Equine Protozoal Myeloencephalitis, also known by the acronym EPM, is one of the most commonly diagnosed neurological disorders in horses. The symptoms include muscle atrophy, loss of coordination, trouble swallowing, stumbling, drowsiness, general weakness, sore back,tilted head and drooping eyelids. Several neurological disorders have similar or identical symptoms to EPM; subsequently, horses are sometimes diagnosed with EPM when in fact a different disorder is present. Alternatively, a horse with EPM may be wrongly diagnosed with a different neurological condition that mimics EPM's symptoms.
West Nile Virus
West Nile Virus (WNV) is transmitted by mosquitos and affects an infected horse's central nervous system. Neurological symptoms produced by WNV mimic those of EPM. These include lameness, falling down on the front knees, toe dragging, drowsiness, fever and additional symptoms such as violent behaviour or extreme sensitivity to touch, light and sound. About half of all horses who contract WNV will survive the infection, and a vaccine is available for those horses who have not been infected.
Two types of equine encephalitis -- Eastern Equine Encephalitis or "EEE" and Western Equine Encephalitis or "WEE" -- are transmitted to horses by mosquitoes. A horse infected either of these conditions may display symptoms that mimic those associated with EPM: lethargy, weakness, a lack of coordination, recumbency or even death. Preventive vaccines are available, but once a horse is infected there is no cure for EEE and WEE. Some horses will independently recover from these diseases, but many are euthanized to save additional suffering to the horse when recovery is unlikely.
Equine Herpes Virus Type I
Equine Herpes Virus Type I, known by the acronym EHV-1, is usually first noticed as a form of respiratory disease. However, EHV-1 can sometimes take a form that affects the horse's nervous system, with symptoms similar to those associated with EPM. These may include weakness, hind-leg paralysis, recumbency and death. While no particular treatment for EHV-1 exists, care and therapeutic treatment of symptoms can help a horse to recover from the virus.