Anaplasmosis (human granulocytic anaplasmosis)
Anaplasmosis is a tick-borne febrile illness caused by the obligate intracellular bacterium Anaplasma phagocytophilum, transmitted by Ixodes ticks and infecting neutrophils, often coinfecting with Lyme disease or babesiosis. It is treated empirically with doxycycline without awaiting confirmatory PCR or serology.
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What this article covers
- Overview
Tick-borne granulocytic infection: anaplasmosis (human granulocytic anaplasmosis) is a nonspecific acute febrile illness caused by Anaplasma phagocytophilum, a gram-negative obligate intracellular…
- Epidemiology
Geographic distribution: most cases occur in the northeastern and upper Midwest United States, the same Lyme-endemic geography as the blacklegged tick.
- Risk factors
Outdoor exposure in a Lyme-endemic region: hiking, camping, gardening, or occupational work in wooded or grassy areas of the northeastern or upper Midwest United States during Ixodes tick season…
- Pathophysiology
Obligate intracellular replication in neutrophils: Anaplasma phagocytophilum, a gram-negative bacterium that lacks a classic peptidoglycan cell wall, is inoculated into the skin at the tick bite site…
- Clinical features
Nonspecific febrile illness: fever, headache, myalgias, and chills begin 1 to 2 weeks after a tick bite; this is the most consistent presenting picture and is often mistaken for a viral syndrome.
- Differential diagnosis
Ehrlichiosis: shares the fever-headache-myalgia picture but is transmitted by the Lone Star tick in southeastern and south-central geography, infects monocytes rather than neutrophils, and runs a…
- Diagnosis
No formal criteria; diagnosis rests on compatible exposure, clinical picture, and confirmatory microbiology: a tick-exposure history in a Lyme-endemic region plus fever, headache, and myalgia with…
- Management
First, start doxycycline empirically as soon as anaplasmosis is suspected, without waiting for confirmatory testing: delayed treatment is associated with increased mortality, so treatment decisions…
- Complications
Sepsis and multi-organ dysfunction: severe untreated or delayed-treatment cases can progress to septic shock with organ dysfunction, though this is less frequent than in ehrlichiosis.
- Prognosis
Case fatality under 1%, lower than the approximately 3% fatality of ehrlichiosis, reflecting the generally milder overall clinical course of anaplasmosis.
- Prevention
Tick avoidance in Ixodes-endemic areas: apply an EPA-registered repellent containing 20 to 30% DEET to exposed skin and treat clothing and gear with permethrin before outdoor activity in the…
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Related articles
- Ehrlichiosis (human monocytic ehrlichiosis)
Ehrlichiosis is a tick-borne febrile illness caused by the obligate intracellular bacterium Ehrlichia chaffeensis, transmitted by the Lone Star tick and infecting monocytes. It is treated empirically with doxycycline without awaiting confirmatory PCR or serology, since delayed treatment raises mortality.
- Lyme disease
Lyme disease is a tick-borne spirochetal infection caused by Borrelia burgdorferi that progresses from erythema migrans through early disseminated cardiac and neurologic disease to late arthritis, diagnosed clinically when erythema migrans is present and otherwise by two-tiered serology, and treated with staged doxycycline, amoxicillin, or cefuroxime regimens.
- Babesiosis
Babesiosis is caused by the intraerythrocytic protozoan Babesia microti, transmitted by the blacklegged deer tick or by blood transfusion, producing a hemolytic febrile illness diagnosed on thin blood smear and treated first-line with atovaquone plus azithromycin.
- Rocky Mountain spotted fever
Rocky Mountain spotted fever is the most common and most severe spotted fever rickettsiosis in the United States, caused by Rickettsia rickettsii and transmitted by the dog tick. The hallmark petechial rash typically lags days behind fever onset, so empiric doxycycline must be started on clinical suspicion alone, since treatment delay drives the disease's disproportionate mortality.