Equine Protozoal Myeloencephalitis

Equine Protozoal Myeloencephalitis (EPM) is a disease that affects the central nervous system of horses, leading to a variety of neurological symptoms. It is caused by the protozoan parasites Sarcocystis neurona and less commonly, Neospora hughesi. The disease is significant in the equine community due to its potential to cause severe and sometimes irreversible damage to the affected horses.

Etiology

EPM is primarily caused by the protozoan Sarcocystis neurona. Horses become infected by ingesting food or water contaminated with opossum feces, which contain the infective sporocysts of the parasite. Although horses are a dead-end host for Sarcocystis neurona, meaning they do not contribute to the spread of the disease, the impact on an individual horse can be devastating. Neospora hughesi has also been identified as a cause of EPM, but it is much less common.

Pathogenesis

After ingestion, the sporocysts release sporozoites that penetrate the intestinal lining and enter the bloodstream. These sporozoites then migrate to the central nervous system (CNS), where they cause inflammation and damage to the brain and spinal cord. This damage results in the wide range of neurological symptoms associated with EPM.

Clinical Signs

The clinical signs of EPM can vary widely depending on the areas of the CNS affected. Common symptoms include:

• Ataxia (lack of coordination)
• Muscle atrophy
• Weakness or paralysis of limbs
• Seizures
• Behavioral changes
• Difficulty swallowing

Because these symptoms can also be indicative of other neurological diseases, a thorough diagnostic process is necessary to confirm EPM.

Diagnosis

Diagnosis of EPM is challenging due to the variability of symptoms and the need to differentiate it from other neurological disorders. Diagnostic methods include:

• Serological tests to detect antibodies against Sarcocystis neurona and Neospora hughesi
• Cerebrospinal fluid (CSF) analysis to detect inflammation and the presence of protozoan antibodies
• Advanced imaging techniques, such as MRI, to identify lesions in the CNS

Treatment

Treatment for EPM involves the administration of antiprotozoal medications to kill the parasites. The most commonly used drugs are:

• Pyrimethamine and sulfadiazine
• Ponazuril
• Diclazuril

In addition to antiprotozoal therapy, supportive care, including anti-inflammatory medications and physical therapy, may be necessary to help the horse recover from neurological damage.

Prevention

Preventive measures focus on reducing the risk of exposure to the parasite. Strategies include:

• Regularly cleaning feed and water containers to prevent contamination with opossum feces
• Implementing measures to discourage opossums from entering horse-keeping areas
• Providing clean, high-quality feed that is less likely to be contaminated

Prognosis

The prognosis for horses with EPM varies. Early diagnosis and prompt treatment can improve the chances of recovery, although some horses may have residual neurological deficits. The severity of the disease at the time of diagnosis is a critical factor in determining the outcome.