Equine Protozoal Myeloencephalitis (EPM) is a progressive neurologic disease caused by infection of the central nervous system with the protozoan parasite *Sarcocystis neurona*. It can cause a wide range of neurologic deficits and is one of the most common infectious neurologic diseases of horses in the Americas. ## What it is Horses become infected by ingesting sporocysts of *Sarcocystis neurona* shed in the feces of opossums, the definitive host. The parasite migrates to the central nervous system, where it causes inflammation and damage to the brain and spinal cord. The disease is highly variable in its presentation because the parasite can affect any part of the CNS. Clinical signs depend on the location and severity of the lesions. EPM is not contagious between horses. Opossums are the main source of infection, and horses are considered dead-end hosts. ## Signs and symptoms - Asymmetric incoordination (ataxia), often worse in the hind limbs - Muscle atrophy, especially of the gluteal or shoulder muscles - Head tilt, facial nerve paralysis, or difficulty swallowing - Weakness, stumbling, or toe dragging - Behavioral changes or lethargy - In severe cases, recumbency or seizures - Signs can be acute or slowly progressive ## Causes and risk factors EPM is caused by *Sarcocystis neurona*. Risk factors include exposure to opossum feces (contaminated feed, water, or pasture), stress, immunosuppression, and young age. The disease is more commonly diagnosed in horses in the eastern and central United States but can occur anywhere opossums are present. ## How it is diagnosed Diagnosis is based on clinical signs, neurologic examination, and laboratory testing. The most common tests are serum and cerebrospinal fluid (CSF) antibody tests (IFAT or ELISA) to detect exposure and evidence of central nervous system infection. Ruling out other neurologic diseases is important. Advanced imaging (MRI) can help identify lesions in some cases. ## Treatment and management Treatment involves prolonged courses of antiprotozoal medications, most commonly ponazuril or diclazuril, often combined with anti-inflammatory drugs such as flunixin meglumine or dexamethasone in the early stages. Supportive care, including rest, physical therapy, and nutritional support, is important. Treatment duration is typically 1 to 3 months or longer, and response varies. Some horses recover well, while others have permanent neurologic deficits. ## When to call the vet Contact your veterinarian immediately if your horse shows any signs of incoordination, muscle atrophy, head tilt, or other neurologic abnormalities. EPM can progress rapidly, and early treatment improves the chance of a favorable outcome. ## Prevention Prevention focuses on reducing exposure to opossum feces. Keep feed and water sources covered and clean, control opossum populations around barns when possible, and avoid feeding hay or grain that may have been contaminated. Stress reduction and good overall health management may help lower susceptibility. ## Frequently asked questions **Is EPM contagious between horses?** No. Horses cannot transmit EPM to each other. Opossums are the definitive host that sheds the infective stage. **Can a horse fully recover from EPM?** Some horses make a full recovery with early and aggressive treatment. Others are left with permanent neurologic deficits depending on the extent of damage. **How long does treatment for EPM take?** Treatment typically lasts 1 to 3 months or longer, with regular monitoring of clinical response and antibody levels. This information is for educational purposes only. Always consult with a licensed veterinarian for diagnosis and treatment of your horse.
Asymmetric incoordination (ataxia), often worse in the hind limbs; muscle atrophy, especially of the gluteal or shoulder muscles; head tilt, facial nerve paralysis, or difficulty swallowing; weakness, stumbling, or toe dragging; behavioral changes or lethargy; in severe cases, recumbency or seizures; signs can be acute or slowly progressive
Equine Protozoal Myeloencephalitis (EPM) is a progressive neurologic disease caused by infection of the central nervous system with the protozoan parasite *Sarcocystis neurona*. It can cause a wide range of neurologic deficits and is one of the most common infectious neurologic diseases of horses in the Americas. ## What it is Horses become infected by ingesting sporocysts of *Sarcocystis neurona* shed in the feces of opossums, the definitive host. The parasite migrates to the central nervous system, where it causes inflammation and damage to the brain and spinal cord. The disease is highly variable in its presentation because the parasite can affect any part of the CNS. Clinical signs depend on the location and severity of the lesions. EPM is not contagious between horses. Opossums are the main source of infection, and horses are considered dead-end hosts. ## Signs and symptoms - Asymmetric incoordination (ataxia), often worse in the hind limbs - Muscle atrophy, especially of the gluteal or shoulder muscles - Head tilt, facial nerve paralysis, or difficulty swallowing - Weakness, stumbling, or toe dragging - Behavioral changes or lethargy - In severe cases, recumbency or seizures - Signs can be acute or slowly progressive ## Causes and risk factors EPM is caused by *Sarcocystis neurona*. Risk factors include exposure to opossum feces (contaminated feed, water, or pasture), stress, immunosuppression, and young age. The disease is more commonly diagnosed in horses in the eastern and central United States but can occur anywhere opossums are present. ## How it is diagnosed Diagnosis is based on clinical signs, neurologic examination, and laboratory testing. The most common tests are serum and cerebrospinal fluid (CSF) antibody tests (IFAT or ELISA) to detect exposure and evidence of central nervous system infection. Ruling out other neurologic diseases is important. Advanced imaging (MRI) can help identify lesions in some cases. ## Treatment and management Treatment involves prolonged courses of antiprotozoal medications, most commonly ponazuril or diclazuril, often combined with anti-inflammatory drugs such as flunixin meglumine or dexamethasone in the early stages. Supportive care, including rest, physical therapy, and nutritional support, is important. Treatment duration is typically 1 to 3 months or longer, and response varies. Some horses recover well, while others have permanent neurologic deficits. ## When to call the vet Contact your veterinarian immediately if your horse shows any signs of incoordination, muscle atrophy, head tilt, or other neurologic abnormalities. EPM can progress rapidly, and early treatment improves the chance of a favorable outcome. ## Prevention Prevention focuses on reducing exposure to opossum feces. Keep feed and water sources covered and clean, control opossum populations around barns when possible, and avoid feeding hay or grain that may have been contaminated. Stress reduction and good overall health management may help lower susceptibility. ## Frequently asked questions **Is EPM contagious between horses?** No. Horses cannot transmit EPM to each other. Opossums are the definitive host that sheds the infective stage. **Can a horse fully recover from EPM?** Some horses make a full recovery with early and aggressive treatment. Others are left with permanent neurologic deficits depending on the extent of damage. **How long does treatment for EPM take?** Treatment typically lasts 1 to 3 months or longer, with regular monitoring of clinical response and antibody levels. This information is for educational purposes only. Always consult with a licensed veterinarian for diagnosis and treatment of your horse.
Asymmetric incoordination (ataxia), often worse in the hind limbs; muscle atrophy, especially of the gluteal or shoulder muscles; head tilt, facial nerve paralysis, or difficulty swallowing; weakness, stumbling, or toe dragging; behavioral changes or lethargy; in severe cases, recumbency or seizures; signs can be acute or slowly progressive