The Table Topic forum on Infectious Neurologic Diseases at the 2010 American Association of Equine Practitioners Annual Meeting, held Dec. 4-8 in Baltimore, Md., was well-attended with 20-30 practitioners in and out during discussions. A list of common neurologic infectious diseases found in North America was presented to the attendees. Practitioners were asked to choose the most pertinent diseases, and the list for further discussion included Eastern equine encephalitis (EEE), rabies, equine protozoal myeloencephalitis (EPM), and West Nile virus (WNV).

EEE cases were on the rise throughout the 2010 mosquito season, especially in Michigan. Cases have been seen in many states within the Midwest and Mid-Atlantic regions, primarily in unvaccinated horses. This provides significant evidence for the need to continue to vaccinate against this frequently fatal disease. Veterinarians continue to recommend annual vaccination for horses residing in areas where mosquitoes are seasonal during the spring months and biannual vaccination for horses in year-round mosquito season areas.

The primary reason for the lack of vaccination for EEE has been blamed on the nation's economic status. Horse owners are sometimes making hard economic trade-off decisions regarding horse healthcare and preventive medicine. These decisions can have catastrophic consequences for horses. EEE is a core vaccine according to the AAEP, and this current rise in cases demonstrated the wisdom of existing guidelines. Horse owners and veterinarians can refer to the AAEP's Vaccination Guidelines for EEE and other infectious disease prevention recommendations.

Rabies is also on the rise throughout the United States, and horse cases are becoming more frequent in states where cases have always existed and have been found in states previously free of cases. Like EEE, this disease is preventable with vaccination. In addition, in 2008 rabies became part of the core vaccine requirements recommended by the AAEP.

EPM was a topic of significant interest during the presentation, and moderators devoted significant time to covering all aspects of the disease including exposure distribution, pathophysiology, diagnosis, and treatment. The regional representation of members demonstrated exposure rates that were dissimilar throughout the country. It is now better understood that the parasite gains access to the central nervous system by hitching a ride on the white blood cells, and this information is now being exploited to develop a model to study EPM.

Much time was spent on the topic of EPM diagnosis--one of the more controversial aspects of the disease. Diagnosis is made with a clinical exam consistent with EPM, sometimes by cerebrospinal fluid (CSF) and/or blood testing, and sometimes via response to therapy. Amy L. Johnson, DVM, Dipl. ACVIM-LAIM, explained the pros and cons of existing immuno-diagnostics for blood and CSF as well as new tests available. Practitioners were interested in the improved diagnostics.

Practitioners also had questions about Protazil, which was launched at the convention as a new treatment for EPM. The product claims to provide increased efficacy and convenience at a lower cost over existing treatment options. It is fed as a top dress alfalfa pellet for 28 days.

West Nile virus infections are still being diagnosed in horses, although case numbers have declined. The horses diagnosed with WNV have primarily been unvaccinated as was the case with EEE. West Nile virus appears to be here to stay and should remain on horse owners' radars for core vaccine disease prevention.

This session was moderated by Joe Manning, DVM, MBA, Equine Technical Services Veterinarian with Intervet/Schering-Plough Animal Health, and Amy L. Johnson, DVM, Dipl. ACVIM-LAIM, of the University of Pennsylvania's New Bolton Center.

About the Author

Joe Manning, DVM, MBA

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