Transmission and Epidemiology

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, also known as human granulocytic anaplasmosis, is a tickborne disease caused by the bacterium Anaplasma phagocytophilum.

Transmission

Tick Bites

Primarily, through infected tick bites.
- Blacklegged tick (Ixodes scapularis) pdf icon[PDF – 1 page] widely distributed across the eastern United States.
  - The blacklegged tick also transmits other pathogens (including Borrelia burgdorferi) in certain geographic areas, and coinfections have been reported.
- Western blacklegged tick (Ixodes pacificus) pdf icon[PDF – 1 page] along the West Coast.

Less commonly, through blood transfusion and organ transplant

A. phagocytophilum can be transmitted through blood transfusions.
A. phagocytophilum has been shown to survive for more than a week in refrigerated blood.
Several cases of transfusion-transmitted anaplasmosis have been reported, including in cases of asymptomatic donors.
Patients who develop anaplasmosis within a month of receiving a blood transfusion or solid organ transplant should be reported to state health officials for prompt investigation.
Leukoreduction might reduce the risk of Anaplasma transmission; but it does not eliminate it. Cases associated with the use of leukoreduced blood products have been documented.
Blood products are not routinely screened for the presence of A. phagocytophilum.
For more information about anaplasmosis and blood transfusions see the Special Considerations section of: Diagnosis and Management of Tickborne Rickettsial Diseases: Rocky Mountain Spotted Fever and Other Spotted Fever Group Rickettsioses, Ehrlichioses, and Anaplasmosis — United States: A Practical Guide for Health Care and Public Health Professionals (2016) pdf icon[PDF – 48 pages]

Epidemiology

Figure 2: Incidence (per million population) for anaplasmosis, United States, 2017.

More

Geographic range: Anaplasmosis is most commonly reported in the Northeastern and upper Midwestern states, although the geographic range of anaplasmosis cases appears to be expanding.
Peak transmission: Most cases occur during June–November. Two peaks of increased case reporting usually occur, with the first peak during June–July and a smaller peak during October-November.
- For more information, see: Seasonality

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)