Human Anaplasmosis

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Anaplasmosis is a tick-borne disease caused by the bacterium Anaplasma phagocytophilum. It was previously known as human granulocytic ehrlichiosis (HGE) and has more recently been called human granulocytic anaplasmosis (HGA). Anaplasmosis is transmitted to humans by tick bites primarily from the black-legged tick (Ixodes scapularis) and the western black-legged tick (Ixodes pacificus).

Of the four distinct phases in the tick life-cycle (egg, larvae, nymph, adult), nymphal and adult ticks are most frequently associated with transmission of anaplasmosis to humans. Typical symptoms include: fever, headache, chills, and muscle aches.

Usually, these symptoms occur within 1-2 weeks of a tick bite. Anaplasmosis is initially diagnosed based on symptoms and clinical presentation, and later confirmed by the use of specialized laboratory tests. The first line treatment for adults and children of all ages is doxycycline. Anaplasmosis and other tick-borne diseases can be prevented.

The following ticks are known to be carriers of the pathogens which cause anaplasmosis in humans:

  • Blacklegged Tick  (Ixodes scapularis)
  • Western Blacklegged Tick  (Ixodes pacificus)


Signs + Symptoms

Common signs and symptoms of anaplasmosis may include, but are not limited to:

  • Fever
  • Headache
  • Muscle Pain
  • Malaise
  • Chills
  • Nausea & Abdominal Pain
  • Cough
  • Confusion
  • Rash (rare)



Doxycycline is the first line treatment for adults and children of all ages and should be initiated immediately whenever anaplasmosis is suspected.

Use of antibiotics other than doxycycline or other tetracyclines has been associated with a higher risk of fatal outcome for some rickettsial infections. Doxycycline is most effective at preventing severe complications from developing if it is started early in the course of disease. Therefore, treatment must be based on clinical suspicion alone and should always begin before laboratory results return.

If the patient is treated within the first 5 days of the disease, fever generally subsides within 24-72 hours. In fact, failure to respond to doxycycline suggests that the patient’s condition might not be due to anaplasmosis. Severely ill patients may require longer periods before their fever resolves. Resistance to doxycycline or relapses in symptoms after the completion of the recommended course have not been documented.