In the December 2024 issue, we introduced part one of our four part series on “Understanding Equine Protozoal Myeloencephalitis (EPM).” We explored why this disease is so challenging. Even with swift treatment, EPM can lead to long-term effects and potential relapses.
Now, in part two, we focus on identifying the early signs and symptoms of EPM in horses, which can range from subtle, mild changes to more advanced stages. Recognizing early, mild symptoms and indicators is essential for taking timely action and ensuring effective treatment.
Signs and Symptoms of EPM
EPM is complex to diagnose because when a horse tests positive for it, it only indicates they have been exposed; however, exposure does not mean the horse will develop the disease or show symptoms. Some horses have a significant immune response to the protozoa, which helps keep the disease at bay. EPM is considered an “opportunistic” disease, meaning it can stay dormant in the body until conditions allow it to flourish.
According to Dr. Lew Strickland, Extension Veterinarian at the University of Tennessee Knoxville, “clinical signs of EPM can vary and often mimic other neurological conditions.” Mild symptoms of EPM include a slight lameness or paralysis. This is troublesome because EPM can often be overlooked or mistaken for other less concerning issues by owners. The subtle lameness or paralysis exhibited by horses with mild EPM symptoms may be attributed to muscle strains, injuries, or general fatigue. This misdiagnosis or lack of recognition can be concerning because, according to studies published in the Journal of the American Medical Association (JAMA), untreated conditions can progress and lead to more severe symptoms over time. This highlights the importance of timely and accurate diagnosis to prevent long-term complications.
The delayed diagnosis or misinterpretation of mild EPM symptoms can have detrimental consequences for horses. As the disease progresses, the protozoa responsible for EPM can continue to damage the nervous system, causing more severe and debilitating effects. Advanced symptoms can and will lead to a poor quality of life and decreased ability to perform regular activities for the horse.
The challenge lies in recognizing that mild symptoms in horses may be indicative of a more serious underlying condition like EPM. Prompt identification and accurate diagnosis are crucial for timely intervention and treatment. Veterinarian involvement is essential in ruling out other conditions and conducting thorough examinations to identify the true cause of the horse’s symptoms. By addressing potential EPM cases early on, appropriate treatment plans can be implemented and tracked, potentially mitigating the progression of the disease and preventing the onset of more advanced symptoms.
As EPM progresses, the symptoms can become more severe and distressing for the affected horse. While early signs may include subtle gait abnormalities, such as stumbling or incoordination, more advanced symptoms indicate a progression of the disease. These symptoms include asymmetric ataxia, where the horse exhibits a lack of coordination on one side of the body, weakness in the limbs, and muscle atrophy, particularly in the gluteal muscles. Facial paralysis, head tilt, dysphagia (difficulty swallowing, which can cause choke in horses), seizures, collapsing episodes, abnormal sweating, and loss of sensation may also manifest as the disease advances. These progressive symptoms highlight the urgent need for prompt veterinary intervention and treatment.
Early Diagnosis and Intervention
“Early detection is key to a horse’s recovery. If you suspect your horse has EPM, you should contact your veterinarian for the latest recommended treatment,” according to Dr. Strickland. “Without treatment, EPM is often fatal, but the severe signs, particularly recumbency, may not occur for years after infection. The disease can progress steadily or in a stop-start fashion,” Dr. Strickland states.
According to research, approximately 50-60% of horses with EPM can recover fully with proper veterinary intervention and treatment. However, it is important to note that not all horses respond favorably, and around 20-30% may not fully recover despite treatment. Additionally, a small percentage of horses, around 10-20%, may experience relapses or a recurrence of symptoms even after initial improvement.
As outlined EPM can be challenging to diagnose early due to subtle symptoms, but it’s crucial to catch as early as possible for the best chance at recovery. In February’s Part Three of this series, we’ll dive into treatments, including common medications, the duration of treatment, and therapies like physical therapy exercises to help horses regain strength and recover fully.
Kyla Szemplinski, MS, serves as an Extension Agent I for 4-H Agricenter Youth Development with the UT TSU Shelby County Extension. She supports the equine community in Shelby County, Tennessee, offering guidance and expertise. Kyla can be reached at the Shelby County office by calling 901-752-1207 during regular business hours, Monday through Friday, 8:00 AM to 4:30 PM CST.
