Equine Infectious Anemia

By Tim Cordes, DVM and Charles Issel, DVM, PhD

Equine infectious anemia (EIA) is a potentially fatal blood-borne infectious viral disease that produces a persistent infection among equids nearly worldwide. Although the disease has been recognized for centuries, its prevalence began to rise in the 1930s and reached its destructive peak in the United States between the ’60s and ’70s. In 1975, 10,371 cases of EIA infection were detected in the United States; many of these cases exhibited severe clinical signs, and some resulted in death.

The most common vectors for spreading EIA are biting flies, or tabanids, particularly horseflies. These large blood feeders can carry virus-bearing blood on their mouth-parts from an infected horse to others.

If a horse becomes infected, the clinical signs of disease can vary dramatically, from an acute infection with slight to high fever for a few days and perhaps small hemorrhages, to progressive weakness, weight loss, depression, and disorientation. Some cases are characterized by rapid death, but EIA fatalities are not commonly encountered in the U.S. horse population today. There is no vaccine or treatment for the disease, and it is often difficult to differentiate EIA from other fever-producing diseases, including anthrax, influenza, and equine encephalitis.

The most commonly diagnosed form of the disease is the chronic form, in which the individual has repeated fever episodes and develops other clinical signs including edema (swelling), weight loss, and severe anemia. EIA also has an inapparent form; affected horses might only show a slight fever for a day.

In horses with the chronic form of the disease, the virus takes up permanent residence in a horse’s tissues, and he is always infectious to others, although the virus concentration in blood is much higher in horses with clinical disease.

EIA was difficult to diagnose and identify until 1970, when the agar-gel immunodiffusion test, commonly known as the “Coggins test,” was developed. More recently, enzyme-linked immunosorbent assays (ELISA tests) reduced the time for a lab result from at least 24 hours to less than one hour. Accurate tests allow us to identify and remove positive reactors from herds and effectively block the spread of EIA among tested populations. Categories of horses that require testing include:

  • Equids being entered into exhibitions or competitive events;
  • Equids being moved interstate;
  • Equids entering the United States;
  • Equids changing ownership; and
  • Equids entering horse auctions or sales.

Today the wide availability of the EIA tests, laws, and regulations that control movement of equids, and universal precautions taken to avoid spreading contaminated blood to other horses have reduced EIA disease incidence to a manageable level. Horse population losses in the United States dropped from thousands a year in 1975 to negligible losses in 2010.

EIA, though, is still a threat. The virus is categorized as a retrovirus: It contains RNA genetic material, which is used to produce DNA. This DNA is then incorporated into the genetic makeup of infected cells. A dangerous characteristic of the EIA virus is mutation: The virus genome mutates relatively rapidly, allowing the virus to escape immune surveillance because of its new antigen identity.

This identity change makes EIA virus particularly difficult to control, both in individual equids and in populations, for two reasons. First, an effective vaccine would require a relatively stable antigen pattern to confer immunity. Second, a virus mutation inside an individual equid could cause an inapparent disease carrier to quickly become very ill and significantly more infectious. In addition, the virus appears to become more virulent as it is passed from horse to the next.

Furthermore, not all equid populations are tested regularly. This increases the chances that the virus could be lurking in reservoirs in an unknown number of inapparent carriers that have not yet been identified through testing.

Finding these “hidden cases” and separating them by 200 yards from other animals at least allows us to make headway against the spread of the EIA virus. Also, it can reduce costs for dedicated owners who have tested their horses on a regular basis.

Courtesy of The Horse magazine April 2011.

Equine Infectious Anemia (EIA) or Coggins

Equine infectious anemia is a viral disease that affects the horses’ immune system.

It is transmitted via blood-sucking insects; flys and mosquitos.

The virus actually reproduces bad blood cells and circulates them throughout the body.  The horse’s immune system attacks the blood cells and destroys them, causing anemia.  This can cause inflammation and damage to vital organs.  With the immune system in a weakened state, the threat of secondary infections occurring is another great concern.

There is no known cure for EIA, so it is crucial that you test your horse for this viral disease.

You should have your horse tested every year for Coggins.

We offer Coggins testing ranging from $44.00 – $112.00 (subject to change).

Texas was the number one state reporting EIA in 1993.

Heartworm Guidelines

The Companion Animal Parasite Council (CAPC) has altered guidelines after evidence of preventive-resistant Diofilaria immitis strains was presented at the American Association of Veterinary Parasitologists Conference at the end of July in Chicago.

Researchers have now identified heartworm isolates from the Mississippi Delta region that develop in adult dogs receiving routine monthly heartworm preventives.

  1. This means treatment of heartworm positive dogs should be immediate and aggressive, as noted in the newly revised CAPC guidelines (for details, see capcvet.org).
  2. The “slow kill” therapy sometimes prescribed by veterinarians is no longer appropriate, as researchers have demonstrated that using this modality –repeated macrocyclic lactone administration over a period of time — increases the proportion of circulating microfilariae that possess resistance markers.
  3. Dogs should be tested for heartworms once a year. Existing infections should be aggressively treated with an approved adulticide and microfilariae should be eliminated.
  4. CAPC recommendations for year-round prevention with a broad-spectrum parasiticide should be followed.
  5. Pet owners should be encouraged to reduce exposure to mosquitoes as much as possible.

Specialists emphasize that evidence of resistance does not mean abandoning current protocols but that they be followed even more rigorously. The new evidence confirming heartworm resistance underscores the importance of protecting pets year-round without gaps in prevention.

Preventions are still the best protection we have and consistently administering them is key to maintaining pet health.

Fecals on Horses

We do intestinal parasite screens (fecal) here at the clinic.

We do parasite and sand test to see if the horse needs to be dewormed.

The sand test is to see how much sand has been consumed by the horse and if there is an overwhelming amount it would need to be treated with . If he has too much sand it can cause your horse to colic, because it cannot pass through their system. So, we give them a psyllium product that helps remove it through their feces.

The parasite test is to check to see if your horse has worms. This will reflect that the wormer being used works for your horse. If you use only one kind of wormer for several dewormings in a row then it can cause some parasite resistance in your horse. So, we recommend to do a fecal on your horse regularly to see if it needs to be dewormed.

They are classified as high, medium and low shedders.
High shedders have 15+ eggs per slide
Medium shedders have 4-15 eggs per slide
Low shedders have less than 3 eggs per slide.

If you deworm with Moxidectin we recommend doing a fecal about 16-18 weeks after deworming him.

Ivermectin about 12 weeks after deworming
Fenbendazole or Pyrantel we do about 9 weeks after deworming.
We carry some wormers here at the clinic such as:

  • Eqvalan(ivermectin)
  • Quest Pluss(moxidectin/praziquantel)
  • Panacur(fenbendazole)


Equine Nutritional Consultation

Monday afternoons from 2:00 pm – 5:00 pm
Jim Ward, D.V.M. will be available at Ward Animal Hospital for equine nutritional consultations.
Come by and talk to him, give him a call or schedule an appointment to bring your horse in for him to examine.

Jim Ward, D.V.M. is a 1965 graduate of Texas A & M University School of Veterinary Medicine. He practiced equine veterinary medicine for forty years, emphasizing equine reproduction. He has been extensively involved in the equine industry, owning and managing several breeding farms. He is a Life Member, former board member and a past president the Texas Thoroughbred Association. He was also a board member of the Breeders Cup Ltd and Texas Racing Agri-Industry Council. Jim is currently the Equine Management Consultant for Cargill, Inc., a position he has held since 2000. He is a member of the Cargill Production Development Team and the Cargill Equine Enterprise Team. His passion has been to develop feeds that would provide solutions for veterinarians and horse owners for diseases such as Colic, Laminitis, Tying-up, Developmental Orthopedic Disease, Cushing’s Disease and Equine Metabolic Syndrome. In 2004 he received the Cargill Innovation award for his role in the development of the feed, SafeChoice. He received the Trailblazer award from Cargill in 2015.

Ward is the owner/ manager of the Center Veterinary & Reproductive Services and serves in a consultative role at Center Ranch and Ward Animal Hospital. He does nutrition consulting at major ranches including 6666 Ranch, EE Ranches, Time McQuay Stables and Hartman Equine Reproduction Center. Ward does nutrition consultative work with equine veterinary practices including Texas A & M University Large Animal Hospital, Lone Star Park Equine Hospital, Brazos Valley Equine Hospital, Elgin Veterinary Hospital, Premier Equine Veterinary Services, Hill Country Veterinary Hospital and Retama Equine Hospital.

He serves on the Texas A & M University College of Veterinary Medicine Development Council. He is an Adjunct Professor at the College of Veterinary Medicine where he presents lectures on equine nutrition to veterinarians, veterinary students and equine industry members. He received the Distinguished Alumnus award from Texas A & M University College of Veterinary Medicine and Biomedical Sciences. Ward has recently developed a series of online learning lessons on Equine Nutrition that have been approved by the Texas Board of Veterinary Medical Examiners for C.E. credit. He is a member of the American Veterinary Medical Association, American Association of Equine Practitioners, Texas Veterinary Medical Association, and the Texas Equine Veterinary Association.

Internal Equine Parasites

Internal parasites, or worms, may cause extensive damage to the gastrointestinal tract of your horse.  Effects of parasites may appear externally as; dull hair coat, depression, loss of body condition, diarrhea, swollen abdomen (typically in younger horses). Parasites can compromise the horse’s immune system and may even cause colic. In rare cases, death.

To find out your horse’s situation involving parasites, bring in samples for routine fecals. We recommend worming on an “as needed” basis and rotating your wormer brands. Remember not all horses need to be wormed all the time. Unnecessary worming leads to the parasite resistance problem.

Did you know there are over 150 internal parasites that can affect horses?

Monitoring Equine Parasites Via Fecal Egg Per Gram

By Dr. Bryan Waldridge · April 29, 2011

Fecal egg per gram (EPG) counts are valuable to actually determine the number of worm eggs in a horse’s manure. Routine fecal floats determine if parasite eggs are present but cannot differentiate a heavy-shedding horse from one shedding fewer worm eggs.

Manure for EPG determination is weighed, floated in a standard volume-of-egg flotation solution, and worm eggs are counted under a microscope using a special slide.

Your veterinarian can perform EPG counts and is the best source of information to tailor a deworming program that is best for your farm.

An excellent study from Denmark found that horses tend to be consistent in the amount of worm eggs shed in their manure.

Less than 200 EPG is considered a low level of shedding. Horses that had two previous EPG counts performed six months apart that were both less than 200 EPG had an 84% chance that their third EPG count would also be low. Similarly, if a horse had two previous EPG counts greater than 200, the chance of being greater than 200 EPG on the third count was 59%. This demonstrated that horses with low EPG counts tend to keep low EPG counts and those that are high also tend to stay high.

These findings help to target deworming to reduce resistance and allow for the classification of horses into low or high EPG shedders. Horses that consistently have low EPG counts do not require frequent deworming, and deworming twice a year is probably sufficient. Horses that have a consistently high EPG count can be segregated to reduce overall pasture parasite egg contamination, and these horses may benefit from more frequent deworming.

Your veterinarian can perform EPG counts and is the best source of information to tailor a deworming program that is best for your farm. EPG counts also help slow the development of resistance to dewormers, and less frequent deworming reduces costs.

AAEP Intestinal Parasite Information

Fecals on Horses

Strategic Deworming



Pigeon Fever

Pigeon Fever, also called dryland distemper or false strangles, is not the most serious disease that can affect a horse. It is a bacterial infection that creates purulent abscesses. Corynebacterium pseudotuberculosis thrives in soil contaminated with manure, especially in hot, droughty conditions. When horses roll or lie down in paddocks or churn up clouds of bacteria-laden dust, the organisms may enter wounds, insect bites or breaks in the skin. House flies, stable flies and horn flies have all been found to be carriers and may transmit the infection from horse to horse. Composting manure or removing it from your property also helps keep fly populations down.

  • Isolate infected horses. The pus that drains from a pigeon fever abscess is loaded with bacteria that can easily persist in that soil and infect other horses.
  • Quarantine new horses. Horses may carry pigeon fever for three to four weeks before showing signs and the shipment of carriers around the country may be contributing to the spread of the infection beyond its former boundaries. When bringing new horses onto your property, keep them isolated from resident horses long enough to be sure they are not incubating any infections. House newcomers in a separate barn or pen as far as possible from other horses for at least three weeks.

The disease takes three forms:

  • External abscesses form under the skin or in the musculature.
  • Internal abscesses form within the internal organs, usually the lungs, liver, spleen or kidneys.
  • Ulcerative lymphangitis affects the lower legs.

Protect your pet!

Fleas and ticks– if you have wildlife or stray animals around your home then your pets should be protected.

Heartworm disease– standing water around your home is a breeding ground for those pesky mosquitoes, which can cause heartworms

Canine topical flea prevention

  • Vectra 3D-Provides a 6-way protection: repels and kills fleas, ticks mosquitoes, biting lice, sand flies and mites.

Canine oral flea/ tick prevention

  • Simparica- prevents fleas/ticks for 30 days
  • Bravecto – prevents fleas/ ticks for 12 weeks

Canine oral flea/heartworm disease/ intestinal parasite prevention

  • Trifexis- Kills and prevents fleas, prevents heartworms and controls intestinal parasites (hookworms, whipworms, and roundworms).

Feline topical prevention

  • Revolution- Controls and prevents flea infestations, prevents heartworm disease, controls ear mites and intestinal parasites for 30 days.
  • Catego- prevents flea/ ticks for 30 days.

Pets should be protected year round for complete effectiveness.
All oral preventions are given monthly and by prescription only.
Revolution is a feline monthly topical prevention that is by prescription only.

Office: 936-564-4341         E-mail: info@wardanimalhospital.com
3825 NW Stallings, Nacogdoches, Texas 75964
Monday- Friday 8AM-6PM
Saturday 8:30AM- 12:30PM