Anaplasmosis, 2015

Human anaplasmosis, caused by Anaplasma phagocytophilum, is transmitted to humans by bites from Ixodes scapularis (the blacklegged tick or deer tick). Although anaplasmosis was initially referred to as human granulocytic ehrlichiosis, anaplasmosis and ehrlichiosis (due to Ehrlichia chaffeensis) are distinct diseases caused by different rickettsial species, and only Anaplasmosis is endemic in Minnesota. In Minnesota, the same tick vector also transmits the etiologic agents of Lyme disease, babesiosis, ehrlichiosis (due to E. muris-like), and a strain of Powassan virus. A. phagocytophilum can also be transmitted by blood transfusion.

In 2015, 613 confirmed or probable cases of anaplasmosis (10.8 cases per 100,000) were reported, up from the 448 cases reported in 2014 (Figure 1). Despite small annual fluctuations in reported cases, the overall trend is an increase in yearly case totals over time. Three hundred eighty-five (63%) cases were male. The median age of cases was 58 years (range, 10 to 94 years), 14 years older than the median age of Lyme disease cases. As is typical, most cases had illness onsets during the summer months, with 56% of cases reporting illness onsets in June and July. One hundred sixty-eight (27%) cases were hospitalized at some point due to their infection, for a median duration of 4 days (range, 1 to 38 days).

• For up to date information see>> Anaplasmosis
• Full issue>> Annual Summary of Communicable Diseases Reported to the Minnesota Department of Health, 2015