Transmission

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

Approximate distribution of the Blacklegged tick in the United States of America
Map of the United States showing the approximate distribution of the Western blacklegged tick. The area affected is the western coast.

Anaplasmosis is a tickborne disease caused by the bacterium Anaplasma phagocytophilum.

Tick bites
- A. phagocytophilum is primarily spread to people by the bite of an infected tick.
- In the United States, the bacteria is carried by the blacklegged tick (Ixodes scapularis) in the Northeast and Midwestern United States and the western blacklegged tick (Ixodes pacificus) along the West Coast.
Blood transfusion
- In rare cases, A. phagocytophilum has been spread by blood transfusion.

Anaplasmosis is most commonly reported in the Northeastern and upper Midwestern states.

Page last reviewed: January 11, 2019

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