EEE Found in Two Additional Wisconsin Horses

The mosquito-borne disease called Eastern equine encephalitis, or EEE, has been diagnosed in two horses in two adjacent north central Wisconsin counties, prompting a second warning from the Wisconsin State Veterinarian.

Blood samples from a 7-year-old American Quarter Horse in Price County and a 6-year-old Belgian mare in Taylor County were submitted to Wisconsin Veterinary Diagnostic Laboratory Aug. 11 and Aug. 12, respectively. Both showed signs of neurological disease, and neither had been vaccinated for EEE. It is not known whether the horses survived.

"Vaccinate your horses if you haven't already, or get boosters for those you vaccinated earlier in the year," said state veterinarian Robert Ehlenfeldt, DVM. "EEE has a mortality rate in excess of 90% (in horses). The vaccine is not expensive, it's effective, and if we've found EEE in these three counties, it's reasonable to assume it's more widespread. Unless we have a really early killing frost, we still have a lot of mosquito season ahead of us."

Ehlenfeldt issued his first warning Aug. 9, after his office received notification that two llamas in Dunn County had died from EEE and a horse on the same farm had been sickened.

Rarely, humans may also contract EEE, but no human cases have appeared in Wisconsin.

In addition to vaccination, Ehlenfeldt advised owners can take steps to reduce their animals' exposure to mosquitoes. They should eliminate standing water by removing objects like old tires or even the folds in tarps where water collects, and frequently changing water in water troughs, bird baths and similar containers. If possible, owners should also keep their animals inside barns if possible from dusk through dawn, when mosquitoes are most active.

A viral disease, EEE affects the central nervous system and is transmitted to horses by infected mosquitoes. The fatality rate for EEE-affected horses is 75-95%. The course of EEE can be swift, with death occurring two to three days after onset of clinical signs despite intensive care. Horses that survive might have long-lasting impairments and neurologic problems.

Clinical signs for EEE include moderate to high fever, depression, lack of appetite, cranial nerve deficits (facial paralysis, tongue weakness, difficulty swallowing), behavioral changes (aggression, self-mutilation, or drowsiness), gait abnormalities, or severe central nervous system signs, such as head-pressing, circling, blindness, and seizures.

Wisconsin experienced a major outbreak of EEE in 2001, with 69 confirmed or presumptive positive cases, mostly in northwestern Wisconsin. Since then, sporadic cases have occurred. Because EEE follows mosquito populations, it normally occurs beginning in mid- to late summer and remains a threat until the first killing frost.

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