The state Health Department on Thursday confirmed two additional cases of West Nile virus in Oklahoma.
That brings the number of confirmed cases to 166, the highest number of cases Oklahoma has seen since the virus entered the U.S. in 1999. Nine residents have died from West Nile this year, according to the Health Department.
Nationwide, 4,249 cases have been reported in 2012, the highest number of West Nile virus disease cases reported to Centers for Disease Control and Prevention through the second week of October since 2003.
Humans contract West Nile virus when bitten by an infected mosquito. The virus is not transmitted from human to human. There is no cure or vaccine for West Nile virus.
Public health officials recommend residents continue to use mosquito repellent and wear long-sleeved shirts and pants when outside. Also, people are urged to remove stagnant water from around their homes because it can serve as a mosquito breeding ground.
About 80 percent of people who contract West Nile virus never show symptoms, and most people who do become sick don't develop a serious illness.
Adults older than 50 are most at risk of developing the more severe symptoms of West Nile virus, including paralysis, brain swelling and meningitis.