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Anaplasmosis is caused by Anaplasma phagocytophilum and it is related to the rickettsial diseases. Both are transmitted to humans by ticks. Symptoms resemble those of Rocky Mountain spotted fever except that a rash is much less common. Onset of illness, with fever, chills, headache, and malaise, is abrupt. Anaplasma phagocytophilum (formerly E. phagocytophila) causes human granulocytic anaplasmosis, which occurs in the Northeast, mid-Atlantic, upper Midwest and West Coast of the US, where its arthropod vector (ixodid ticks) are endemic.
Some infections are asymptomatic, most cause abrupt onset of an influenza-like illness with nonspecific symptoms such as fever, chills, myalgias, weakness, nausea, vomiting, cough. headache, and malaise, usually beginning about 12 days after the tick bite. Anaplasmosis may result in disseminated intravascular coagulation, multiorgan failure, seizures, and coma. Diagnostic serologic tests are available, but PCR of blood is more sensitive and specific and can result in an early diagnosis because serologic tests require comparison of serial titers. Cytoplasmic ehrlichial inclusions in monocytes or neutrophils may be detected. Blood and liver functions tests may detect hematologic and hepatic abnormalities, such as leukopenia, thrombocytopenia, and elevated aminotransferase.
Primary treatment is doxycycline 200 mg po once followed by 100 mg bid until the patient improves and has been afebrile for 24 to 48 h but is continued for at least 7 days. Chloramphenicol is no longer effective. Some patients continue to experience headache, weakness, and malaise for weeks after adequate treatment. In 2014, 448 confirmed or probable cases of anaplasmosis (8.3 cases per 100,000 population) were reported, down from the 627 cases reported in 2013. Despite these occasional decreases in reported cases, the overall trend is an increase in yearly case totals over time. Two hundred ninety-two (65%) cases reported in 2014 were male. The median age of cases was 59 years (range, 3 to 87 years), 20 years older than the median age of Lyme disease cases. As is typical, most cases had illness onsets during the summer months, with 58% of cases reporting illness onsets in June and July. In 2014, 124 (28%) anaplasmosis cases were hospitalized at some point for their infection, with a median duration of 4 days (range, 2 to 17 days).