DOMESTIC EQUINES · OWNER EDUCATION
Equine Protozoal Myeloencephalitis (EPM)
EPM is a neurologic disease caused by protozoal infection that can produce uneven weakness, incoordination or muscle loss.
THE SHORT VERSION
What matters for your animal?
Start with the warning signs and when-to-contact sections if your animal is unwell. The same outward change can have several causes, so this guide helps you prepare questions rather than identify a diagnosis on your own.
What is this condition?
EPM is a neurologic disease caused by protozoal infection that can produce uneven weakness, incoordination or muscle loss. The same outward signs can occur with several diseases, so an examination and appropriately selected testing are important.
EPM can affect neurologic function, but poor coordination has several possible causes. Testing must be interpreted with the examination because evidence of exposure is not automatically proof that it explains the signs. The veterinarian establishes the likely location and cause of dysfunction before selecting treatment. Monitoring should track measurable changes in function and safety rather than relying on a general impression of improvement.
Which species does this guide cover?
The species listed above are the focus of this guide, rather than a complete list of every animal that can develop this condition. Causes, testing and treatment may differ between species and individual patients.
Why can it happen?
- Exposure to infective material associated with opossum feces; exposure alone does not mean a horse has EPM.
- Clinical disease depends on infection reaching the nervous system and the individual response.
What might an owner notice?
- Uneven weakness, stumbling, abnormal gait or muscle loss.
- Difficulty swallowing, facial asymmetry or behavior change in some horses.
How is the problem investigated?
Complete neurologic examination and exclusion of other causes. Blood and cerebrospinal-fluid testing interpreted together with signs and regional exposure.
A neurologic examination helps locate where a problem may be occurring, such as the brain, spinal cord, peripheral nerves, or balance system. The location then guides the choice of tests. Weakness caused by low blood sugar or another body-wide problem can resemble a primary neurologic disorder, so blood testing may be important even when movement is the main concern. Imaging can provide structural information, but it is selected in the context of the examination rather than ordered identically for every animal.
Blood-cell testing and a chemistry profile provide complementary information. Cell counts can help assess anemia, inflammation, and platelets; chemistry measurements help assess organs and internal balance. Results are interpreted against the species, examination, hydration, medication history, and previous values. A value just outside the reference interval is not automatically the cause of illness. Trends can be more useful than one result, particularly when the aim is to monitor a chronic problem or check that treatment remains safe.
What might treatment involve?
Veterinarian-selected antiprotozoal medication and supportive care. Rehabilitation and monitoring based on neurologic deficits.
Parasite control depends on the organism, its life cycle, and the host species. A medicine effective against one parasite may not cover another, and a product safe for one species may be dangerous for a different animal. Testing may be needed before treatment and again when assessing response or ongoing exposure. Environmental stages and untreated contacts can contribute to reinfection. The plan therefore may combine a specific medicine with cleaning, husbandry, and prevention instead of relying on a single dose.
This is an overview, not a prescription or a recommendation for a specific individual animal.
What can owners do at home?
Write down when the problem began and track appetite, drinking, waste, activity, breathing and medication use. Bring clear photos or short videos when they can be taken without stressing the animal. Follow the veterinary team's instructions for medication, feeding, isolation, environmental changes and rechecks.
Loss of coordination or strength can make ordinary feeding, resting, and toileting unsafe. The animal may need a protected area and assistance suited to the diagnosis and species. Ask for practical handling instructions, including how to move the patient without worsening injury and how to recognize loss of bladder or swallowing function. Do not assume that attempts to walk constitute useful exercise. The recovery plan should specify permitted movement and a clear route to urgent reassessment if function deteriorates.
Avoid actions that could make care less safe.
- Do not use human medication, leftover antibiotics or another animal's treatment without veterinary direction.
- Do not force food or water into an animal that cannot swallow normally, is struggling to breathe or may have an obstruction.
- Do not delay veterinary care when pain, breathing, appetite, urination, movement or responsiveness changes quickly.
What can the longer-term outlook involve?
The outlook depends on the underlying cause, severity, species and how quickly effective care begins.
A recheck is not simply a repeat of the first appointment. It assesses whether the original problem is improving, whether complications are appearing, and whether the treatment remains appropriate. The useful measures may include comfort, function, intake, body weight, examination findings, or selected tests. Ask which changes are expected before the visit and which should trigger an earlier call. Improvement in one sign does not always mean that every part of the disease has resolved.
Can risk be reduced?
Provide species-appropriate nutrition, housing, sanitation and routine veterinary care. Learn the animal's normal behavior, appetite, body condition and waste pattern so meaningful changes are noticed early.
When should you arrange care?
- Contact a veterinarian promptly for uneven weakness, stumbling, abnormal gait or muscle loss. or difficulty swallowing, facial asymmetry or behavior change in some horses..
- Arrange reassessment if signs return, worsen or do not improve as expected.
Seek urgent veterinary advice if you notice:
DO NOT DELAY URGENT CARE- Horse unable to stand, rapidly worsening incoordination, choking, seizure or severe injury risk.
What information helps the care team?
Record which animals are affected, feeding or housing changes, recent arrivals, treatments and any losses. For a flock or herd problem, the number affected and the pattern over time may be as important as one animal's examination.
How should you understand the tests?
Ask what each proposed test is intended to answer. Some tests identify a cause; others assess severity, organ function or treatment safety. Results are interpreted with the examination and history. A normal result does not exclude every problem, and an abnormal result does not always explain every sign.
Questions to ask before leaving
- What is confirmed, and which other explanations are still being considered?
- What changes should we expect with the proposed plan, and when should we reassess if they do not occur?
- Which observations should I record, and which changes mean I should call sooner?
- What medicine or home-care problems should I report, and what are the instructions for a missed dose or suspected side effect?
- When is the recheck, what will it assess, and whom should I contact after hours?
A care plan may be adjusted as results or the response become clearer. Keep the written instructions and tell the team if cost, handling or administration difficulty makes the plan hard to follow.
Sources behind this guide
VeterinaryPartner — client education from the Veterinary Information NetworkVeterinary, university or animal-health guidance ↗American Association of Equine Practitioners: horse-owner resourcesVeterinary, university or animal-health guidance ↗Content last reviewed: September 17, 2026. Review status: veterinary-informed; independent veterinarian review not yet completed.