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EHV-1 outbreak is reminder to practice biosecurity

Dr. Kevin Cox, DVM TFC Staff Veterinarian 8/4/2011

Recently, there was an outbreak of a serious horse disease in the western part of the U.S. Reports of nearly 100 cases of equine herpes virus 1 (EHV-1) caused serious concern among horse owners, and rightfully so. Information and education are powerful weapons against serious outbreaks like these, so I felt it wise to give an update on the outbreak of EHV-1 that occurred in late April and May.

Several horses that were at a cutting horse show in Ogden, Utah, as well as some horses that were directly exposed to horses from the show, were diagnosed with the neurologic form of EHV-1, equine herpes myeloencephalopathy (EHM). The final situation report from the U.S. Department of Agriculture (USDA) on June 23 confirmed that a total of 90 cases of EHV-1/EHM were reported in 10 states. Of the 90 confirmed cases, 54 were at the Utah event. Thirteen horses died or had to be euthanized.

EHV-1 has several manifestations: respiratory problems, abortions, neurologic disorders, and weak foal syndrome. The EHV-1 virus is included in many combination-type vaccines and may be listed as rhinopneumonitis on some products. However, these vaccines are only labeled to control the respiratory and abortive forms of EHV-1. No vaccines on the market are currently labeled to prevent the neurologic manifestation of EHV-1.

To further complicate this outbreak, it is highly suspected that the EHV-1 strain that is causing the current outbreak may be highly virulent and have a genetic mutation allowing it to be very pathogenic. A similar event occurred in 2008 in some racehorse barns in Kentucky, and a mutated strain of EHV-1 was found in those horses. This mutated strain of EHV-1 exhibits the neurologic manifestation (EHM) more aggressively. While EHM is not 100-percent fatal, there is no specific treatment, and care is purely supportive. Anti-viral drugs may be somewhat successful if used after infection with EHV-1 but before neurological symptoms develop.

The best defense against this particular virus is stringent biosecurity measures to reduce the chances of an infectious disease being carried onto your farm by people, animals, equipment, or vehicles. While biosecurity is always important, it is critical during times of disease outbreaks. Though biosecurity steps can sometimes seem tedious and somewhat unnecessary, doing them is what breaks the cycle of the disease. A well-planned vaccination protocol — although never a substitute for sound biosecurity practices — should be given to horses to boost their immunity to certain diseases. Proper preventive health care should be implemented for all horses, including those on farms as well as those used in off-farm activities. Consult your veterinarian with questions about effective biosecurity measures and vaccination protocols. USDA also outlines suggested biosecurity measures in an online brochure:

Thankfully, there were no reported cases of EHV-1/EHM in Tennessee. However, education and preparedness are important to preventing and responding to outbreaks like these. Enjoy a safe and successful summer with your horse!

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