KLAMATH FALLS, Ore. – Klamath County Public Health (KCPH) officials today announced West Nile Virus, a disease spread by mosquitoes, was detected in a horse in Klamath County.

The horse in Klamath Falls is the first to test positive for the disease in Oregon in 2021.

KCPH officials are advising people in Klamath County to take precautions against mosquitoes to avoid the risk of infection. West Nile Virus is transmitted through the bite of infected mosquitoes. Horses become infected from mosquitoes that previously fed on infected birds.


“It is critical that all horses be vaccinated,” recommends Emilio DeBess, DVM, public health veterinarian at the Oregon Health Authority’s Public Health Division. “If your horse has not been vaccinated, you are encouraged to vaccinate now. If your horse is displaying signs of illness, call your veterinarian immediately.”

The virus can infect the central nervous system of horses and cause symptoms of encephalitis that include weakness or paralysis of hind limbs, hyper-excitability and convulsions. Not all horses with clinical signs of encephalitis have West Nile.

Horses are considered “dead-end” hosts, which means they don’t develop enough virus in the bloodstream to infect mosquitoes. Only birds are known to pass the virus through mosquitoes to other birds, animals or humans.

People at risk of serious illness include individuals 50 and older, and those with chronic disease. West Nile symptoms may include fever above 100 degrees and severe headache, stiff neck, mental confusion, muscle weakness, shaking, paralysis or rash. People should contact their health care provider if experiencing any of these symptoms.

KCPH officials offer the following tips to prevent mosquito bites:

  • Eliminate sources of standing water that are a breeding ground for mosquitoes. This includes watering troughs, bird baths, clogged gutters and old tires.
  • When outdoors at dusk and dawn when mosquitoes are most active, protect yourself by using mosquito repellants containing DEET, oil of lemon, eucalyptus or Picardin, and follow the directions on the container.
  • Wear long-sleeved shirts and long pants in mosquito-infested areas.
  • Make sure screen doors and windows are in good repair and fit tightly.

In 2019, the last time there were cases of West Nile virus in horses, there were seven cases in Oregon horses. There also were nine human cases that year. So far in 2021, 26 mosquito pools—samples of about 50 mosquitoes each—and one bird were found to be carrying the virus throughout Oregon. None were in Klamath County.