INFECTIOUS DISEASES
What Causes
EPM in Horses? B y
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EPM THEN AND NOW A retrospective look at how far we have come in understanding, diagnosing and treating this important infectious neurological disease. In this four-part series, Nicola Pusterla, DVM, PhD, DACVIM, will guide us through a reflective account on equine protozoal myeloencephalitis (EPM), including advances in testing and diagnosing, as well as treatment and preventive measures.
Part 1 of this series provides a brief review of what causes EPM.
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Equine protozoal myeloencephalitis (EPM) was first recognized as a condition in 1976, and it remains one of the most common infectious neurologic diseases of horses in North America. A progressive disease, EPM can affect any horse and cause irreversible damage to the brain or spinal cord if left unchecked. Unlike most infectious diseases, EPM management is not black and white, which is cause for much frustration among equine practitioners. The “gray area” surrounding this disease has prevailed since it was originally discovered. As 1 mystery is solved another arises, beginning with the most basic question: What causes EPM in the horse? The main culprits
Originally thought to be caused by Toxoplasma gondii, it took nearly 20 years after the disease was recognized to identify its primary causative agent as Sarcocystis neurona. Today, we know EPM can be caused by both S. neurona and Neospora hughesi. It may come as a surprise, however, that T. gondii is back in the mix as a possible cause (although less is known about this organism’s role). Table 1 depicts the common characteristics of each parasite that can cause EPM.
Sarcocystis neurona
The most common cause, S. neurona encompasses almost every single clinical presentation and 8
Issue 5/2021 | ModernEquineVet.com
