West Nile Virus Risk Level & Surveillance Results

West Nile Virus (WNV) is the most common mosquito-borne disease in Kansas and the United States. Several species of mosquitoes are responsible for transmission of arboviruses but Culex species are the primary vector for West Nile virus in Kansas and the United States. The Kansas Department of Health and Environment, with funding from the Centers of Disease Control and Prevention, conducts mosquito surveillance in three counties (Reno, Sedgwick, and Shawnee). Mosquito surveillance data from these counties is used as a proxy for mosquito activity in all regions of Kansas.

The risk of acquiring WNV infection depends on various factors including time of year, number and location of infected Culex species of mosquitoes, and the number of days with sufficient heat. Warm temperatures increase the rate of mosquito larvae development which increases the mosquito population size. The risk of WNV transmission is lower in the spring but rises through the early and midsummer months and usually reaches peak transmission during July, August, and September.

WNV risk levels have been developed for Kansas based on the following criteria:

  • Average temperature for the previous two weeks.
  • Historical data indicators for the weeks of increased WNV human cases.
  • Presence and abundance of Culex spp. of mosquitoes.

Regardless of the West Nile virus risk level for your area, there is no such thing as being 'risk-free'. Take precautions when you are out in areas where mosquitoes are present.

Methods for Risk Assessment

We utilize three factors in our risk assessment model; temperature, mosquito surveillance data, and human cases of WNV. Each factor has set benchmarks and each benchmark is assigned a value. The values from these three categories are averaged. The average rating is assigned a WNV risk level for each week. The three factors are as follows:

  • High-risk environmental conditions include above-normal temperatures with or without above-normal rainfall. We use the average daily temperature during the prior 2 weeks as our benchmark.
  • Culex species of mosquitoes serve as the main source of WNV transmission to people and horses. Relative abundance of Culex species mosquitoes compared to the same week in the previous year and the number of Culex species mosquitoes are evaluated each week. Greater than 40 Culex species mosquitoes collected in a week increases this factor to its maximum value.
  • Number of human cases of WNV each week based on the average number of cases in the previous five years.

For WNV human case counts updated weekly visit the Cumulative Case Reports of Disease page.

For more information on arboviral disease surveillance in Kansas call the Kansas Department of Health and Environment's Infectious Disease Epidemiology and Response section at 877-427-7317 or via email.

Past Yearly Archived West Nile Virus Risk Weekly Reports

Mosquito Bite Prevention

Avoid mosquito bites by following the three Ds:

  • Drain - eliminate standing water where mosquitoes live and breed
    • Empty standing water from tarps, old tires, buckets, and other places where rainwater collects. Use larvicide in low-lying areas where water cannot be removed.
    • Refresh water for bird baths, pet bowls, and wading pools at least every three days.
  • Dress - cover your skin with clothing when outdoors
    • Wear protective clothing when practical (long sleeves and pants).
    • Limit outdoor activities when mosquitoes are most active.
  • Deet - use insect repellents that contact DEET or other EPA-approved repellents
    • When used as directed, EPA-registered insect repellents are proven safe and effective, even for pregnant and breastfeeding women.
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