West Nile Virus in Horses


West Nile Virus (WNV) is a viral disease that can cause encephalitis or meningitis, infection of the brain and the spinal cord or their protective covering. The virus is transmitted by mosquitoes. The mosquito is infected by feeding from an infected bird. Once the mosquito is infected, it may transmit the virus to people or horses when it bites them. There is no evidence that horses can transmit WNV to other horses, birds, or people.

In horses that become clinically ill, the virus infects the central nervous system and causes symptoms of encephalitis. Clinical signs of encephalitis in horses include loss of appetite and depression, in addition to any combination of the following signs: fever, weakness or paralysis of hind limbs, muscle fasciculations or muzzle twitching, impaired vision, ataxia (incoordination), head pressing, aimless wandering, convulsions, inability to swallow, circling, hyperexcitability, or coma. It is important to note that not all horses with clinical signs of encephalitis have West Nile encephalitis. Other diseases, including rabies, botulism, equine protozoal myeloencephalitis (EPM), and other mosquito-borne viral encephalitic diseases of horses caused by Eastern, Western, and Venezuelan encephalitis viruses, can cause a horse to have symptoms similar to WNV. If you are concerned your horse may be exhibiting signs of encephalitis, please contact your veterinarian immediately. Only laboratory tests can confirm the diagnosis of West Nile encephalitis. The incubation period for WNV is three to 15 days.

Currently, there is no specific treatment for West Nile encephalitis in horses. Supportive veterinary care is recommended. Catching the disease early and treating it aggressively is imperative to recovery. Supportive care includes suspending the horse into a standing position, treating any pressure sores resulting from the horse being recumbent, administering anti-inflammatory drugs including steroids, and aiding in food and water consumption. The rate and degree of recovery depends on how early the symptoms are recognized and how aggressively the disease is treated.

There are vaccines available against West Nile Virus. It is imperative that horses are vaccinated
according to the label on the vaccine. At least one yearly booster is recommended after the initial series. Horses that are stressed, such as show and race horses, should have two boosters annually. In these cases boosters should be administered in April and late July. Horses vaccinated against Eastern, Western, and Venezuelan equine encephalitis are not protected against West Nile Virus. Mosquito population control as well as limiting exposure to mosquitoes at dawn and dusk is also important to controlling the spread of West Nile Virus.

Let's Cut To The Chase About EHV

Equine Herpes Virus

EHV-1 stands for “Equine Herpes Virus-1.”  It’s given the “1″ because there are several herpes viruses that affect horses and this one was named first.  Otherwise, the “1” has no significance.  Herpes viruses are very successful viruses, if you measure success in terms of how many of them there are, and how many mammalian species are affected.  There are herpes viruses of horses, and people, and dogs, and cats, and pigs, and cattle, probably several other animals as well.    Herpes viruses are successful for two main reasons:

1)They usually don’t hurt the host very much.  That’s right, most of the time, herpes viruses are unnoticed by the host.  It doesn’t do a virus much good to go killing off its host – that’s one reason why you don’t see Ebola virus spreading rapidly around the world.  If the host doesn’t live, the virus can’t spread.  Mostly, herpes viruses don’t cause much fuss.  They are sort of like the quiet family that lives in the dark house down the street, or in the apartment down the hall.  If you didn’t know that they were there, you wouldn’t know that they were there.

2)They have cleverly figured out how to evade the body’s immune system.  Once a horse gets infected with a herpes virus, the virus finds a nice home, usually in and around nerves.  There, they stay nice and quiet (medical folk say latent), until some stress causes the virus to activate and start causing trouble.  And the fact that they can evade the body’s immune system also means that, so far, nobody has been able to develop an really effective vaccine against them.

Do you get cold sores?  Something like 70% of the human population does.  Most of the time, people with cold sores have perfectly normal looking lips.  But add some stress – say, illness, tax returns, school (for kids) – and, BOOM, you end up with a big, painful knot on your lip.  Then, the body fights it off, and the virus goes latent, waiting for another stressful opportunity.

In horses, depending on the study you read, it’s estimated that as many as 50% (or more) carry the latent EHV-1 virus in some form.  Sending 700-some horses to Ogden, Utah to compete in a horse show was the equine equivalent of sending the kids to school.  Panicked, excited, stressed, and packed together, it was an absolutely perfect scenario for the herpes viruses to come out and play.  So, some poor horse – one of hundreds that were probably carrying the virus – stressed, and far away from home, broke with the virus, which reproduced, and then spread to other horses.  Think kids in school with a cold:  one of them gets sick, and before you know it, everyone gets sick.

Remember when I said that herpes viruses usually don’t hurt the host very much?  Well, that’s usually true.  Unfortunately, in some cases, the EHV-1 virus gets into the horse’s nervous system and causes a great deal of mischief.  It can even cause horses to die.  This is unfortunate, and also not uncommon with viruses.  And, we do not completely understand why some horses will develop the neurologic form and other horses do not.  Researchers believe that the variety or strain of virus, the horse’s own immune system and the environment all play a role in determining which horses will develop the neurologic form.  The good news is most horses that get exposed to the EHV-1 virus DON’T get neurologic disease.   

Of course, no one wants any horse to get sick, ever, so, understanding that, your reasonable question would be, “What can/should we do?”

And my response would be, “Go out and enjoy your horse.  The EHV-1 virus is pretty much everywhere.  Your horse has probably already been exposed at some point in his life. 

A big question exists concerning vaccination for herpes virus.  Unfortunately, there’s no really good herpes virus vaccination that completely prevents any form of the disease caused by herpes virus.  This isn’t just a horse thing; there’s no really good herpes virus vaccination against any disease of any species.  (And, that is another reason why herpes viruses are so successful).  With that said, there are several, commercially-available vaccines that we use routinely in horses.  These vaccines are labeled (approved by the FDA) to prevent infection or reduce disease of the respiratory and abortion strains.  No vaccine prevents the neurologic form of herpesvirus.  Vaccinating against herpes virus might help to decrease the shedding of the virus and the spreading of the virus among horses.  The best advice is to consult your veterinarian concerning vaccination---not only when discussing herpesvirus but to develop an entire vaccination program that best works for you and your horse. 

The best things that you can do to avoid herpes virus is to practice good hygiene measures, that is, the types of things that people should do with their horses anyway (but often don’t).

For example, new arrivals to farms should be quarantined for a few weeks before being introduced to new horses.  People working around horses should wash their hands often so that they don’t carry disease.  If you’re working around a sick horse, change your clothes before moving on to the next horse.  Don’t crowd horses together.  Feed them well.  Get them fresh air and exercise.  All common sense and but  important, too.

Bottom line is EHV-1 can be a bad deal for individual horses.  Quarantining sick horses, or horses that were exposed at the show in Utah was absolutely the right thing to do.  But for most horses, EHV-1 will not cause disease.  So, be prudent and be cautious.  Use good hygiene measures.  And discuss with your veterinarian the risks and benefits of vaccination. 


A special thanks to Dr. David Ramey in Sunland, CA for letting me "steal" his information about EHV-1.  Check out his website for more great equine information @ www.doctorramey.com

EHV Outbreak

Equine Herpesvirus

Other common names

EHV, Equine Rhinopneumonitis, EHV-1, EHV-4

Equine herpesvirus (EHV) is a highly contagious group of viruses that causes disease in horses worldwide. EHV is one of the most costly viral diseases in the equine industry due to its ability to affect many organ systems causing both economic and animal welfare losses. EHV is responsible for causing the neurologic form or equine herpesvirus myleoencephalopathy (EHM).


Frequently Asked Questions:


1. How do we handle horses returning from events where they might have been exposed to this infection?

For horses that might have been exposed to the risk of infection, there are some steps to take to mitigate the risk at their home facility. Even if these horses are returning home from events at which no disease was reported, and even if these horses appear healthy, precautions are needed at this time as these horses could bring it home and spread it at their home farm – this is the classic way this disease spreads:

• These horses should be isolated from any other horses when they return to their home facility. Isolation requires housing them away from other horses, using different equipment to feed, clean and work with them that is used with any other horses, and rigorous hygiene procedures for horse handlers (hand hygiene, wearing separate clothes when contacting the horses, etc.).

• These horses should have their temperature taken twice a day, as temperature is typically the first and most common sign of infection–horses with elevated temperatures (101.5 degrees Fahrenheit or greater) should be tested to find out whether they are shedding EHV-1.

• If a horse develops a fever and is found to be shedding EHV-1 then the level of risk to other horses on the premises increases significantly.

• Horses that do not develop fevers should be isolated for 14-21 days.


2. What do we do if we already have a potentially exposed horse on a farm?

It still makes sense to isolate this horse from other horses. Even though it might have already been in contact with them, start isolation procedures to stop further exposure. It is important to not mix horses from different groups to accomplish this. Try to isolate the suspect horse without moving other horses from one group to another– segregation of horse groups is the key, because this will help you reduce spread if an outbreak starts. Check temperatures of all horses on the farm twice daily (fever spikes can be missed if you check once daily). If fevers are detected, then test for EHV-1.

• Any horse with signs of a contagious respiratory disease should be quarantined or isolated. Horses should neither enter nor leave the premises. In the case of EHV, quarantine should last for at least three weeks.

• Mares that abort should be isolated from other mares.

• Do not share equipment or tack among infected horses and normal horses on the facility.

• Proper hygiene should be implemented among horse handlers. Wearing gloves, thorough hand washing and disinfecting footwear can minimize the spread of the virus. Sick horses should be handled last.


3. Is there any value to using booster vaccinations against EHV-1 at this time?

Unfortunately, there is no evidence at this time that current EHV-1 vaccines can prevent EHM.

The more potent EHV-1 vaccines have been shown to reduce nasal shedding and in some cases reduce viremia and possibly lessen the severity of EHM. These products might have some theoretical value against EHM (by reducing viremia), and certainly against spread of the virus.

At this time, the Arthur Veterinary Clinic is recommending vaccinating against EHV-1 with Pneumabort K if your horse is traveling to a show, breeding farm or equine event where contact with other horses may occur.

General Information on EHV


Herpesviruses are a family of viruses which cause disease in both animals and humans. These viruses are species specific, meaning the equine herpesvirus cannot infect humans and the human herpesvirus cannot infect horses. Herpesviruses have the ability to produce a latent infection meaning the virus can remain dormant in the animal without producing any visible symptoms. This results in an inexhaustible reservoir of virus for continual transmission of infection among horses.

There are five types of herpesviruses (numbered EHV-1 through EHV-5) associated with illness in the domestic horse. Of the five types, EHV-1 and EHV-4 are the most common and detrimental.

EHV-1: Causes respiratory disease, abortion, neurologic disease and disease in the newborn foal. Young horses under the age of three which are housed in close confinement such as racetracks and show barns are most commonly affected with the respiratory form. EHV-1 also causes abortions in broodmares during the last four months of gestation. The neurologic form of EHV-1 is seen with increasing frequency and is the most devastating form. Foals born with EHV-1 rarely survive.

EHV-4: Causes an upper respiratory disease in young horses. Respiratory disease is not usually severe but loss of performance can be significant.

Most horses have been infected with EHV by two years of age. The initial exposure can occur in foals from contact with their mothers. The virus can then become latent or inactive in the foal’s body and it becomes a life-long carrier, showing no clinical signs. However, the virus can become reactivated during times of stress such as weaning, long-distance hauling or strenuous exercise and these horses can then spread the virus to other horses. Most mature horses develop some immunity through repeated natural exposure and become less susceptible to respiratory disease caused by EHV.

The incubation period of EHV is 2-10 days after infection until clinical signs appear. EHV is spread by several different routes including:

• Respiratory: A recently infected horse spreads the virus to other horses by direct contact of respiratory secretions or from infective viral particles being picked up in the air. The virus can be shed for 7-10 days from an infected horse. Infected foals are highly contagious. Mares can abort from two weeks to several months following exposure and most likely acquire the virus via the respiratory route.

• Indirect Contamination: EHV can live for days in the environment and be spread through the use of contaminated tack, handlers or equipment or from an aborted fetus and its associated tissues and fluids.

• In Utero: The virus can cross the placenta from an infected mare to her unborn foal.

Clinical signs

Respiratory-These signs can be mild to severe and include a high fever, nasal discharge, loss of appetite, lethargy, increased respirations, cough and ocular discharge. Secondary bacterial infections and pneumonia can occur.

Abortion-Mares that abort due to EHV seldom show clinical signs. The placenta is usually expelled with the aborted fetus still in the amniotic sac. One to two mares may abort in a group or abortion storms (a high number of abortions in a herd) can occur.

Neurologic-This form produces weakness of the hind limb muscles causing incoordination, gait abnormalities and inability to rise from a sitting position. These horses frequently develop urinary incontinence. Horses can become paralyzed and unable to rise. Older horses are more likely to develop the neurologic form of EHV.

Newborn Foals-Foals born with EHV are very weak and suffer from severe pneumonia. These foals usually die within 1-2 days of birth.

Hooty and Quincy

Best Friends Forever

The Arthur Veterinary Clinic and its staff are committed to finding these little fella's good homes. We are not a rescue but couldn’t let these two sweet dogs be euthanized. Both dogs are what some may consider as "special needs". Please find it in your heart to help them out. These guys have had a rough start in life, but they are very sweet and deserve nothing but the best!

Hooty was found running along the road in sub-zero temperatures a few weeks ago. He is a little timid, but very sweet. We estimate that he is about 5yrs old. When he arrived he was in poor body condition and a matted mess. He does not have any teeth and is vision is not the best, but he has a heart of gold and is very loyal. We have treated him medically, given him a haircut and a good scrubbing, and he is now in tip top shape for his new home!
Quincy was relinquished by his owners. He has bilateral cataracts and is mostly blind in both eyes but manages to do VERY well getting around. A good bath and clipping some mats away and this guy is ready to go home with someone who will enjoy the company of an amazingly adaptable little doggy. Quincy is very social and loves attention. He is going to make a great addition to a very lucky home.

Check out the Hooty and Quincy album on Facebook for more pics of these cute little guys. Please call the Arthur Vet Clinic for more information. 217-543-3533

Quincy

Hooty

Foaling Season has begun!

Congratulations to Iron Horse Farm and Dr. Linda Harmon-Dodge on the arrival of Jane's stud foal "Race".

Congratulations to Bella Vista Farm and Fred Helmuth on the arrival of Della's healthy filly foal.

Congratulations to Homer Miller of Arthur IL on the arrival of Shania's filly foal.

Congratulations to Harmony Hill Farm and Bill and Cathy Clark on the arrival of Kandy's filly foal "Kendra".

Congratulations to Harmony Hill Farm and Bill and Cathy Clark on the arrival of Rainey's filly foal "CaLin".

The Maternity Ward at the AVC

Spring is the time for mares to foal or give birth. We use the Foalert mare monitoring system which alerts us when the mare begins to foal. This allows us to attend every foaling. When a mare arrives at the AVC to foal out, we suture (stitch) a "transmitter" to her vulva. This is a picture of a transmitter sutured in a mare. This mare is a Belgian mare named Betty who arrived to foal today!

This transmitter is triggered when the mare begins labor, transmitting a signal to a receiver which is attached to an autodialer. The autodialer then dials our pagers to alert us of labor. Here's a picture of the receiver and autodialer.

It is not uncommon for us to have 3-5 pregnant mares due to foal in the clinic at one time. Talk about an unusual maternity ward! And even though I have attended hundreds of foalings, a newborn foal still makes me smile! The other great thing about foaling out mares is we can watch these foals develop from newborns to yearlings to adults.

Here's a picture of "Emerald Mountain Lau", owned by Marylee McGee, as a newborn foal. She was born on March 5, 2008. And here's a picture of "Emerald" almost a year later as a yearling! Oh...and her mother's name is "Diamond Godiva".

Trivia Question: How long is a mare's gestation? Post your answer as a comment!

Artificial Insemination in Mares

Most horse owners are familiar with artificial insemination (AI). For those of you which are not, AI is big business in the equine industry. The last 20 years has seen a huge increase in the number of breed registries which allow artificial insemination. This blog will explain AI from the mare's perspective.

Artificial insemination is performed by depositing a sample of equine semen into the mare's reproductive tract or uterus. The semen can be either fresh, cooled or frozen. Semen that is classified as fresh is collected from the stallion and then inseminated into the mare within a short period of time on the same farm. For the most part, cooled and frozen semen is transported from the collection farm to another location. This allows mare owners to breed their mares to stallions located in a different part of the country or countries. Semen that is cooled is also collected from the stallion but then processed and packaged in special containers to cool the semen at a specific rate.

Here's two pictures of shipping containers for cooled semen. The blue container is called an Equitainer and is shown with the special coolant can. These containers are meant to be reused.

This is a picture of a disposable container which utilized frozen packs to chill the semen.

This is a picture of the inside of a disposable shipper container with the semen packaged and sent in a syringe.

Cooled semen is meant to be inseminated in the mare within 24-48 hours of collection. Cooled semen is typically either sent via an overnight carrier (UPS, Fedex...etc) or placed on an airline as a cargo shipment. Transporting semen via an airline is typically called "counter to counter" shipments and this method allows mare owners to receive semen the same day and on the weekends. Semen that is frozen is collected from stallions, processed and then frozen. Theoretically, frozen semen can be stored in a frozen state indefinately. Because of this, a mare could be bred with frozen semen after the stallion has died.

Breeding a mare with cooled, transported semen (CTS)

The key to breeding a mare with CTS is the timing of the breeding. Ask any experienced reproductive veterinarian and they will tell you that the most successful veterinarians develop a keen sense or intuition. I guess what I'm saying is breeding mares is really an "art". You must use science and technology to be successful but without a good "feel" for how a mare cycles, all the science and technology in the world will not produce a pregnancy. There are several factors or signs to consider when breeding a mare with CTS. However, to avoid this blog sounding like a class in equine reproductive physiology, I will just explain the follicle development. Ideally, the semen is deposited into the mare's reproductive tract prior to ovulation. The closer the mare is bred to ovulation the better. When a mare is in estrus or heat, she develops a follicle which contains the egg. As the follicle matures or ripens, it becomes larger and softer. So, the ideal time to breed a mare is when she has a large, soft follicle....just before it ovulates and releases the egg into her oviduct. To determine the size and maturity of the follicle, the reproductive tract of the mare is "palpated" (to palpate means to touch or feel). Usually when a mare is palpted an ultrasound is used to actually view the follicle. The follicle can then be measured and recorded.

Here's a picture of one of our portable ultrasounds. This is the same ultrasound we use for pregnancy determination in mares.

This is a great picture of a large follicle. The round, black structure on the ultrasound screen is the follicle. This follicle measure ~49mm.....a good size for breeding.

Ultrasounding or sonogramming or palpating a mare

Every other day or daily palpations/sonograms begin when a mare first shows signs of heat. Typically, I will order semen when a mare has a 35mm-40mm follicle......depending on the mare, breed of mare and availability of semen. The semen is ordered and shipped either overnight or on a airplane. I will usually give the mare an injection of an ovulatory medication to ensure she ovulates when I want her to.....which is hopefully 12-24 hours after she is bred.
The picture below shows the supplies used to inseminate a mare. Sterile OB pipette, sleeve and lubricant. If the semen was not shipped in a syringe, it is transferred to a syringe for insemination.
Inseminating a mare.

After the mare is inseminated, I save a small sample of the semen to evaluate under a microscope. The two main criteria used to evaluate cooled semen are total sperm count and sperm motility. The recommended total count for breeding a mare with cooled, transported semen in 1 billion spermatozoa. Hopefully, the breeding farm collecting the stallion will send the sperm count data with the sample. Just as important or more so, though, is the sperm motility. Motility is defined as forward, progressive movement of a sperm cell. In other words, it does no good for sperm to be circling or going backwards. These sperm are not healthy and are infertile. we like to see motility of greater than 50% with cooled, transported semen. For evaluating semen, we have a video microscope which has a small screen for viewing the sperm. This type of microscope allows better determination of motility plus clients can see what we are seeing when evaluating a semen sample. We love this piece of equipment. And while you can certainly use a traditional microscope for evaluating semen, years ago we splurged and bought this "toy"!

Videomicroscope. The semen sample is placed on a slide which is placed on the microscope stage which is the blue box-like unit on the right. The sperm cells are seen on the screen as white dots or flecks. And voila'....here's a video of live, cooled, transported semen received via UPS from Texas at 24 hours old. This is a good sample of cooled, transported semen....(and one of the main reasons I wrote this blog.....I videoed this sample using my Flip video recorder while the sample was on the videomicroscope......isn't technology grand!!)