WNV in Ohio horses

On Oct. 16 the Equine Disease Communication Center (EDCC) reported that the Ohio Department of Agriculture (ODA) has confirmed five more cases of equine West Nile virus (WNV). According to EDCC data, officials have now confirmed 43 cases of WNV in Ohio horses so far this year—more than triple the number of cases confirmed last year.

According to the EDCC and ODA:

  • A 6-year-old Standardbred mare from Trumbull County developed clinical signs on Sept. 19; the owner called the veterinarian regarding a neurologic horse that was wobbly. Despite treatment, the next evening the mare became recumbent (down and unable to rise) and the owner elected euthanasia. A serum sample submitted to the National Veterinary Services Laboratory (NVSL) had an IgM capture ELISA titer of 1:400 or greater, suggesting recent WNV exposure. The horse was not vaccinated against WNV.
  • An adult Standardbred gelding from Holmes County developed clinical signs on Sept. 22; the owner called the veterinarian when, after driving the horse, he noticed the gelding had weak hind limbs, was pulling to the right, and dragging his hoofs. The veterinarian found the horse was agitated and had muscle fasciculations (involuntary twitching) and began treatment immediately. A serum sample submitted to NVSL had an IgM capture ELISA titer of 1:400 or greater, suggesting recent WNV exposure. The horse was not vaccinated against WNV. As of Sept. 24, the horse was reported to be alive and recovering.
  • A 4-year-old Friesian gelding from Holmes County began exhibiting clinical signs on Sept. 21; the owner called the veterinarian to report that the horse wasn’t eating, was refusing to move, and had muscle fasciculations. The horse was vaccinated against WNV one week prior to showing clinical signs. A serum sample submitted to NVSL had an IgM capture ELISA titer of 1:400 or greater, suggesting recent WNV exposure. As of Sept. 24, the horse was reported to be alive and recovering.
  • An adult Standardbred from Geauga County developed clinical signs on Sept. 24. The owner called the veterinarian after noticing the horse had stiff limbs and had stopped eating. The veterinarian responded, treated the horse, and left medication for the owner to administer. A serum sample submitted to NVSL had an IgM capture ELISA titer of 1:400 or greater, suggesting recent WNV exposure. The horse was not vaccinated against WNV. As of Sept. 24, the horse was reported to be alive and recovering.
  • An adult Standardbred gelding from Ashtabula County began exhibiting clinical signs on Sept. 29; his owner called the veterinarian after finding him wobbly and having difficulty standing. The veterinarian responded and treated the horse. A serum sample submitted to NVSL had an IgM capture ELISA titer of 1:400 or greater, suggesting recent WNV exposure. The horse was not vaccinated against WNV. As of Sept. 29, the horse was reported to be alive and recovering.

In 2017, officials confirmed 14 cases of WNV in Ohio horses, according to USDA Animal and Plant Health Inspection Service data.

WNV 101

West Nile virus is transmitted to horses via bites from infected mosquitoes. Not all infected horses show clinical signs, but those that do can exhibit:

  • Flulike signs, where the horse seems mildly anorexic and depressed;
  • 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); and
  • Spinal signs, including asymmetrical weakness; and
  • Asymmetrical or symmetrical ataxia.

West Nile has no cure, however some horses can recover with supportive care. Equine mortality rates can reach 30-40%.

Studies have shown that vaccines can be effective WNV prevention tools. Horses vaccinated in past years need an annual booster shot, but veterinarians might recommend two boosters annually—one in the spring and another in the fall—in areas with prolonged mosquito seasons. In contrast, previously unvaccinated horses require a two-shot vaccination series in a three- to six-week period. It takes several weeks for horses to develop protection against the disease following complete vaccination or booster administration.

In addition to vaccinations, owners should work to reduce mosquito population and breeding areas and limit horses’ mosquito exposure by:

  • Removing stagnant water sources;
  • Dumping, cleaning, and refilling water buckets and troughs regularly;
  • Keeping animals inside during the bugs’ feeding times (typically early in the morning and evening); and
  • Applying mosquito repellents approved for equine use.