Anaplasmosis, 2013

Human anaplasmosis, caused by Anaplasma phagocytophilum, is a rickettsial disease transmitted 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 Ehrlichia muris-like), and a strain of Powassan virus. A. phagocytophilum can also be transmitted by blood transfusion.

In 2013, 627 confirmed or probable anaplasmosis cases (11.7 cases per 100,000 population) were reported (Figure 1). This represents a 24% increase from the 507 cases in 2012, although it is considerably lower than the record 788 cases in 2011. Despite these fluctuations, the trend is an increase in yearly case totals over time. Three hundred ninety-two (63%) cases reported in 2013 were male. The median age of cases was 56 years (range, 2 to 93 years), 14 years older than the median age of Lyme disease cases. As is typical, most cases had illness onsets during the summer months, although the peak occurred in July (34% of cases) rather than in June as in recent years. In 2013, 160 (26%) anaplasmosis cases were hospitalized at some point for their infection, with a median duration of 4 days (range, 1 to 90 days).

• For up to date information see>> Anaplasmosis
• Full issue>> Annual Summary of Communicable Diseases Reported to the Minnesota Department of Health, 2013