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West Nile Virus

West Nile virus (WNV) is a reportable disease in Oklahoma.  WNV is primarily transmitted by the bite of an infected Culex mosquito.  Persons are at greatest risk of exposure to infected mosquitoes from July through October in our state.  Persons of any age can become ill after being bitten by an infected mosquito, but those over the age of 50 are at greater risk of developing serious illness involving the nervous system.  Over 80% of people infected with the virus never become ill.  If people do become ill, most cases have symptoms such as a fever, headache, tiredness and body aches that go away on their own.  Some people may develop a rash on the trunk of the body.  In more severe cases, persons can develop meningitis or other neurologic disease. 

It is helpful to know some key points about the differences in types of mosquitoes and the features of West Nile virus transmission:

  • The type of mosquitoes that hatch after severe flooding are primarily the species of mosquitoes classified as “nuisance mosquitoes”.  They bite aggressively and cause lots of itchy bites, but they are not typically involved with transmission of diseases.
  • Floodwater mosquito populations tend to die out 3 weeks after the rains stop and the sun dries out affected low lying areas.
  • Culex species of mosquitoes (see photo top right) are the primary vector of West Nile virus.  This type of mosquito increases in numbers during mid to late summer when the temperatures climb and the weather pattern is drier.
  • Since WNV was introduced into Oklahoma, there have been 3 outbreak years – 2003, 2007 and 2012.  Each of these seasons were characterized by higher than normal summer temperatures and drought.

The Oklahoma State Department of Health advises use of insect repellents—particularly those containing DEET, picaridin, oil of lemon eucalyptus (PMD), or IR 3535—when enjoying outdoor activities like gardening, yard work, camping, or other leisure activities.  The type of mosquitoes that transmit WNV are most active during early evening through early morning (dusk to dawn) hours, so it is important to take mosquito bite precautions during that time of the day.  It is also recommended to drain or treat standing water around your home with a mosquito larvacide to reduce mosquito breeding sites.

West Nile virus Surveillance Data and Statistics:  2021

West Nile virus Fact Sheets and Information:

External West Nile virus Resources:


This page last updated October 31, 2019.

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