New York Officials Confirm Horse with EEE and WNV

The mare had also been diagnosed with strangles a week before testing positive for EEE and WNV.
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Cattaraugus County
The mare had also been diagnosed with strangles a week before testing positive for EEE and WNV. | Photo: Wikimedia Commons

On Sept. 10, officials at the New York State Department of Agriculture and Consumer Services (NYSDACS) confirmed a horse with both Eastern equine encephalomyelitis (EEE) and West Nile virus (WNV).

The affected horse, a 7-year-old mare from Cattaraugus County, experienced onset of clinical signs that included recumbency (down and unable to rise) on Sept. 6. She was unvaccinated for EEE and had also been diagnosed with strangles a week before. She is deceased.

EEE 101

Eastern equine encephalomyelitis is caused by the Eastern equine encephalitis virus, for which wild birds are a natural reservoir. Mosquitoes that feed on EEE-infected birds can transmit the virus to humans, horses, and other birds. Horses do not develop high enough levels of these viruses in their blood to be contagious to other animals or humans. Because of the high mortality rate in horses and humans, EEE is regarded as one of the most serious mosquito-borne diseases in the United States.

RELATED CONTENT | Health Alert: EEE, WEE, and VEE (Video)

Tips for preventing mosquito-borne diseases include:

  • Avoid mosquito bites: Use insect repellent when outdoors, especially from dusk to dawn.
  • Look for EPA-labeled products containing active ingredients such as DEET, picaridin (KBR3023), or oil of lemon eucalyptus (p-menthane 3,8-diol).
  • Apply more repellent, according to label instructions, if mosquitoes start to bite.
  • Mosquito-proof homes: Fix or install window and door screens, and cover or eliminate empty containers with standing water where mosquitoes can lay eggs.
  • Protect your horses: Veterinarians recommend commercially available licensed vaccines against EEE for all horses in the U.S. Horses should be vaccinated at least annually (recommendations vary in high-risk areas). It’s not too late this year to vaccinate your horses.
  • Use approved insect repellents to protect horses.
  • If possible, put horses in stables, stalls, or barns during the prime mosquito exposure hours of dusk and dawn.
  • Eliminate standing water, drain water troughs, and empty buckets at least weekly.
  • Stock water tanks with fish that consume mosquito larvae (contact your local mosquito control for assistance), or use mosquito “dunks” (solid “donuts” of Bacillus thuringiensis israelensis, which are nontoxic to horses) available at hardware stores.

About West Nile Virus

WNV transmission occurs when infected mosquitoes feed on animals, as well as humans, after having fed on infected birds.

Health Alert: West Nile Virus in Horses
RELATED CONTENT | Health Alert: West Nile Virus in Horses (Video)

Clinical signs of WNV in horses include:

  • Mild anorexia and depression
  • Fine and coarse muscle and skin fasciculation;
  • Hyperesthesia (hypersensitivity to touch and sound);
  • Changes in mentation (mentality), when horses look like they’re daydreaming or “just not with it”;
  • Occasional drowsiness;
  • Propulsive walking (driving or pushing forward, often without control);
  • Spinal signs, including asymmetrical weakness; and
  • Asymmetrical or symmetrical ataxia.

West Nile virus has no cure; however, some horses can recover with supportive care. Equine mortality rates can reach 30-40%. The American Association of Equine Practitioners includes WNV as one of the core diseases all horses should be vaccinated against at least annually.

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