Equine Herpesvirus 1 – What you need to know when facing current outbreaks

Outbreaks of diseases are scary.  The disease can be a brand new virus, a bacterial “superbug”, a virus that has mutated, a parasite that has spread to a new geographic location – you get the idea.  The recipe for a contagious disease outbreak calls for two basic things:

Ok, we aren't talking about an outbreak of zombies, but horse disease outbreaks are scary too! Source:  inkace.com
Ok, we aren’t talking about an outbreak of zombies, but horse disease outbreaks are scary too!
Source: inkace.com

1) a susceptible population of living things (humans, animals, plants, etc) that do not have immunity to the pathogen

2) a pathogen (virus, bacteria, etc) that is easily transmitted between individuals it infects

The disease does not have to be deadly, its main goal is just to replicate in its host.  For instance, the flu virus is not often deadly but it transmitted very easily between individuals.  This ability allows the virus to find a new host before it is destroyed by the original host’s immune system.  The ease of transmission causes a lot of individuals to become sick in a short amount of time.  Additionally, if the pathogen can replicate in its host, and that individual becomes contagious before they realize they are sick, the disease has an extra advantage.

So how does all of this figure into the current outbreaks of Equine Herpesvirus-1 (EHV-1)?  Well, first I am going to discuss a little bit of background information on this virus (which is not a new virus, by the way).  Then I will delve into how it has evolved to cause current outbreaks of disease.  Finally, I will go over ways horse owners can prevent and prepare for an outbreak of EHV-1.

What is EHV-1?

Source: Gluck Center at University of Kentucky
An electron photomicrograph of EHV-1          Source: Gluck Center at University of Kentucky

EHV-1 stands for Equine Herpesvirus Type 1.  There are several types of Equine Herpesviruses but the main ones that cause serious health problems  in horses are Types 1, 3, and 4.  In this post I am only going to discuss EHV-Type 1.  EHV-1 can cause 4 different manifestations or clinical presentations:

1.  Neurologic – aka Equine Herpesvirus Myeloencephalopathy (EHM).  This form affects the nervous system (brain and spinal cord).

Just to be clear – EHM is a form of EHV-1 – not a separate disease.

2.  Respiratory – Affects the respiratory system (lungs, sinuses, trachea, nasal passages, etc.)

3.  Abortive – Affects the reproductive tract of a pregnant mare causing fetal death and subsequent abortion

4.  Neonatal – Newborn foal is born apparently normal but then becomes severely ill 1-2 days after birth.  Despite the best supportive care these foals often die from severe respiratory disease and it’s complications.

How does EHV-1 affect the horse?

The virus can affect 3 different types of body systems: neurologic, reproductive, and respiratory.  Once a horse is infected with the virus, the virus travels to the lymph nodes and infects certain types of white blood cells.  The infected cells are released out into circulatory system, where they travel in the blood to different sites in the body.  They can travel to the lungs, uterus, or spinal cord.

One key point here is that it is unknown why the virus attacks certain areas of the body.  There is research currently being performed that is attempting to figure out why an outbreak of neurologic disease will affect one group of horses, but another group may only show up with respiratory disease.  One recent finding is that there seems to be some genetic varieties of the virus that tend to cause the neurologic form more often, but not all cases of EHM are caused by these mutant varieties.

How is EHV-1 transmitted or spread?

EHV-1 has several of what I like to call “superpowers”.  The way it is transmitted is one of its superpowers.  Most of the time the virus is transmitted by horse-to-horse contact.  We all know how curious horses like to smell everything and everyone, especially new horses.  In fact, most horses introduce themselves by intensely smelling one other’s nose – it’s like they are smelling each others breath!  EHV-1 (cleverly) is easily transmitted through nasal secretions from one horse to another.

Horses naturally communicate with one another by touching noses and smelling.  EHV-1 has adapted so that it is transferred to a new horse when this happens.   Source: thehorse.com
Horses naturally communicate with one another by touching noses and smelling. EHV-1 has adapted so that it is transferred to a new horse when this happens.
Source: thehorse.com

However, EHV-1 has also evolved to be able to survive on the surfaces of objects that are contaminated by an infected horse (tack, human clothing, stalls, fences, etc).  And that’s not all – the virus can live (in the ideal conditions) up to 21 days on an object!  Furthermore, foals can be infected in utero and other horses can be infected by contact with an infected placenta or fluids from the mare.

So I can just keep my horse away from sick horses and he will be fine, right?

Wrong :(.  Another superpower of EHV-1 is that it can infect a horse and the horse can become contagious to others even before it shows physical symptoms of being ill.  By the time you see that the horse is sick he could have already infected all of his pasture mates.

A third superpower of EHV-1 is it’s ability to become latent (dormant).  A horse can be a “carrier” of this virus (a reservoir) and not show any outward abnormalities.  At some point, though, the virus can be reactivated in the carrier horse – who can now spread the disease to others.  Things like stress or a different illness can cause EHV-1 to be reactivated.  It is no wonder that  weaning, training at the racetrack, and traveling for shows are common times where we see outbreaks of EHV-1.

What about vaccines?

Vaccination is an excellent way to prevent spread of EHV-1 and has worked wonders for the breeding industry in preventing abortion outbreaks.  It also seems to protect against respiratory disease.  However, there is no current vaccination that is able to completely prevent the neurologic form of the disease.  This is a hot area of research and scientists are working on ways to improve the current vaccines or possibly manufacturing new vaccines to protect against EHM.

Source:  The Gluck Center at the University of Kentucky
Source: The Gluck Center at the University of Kentucky

EHV-1 has been around for a long time.  Why the big concern about it now?

The concern over the recent outbreaks has to do with the fact that EHM (caused by EHV-1) is an emerging disease.  The neurologic form of EHV-1 (EHM) used to be quite rare.  However, in the early 2000’s we started to see outbreaks of horses affected with EHM in various spots across the US and the world.  The virus has seemed to change in its severity and/or behavior in affected animals.  Furthermore, since vaccinations do not protect against this form of the virus, there is no way to systematically control it.  And remember how easily it is spread (its superpowers)?  The fact that the virus can spread to hundreds of horses without seeing a single horse look sick makes it a big cause for concern.

What are the clinical signs of EHV-1 and EHM?

Screen Shot 2015-04-24 at 10.59.00 AM

The signs listed in the tables above are seen with lots of diseases – not just EHV-1 or EHM!  One important characteristic is that your horse needs to have made contact with new horses or their bodily fluids, and that the onset of the neurologic signs is very fast.  Usually the signs show up and progress for 24-48 hours and then stop progression.  After that 48 hour period, the worst appears to be over and how bad each individual horse is affected will determine their prognosis.  If the horse goes down and can’t get back up then the prognosis is grave.  If the horse is only minimally affected then the odds are good that they will gradually recover.

What about treatment?

There is currently no specific treatment for EHV-1 and EHM.  Because they are viruses, antibiotics will not fight them.  However, sometimes horses are given antibiotics to prevent opportunistic bacterial infections because the horse’s immune system is working overtime on fighting the virus.

There is no specific treatment for EHV-1 and EHM, so we rely on supportive treatments (like IV fluids) assist the horse in it's recovery.
There is no specific treatment for EHV-1 and EHM, so we rely on supportive treatments (like IV fluids) assist the horse in its recovery.

The treatments your horse will receive are all supportive – meaning they are just supporting his basic bodily functions until his immune system takes care of the virus and healing takes place.  Examples of supportive treatments are IV fluids and anti-inflammatory drugs.

How can I prevent my horse from getting EHV-1 or EHM?

Even though the vaccine does not specifically protect against the neurologic form of EHV-1 (EHM), it is still a good idea to vaccinate your horse for EHV-1.  The vaccination does protect against the respiratory form and the abortive form of EHV-1, so your horse will be protected against those manifestations of this disease.  The vaccine does also seem to decrease viral shedding, so if your horse does become infected with the neurologic form you can help prevent shedding and infecting other horses with the virus.

Another was to prevent EHV-1 and EHM is to practice good biosecurity around the farm.  This means that any incoming horses are isolated from your herd for a period of at least 21 days.  That means that nothing that the isolated horse touches is allowed to touch anything that your herd horses may touch (tack, buckets, stalls, fences, etc).  Wash your hands between caring for your new horse and the rest of the herd.  Take the temperature of the new horse twice daily to make sure he does not spike a fever.  Isolating new horses protects against many diseases, including all the forms of Equine Herpesvirus and Strangles.

Horses that travel to shows or clinics should also be isolated from your herd when returning.  It is a good idea to take the temperature of your horse twice daily for 14 days before returning him to the herd.  If he develops a fever, call your vet.

There is a ton of information on the internet regarding what happens if your horse is at a show when there is an outbreak and various scenarios of the like.  Sources that are reputable include AAEP and APHIS.USDA.gov.  Another thing you can do is call your vet and see if they know about any current outbreaks in the area.  And it is never a bad idea to contact the shows and places you are traveling to see if they know of any outbreaks or precautions you should take to protect your horse.

Advertisements

Vaccinating Your Horses – What, When, and Why?

For an equine vet, springtime is extremely busy – foaling, breeding, vaccination, Coggins, etc.  Our clinic typically vaccinates over 100 horses per week from March until May.  That’s a lot of vaccinations!

Some vaccines are recommended for all horses, others just for "at risk" horses.  Each horse should have a tailored vaccination program designed by your veterinarian.   Source:  thehorse.com
Some vaccines are recommended for all horses, others just for “at risk” horses. Each horse should have a tailored vaccination program designed by your veterinarian.
Source: thehorse.com

I would like to write about this topic today because recently there have been outbreaks of diseases that could have been prevented or mitigated had the horses been vaccinated.  Additionally, because medical topics that affect humans (such as vaccination risks vs. benefits) often trickle over into vet medicine, I would like to address the risk vs. benefits of equine vaccines.

The recommendations for vaccinating in this post are taken from the American Association of Equine Practitioners Vaccination Guidelines.  As always, please discuss vaccinations for your horses with your personal vet for reasons you will learn about as you continue to read.

What Vaccinations Should My Horse Receive?

It depends…..

Several factors to consider include:

1.  The job of the horse

Some diseases that we vaccinate for are transmitted from horse to horse.  Others are transmitted to the horse from other animals.  Still others are contracted from the environment.  Horses that stay on the farm the majority of the time and rarely come into contact with other horses have a low risk of picking up diseases that are communicable.  In contrast, horses that are going to clinics and shows every weekend have a high risk of picking up these type of “bugs”.

2.  The location of the horse:

Different areas of the United States, and other countries for that matter, carry different risks for picking up particular pathogens.  For instance, Potomac Horse Fever is not prevalent everywhere in the US.  Some areas, such as the mid-Atlantic region, carry a very high risk for PHF yet other areas have relatively low risk.

3.  The health status, age, and medical history of the horse:

There is always a risk with vaccinating horses, as with anything you put into their body that is foreign (medication, food, etc).  Some horses are prone to vaccine reactions, which may include fever, lethargy, anorexia, and swelling of the vaccination site.  For these “sensitive” equids we try to only vaccinate with the bare essentials.  Additionally, different age groups of horses have higher risk of contracting specific diseases, so sometimes vets will recommend a vaccination for a young horse but not your geriatric horse.

4.  Recent disease outbreaks:

Disease outbreaks scare all of us and can lead to widespread panic amongst horse owners.  Couple that with the misinformation gained from social media and suddenly vets are receiving dozens of phone calls from frantic horse owners wanting their horse immediately vaccinated for X,Y, and Z.  This week there was a confirmed case of EHV-1 at Michigan State University in a barrel horse.  Two days later we are getting calls from people asking if they should not take their horse to any barrel races in the near future.  Cases like this can be scary, but it is very appropriate to discuss the risk of these diseases with your vet before vaccinating your horse.  Your vet will be the best source of information regarding any recent disease outbreaks in the area and if your horse should be vaccinated.

Map of EHV-1 Myeloencephalitis cases from March 2014 to March 2015.  Your vet can help you decide what vaccines are appropriate based on recent disease outbreaks.   Source: wormsandgermsmap.com
Map of EHV-1 Myeloencephalitis cases from March 2014 to March 2015. Your vet can help you decide what vaccines are appropriate based on recent disease outbreaks.
Source: wormsandgermsmap.com

Even though some vaccinations may not be necessary for your horse, there are a few vaccines that are considered “core” – meaning all horses in the US should receive these vaccines.  At a bare minimum the AAEP recommends all horses get vaccinated for:

– Tetanus

– Eastern and Western Equine Encephalomyelitis (EEE and WEE)

– Rabies

– West Nile Virus (WNV)

Risk-based vaccines are administered based on each horse’s particular risk for contracting the respective disease.  Some risk-based vaccines are:

– Potomac Horse Fever

– Strangles (Streptococcus equi)

– Equine Herpesvirus Type 1 and 4 (EHV-1, EHV-4) a.k.a Rhinopneumonitis

– Equine Influenza

– Botulism

For more details regarding each of these vaccinations and their recommendations, please visit the AAEP Vaccination Guidelines page.

When Should My Horse Get Vaccinated?

Many diseases are transmitted by insects, which are seasonal depending on where you live.  Your vet will help you decide the optimum timing for your horse's vaccinations. Source: ocalapost.com
Many diseases are transmitted by insects, which are seasonal depending on where you live. Your vet will help you decide the optimum timing for your horse’s vaccinations.
Source: ocalapost.com

For most vaccines it takes two weeks to develop immunity or protection from disease.  That means your horse should be vaccinated a minimum of two weeks before he needs protection.  Many of the diseases we vaccinate for are transmitted by insects or mosquitoes (PHF, EEE, WEE, WNV), so we recommend vaccinating a short time before these insects are active, and repeat yearly.  additionally, for communicable diseases such as Equine Influenza, your vet may suggest a second vaccination in the autumn if your horse will continue to travel through the winter.  It is less than ideal to wait until July or August to vaccinate your horse because insects will have already been active and could transmit disease before then.

Why Should My Horse Get Vaccinated?

My guess is that your horse is more than just an animal to you.  He or she is probably your companion and you love them.  Because you love your horse, you would not want to see him sick.  Many of the diseases we can vaccinate for are not pretty to see.  I know many horse owners who feel guilty if there horse gets injured or sick, even though there is not way they could have prevented it.  Imagine how it would feel to know that a horse is sick but it could have easily been prevented.

Vaccines are rigorously tested and inspected before being allowed to be administered.  This is to ensure their safety and effectiveness in preventing disease.  Although the rare horse will have a reaction to a vaccine, by far the majority are mild and temporary.  So yes, there are risks with giving a vaccine, but the benefits (protection from deadly disease) are greater.

Screen Shot 2015-03-27 at 10.24.12 AM

Finally, the cost of treatment FAR surpasses the cost of a vaccine.  For instance, a vaccine may cost anywhere from $15-80 plus any additional services or fees.  An emergency call for an acute neurologic disorder may run you into the $1000’s in just one night.

Veterinarians are not doing the job for the money.  We are not pushing vaccines to try to please “big pharma” and get fancy rewards from drug companies.  I know conspiracies are interesting, but honestly, we make very little money in administering vaccines to horses.  It is not fun to spend the day jabbing horses with needles and giving injections.  We just want to keep your horse healthy and happy – like you!