspired to work after I've had a rest. I'm also loving my work more when I don't feel I have to be chained to my desk or running around from call to call for the customary 8 hours a day.
     And I'm finally starting to feel less exhausted.


The same principle applies to our animals, particularly to those who work for us. To the best of your ability, allow the animals in your care to rest during the day when they're tired, and to get a good night's sleep. Try turning off the radio in the barn and the radio or TV in the house if you're in the habit of keeping it on for "company." In my experience, animals are not as comforted by all that noise as we are. I'm not even sure we're all that comforted, either. In fact, domestic animals seem to me to be every bit as overstimulated and under-rested as we are.
   At nightfall, turn off the barn lights and let the horses settle down for the night. Try to do the same in the house for your dogs and cats, at least in the rooms you're not using. Ms. Lilly has been my best instructor here.
     At first it amused me, and then as I got to thinking about it, it intrigued me that Ms. Lilly puts herself to bed at nightfall, whatever time that is during the year. As soon as it's dark, she puts herself to bed, usually in the darkest one of her favourite sleeping places if I'm still up. In the summer months, when it may be light outside until after 10 pm, I have to practically drag her inside when I'm ready to go to bed. But in the depths of winter, when it is starting to get dark by 4:30 pm, she's ready for bed right after dinner (which she also wants earlier than usual). It's been a very valuable lesson for me on listening to one's biorhythms and following the ebb and flow of the seasons. When I follow her lead, I feel much better in all respects.
     In fact, what she's taught me about appropriate proportions of rest and activity, and of sleep and wakefulness could be summed up thus: follow the rhythms of the earth -

• get up when it's light, go to bed when it's dark
• be more active when the days are long, be less active when the days are short
• listen to your body during the course of every day and follow every period of activity with a period of rest, just as every in-breath is followed by an out-breath

     The whole show oscillates in various rhythms, each overlaid and already orchestrated for us: breaths, days, months, seasons, years, life phases, lifetimes. Our patterns of activity likewise should oscillate around a life-sustaining centre, wherein a period of activity is always followed by a period of rest - not necessarily of equal length, but of equal revivifying quality. The activity should be thoroughly engaging, and the rest equally restorative. Therein we find our balance.
     When it comes to working animals, rest is restorative for both body and mind. During a schooling lesson, for example, letting the horse (and rider) take short rests during the lesson can be a very useful training tool that, in my opinion, is vastly underused. Every animal (and human) I've ever met learns best - fastest and with better retention - when the work is interesting, fun, and rewarding. It can be physically challenging, yes, but it must also be something the animal (and human) enthusiastically participates in and feels the better for having done so, otherwise it's largely a waste of effort. Periods of rest and reward during training are an essential component of optimal learning.
     The same goes for work in general, even work that is not primarily done for training purposes. To be most productive and least destructive, a period of work must be followed by a period of rest - not necessarily of equal length, but most definitely of equal quality. When the work is thoroughly engaging and the rest equally restorative, wonderful things can come of it - not the least of which is a life well lived.
     And if that isn't enough to convince you, then consider this: more injuries occur in a tired body than in a well-rested, well-prepared body. I'll have much more to say about healthy exercise habits and exercise physiology in future posts.


     This'll be a topic for another time, too, but while we're on the subject of rest and sleep, it's also important to provide a comfortable, safe, and secure place for your animals to rest and sleep. Particularly with herd species such as horses, being isolated - whether literally (i.e. no other horses nearby) or perceptually (i.e. no other friendly horses nearby) - is a real challenge. We all need to feel safe and secure in order to let ourselves fall into a state of deep, restful, restorative sleep.
     Behavioural problems are one of the consequences of lack of sleep in animals, just as they are in humans. In horses, chronic lack of sleep can also lead to sudden loss of consciousness which causes collapse, often with self-injury. Commonly mislabelled narcolepsy, it's a condition that in humans is called inappropriate or excessive daytime sleep (EDS), and it can occur out at pasture, in the stall, and even in cross-ties. Sometimes the reason the horse is not sleeping well is because of a painful condition that makes it difficult for the horse to lie down or get up with ease. But often no such reason can be found, and the solution lies in making the sleeping environment quieter, darker, and safer - from the horse's perspective, not ours.


OK. That's about it for now. Until next time, sleep well!


-Dr. Chris King-
Nature's Apprentice
www.animavet.com