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Anaplasmosis formerly called human granulocytic ehrlichiosis (HGE), is a disease caused by the bacterium Anaplasma phagocytophilum. The bacteria are transmitted to people by the bite of an infected black-legged tick also known as the deer tick. In rare cases, A. phagocytophilum has been spread by blood transfusion. This bacterium infects white blood cells in the immune system. People with anaplasmosis will often have fever, headache, chills, and muscle aches. Treatment is available; however, if it is delayed, or there are underlying medical conditions, symptoms can become more severe. Doxycycline is the drug of choice for adults and children of all ages. The best way to prevent anaplasmosis is by avoiding tick bites.


Anaplasmosis typically begins within 1–2 weeks after the bite of an infected tick. Tick bites are usually painless, and many people do not remember being bitten.

Early Illness

Early signs and symptoms (days 1-5) are usually mild or moderate and may include:

  • Fever, chills
  • Severe headache
  • Muscle aches
  • Nausea, vomiting, diarrhea, loss of appetite

Late Illness

Rarely, if treatment is delayed or if there are other medical conditions present, anaplasmosis can cause severe illness. Prompt treatment can reduce your risk of developing severe illness.

Signs and symptoms of severe (late-stage) illness can include:

  • Respiratory failure
  • Bleeding problems
  • Organ failure
  • Death

Risk factors for severe illness:

  • Delayed treatment
  • Age: being older puts you at risk
  • Weakened immune system: People with weakened immune systems (such as those receiving some cancer treatments, individuals with advanced HIV infection, prior organ transplants, or people taking some medications) are at risk for severe illness


Early recognition and treatment of anaplasmosis is crucial to prevent complications. If you suspect you have been exposed to ticks or are experiencing symptoms consistent with the disease, it is important to seek medical attention promptly. Early treatment with the antibiotic doxycycline can prevent death and severe illness Doxycycline is the recommended antibiotic treatment for anaplasmosis in adults and children of all ages.


Prevention begins with you! Limiting exposure to ticks is the most effective method of prevention of tick-transmitted diseases because there is no vaccine. In persons exposed to tick-infested habitats, prompt, careful inspection, and removal of crawling or attached ticks is an important method of preventing disease. It may take several hours of attachment before the organisms are transmitted from the tick to the host.


CDC Information on Anaplasmosis

Page last updated: November 14, 2023