Ehrlichiosis: Causes and How It Spreads

Key points

  • Most people get ehrlichiosis from the bite of an infected tick.
  • Ehrlichiosis can be spread through blood transfusion and organ transplant.
  • Ehrlichiosis is most frequently reported from the southeastern and south-central United States, from the East Coast extending westward to Texas.
Closeup of a lone star tick on a blade of grass.

Causes

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.

How it spreads

Ticks

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 (Amblyomma americanum), found primarily in the south-central and eastern United States.

A map of the United States with regions with the lone star tick highlighted.
Estimated geographic distribution of lone star ticks.

E. muris eauclairensis is carried by the blacklegged tick (Ixodes scapularis). While the blacklegged tick is widely distributed in the eastern United States, E. muris eauclairensis cases have only been reported from Wisconsin and Minnesota.

Map of the United States highlighting the distribution of blacklegged ticks.
Estimated geographic distribution of blacklegged ticks.

Blood transfusion and organ transplant

In rare cases, Ehrlichia species have been spread through blood transfusion and organ transplant.

Range

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.

Print
Content Source:
National Center for Emerging and Zoonotic Infectious Diseases (NCEZID)