Human anaplasmosis (HA) is the new nomenclature for the disease formerly known as human granulocytic ehrlichiosis. HA (caused by the rickettsia Anaplasma phagocytophilum) is transmitted to humans by Ixodes scapularis (deer tick or blacklegged tick), the same tick that transmits Lyme disease.
HA case numbers increased from 139 cases in 2004 (2.8 per 100,000 population) to a record high of 186 cases (3.6 per 100,000 population) in 2005. One hundred twenty-seven (68%) case-patients reported in 2005 were male. The median age of case-patients was 57 years (range, 2 to 92 years). The peak in onsets of illness occurred in June and July (116 cases [62%]). Co-infections with Lyme disease and HA can occur from the same tick bite; during 2005, eight HA case-patients (4%) also had objective evidence of Lyme disease. The risk for HA is highest in many of the same Minnesota counties where the risk of Lyme disease is greatest, including Aitkin, Cass, Crow Wing, and Pine Counties.
For a discussion of the recent increase in tick-borne disease in Minnesota and the distribution of ticks that transmit HA and other tick-borne diseases, see “Expansion of the Range of Vector-borne Disease in Minnesota” in the March/April 2006 issue (vol. 34, no. 2) of the DCN.
Note: For up to date infromation see: Human Anaplasmosis (HA)