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 levels.