Recent disease surveillance testing reveals a trio of rare equine diseases in three different Minnesota counties: Otter Tail, Pine and Swift. Two of the diseases, Eastern equine encephalitis (EEE) and West Nile virus (WNV), are spread by mosquitoes and pose a risk to horses and people. The third disease, Equine infectious anemia (EIA), is not known to affect people, but requires infected horses to be euthanized or quarantined for life because there is no treatment or vaccine.

A Minnesota veterinarian reported a case of Eastern equine encephalitis (EEE), a viral disease that causes inflammation of a horse’s brain and spinal cord, in a 14-year-old Belgian mare in Otter Tail County. Distribution of the disease in horses has historically been restricted to eastern, southern and southeastern states, although cases have been recently confirmed in Wisconsin. There were also three cases in Minnesota horses in 2001 in Blue Earth, Kanabec and Anoka Counties. The EEE positive horse was euthanized Thursday, August 1 after displaying symptoms of neurologic disease including uncontrolled leg movements, a limp tongue, and inability to rise on her own.

A Minnesota veterinarian reported suspected West Nile virus (WNV) in a 25-year old mare in Swift county. Clinical signs of neurologic illness progressed very quickly. The mare’s owners reported the horse fell ill in the evening and was unable to rise the next morning. The horse was euthanized by the attending veterinarian who submitted a blood sample to the University of Minnesota Veterinary Diagnostic Laboratory for WNV testing. Test results confirmed exposure to WNV (a Plaque Reduction Neutralization Test (PRNT) was positive). The horse had no documented history of vaccination against WNV.

The Minnesota Board of Animal Health encourages all horse owners to work with their veterinarians to get their horses vaccinated and booster vaccinated horses, especially if housed near the area where the disease was confirmed.

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