What protozoa causes Equine Protozoal Myoencephalitis?

Equine Protozoal Myeloencephalitis (EPM) is primarily caused by the protozoan parasite Sarcocystis neurona. This parasite infects horses and can lead to serious neurological conditions as it invades the central nervous system, resulting in clinical signs such as ataxia, weakness, and behavioral changes.

Sarcocystis neurona is specifically adapted to affect equines, and it is often transmitted through ingestion of infected sporocysts found in the feces of opossums, which are considered a primary host for this parasite. Understanding the life cycle and transmission of Sarcocystis neurona is crucial for managing and preventing EPM in horses.

The other protozoa listed do not typically cause EPM in horses. Cryptosporidium primarily affects the gastrointestinal tract of a variety of species, Toxoplasma is known for its effects on cats and other mammals, while Giardia predominantly causes intestinal issues in various animals, including humans. This distinct specificity of Sarcocystis neurona for equines establishes its significance as the causative agent of EPM, making it the correct answer.