According the Equine Disease Communication Center and the Florida Department of Agriculture and Consumer Services, a Thoroughbred colt at a private facility in Marion County, Fla., has tested positive for West Nile. According to the EDCC alert, an unknown number of other horses have been exposed at the facility.

No quarantine has been issued.

The yearling Thoroughbred colt was confirmed on Sept. 12 after showing signs of apprehension, depression, aimless wandering and head pressing. The unvaccinated horse is affected and alive.

This is the second confirmed case of West Nile in Florida in 2024.

Frank 60 Photo

According to the Equine Disease Communication Center, West Nile virus (WNV) is a mosquito-borne flavivirus. WNV primarily causes disease in birds, humans, and horses and is transmitted by many different species of mosquitoes. Since 1999, more than 27,600 U.S. horses have been confirmed with WNV neuro-invasive disease with an estimated average case fatality rate of 30–40%. During 2002 alone, over 15,000 horses were affected in the U.S. WNV is now considered endemic with yearly activity in the U.S. (with an average 300 cases per year), Canada, Mexico and the Caribbean.

 

Clinical Signs for West Nile Virus include the following: 

  • Depression and anorexia without fever when initially infected
  • Mild low-grade fever (101.5-103.5°F or 38.6-39.7°C) in about 25% of affected horses
  • Lack of appetite
  • Lethargy/drowsiness
  • Neurologic signs- Onset of neurologic disease is frequently sudden and progressive
    • Periods of hyperexcitability, apprehension and/or drowsiness o
    • Fine tremors and fasciculations of the face and neck muscles
    •  Cranial nerve paralysis– facial paralysis and weakness of the tongue are very common
    • Head tilt, droopy lip, muzzle deviation o Weakness, ataxia, and dysmetria (incoordination) in one or all limbs
    • Complete paralysis of one or more limbs
    • Colic
    • Recumbency (inability to stand)
    • Death

Diagnosis:

Diagnosis is made by a veterinarian by serum (a component of whole blood) on ELISA (enzyme-linked immunosorbent assay), by measuring for titers or, less commonly, with CSF (cerebrospinal fluid) on PCR.

Treatment: There is no cure for West Nile Virus. Supportive care is administered in cases which show clinical signs.

Prevention: Keep all horses up to date on vaccinations. Initial vaccination is followed in 4 to 6 weeks with a booster; yearly revaccination is recommended after. More frequent boosters (i.e. twice yearly) are recommended in areas with year-round mosquito seasons and in endemic areas. Practice vector management on all properties where horses are kept:

  • Use insect repellents frequently; re-apply after rain.
  • Keep horses in at night when possible and apply insect repellant.
  • Eliminate or minimize standing water. o Stock tanks or ponds with mosquito-feeding fish.
  • Eliminate brush piles, gutters, old tires and litter.
  • Remove all equipment in which standing water can collect

If you have any further questions or concerns, please contact your veterinarian.

The Equine Disease Communication Center (EDCC) is an industry-driven service which works to protect horses and the horse industry from the threat of infectious disease in North America. Our communication system is designed to seek and report real-time information about diseases and help prevent the spread of infectious disease.

Due to the rise in Eastern Equine Encephalitis and West Nile Virus cases, the EDCC has published new information on the importance of vaccinations for your horses.

Return to the September 14 issue of Wire to Wire