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Anaplasmosis is an infection caused by the bacterium Anaplasma phagocytophilum, which is transmitted in Indiana by the bite of an infected blacklegged tick (Ixodes scapularis). The bacterium was previously known by other names, including Ehrlichia equi and Ehrlichia phagocytophilum, and the disease was previously known as human granulocytic ehrlichiosis (HGE).

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Transmission | Signs and Symptoms | Diagnosis | Treatment | Prevention | Maps and Statistics | Information for Providers

Anaplasma phagocytophilum inside a white blood cell. Photo: Centers for Disease Control and Prevention.


The bacteria that causes anaplasmosis is transmitted in Indiana by the bite of a blacklegged tick (Ixodes scapularis). In rare cases, the bacterium may be transmitted by blood transfusion.

Signs and Symptoms

Signs and symptoms of anaplasmosis usually appear within 1–2 weeks after the bite of an infected tick. People in the early stages of illness can experience flu-like symptoms, such as:

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

Untreated anaplasmosis can rapidly progress to a serious and life-threatening illness. Older people and those with weakened immune systems are more likely to develop serious illness.


Diagnosis of anaplasmosis is based upon the patient’s signs and symptoms, a history of possible exposure to ticks, and appropriate laboratory testing. Early recognition of symptoms is important for prompt diagnosis and treatment. If you think you have anaplasmosis, contact your health care provider right away.

People who have removed an attached tick sometimes wonder if they should have it tested for tick-borne diseases. Although some laboratories offer this testing, ISDH does not recommend it. If the tick tests positive, it does not necessarily mean that you have been infected; if the tick tests negative, it may provide a false sense of security because you may have been unknowingly bitten by a different tick that was infected.


Doxycycline is the treatment of choice for adults and children of all ages with suspected anaplasmosis. Doxycycline is most effective at preventing severe complications and death if it is started early in the course of illness. Treatment should be started for anyone with suspected anaplasmosis and should never be delayed while waiting for laboratory results.


The best way to prevent anaplasmosis is to avoid tick bites. Please see our tick prevention page for more information.

For more information about anaplasmosis, please visit the CDC Anaplasmosis webpage.

Maps and Statistics

Due to the close relationship between the bacteria, cases of anaplasmosis and ehrlichiosis are currently reported together in Indiana.  For anaplasmosis maps and statistics in Indiana, please visit:

National statistics for anaplasmosis can be found at the CDC Anaplasmosis Epidemiology and Statistics webpage.

Information for Providers

For anaplasmosis diagnosis, treatment, and testing information, click here.

Physician Reference: Common tick-borne diseases

Tickborne Diseases of the United States.

A practical guide for health care professionals on anaplasmosis and other tick-borne diseases.

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