Multiple Livestock Put Down Following Possible West Nile Virus Infection

By on Friday, September 15th, 2023 in Featured Stories Northeastern Oregon News

UNION COUNTY – Though common every year, the summer of 2023 proved to be an especially active time for West Nile Virus (WNv). Numerous mosquito pools were confirmed to be carrying the virus throughout August, with county vector control offices working hard to track and, if necessary, contain the nasty little bugs. Sadly, WNv may have caused the recent deaths of several livestock in Union County.

Information provided by Union County Vector Control Manager Chris Law, following unofficial reports of a sick mule in Summerville, indicates that three livestock animals were put down following possible WNv infection. According to Law, a veterinarian at the Animal Health Center in Island City examined two sick horses and a mule from the Summerville/Elgin area (the names of the persons the animals belonged to were not provided due to confidentiality concerns) which showed signs of a neurological disorder. Given the heavy presence of WNv in Northeast Oregon this year, the vet in question felt it very probable that the animals had been infected with WNv.

Note that definitive testing was not carried out by the vet before the animals had to be put down. The Animal Health Center put down two of the animals (which ones specifically were not specified) while the third was put down by its respective owner. Unofficial reports also indicate that a horse belonging to a City of Union resident may have also been infected. This horse is allegedly recovering after being treated at a veterinary clinic in Idaho. An exact timeline of when the animals became sick is unknown. Unofficial reports of a sick mule in Summerville were initially noted around September 9 while other reports indicate the horse in Union may have shown signs of WNv infection around September 5.

Of the four animals believed to be infected, only the mule had received a prior vaccination. According to details from the Animal Health Center, this vaccination was provided in a dose alongside five other vaccinations, making it less effective than a dedicated WNv vaccination. Dr Terrence McCoy at the Animal Health Center also commented that many livestock owners in Union County are not actually vaccinating their horses against WNv anymore. It’s speculated this is due to the relatively limited number of cases of WNv in Union County over the past few years and the unpredictability of the virus’s prevalence.

Going forward, Law recommends the following precautions for livestock owners to avoid further WNv deaths:

  • Make sure all their animals that can be vaccinated are fully vaccinated.
  • Search for and empty any containers that are holding water weekly.
  • Ensure water troughs are emptied and cleaned weekly or have us treat them.
  • Properly irrigate to prevent standing water that could breed mosquitoes.
  • If they have a water storage system for sprinklers, make sure we have access to be able to treat it.
  • There are approved mosquito replants specifically for horses and other animals.
  • Livestock owners can contact Union County Vector Control for further assistance.

Union County residents can visit for more information or reach out to Union County Vector Control at 541-963-2974 and For more details on West Nile Virus specifically, see our previous interview with Chris Law at