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West Nile virus, a disease spread by mosquitoes, has been detected in a horse in Crook County, according to Oregon Public Health officials and the Crook County Health Department.
The horse, which became ill in September, is the first to test positive for the disease in Crook County since testing began in 2004. The horse had spent time in both the Prineville and the Post/Paulina areas, and had not traveled outside of the county during its exposure period.
West Nile virus is transmitted through the bite of infected mosquitoes. Horses and humans become infected from mosquitoes that have previously fed on infected birds. Even though it is late in the season, Crook County health officials are advising people in our area to take precautions against mosquitoes to avoid the risk of infection.
“It is critical that all horses be vaccinated,” recommends Dr. Rene Villagrana, a local veterinarian. “If your horse has not been vaccinated, you are encouraged to vaccinate before mosquito season next spring. If your horse is displaying signs of illness, call your veterinarian immediately.”
West Nile 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. In Oregon, about 95 percent of horses diagnosed with WNV had not been vaccinated. Symptomatic West Nile illness in horses is usually fatal.
Horses are considered “dead-end” hosts, which mean they don’t develop enough virus in the bloodstream to infect mosquitoes. Only birds are known to pass the virus to mosquitoes, which can then transmit the disease to other birds, animals or humans.
About one in five people infected with West Nile virus may show symptoms. People at risk of serious illness include individuals 50 and older, and people with immune-compromising conditions, such as diabetes and high blood pressure.
According to Karen Yeargain, LPN, communicable disease coordinator at the Crook County Health Department, 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. So far, there have been no residents of Crook County diagnosed with West Nile illness.
Dr. Emilio DeBess, veterinarian at the Oregon Health Authority’s Public Health Division, offers 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.
- Use agricultural methods that decrease the chance of mosquito-breeding habitat.
- When engaged in outdoor activities at dusk and dawn when mosquitoes are most active, protect yourself by using mosquito repellants containing DEET, oil of lemon eucalyptus or Picaridin, 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, Oregon has had eight human cases of West Nile virus in three counties. The virus was found in 83 mosquito pools (samples of about 50 mosquitoes each) and seven horses. In 2018, there were two human cases of West Nile virus in Harney and Clackamas counties; one bird, 58 mosquito pools and two horses were positive in that year. The virus also can be found in, but not transmitted by, chickens, squirrels and dogs.
Climate change effects such as increased temperature and changes in rainfall have led to longer mosquito seasons and are contributing to the spread of West Nile virus, health officials say. They agree these and other climate change indicators must be considered to help people better prepare for future transmission of the disease.
Additional information about West Nile virus is available at:
Oregon Health Authority website: public.health.oregon.gov/DiseasesConditions/DiseasesAZ/WestNileVirus/Pages/survey.aspx
U.S. Centers for Disease Control and Prevention:
cdc.gov/ncidod/dvbid/westnile/ index.htm
Washington State WNV activity
Idaho WNV activity
For additional information contact Karen Yeargain, LPN, at 541-447-5165, or Cliff Kiser, 541-419-1101
