Understanding EPM in Horses- Symptoms, Diagnosis, and Treatment Options

Equine Protozoal Myeloencephalitis (EPM) is a neurological disease that can have devastating effects on a horse’s central nervous system. It is caused by a protozoal parasite that infects the spinal cord and brain, leading to muscle atrophy, coordination issues, and in severe cases, death. EPM is one of the most common causes of neurological problems in horses in North America, affecting a significant portion of the equine population. Its impact is not just physical but also emotional and financial, given the long-term care required for affected horses. Understanding the symptoms, diagnosis, and treatment of EPM is essential for horse owners and veterinarians alike.

This blog post will provide a comprehensive guide to EPM, focusing on its symptoms, causes, risk factors, diagnosis, treatment options, and preventive measures. Early diagnosis and intervention are critical for improving the prognosis of horses affected by EPM.

Symptoms of EPM in Horses

Recognizing the symptoms of EPM early on can greatly influence the outcome of the disease. EPM is often referred to as the “great imitator” because it can mimic other neurological conditions, making diagnosis challenging. The clinical signs vary depending on the areas of the central nervous system that are affected, but common symptoms include:

1. Asymmetry: One of the hallmark symptoms of EPM is the asymmetry of clinical signs. Horses may display uneven muscle atrophy, often more prominent on one side than the other. This can manifest as one-sided drooping of the face, unevenness in muscle tone, or dragging of limbs.
2. Ataxia: Horses with EPM often show signs of incoordination or lack of balance, known as ataxia. They may stumble, drag their feet, or sway as they walk. The condition may worsen over time, and horses may become reluctant to move or hesitant in their gaits.
3. Muscle Atrophy: Affected horses can exhibit muscle wasting, particularly in the hindquarters or along the topline. This muscle loss can be slow and progressive, making it harder to detect in the early stages.
4. Weakness: Weakness is another common sign of EPM. Horses may tire easily, struggle to carry out simple tasks, or show signs of fatigue during exercise. In some cases, they may resist moving forward or backing up.
5. Neurological Deficits: EPM can lead to a range of neurological issues, such as facial paralysis, head tilts, difficulty swallowing, and eye abnormalities. These symptoms arise when the parasite affects specific parts of the brain or brainstem.
6. Behavioral Changes: In some horses, EPM can cause changes in behavior. These can include depression, irritability, or a reluctance to be handled or ridden. While less common, these signs can indicate that the disease has progressed to the brain.

It is important to note that not all horses with EPM will show all of these symptoms, and the severity can vary from mild to severe. The progression of the disease can also be rapid or slow, making it essential for owners to monitor their horses closely if they suspect EPM.

Causes and Risk Factors

Equine Protozoal Myeloencephalitis is primarily caused by the protozoan parasite Sarcocystis neurona, though in rarer cases, Neospora hughesi can also be a culprit. Horses become infected through exposure to the protozoa, which is most commonly spread by opossums. The life cycle of Sarcocystis neurona involves multiple hosts:

1. Opossums: These animals are the definitive hosts of Sarcocystis neurona, shedding the parasite in their feces. When horses come into contact with contaminated feed, water, or soil, they can inadvertently ingest the parasite.
2. Intermediate Hosts: Other animals, such as raccoons, skunks, and armadillos, act as intermediate hosts. These animals harbor the parasite, which then infects the opossum when consumed. The opossum completes the cycle by shedding the parasite into the environment.

Risk Factors:

• Geography: EPM is more prevalent in areas where opossums are common, particularly in North and South America.
• Age and Immune System: Horses of all ages can contract EPM, but younger horses and those with weakened immune systems are more susceptible. Stress, illness, and poor nutrition can increase the likelihood of infection.
• Exposure to Opossums: Horses that graze or are housed in areas frequented by opossums are at higher risk of coming into contact with the parasite.

While not all horses exposed to Sarcocystis neurona will develop EPM, factors such as stress, injury, or concurrent illness can trigger the disease in those who have been exposed.

Diagnosis and Treatment

Diagnosing EPM can be a complex process due to its similarity to other neurological conditions. Veterinarians typically use a combination of clinical examination, diagnostic tests, and response to treatment to confirm EPM.

Diagnosis

1. Neurological Examination: A veterinarian will perform a thorough neurological examination to assess coordination, muscle tone, reflexes, and strength. Asymmetrical symptoms or deficits in balance and coordination may raise suspicion of EPM.
2. Blood Tests: While blood tests alone cannot definitively diagnose EPM, they can detect antibodies to Sarcocystis neurona or Neospora hughesi. A positive result indicates exposure, but not necessarily active disease. More specific testing is needed to confirm EPM.
3. Cerebrospinal Fluid (CSF) Analysis: Collecting and analyzing cerebrospinal fluid is a more reliable method of diagnosing EPM. By measuring antibody levels in the CSF, veterinarians can determine if the central nervous system has been exposed to the parasite. However, this test can still yield false negatives, so clinical signs are considered alongside test results.

Treatment

Once EPM is diagnosed, treatment should begin immediately to halt the progression of the disease. The primary goals of treatment are to kill the protozoa and manage symptoms.

1. Toltrazuril and Ponazuril: These are the most commonly used medications to treat EPM. Ponazuril (marketed under the brand name Marquis) is an FDA-approved antiprotozoal drug that targets Sarcocystis neurona. Toltrazuril, a related drug, is also effective in treating EPM. Both medications work by inhibiting the protozoan’s ability to reproduce, effectively reducing its population in the horse’s central nervous system.
2. Anti-inflammatory Drugs: To manage inflammation and the secondary effects of the protozoal infection, veterinarians may prescribe non-steroidal anti-inflammatory drugs (NSAIDs) such as phenylbutazone or flunixin. These drugs help to reduce swelling in the spinal cord and brain, alleviating some of the neurological symptoms.
3. Supportive Care: Horses with severe muscle wasting or weakness may benefit from physical therapy and supportive care, including stall rest and controlled exercise programs. Nutritional support is also important, particularly for horses that have lost weight or condition during the illness.

Treatment typically lasts for several months, and while some horses recover fully, others may continue to experience neurological deficits even after the infection is cleared. Early intervention and aggressive treatment are key factors in improving the prognosis.

Preventing EPM

Prevention of EPM focuses on minimizing exposure to the Sarcocystis neurona parasite and reducing the risk factors associated with infection.

1. Control of Opossums: The most effective way to prevent EPM is to limit your horse’s exposure to opossums. This can be done by securing feed and water sources to prevent contamination by opossum feces, keeping barns and stables clean, and minimizing attractants such as pet food or trash that may draw opossums to the property.
2. Feed and Water Management: Horses should be fed from elevated feeders, and water sources should be kept clean and covered if possible. This reduces the chances of horses consuming contaminated food or water.
3. Good Pasture Management: Reducing the risk of contamination in pastures is another important preventive measure. Regularly remove manure and keep pastures free of spilled feed or grains that may attract wildlife.
4. Stress Management: Minimizing stress through proper management, nutrition, and care can help reduce the likelihood of a horse developing EPM after exposure. Horses that are stressed or immunocompromised are more susceptible to infection.

By following these preventive measures, horse owners can significantly reduce the risk of their horses contracting EPM.

Conclusion

Equine Protozoal Myeloencephalitis is a serious disease that can cause long-lasting neurological damage in horses. Early diagnosis and treatment are critical for managing the disease and preventing irreversible damage. By understanding the symptoms, causes, risk factors, and treatment options, horse owners can take proactive steps to protect their horses from EPM. While the disease can be challenging to diagnose and treat, advances in medication such as Toltrazuril and Ponazuril have improved the outlook for affected horses. Preventive measures, such as controlling opossum exposure and maintaining clean feeding and watering practices, can also help reduce the incidence of EPM in the equine population. With vigilant care and timely intervention, horses diagnosed with EPM can go on to lead healthy, active lives.