The Equine Disease Communication Center (EDCC) has reported that horses in Wisconsin and Ontario, Canada, have tested positive for Eastern equine encephalitis (EEE) and West Nile virus (WNV).
Wisconsin—On Oct. 30 the EDCC reported that the Wisconsin Department of Agriculture, Trade, and Consumer Protection (WDATCP) confirmed that an unvaccinated 17-year-old Appaloosa-cross mare from Marathon County had tested positive for EEE. She became recumbent (unable to rise) on Oct. 20.
“The attending veterinarian saw the mare on Oct. 20,” the EDCC statement said. “He reported that she had been high-stepping and star-gazing prior to recumbency. In recumbency, he reported that she was twitching and acting delirious. The veterinarian sampled and treated her with anti-inflammatories and steroids; he said she got up and was showing neurologic signs, but is recovering.”
The EDCC said this is Wisconsin’s 24th case of EEE reported this year.
Also on Oct. 30, the EDCC said the WDATCP also confirmed WNV in an unvaccinated 7-year-old Quarter Horse mare from Clark County.
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“She showed minor neurologic signs on Oct. 21 (lip droop, slight incoordination),” the EDCC said. “She went down on Oct. 22 but got back up. On Oct. 23 she went down again and a local veterinarian was called. He sampled and treated her, but she died a couple of days later.”
The USDA National Veterinary Services Laboratory, Ames, Iowa, performed the laboratory diagnostic tests. This is Wisconsin’s 22nd equine WNV case of 2017, the EDCC said.
Ontario—Meanwhile, in Canada, the Ontario Ministry of Agriculture Food and Rural Affairs (OMAFRA) confirmed a case of EEE in a 19-year-old mixed-breed mare unvaccinated against EEE the week of Oct. 23, the EDCC reported Oct. 31.
The mare, which was 11 months pregnant, resided in the District of Muskoka.
“Neurological signs began as muscle tremors and hind end weakness and progressed rapidly to recumbency,” the EDCC said. “The mare was euthanized.”
This is Ontario’s second confirmed EEE case in a horse for 2017.
Further, the EDCC reported Oct. 31 that, since Oct. 19, three equine WNV cases have been reported to the OMAFRA. The affected horses are from Frontenac County, Oxford County, and the Regional Municipality of Halton.
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“The horses included a gelding, a filly, and a mare with ages ranging from 2 to 11 years,” the EDCC said. “Clinical signs ranged from hind end weakness, muscle fasciculations, and hyperesthesia to ataxia. All three are recovering under veterinary supervision. One horse was unvaccinated, one had not been vaccinated for three years, and one 4-year-old had been vaccinated yearly since it was two. The total number of cases reported in Ontario in 2017 is 21.”
A viral disease, EEE affects the central nervous system and is transmitted to horses by infected mosquitoes. Clinical signs of 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. The course of EEE can be swift, with death occurring two to three days after onset of clinical signs despite intensive care; fatality rates reach 75-80% among horses. Horses that survive might have long-lasting impairments and neurologic problems.
Clinical signs for WNV, also transmitted by bites from infected mosquitoes, include flulike signs, where the horse seems mildly anorexic and depressed; fine and coarse muscle and skin fasciculation; hyperesthesia; changes in mentation (mentality), when horses look like they are daydreaming or "just not with it"; occasional somnolence (drowsiness); propulsive walking (driving or pushing forward, often without control); and "spinal" signs, including asymmetrical weakness. Some horses show asymmetrical or symmetrical ataxia. Equine mortality rate can be as high as 30-40%.
Horse owners should also consult their private practicing veterinarian to determine an appropriate disease prevention plan for their horses. Vaccines have proven to be a very effective prevention tool against EEE and WNV. Horses that have been vaccinated in past years will need an annual booster shot; in areas with a prolonged mosquito season, veterinarians might recommend two boosters annually—one in the spring and another in the fall. However, if an owner did not vaccinate their animal in previous years, the horse will need the two-shot vaccination series within a three- to six-week period.
In addition to vaccinations, horse owners also need to reduce the mosquito populations and their possible breeding areas. Recommendations include removing stagnant water sources, keeping animals inside during the bugs’ feeding times, which are typically early in the morning and evening, and applying mosquito repellents approved for equine use.