What are the most important neurologic problems veterinarians face throughout the year? That's the question Debra Sellon, DVM, PhD, Dipl. ACVIM, associate dean of the Graduate School at Washington State University and professor of equine medicine, and this author (Steve Reed, DVM, Dipl. ACVIM, of Rood & Riddle Equine Hospital in Lexington, Ky.) posed to the audience to start the infectious neurologic diseases table topic session at the 2008 American Association of Equine Practitioners convention, held Dec. 6-10 in San Diego, Calif. The facilitators listed seven topics beginning with equine protozoal myeloencephalitis (EPM), equine herpesvirus-1 (EHV-1), and West Nile virus (WNV), followed by a few questions regarding Eastern, Western, and Venezuelan equine encephalomyelitis (EEE, WEE, and VEE). Discussions then turned to the role of the immune system in infectious neurologic diseases.

One of the most important questions surrounding EPM continues to be how to use the available diagnostic testing. At this time everyone seems to agree that the best way to determine if a horse has EPM is to look at the "big picture," which means that the horse is first showing signs of neurologic disease. If the horse has evidence of both upper and lower motor neuron signs, meaning the horse has muscle atrophy along with gait deficits, the probability has increased that these signs are a result of infection by Sarcocystis neurona (the causative single-celled protozoan parasite that causes EPM).

If the signs show evidence of multifocal nature, e.g., cranial nerve, gait, and muscle atrophy deficits, then the likelihood of an EPM diagnosis is even greater. If this horse has a positive blood test with any available laboratory testing, it again increases the probability the horse has EPM. If, in addition, the horse has no abnormalities visible in radiographs of the vertebral columns (usually only done on the cervical--neck vertebrae--region to rule out wobbler syndrome), and if the horse's cerebrospinal fluid (CSF) tests positive for S. neurona, then the chances the horse has EPM are even greater.

Some practitioners recommended also assessing response to treatment as a help for diagnosis, and finally the gold standard for any testing is comparison of the results of this testing to post-mortem examinations of the suspected cases that do not survive.

In this table topic audience there were several speakers from the neurology sessions at this year's convention, along with David Horohov, DVM, PhD, of the University of Kentucky's Gluck Equine Research Center, who provided an excellent commentary about the role of the immune system in diseases such as EHV-1 and EPM. He also talked about ways to evaluate the role of the cell-mediated immune system, as well as how one might help direct therapy against protozoal and viral infections by manipulating the immune system.

Beyond these topics the group also discussed some specific cases.

Facilitators for this Table Topic were Debra Sellon, DVM, PhD, Dipl. ACVIM, associate dean of the Graduate School at Washington State University, and Steve Reed, DVM, Dipl. ACVIM, of Rood & Riddle Equine Hospital in Lexington, Ky.

About the Author

Stephen Reed, DVM, Dipl. ACVIM

Stephen Reed, DVM, Dipl. ACVIM, joined the Internal Medicine Service department at Rood & Riddle Equine Hospital in Lexington, Kentucky in Jan. 2007, after he retired from Ohio State University as an emeritus professor. His career has been predominantly dedicated to teaching with emphasis on Equine Neurologic Diseases.

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