About Ehrlichiosis

Map of Ehrlichiosis cases by county

Ehrlichiosis is an illness spread by ticks. It is preventable and treatable. In Wisconsin, ehrlichiosis is caused by the bacterium Ehrlichia muris eauclairensis. This type of ehrlichiosis is spread by the deer tick, also known as the black-legged tick. In the southeastern and south-central United States, ehrlichiosis is caused by the bacteria Ehrlichia chaffeensis and Ehrlichia ewingii. Ehrlichia chaffeensis and Ehrlichia ewingii are spread by the lone star tick. Lone star ticks are rare in Wisconsin.

Anyone can get ehrlichiosis. People who spend more time outdoors are at a higher risk of being bitten by an infected tick. Ticks are found in areas with woods, brush, or tall grass. In Wisconsin, ticks are most active from May to November but they can be active anytime temperatures are above 40° F.

Map description

The map to the right shows the annual average number of cases of ehrlichiosis caused by Ehrlichia muris eauclairensis per 100,000 people by county. Ehrlichiosis in Wisconsin is rare, and is more common in the northern region of the state. The deer tick, which spreads ehrlichiosis in Wisconsin, is also more common in northern Wisconsin.

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Ehrlichiosis 101

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Questions about illnesses spread by ticks? We’re here to help.

Bureau of Communicable Diseases
Phone: 608-267-9003
Fax: 608-261-4976

Last revised December 27, 2024