Human granulocytic anaplasmosis

Abstract

Human granulocytic anaplasmosis, a deer tick-transmitted rickettsial infection caused by Anaplasma phagocytophilum, is a common cause of undifferentiated fever in the northeast and upper Midwest United States. Patients are often initially diagnosed with a mild viral infection, and illness readily resolves in most cases. However, as many as 3% develop life-threatening complications and nearly 1% die from the infection. Although coinfections with Borrelia burgdorferi and Babesia microti occur, there is little evidence to suggest synergism of disease or a role for A phagocytophilum in chronic illness. No vaccine is available.

Keywords: Anaplasmosis; Diagnosis; Granulocytic; Human; Management.

Figure 1

Reported cases of tick-borne rickettsial infections in the U.S., 1987-2013. The cumulative area plots demonstrate the overall burden of infection during this time interval. HGA – human granulocytic anaplasmosis; HME – human monocytic ehrlichiosis; spotted fever – spotted fever group rickettsioses, including Rocky Mountain spotted fever; nos – not otherwise specified. Data extracted from Morbidity and Mortality Weekly Reports, 1987-2014.

Figure 2

Anaplasma phagocytophilum-infected band neutrophil in human peripheral blood (Wright stain, original magnification × 260). The top left inset shows the same band neutrophil and demonstrates several morulae with a stippled basophilic appearance corresponding to individual bacteria (magnification × 520). The bottom right insert shows A. phagocytophilum cultivated in vitro in the human promyelocytic leukemia cell line HL-60. Here, the individual basophilic bacteria are easily visualized within vacuoles of the infected cell (LeukoStat stain; magnification × 520).