Wisconsin West Nile and Mosquito-Borne Disease
5 human cases of mosquito-borne disease reported in Wisconsin so far this year, and activity in 13 counties. Reported cases, by county of residence, as CDC ArboNET has them. CDC updates the current season every one to two weeks from June through December; reports lag illness by weeks, states may publish newer counts, and mild cases are often never reported.
Human cases by county, 2026
All five viruses together, by the patient’s county of residence. Hatched: mosquitoes, birds, horses or sentinel animals tested positive, but no human case.
- 1
- 2 to 4
- 5 to 9
- 10 or more
- Activity, no human case
- Nothing reported
CDC data current as of September 22, 2026.
This year
| Virus | Human cases | Neuroinvasive | Counties with cases | Counties with any activity |
|---|---|---|---|---|
| West Nile virus | 2 | 2 | 4 | 10 |
| Eastern equine encephalitis virus | 0 | 0 | 0 | 1 |
| La Crosse virus | 1 | 1 | 1 | 1 |
| Jamestown Canyon virus | 2 | 1 | 2 | 2 |
By county
Non-human activity is a positive mosquito pool, bird, horse or sentinel animal. By county of residence, which is not always where the bite happened. Absence of reports is not absence of risk.
| County | Virus | Activity | Human cases | Neuroinvasive |
|---|---|---|---|---|
| Brown County | West Nile | Human cases and non-human | 1 | 1 |
| Chippewa County | Jamestown Canyon | Human cases | 1 | 1 |
| Dane County | La Crosse | Human cases | 1 | 1 |
| Sauk County | West Nile | Human cases | 1 | 1 |
| Jackson County | Jamestown Canyon | Human cases | 1 | |
| Bayfield County | West Nile | Non-human only | ||
| Dane County | West Nile | Human cases | ||
| Grant County | West Nile | Non-human only | ||
| Lafayette County | West Nile | Non-human only | ||
| Milwaukee County | West Nile | Non-human only | ||
| Ozaukee County | West Nile | Human cases | ||
| Portage County | EEE | Non-human only | ||
| Rock County | West Nile | Non-human only | ||
| Saint Croix County | West Nile | Non-human only |
Sources
Mosquito-borne disease: CDC ArboNET current-year data, National Center for Emerging and Zoonotic Infectious Diseases, public domain. CDC data current as of September 22, 2026. Reported cases, by county of residence, as CDC ArboNET has them. CDC updates the current season every one to two weeks from June through December; reports lag illness by weeks, states may publish newer counts, and mild cases are often never reported. State and local health departments may have newer counts.