Anaplasmosis, 2004

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 black-legged tick), the same tick that transmits Lyme disease. Similar to Lyme disease, HA case numbers also increased during 2004, from 78 cases in 2003 (1.6 per 100,000 population) to 139 cases (2.8 per 100,000). The record high occurred in 2002, with 149 cases (3.0 per 100,000 population). Eighty-one (58%) case-patients reported in 2004 were male. The median age of case-patients was 59 years (range, 1 to 89 years). The peak in onsets of illness occurred in June and July (77 cases [56%] of 137 cases with known onset). Co-infections with Lyme disease and HA can occur from the same tick bite; during 2004, two HA case-patients (1.4%) 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, Hubbard, and Pine Counties.

For additional information, see “Dramatic Increase in Lyme Disease and Other Tick-borne Diseases, 2004” in the May/June 2005 issue of the Disease Control Newsletter.

• For up to date information see>> Anaplasmosis
• Full issue>> Annual Summary of Communicable Diseases Reported to the Minnesota Department of Health, 2004