Transmission

Figure 1: Estimated geographic distribution of lone star ticks (above) and blacklegged ticks (below)

Map of the United States showing the approximate distribution of the Lone Star tick. The area affected is the eatern half of the country.

Ehrlichiosis is the general name used to describe diseases caused by the bacteria Ehrlichia chaffeensis, E. ewingii, or E. muris eauclairensis in the United States. The majority of reported cases are due to infection with E. chaffeensis.

Tick bites
- Most people get ehrlichiosis from the bite of an infected tick.
- In the United States, E. chaffeensis and E. ewingii are carried by the lone star tick (A. americanum) pdf icon[PDF – 2 pages], found primarily in the south-central and eastern United States.
- E. muris eauclairensis is carried by the blacklegged tick (I. scapularis) pdf icon[PDF – 1 page]. While the blacklegged tick is widely distributed in the eastern United States, E. muris eauclairensis has only been found in Wisconsin and Minnesota.
Blood transfusion and organ transplant
- In rare cases, Ehrlichia species have been spread through blood transfusion and organ transplant.

Ehrlichiosis caused by E. chaffeensis and E. ewingii is most frequently reported from the southeastern and south-central United States, from the East Coast extending westward to Texas.

Page last reviewed: January 17, 2019

Content source: Centers for Disease Control and Prevention, National Center for Emerging and Zoonotic Infectious Diseases (NCEZID), Division of Vector-Borne Diseases (DVBD)