Equine Protozoal Myeloencephalitis; A Veterinarian's Perspective

EPM has plagued horse owners for several decades with an estimated clinical prevalence of less than 5% of horses being affected, causing not only a potential loss of function and performance but also high costs to the owner in terms of diagnostics and treatment.  When I was in vet school, the disease was first being clinically recognized and treated.  In those days, we saw the worst of the cases that were admitted into the veterinary school and many of these horses were recumbent and unable to stand or even turn themselves.  As students on the late night watch, we were often given the chore of hooking these horses to overhead hoists and physically turning them every few hours to minimize bed sores.  It seemed futile in many cases as often, they were unable to eat due to body positioning, which contributed to the body wasting and further muscle weakness.

Cause:

The disease is caused by a parasite called Sarcocystis neurona, which gains entrance the body and then targets peripheral nerves or the central nervous system, eliciting an inflammatory reaction which impairs nerve function.  The parasite is thought to be transmitted by the opossum primarily, but barn cats and various birds have also been implicated in the past, with the horse inevitably being exposed while grazing on pasture or through contaminated feed.  The horse is considered an aberrant host and once infected, they are not a risk to spreading the parasite to other horses.

Prevalence:

In my practice, the exact prevalence of the disease amongst our patients was less than 5%, but may be higher in other regions of the country.  Blood testing of horses has indicated a positive antibody titer in up to 80% of horses (in my practice area), but the majority of these do not demonstrate clinical signs. A positive serum Western Blot simply implies exposure to the parasite and does not define clinical infection. It seems as if the prevalence of the disease, at least in my area, has actually declined over the past several years or quite possibly, they are just not being recognized as having a problem by their owners.

Clinical Signs:

When I was a student, we saw the worst of the worst when it came to EPM cases.  Upon graduation, often we were misled in thinking that they always presented this way.  With more clinical practice years under my belt,  I learned that there were many clinical presentations with the majority of them being mild.  In many cases, mild EPM cases have presented as an unexplained or ‘shifting’ lameness.  The lameness may be present in one limb one day then the next in another area.  If I was presented with a lameness that I could not pinpoint or localize, we would often screen for EPM.  The clinical examination involves not only a full physical exam, but evaluation of neurological function.  Peripheral and cranial nerves are evaluated for deficits, which may help us in localizing the disease.  Limbs may be flexed and evaluated for lameness, but they will also be evaluated for conscious proprioception (CP) by crossing the limbs at times.  In most cases, when limbs are crossed over, they are quickly replaced to normal position by the horse.  Those with neurological impairment may have a delayed or no response.  Tail and anal tone are also evaluated, in addition to the tail pull to determine if there is muscle weakness present. The parasitic infection generally targets nerves and with this, we can have many types of presentation with varying degrees of severity. The condition is progressive in most cases, with time being of the essence in terms of best outcomes for treatment. The most common types of presentations would involve one of the following

• ·         Lameness

• ·         Muscle weakness / atrophy

• ·         Poor performance/intolerance

• ·         Ataxia (uncoordination)

• ·         Stumbling or tripping

• ·         Recumbency/unable to stand

• ·         Difficulty eating/swallowing or ‘choke’

• ·         Head tilt

• ·         Behavioral changes

Diagnosis:

The diagnosis of EPM can be tricky, but in most cases we base the diagnosis upon the combination of clinical signs in addition to other laboratory data.  In our patients, if there is a suspicion of EPM, we would submit a blood antibody titer (Western Blot) to rule in or out the disease.  A positive test on blood is NOT confirmative for a diagnosis of EPM, but a negative result generally rules out the parasite.  If the blood test is positive, which equates to a history of exposure to the parasite, often the next step is to perform a spinal tap in the lumbar region, again looking for antibodies or parasite DNA (PCR) in the spinal fluid. In more recent years, technology has allowed for more refined antibody testing of serum in order to obtain specific titers, which may help to differentiate between exposure and actual clinical disease.

Several issues have risen over the past few years regarding spinal taps.  First thing to remember is that there is risk to the procedure for both the patient and veterinarian.  It can be painful at times, resulting in a horse kicking out to the side which may injure people around the horse.  In other cases, horses have been known to buckle upon insertion of the needle, resulting in potential injuries.  Spinal taps may also potentially worsen ataxia or uncoordination in clinical horses and may be difficult to perform successfully in recumbent animals. The biggest problem with spinal taps is blood contamination of the sample.  If a horse is positive, they will have antibodies present in the bloodstream.  In order to perform a spinal tap in the horse, the needle actually has to pass through several inches of muscle, which are saturated with blood.  The current thought process is that there is a potential for the needle to be exposed to the blood, gather antibodies and thus produce a positive spinal fluid sample.  In the end, it is hard to prove that a positive spinal tap is not due to blood contamination and thus a false positive.

Due to this fact, we stopped performing spinal taps several years ago and have more or less relied on clinical signs along with a positive blood antibody titer.  It certainly is not 100% definitive, but is safer and less expensive in the short run to gather data and assess for a response to medications.

Differential Diagnosis:

Other considerations for a horse demonstrating neurological clinical signs includes toxicity, herpes viral infection, Easter/Western encephalitis, West Nile, Rabies, equine degenerative myelopathy, equine lower motor neuron disease and cervical vertebral stenosis (wobbler syndrome).  Either clinical signs or further testing can help to rule in or out these diagnoses.

Treatment:

For many years, we have used a combination of antibiotics; sulfatrimethoprim with rifampin, to help manage the parasite infection.  The combination was often fairly successful, but required many months of therapy.  Over the past decade, we have seen some improvement in therapies, which include a medications such as diclazuril, toltrazuril, ponazuril and NTZ, which have all shown promise and require less time for treatment.

Results from therapy can be variable with noted improvement in less than 75% of cases and a full recovery in less than 25%.  In some cases, the patients would actually get worse during therapy for a brief period due to the parasite being killed off and eliciting an inflammatory type reaction.  In many cases, the patients would recover but continue to have neurological issues or deficits resulting in loss of use, decreased performance and even euthanasia in some cases.

One of the biggest problems when treating an EPM horse are relapses, which can be quite high.  In many situations, horses would appear to recover, only to demonstrate clinical signs again within the next 6-12 months.  This is not only frustrating but expensive for the owner as it often entailed another course of medication.

Other therapies often used adjunctively include non-steroidal anti-inflammatories, corticosteroids, DMSO and antioxidants, with vitamin E being most commonly used.

Thoughts / Prevention:

Many years back, an astute veterinarian raised the question as to how the parasite was gaining access to the systemic circulation.  After all, most bacteria and parasites are killed off by high acid levels in the stomach or by other factors in the gut.  In order for the parasite to gain access, there would have to be a breakdown in the gut barrier in some shape or form.  Upon further exploration of this theory, it was proposed that many of these clinical horses had gastric ulcers, which may be allowing the parasite to gain access to the body.  There are many theories out there, many of them still unproven, but this ulcer theory opens the door to many questions.

If we blood test 10 horses for antibody titers, approximately 8 of them will be positive and maybe 1-2 of those 8 will actually be clinically sick.  Why?  What makes those 1-2 horses different or more susceptible to clinical disease?  When we look at the ‘ulcer theory’, this raises the question regarding the impact of stress on the body, which may be hindering the immune response.  The body creates many barriers to prevent invasion by bacteria, viruses and other parasites, but the immune system is ultimately responsible for detecting and eliminating invaders into the body.  So, what potentially causes a deficiency in the immune response?  This can be a genetic cause, dietary related, stress induced….the list goes on.  It has been noted that stress and immune compromise increase the susceptibility to a horse contracting EPM.  Likewise, the incidence of EPM also appears to be higher in competitive horses, which may be undergoing increased levels of stress.

What I have found and explore with these patients is the status of the immune response.  In all of our cases, I have submitted what is termed a CBC (complete blood count), which is fairly routine.  What I am looking for is the level or status of the white blood cells, specifically the lymphocyte.  I have noticed that many EPM cases have lowered lymphocyte levels upon presentation. Those horses with lowered lymphocyte counts also appear to be more likely to experience relapses.  It is potentially a crude means of evaluating the immune response and predicting relapse rates, but none the less is valuable in my opinion.

When we were first treating these patients years ago, I would almost always add in some type of immune supplement along with traditional therapies.  Originally, I would use a cattle dewormer called Levamisole, which has demonstrated immune enhancing properties.  It would help in most cases, but there was always a need for something better.  Several years later, I discovered and researched medicinal mushrooms and their impact on immune health.  There are several types of mushrooms that demonstrate immune enhancing capabilities and have been researched for decades with verifiable results.  We soon developed and began to utilize what became our EQ Immune &Repair formula in our EPM cases and noted a tremendous impact along with traditional therapies.  The patients did better overall and recovered more completely. 

Aside from the immune component, we have to remember that there is also a strong inflammatory reaction that is occurring and contributing to neurological deficits.  In many severe cases, especially in recumbent horses, clinicians would utilize a steroid or DMSO to help combat the inflammation.  The steroid would help in a high percentage of cases, but potentially came at a cost due to a high incidence of side effects, including gastric ulcers, further immune suppression and even laminitis.  We used these steroids in some of our cases, but needed something more complete, gentler and more effective for systemic inflammation.  We began to utilize our EQ Plus  formula in our EPM cases to combat inflammation as well as provide antioxidants in addition to our Immune & Repair formulas, alongside of the traditional therapies.  Again, we noted a more complete and quicker recovery in a high percentage of cases.  In some cases, due to the expense of pharmaceutical medications, many owners were unable to afford traditional therapies and we were forced to manage them using our EQ Plus and Immune & Repair formulas.  It was stunning to see that a high percentage of these horses recovered and obtained remission without the need for anti-parasitic medications.  The results were achieved based on improving overall immune health and managing inflammation.

Our results have been confirmed by many of our Cur-OST® customers, stating an enhanced recovery as a standalone therapy or even in cases that have relapsed and were no longer responsive to traditional therapies.

Prevention of EPM from my point of view is rather simple. We can make attempts to 'clean up' the environment and make it less attractive to the Opossum, but it is next to impossible to eliminate the parasite completely from the environment.  We can, however, enhance overall health in these patients by improving immune function and controlling ongoing inflammation.  Factors such as stress, lifestyle, diet, genetics and many others directly contribute to inflammation, which then potentially impacts immune health.  It becomes obvious in many EPM cases that inflammation was a preliminary problem as many of these horse have other concurrent issues such as lameness, poor performance, laminitis, COPD and even insulin resistance.  We need to look at the patient as a whole to get a better understanding on how poor health influences the prevalence of these diseases.

In the end, EPM is a complex condition with a multitude of opinions on how to treat and manage.  We need to stop looking to pharmaceutical medications as being the end all be all answer and start looking at the patient as a whole, including their environment and lifestyle.  

All my best,

Tom Schell, D.V.M.
www.curost.com

Colic In The Horse

Colic. . . one of the most dreaded conditions by the average horse owner.  It equates to pain for your companion, potentially long nites of monitoring and even costly veterinary care in the worst scenarios.  The good news is that in the majority of colic cases, the problem often resolves on its own over a short period of time with some TLC and dietary changes.

There are many different types of colic, which essentially means abdominal pain.  Horses tend to have very sensitive gastrointestinal tracts that are susceptible to upset due to stress, dietary changes, parasites, various medications and even changes in barometric pressures.  As a veterinarian, I would often keep tract of incoming weather fronts and would be able to pinpoint which clients I would be hearing from that day or evening.  Barometric pressure plays a major role in the development and movement of gas within the lumen of the horse's bowels and can be quite dramatic at times.

The most common type of colic seen in my practice is what is termed a gas colic, which may be associated with changes in feed, stress, pasture changes or even barometric pressures.  Some feeds are more likely to lead to gas formation, which is especially prevalent in the spring with lush pastures.  The bowels always contain gas at any given time, which exerts a specific pressure outwards on the bowel lining.  When the gas is excessive, the pressure is increased against the lining and pain is perceived as it stretches.  Barometric pressure often changes, which induces changes in the gas pressure as well.

The second most common type of colic, at least in my practice, is that associated with stomach or gastric ulcers.  These horses generally have a history of gastric ulcers, which are flared up due to changes in feed or excessive stress levels.  In these cases, we can have a wide range of pain levels as well as dehydration, dependent on the severity of the ulcer.

Other less common types of colic include impactions or blockages of the stomach, small intestine or large colon.  These conditions are often associated with low water intakes as well as consuming foreign material or feedstuff that is hard to digest.  Large colon impactions are common to certain breeds, but are most often seen when water is limited or is frozen or cold during the winter months.  Displacements or twisting of the bowel is yet another source of colic in the horse, but involves a much lower percentage of horses.

Diagnosis:

Most horse owners are quite astute and know how to recognize if their horse is colicky.  Typical signs include rolling, sweating, pawing with heavy breathing at times.  Pain levels can range quite a bit, dependent on the severity of the condition and it is not uncommon to have some horses with severe impactions just seem "off" to the owner for a day or two with no evident rolling.  In most situations, the clinical signs come on rather quickly and there is no notation of the horse being off his/her feed, but often they seemed just fine even an hour ago, but are now rolling and uncomfortable.

The veterinarian will usually evaluate the heart and respiratory rate initially to help gauge the severity of the condition.  The heart rate tends to climb or increase with pain and the amount of increase can be used by the veterinarian to gauge the severity of the colic and rule in/out causes.  The next step is usually to listen to the abdomen to determine the presence of 'gut sounds', which is movement of gas and feedstuff as the bowels contract.  Generally, the presence of consistent GI sounds is a positive thing, however, one can also determine if there is excessive gas accumulation, which may prove to be troubling.  The gums or mucous membranes will also be evaluated, which help to determine hydration, perfusion as well as the presence of possible toxemia.

After the basic examination is performed, the veterinarian may then chose to perform a rectal examination in order to determine whether if the bowels are in their proper locations and if there is any palpable abnormalities such as a displacement or impaction.  This often times requires sedation to perform safely and to minimize stress to the horse.  A nasogastric tube may also be placed to determine the presence of gas or fluid accumulation within the stomach, which may indicate a stomach or small intestinal obstruction.

Treatment:

The severity of the condition determines the type of treatment offered.  In simple cases of gas accumulation, treatment would include a pain injection as well as possible mineral oil infused through the nasogastric tube to help move the gas onward.  Handwalking is often very useful as it helps to stimulate the gas to move and spread out within the bowel. Colics associated with gastric ulcers can be a little more tricky to manage and involve the use of antacids or acid blockers in addition to pain medications. In more complicated cases, such as with obstructions, other therapies include IV fluids to help rehydrate the horse and move the impaction.  In cases of displacements or torsions, surgery is unfortunately the only option as medical therapies have not been rewarding. 

Prevention:

Colic prevention is the key, but can be tricky as one never knows what can trigger an episode.  There is very little we can do about the barometric pressure, but we can monitor the diet closely to reduce feeds that may produce excessive gas.  Excessive grain intake as well as the use of some pelleted types of feeds are associated with higher levels of gas, stomach ulcers as well as impactions.  The most common cause of impactions in my practice was the improper use of beet pulp.  Certain hays have also been associated with in an increase in colic due to low roughage type content.  Bermuda hay is one of several and the current thinking is that the hay quality is so fine, that it may not stimulate proper GI motility or movement.

Monitoring and maintaining dental health is also key, especially in the older horse.  If the feed is not chewed properly, then the incidence of impactions and stomach upset increase dramatically. Routine deworming is also important in order to minimize parasite loads that can contribute to colic cases.

Gastrointestinal health is a major player in colic prevention and an area that I believe many herbs can prove beneficial.  This is an area we are exploring not only for potential colic prevention, but for those horses prone to gastric ulcers as well.  If this is something you'd like to discuss further, please feel to reach out to me.

All our best,

Tom Schell, D.V.M.
Nouvelle Research, Inc.
tschelldvm@nouvelleresearch.com
www.curost.com

Equine Navicular Disease (Podotrochleosis)

Equine Navicular Disease has many names, including Navicular Syndrome, caudle heel pain as well as podotrochleosis.  The condition is all too common to many horse owners, unfortunately, and can significantly impact performance, general movement and overall quality of life due to pain generally located in the heel region of the front feet.

To understand a disease, one must first understand general anatomy.  The navicular bone is located on the palmar or caudle aspect of all four feet in the horse, generally located between the heel bulbs.  Let's look at a couple of standard x-rays which demonstrate the location.

The image to the left is what is termed a lateral view of the foot or distal limb.  In this image, I have the navicular bone pointed out with a yellow arrow.  As you can see, it is generally located between the pastern and coffin bone on the back aspect of the foot.  What you cannot see in this x-ray is the placement of the flexor tendons, which are thought to contribute to the pain encountered as well as potential deterioration of the condition.  The main tendon that is of interest is the Deep Digital Flexor Tendon (DDFT), which courses down the back of the limb, overtop of the navicular bone and then attaches the bottom of the coffin bone.  More on this tendon in a bit and influences upon motion.

In the image to the right, we have what is termed an AP view of the navicular bone.  The beam of the x-ray is targeted on the top aspect of the junction between the coffin bone and the pastern bone.  Hopefully, enough power is used to penetrate through the pastern bone to visualize the navicular bone.  Again, in this image, I have the navicular bone marked with a yellow arrow.  Sometimes it can be hard to see, but hopefully we can see it in this view.  Overall, what we are looking for in this view is overall shape, thickness and defect evaluation.  This particular image is not ideal, but is pretty close to normal from my view point and this particular horse did not demonstrate any lameness at the time of the x-ray.

Navicular disease is very common in more stocky breeds such as the QH or Appaloosa, in which the horse may be actually carrying more weight on the front limbs.  It is also very common in horses with a foot that is too small genetically speaking or trimmed too small in relation to body size.  Hoof conformation also plays a major role in the syndrome development and the general conformation of long toe, low heel actually predisposes to this condition more readily.  The actual cause of the condition is not completely understood, but we do know that the above influences play a major role.  Essentially what is happening is that the navicular bone is degenerating due to perceived decreased blood circulation.  Pain is encountered due to this deterioration process.  Now, what causes the decreased blood circulation?  Excessive strain on the bone due to low heels, too small of a foot in relation to body size as well as possible genetic factors all play a role.  The decreased blood circulation leads to obvious inflammation, which then contributes to bone resorption and remodeling.  In some cases, the bone can fracture due to weakness.

Clinical Presentation
These horses can present for a wide range of lameness varying from very mild to very obvious.  In some cases, the owners have detected a change in gait or overall movement and can't quite pin point down where the issue is originating.  In other instances, maybe there is a decreased performance, decreased times in various events or an obvious lameness or reluctance to pick up a gait.  Navicular horses are reluctant to put excessive weight on their front heels.  When you watch them walk, they are generally stiff, don't reach forward very well having a shortened anterior stride.  When they turn, they will shift their weight to the rear limbs, much like a laminitic horse.  If you force them to trot or canter, their stride is generally short and choppy.

On physical exam, some of them are quite painful.  Often they will have an increased digital pulse to one or both feet.  Hoof testers are commonly very positive in the heel region which helps to locate the source of pain.  Evaluation of the hoof conformation also is generally a tell tale indicator, as most of them have low heels and overriding the shoes if they are shod.

Diagnostics include not only a physical examination, but also x-rays to determine if there is degeneration present.  Nerve blocks are also performed to locate the source of pain. Sometimes, ultrasounds as well as venograms are performed.  Here is a radiograph of a low grade navicular horse.

This is the AP or front view of the navicular bone.  Again, I have the bone indicated by a yellow arrow.  What we are looking for is changes in shape, thickness of the cortical wall as well as any evident degeneration.  In this particular horse, I have two red arrows pointing towards the front border of the navicular bone.  Here we can appreciate a roughening of the bone border as well as small, black holes that are present within the bone, which indicated bone loss or degeneration.  I often refer to these as "lollipop" lesions as their is usually a black "stick" as well as black "head" to the sucker lesion.  This particular horse was not that bad in terms of lameness, but there was evident degeneration on x-ray.




Treatment Options
A diagnosis of navicular disease is not an end, but one does have to realize that it is not reversible but can be managed in most instances.  First, we have to look at the hoof conformation and correct it when needed.  Understand that the DDFT is coursing on the back side of the navicular bone and if the heel is too low, then the tendon is stretched and puts excessive pressure upon the bone, which may compromise blood flow and overall health.  The same holds true for a large horse with little feet.  In those cases, the heel region is not of adequate size to withstand the weight of the horse.  In cases of low heels, we will often times apply wedge heel shoes to take the strain off of the DDFT.  In other cases, one may choose an eggbar shoe, which allows the horse to distribute more weight caudally beyond the heel region to the shoe, which relieves pressure.

In other cases, we will use NSAID medications such as bute to help reduce inflammation and pain, but we have to understand that these medications are only addressing a small portion of the inflammatory response as we have discussed before.  Some vets will use Isoxsuprine which is intended to increase blood circulation.  Others will use Pentoxifylline, which increases the flexibility of the red blood cells and potentially allows them to squeeze into tight spaces delivering oxygen.  Both of these medications are used heavily in humans with poor circulation and do a good job, however, personally I have not witnessed tremendous benefit in horses.

In severe cases, navicular bursal injections of corticosteroids may be performed.  The intent here is to deliver the medication very close to the bone.  Again, we are not solving any problems with this treatment in my opinion and just buying time through mild inflammation reduction.  In some cases, cold laser therapy or shock therapy may be employed, often times with little results.  The last ditch effort has always been a surgical procedure called a neurectomy, which is a severing of the nerve to the region resulting in a loss of sensation to the heel region.  Obviously, there are no therapeutic effects here, but we are just long term numbing the region.  There can be some serious side effects to this procedure, sometimes with the horse ending up worse than what they were before the procedure.

Conclusion
Navicular disease is a common and serious condition.  If caught early enough, I feel that may horses can do very well with long term changes. Hoof conformation as well as body size of the horse are major players in the development of the disease and one must be conscious of how their horse is trimmed and shod at all times. I agree that there is a blood circulation issue at the root of the problem, but also believe that the inflammatory process plays a major role.

We have used our Cur-OST products, specifically our EQ Plus and EQ Green formulas in many cases of navicular disease with pretty profound results.  Curcumin and boswellia are potent inhibitors of inflammation from a much higher level than NSAIDs or even corticosteroids, helping to modulate the pathway from multiple perspectives.  The antioxidants and nutritive herbs in the formulas help to combat free radical damage to blood vessels as well as surrounding tissue, plus provide many nutrients that aid in overall health.  Interesting enough, curcumin has been shown in several research studies to impact bone remodeling and degeneration by affecting osteoclast activity.  Overall, our findings have been that the Cur-OST formulas improve quality of life, overall function and reduce pain for many of these patients.

Here is a video of an Appaloosa mare that has navicular disease and responded well to Cur-OST.
http://www.youtube.com/watch?v=6cmW87xoYEI&list=UUosRnnrpSG6xjimXii3JV4A&index=1

All our best.

Tom Schell, D.V.M.
www.curost.com