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UC Davis Determines Illness Affecting Horse for Years

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Mudpie’s lingering illness was finally diagnosed as EPM.

--Owners Pleased EPM Was Finally Diagnosed--

VMTH “Case of the Month” – December 2014

When Mudpie, a 17-year-old mustang mare, presented to the UC Davis Veterinary Medical Teaching Hospital, her owner and veterinarians weren’t exactly sure what was wrong with her. She suffered a shoulder injury three years prior, as well as what appeared to be a hip injury or suspected broken pelvis. After several months rest, she seemed to be on the mend.

Although Mudpie was able to be ridden again, she had intermittent relapses of lameness of the left hind limb. Just a few weeks before coming to UC Davis, though, Mudpie re-injured that limb and was also kicked in the same area. Her lameness worsened, so her owners decided it was time to have Mudpie examined by the specialists at the VMTH.

Once at UC Davis, Mudpie was given physical, lameness and neurologic examinations. Veterinarians in the Equine Medicine Service noticed swelling in her hind limbs and some minor lameness. They attributed the swelling to the kick sustained a week earlier, and the lameness to her previous injuries. Neither were of too much concern to the veterinarians and didn’t appear to be the cause of her more serious issues. The neurologic examination was a different story, though.

While there was a chance that Mudpie’s condition could have an orthopedic component, UC Davis specialists—including a board-certified neurologist—thought that the neurologic findings were the likely cause of her problems. They suspected Mudpie could be suffering from a number of ailments, including arthritis along her spine, neoplasia (the formation of a tumor), fungal infection or equine protozoal myeloencephalitis (EPM).

EPM is a debilitating neurologic disease in horses caused by the ingestion of a protozoa. Equine researchers have determined that the host of that protozoa is the opossum, which sheds it in its feces. To determine if a horse has EPM, veterinarians can test its blood to see if the horse has developed antibodies to the protozoa. The greater the antibody response, the more likely the horse has been exposed to or infected with the protozoa that causes EPM.

Mudpie’s blood antibody titer (the measurement of antibodies she produced) was off the charts of EPM indication. Any number above 80 on the particular test performed on Mudpie is indicative of being EPM positive. Samples are tested to an endpoint titer of 2,560 because any value beyond that point is obviously indicative of EPM. Mudpie’s results had reached that threshold. There was no doubt that Mudpie had EPM.

She was immediately started on ponazuril, an anti-protozoal drug, as well as an anti-inflammatory drug for the swelling in her hind limbs. It was also recommended that Mudpie’s food be kept off the ground or in a container, and that precautions be made to keep wildlife, especially opossums, off the property.

Mudpie returned to the VMTH a month later for another EPM test. Her titer had decreased to 320. Now nearly a year later, her titers remain at an EPM-positive level, but her owner reports a dramatic improvement in her condition. UC Davis veterinarians aren’t necessarily surprised that the titer levels remain positive. Titers may remain high for long periods of time despite improvement or resolution of clinical signs, and horses can get re-exposed or re-infected. Mudpie’s last examination at UC Davis by a board-certified neurologist showed marked improvement, from “moderate/severe” signs on her initial presentation, to “mild” signs not noticeable to the untrained eye on her last examination.

Mudpie’s owners are pleased that they are able to ride her again, and that her condition continues to improve.

“For the longest time, we just thought that Mudpie would get better on her own,” said her owner. “But her condition kept going back and forth between getting better and then getting worse again. We’re so happy that we finally got the proper diagnosis of her condition. We wish we had come to UC Davis much sooner.”


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For more information on EPM, including a diagnostic flow chart and videos for veterinarians, please see our EPM website.


About the Veterinary Medical Teaching Hospital
The William R. Pritchard Veterinary Medical Teaching Hospital at the University of California, Davis—a unit of the School of Veterinary Medicine—provides state-of-the-art clinical care while serving as the primary clinical teaching experience for DVM students and post graduate veterinarian residents. The VMTH treats more than 47,000 animals a year, ranging from cats and dogs to horses, cows and exotic species. To learn more about the VMTH, please go to Timely news updates can be received on its Facebook ( and Twitter ( pages.

Rob Warren
VMTH Communications & Marketing Officer