EVA, EIA, EHV, EPM—

Knowing and recognizing the differences between these equine ailments

Part 2 of 2: EIA and EPM 

 

By Kimberly Rinker

 

In this second of a two-part series, Midwest Thoroughbred provides a look at two equine ailments: EIA and EPM. By better understanding these diseases and symptoms, horsemen can better recognize and understand options for prevention and treatment.

 EIA

What it is: Equine Infectious Anemia virus is caused by a retrovirus and transmitted from horse to horse by bloodsucking insects, or through unclean needles. Also known as “Swamp Fever,” EIA is potentially fatal and there is no known vaccine for the disease.

First discovered in France in 1843 and then in the United States in 1888, EIA is a slow-acting virus of the lenti-retrovirus group—the same group that is responsible for causing feline and bovine leukemia and acquired immune deficiency syndrome (AIDS) in people.

“In the early 1970s we used to diagnose EIA much more than now,” said Dr. William Moffett, DVM of Dover, Del. “We’ve had numerous cases over the years, and while the disease was still in its early stages of discovery, we had some horses that were positive, who raced successfully.”

“We’ve pretty much eradicated the disease around the racetracks,” Dr. Moffett added. “You seldom see EIA at the tracks today, but you will find it here and there in other breeds not associated with racing.”

In nearly all cases throughout the United States and Canada, horses are required to have an annual or biannual Coggins test—named after the veterinarian who developed the blood test for EIA antibodies.

“I don’t think EIA is a major issue anywhere in the U.S., and if it is, then it’s much more likely to be prevalent in the southern part of the country than in the north, just because of the higher number of mosquitoes that are present in a warmer climate,” Dr. Langley noted. “In my 20 years of practice as a racetrack vet, I’ve had only two cases of the disease.”

Symptoms: Horses typically get a fever and appear depressed with a low-hanging head; they may begin to lose weight, even though they continue to eat. They are often anemic and can begin retaining water, and will sometimes have an irregular heartbeat. Often, these symptoms will reoccur at two-week intervals.

Treatment: Currently, there is no vaccine for EIA. In most instances, infected horses are euthanized, or housed in a quarantined area for life with supportive care.

“This disease is not commonplace,” Dr. Allen admitted. “However, especially for racehorses, who tend to co-mingle more than most horses, it is imperative to have and keep an up-to-date Coggins test on hand at all times.”

EIA can often be difficult to diagnose because the symptoms—in the acute stage, an elevated temperature—occur quickly. It is extremely contagious, however, as one fifth of a teaspoon of infected blood contains enough of the virus to infect one million horses.

The Skinny: Currently, the Coggins Test—a highly sensitive blood test developed in the early 1970s that checks for EIA antibodies in a horse’s bloodstream—is used to test for EIA, with a 95 percent accuracy rate. People are urged not to co-mingle items such as feed and water buckets or other materials between horses, especially when shipping into new venues, such as racetracks, for brief periods of time. While EIA can be contracted through co-mingled syringes, it is most commonly transmitted between horses through biting insects, such as horse and deerflies.

What You Can Do: Reduce the fly, mosquito and gnat population in and around your barn as much as possible through the utilization of fly catchers, sprays and the like. Use a clean needle each time you need to vaccinate or treat your horse, and never reuse syringes from horse to horse. Avoid interchanging bridles, bandages and other equipment on multiple horses. Keep your Coggins’ test up-to-date and have your horses checked on a regular basis, especially when traveling from state-to-state.

“A lot of folks complain about getting a Coggins test, but for the cost ($15-$25) and knowing that in most cases your horse will test negative, it’s well worth the investment,” Dr. Moffett noted.

 

EPM

What it is: Equine protozoal myeloencephalitis is a disease which began to plague horse populations in the mid-1990s and is one of the most serious neurological diseases in equines today. It is caused by the Sarcocystis neurona, a protozoan parasite that attacks the equine central nervous system, and most often occurs when a horse is in high stress situations such as racing or when their immune systems become depleted due to inadequate nutrition and diet deficiencies.

Opossums are thought to be the main carriers of EPM through their feces that are then collected up into hay bales or ingested by horses eating pasture grasses. The protozoa are also thought to be spread through water supplies, such as creeks and rivers that horses might drink from.

Veterinarians diagnose EPM with a blood or spinal fluid test (Western Blot or ELISA Test), the latter of which is thought to be much more accurate. A blood test will indicate exposure to the parasite but cannot specify if there is an active disease in the horse’s system. The spinal fluid test checks for specific types of antibodies to the parasite.

“With any type of lab test, veterinarians are constantly trying to reduce the number of false positives,” Dr. Allen offered. “These EPM tests are constantly being tweaked and are forever-evolving.”

“I think field veterinarians are much more reluctant to do a spinal now than in the past,” Dr. Langley revealed. “Sedation of horses is not always a clear choice, and sometimes horses that you think are sedated will bolt when you draw fluid from them. There’s much more spinal testing done by the universities nowadays.”

Symptoms: Poor coordination (ataxia), overall soreness, abnormal gait, muscle paralysis of the face, head tilt, diminished muscle contour, urine dribbling, lip-drooping, a limp tail, and an in-ability to uncross forelegs are all signs of EPM.

“With racehorses you’re likely to notice possible EPM troubles in a horse racing at high speeds, or those who are racing on smaller tracks,” assessed Dr. Allen. “It takes a lot more coordination on the part of the horse to go around tighter turns than it does around mile turns. If I see a trainer making dramatic equipment changes to a horse to get him to get around a smaller racetrack, then it makes me think the horse could possibly be an EPM candidate.”

“I’ve seen horses with EPM who would try to run across a field and simply fall down, because they were so uncoordinated,” Dr. Moffett explained. “I’ve treated many of them, however, who have come back and functioned quite well as racehorses after being diagnosed with EPM.”

“For diagnostic purposes, I like looking at a horse from behind and in good light. I think it’s really important to be behind them while they’re moving, to be able to make a clear, sound diagnosis of the problem,” Dr. Allen noted.

Treatment: The treatment for EPM can be both costly and challenging. For the past decade, the universal treatment has been a combination of pyrimethamine and sulfa-deraprim (or a potentiated sulfonamide), taken orally in either a powder or liquid form on a daily basis.

“EPM is a costly disease to treat,” Dr. Moffett admitted. “I’m in favor of taking a blood test from a horse that I suspect may be an EPM candidate. If you pull the blood and the anti-bodies aren’t there, then it would be a waste of time and money to treat them. On the other hand, if the horse is positive, then it is best to test his spinal fluid.”

Pyrimethamine is an anti-protozoal drug and sulfadiazine is a sulfa antibiotic, which, when given together, fight the Sarcocystis neurona that cause EPM. This combination actually doesn’t kill the protozoa, but does inhibit growth and reproduction of the protozoa. This combination typically takes 10 to 24 weeks to become effective and costs between $100 to $150.

There are two other products which are popular treatments against EPM. Marquis is a dose-specific oral paste treatment of the drug ponazuril used to combat acute cases of EPM. Released in July 2001 by Bayer, Marquis was the first drug licensed for the treatment of EPM. Each syringe barrel of Marquis contains enough paste to treat one horse at 1,200 pounds for seven days, based on body weight, and costs $190 to $260.

Navigator, the trade name for the drug nitazoxanide is the other FDA approved medication used for treating EPM-positive horses. Distributed by IDEXX Laboratories, it was approved for use in horses in November 2003. Besides inhibiting protozoa-enabling enzymes, Navigator also compromises other bacteria and viruses, especially of the digestive tract, and therefore its use must be carefully monitored by a veterinarian. A box of 26 doses costs $1,200 or more.

The Skinny: Until there is a vaccination for EPM, horse trainers in North America will continue to be plagued with this aggravating, costly, and often devastating disease. Early treatment, once diagnosed, is the best way to combat EPM. Sixty to 70 percent of EPM horses will improve following treatment and 15 to 25 percent recover completely, according to a 2007 report by the University of Minnesota College of Veterinary Medicine.

“EPM presents a number of issues,” Dr. Allen stressed. “Horses that have the disease a long time are going to have the lowest rate of recovery. The damage that is done to the central nervous system and to the spinal cord by the parasite is going to be dramatic in those horses that have a low parasitic concentration.

“The reason being is that a horse will probably not show dramatic clinical signs of EPM, thus allowing the parasite to do a significant amount of damage over a long period of time. A horse with a high concentration of parasites is more likely to show acute symptoms, such as high fever and coordination troubles. Those horses are typically treated quickly and dramatically, and the bugs are thus killed off quicker.”

Dr. Allen added that for many horses, aggressive treatment for EPM will sometimes cause elevated symptoms of the disease, albeit for a short time.

“Once treatment is instituted, and you’re killing off all of these bugs in the horse’s system, it often takes a while for the bug to be expelled from the system,” he said. “That’s why, in a lot of EPM cases, horses will get worse before they get better.”

“I think horsemen have to start looking for another reason that some of these horses are unsound,” Dr. Moffett declared. “EPM has kind of become the disease of the day, and a lot of horses are misdiagnosed with EPM—and never tested—when they could be having some type of chronic lameness issues. A lot of horses are being treated for EPM who may not have the disease.”

Dr. Langley agreed.

“I whole-heartedly agree with Dr. Moffett,” Dr. Langley noted. “EPM is a tough disease, and racehorses in particular have a lot of chronic lameness issues, and sometimes it seems easier to treat them for a suspected ailment like EPM, than to look further. I think there’s a lot of over-diagnosis of EPM and in some cases horses just have a mixed bag of lameness issues that are hard to pinpoint.”

“However, I don’t think the blood tests carry that much weight,” Dr. Langley continued. “When I was running a lot of blood tests for EPM, a lot more came back positive than negative—which simply means the horse has been exposed to EPM—it doesn’t necessarily mean he or she has it or is a carrier.

“I think the key with a possible EPM horse is to try to find something that is consistent with a neurological disease,” Dr. Langley added. “And even then, there’s a chance that perhaps there’s something else going on neurologically with the horse in terms of a disease that we haven’t yet discovered, and perhaps that’s why we can’t cure EPM.”

What You Can Do: As with any equine ailment, early detection is the key to arresting the disease and implementing immediate therapy. Keeping stable areas, barns and pastures free of opossums helps to lower the risk of EPM, and routinely performing blood tests on your horses to monitor their immune levels can help. A healthy immune system is much more likely to fend off EPM than a weakened one.

“It’s tough—especially on the big racing stables—to keep up-to-date on all the vaccinations that horses require nowadays,” Dr. Moffett stressed. “With horses racing all over this country and in Canada on different days and nights, it can pose a bookkeeping nightmare for a lot of trainers.”

Conclusion

With any serious ailment affecting your horse, it often pays off in the end to get your veterinarian involved from the start. Let them assess the needs of your horse in relation to what disease/infection/virus is troubling them at the time, and then work together with he or she to do what is best for the animal in terms of treatment, recovery, maintenance and future prevention.

For more information

Contact the U.S. Department of Agriculture (USDA), and Animal and Plant Health Inspection Services (APHIS), Veterinary Services National Center for Animal Health Programs, at 4700 River Road, Unit 46, Riverdale, Md. 20737–1231, Telephone 301- 734–3279, Fax: 301- 734–7974 or www.aphis.usda.gov/vs/ceah/index.htm. 

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