Human anaplasmosis (formerly known as human granulocytic ehrlichiosis) is caused by Anaplasma phagocytophilum, a rickettsial organism transmitted to humans by bites from Ixodes scapularis (the blacklegged tick or deer tick). In Minnesota, the same tick vector also transmits the etiologic agents of Lyme disease, babesiosis, one form of human ehrlichiosis, and a strain of Powassan virus. A. phagocytophilum can also be transmitted by blood transfusion.
In 2012, 507 confirmed or probable anaplasmosis cases (9.5 cases per 100,000 population) were reported (Figure 1). The median number of 317 cases (range, 139 to 782 cases) reported from 2004 through 2012 is also considerably higher than the median number of cases reported annually from 1996 to 2003 (median, 56 cases; range, 14 to 149). Three hundred eleven (61%) cases reported in 2012 were male. The median age of cases was 56 years (range, 1 to 99 years), 17 years older that are endemic to other tick-borne diseases transmitted by I. scapularis. POW virus testing is not widely available; however, the PHL is available to test cerebrospinal fluid and serum specimens from suspect cases (i.e., patients with viral encephalitis or meningitis of unknown etiology).
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