Anaplasma Phagocytophilum (Anaplasmosis)

Anaplasma phagocytophilum is an obligate gram-negative, intracellular bacterium that causes an acute febrile illness known as anaplasmosis or human granulocytic anaplasmosis (HGA). The organism is genetically related to rickettsia and is transmitted by Ixodes scapularis in the northeast United States and by Ixodes pacificus in California. The vector also transmits other organisms responsible for diseases such as Lyme, babesiosis, ehrlichioses and Powassan encephalitis. Anaplasmosis was formerly named human granulocytic ehrlichiosis (HGE). In 2001, the organism was reassigned to the genus Anaplasma. Cases of anaplasmosis have been identified worldwide; in the United States, it is mostly reported in the upper Midwest and the Northeast. Disease activity has also been reported in Northern Europe and Southeast Asia. Anaplasmosis generally presents with nonspecific symptoms such as fever, chills, malaise, headache, and myalgias. On rare occasions, a rash may be present. The patient may also report nonspecific gastrointestinal (GI) or respiratory symptoms. A low number of patients manifest with life-threatening complications. Immunosuppressed patients are more likely to get hospitalized and have a higher risk of suffering severe complications. Occasionally, co-infection with other tick-borne organisms (Anaplasma, Lyme, and Babesia) occurs given that Ixodes ticks are the common vector. Anaplasmosis is diagnosed by culture, histopathology, PCR, or serology. Presence of intracytoplasmic aggregates of Anaplasma in peripheral blood neutrophils can be diagnostic in 20% to 80% of symptomatic patients. First line treatment is doxycycline 100 mg orally, twice daily administered for 14 to 21 days or at least 3 days after defervescence.