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Ehrlichiosis and Anaplasmosis

By William A. Petri, Jr, MD, PhD

Ehrlichiosis and anaplasmosis are tick-borne infections that cause fever, chills, muscle aches, headache, and a general feeling of illness (malaise). These symptoms begin suddenly.

Ehrlichia and Anaplasma bacteria, like rickettsiae, can live only inside the cells of an animal or a person. However, unlike rickettsiae, these bacteria inhabit white blood cells ( Ehrlichia in monocytes and Anaplasma in granulocytes).

Ehrlichiosis is most common in the southeastern and south central United States. It also occurs in Europe. Anaplasmosis occurs in the Northeast, mid-Atlantic states, upper Midwest and West Coast of the United States. These infections are most likely to develop between spring and late fall, when ticks are most active. Infection is spread to people through tick bites, sometimes resulting from contact with animals that carry the lone star tick, brown dog tick, or deer tick. A few people have developed anaplasmosis after they had a blood transfusion from a person who had been recently infected or who was infected but had no symptoms.


Symptoms of the two infections are similar. Symptoms usually begin about 12 days after a tick bite. Symptoms begin suddenly. They include fever, chills, muscle aches, weakness, nausea and/or vomiting, cough, headache, and malaise.

A rash may develop on the torso, arms, and legs in some people with ehrlichiosis but is uncommon in people with anaplasmosis. Some people have no symptoms.

Ehrlichiosis may cause widespread blood clotting (disseminated intravascular coagulation), severe malfunction (failure) of several organs, seizures, and coma. Symptoms are more severe in people with a weakened immune system (due to a disorder such as HIV infection or to drugs such as corticosteroids). Death is uncommon but can occur in people with a weakened immune system or who are not treated soon enough.


Doctors do blood tests, which may detect a low white blood cell count, a low platelet count (thrombocytopenia), a high level of liver enzymes, and abnormal blood clotting. But these findings occur in many other disorders. Blood tests to check for antibodies to these bacteria may be helpful, but results are usually not positive until several weeks after the illness begins. The polymerase chain reaction (PCR) technique may be more useful. It increases the amount of the bacteria’s DNA and thus makes the bacteria easier to identify.

Sometimes white blood cells contain characteristic spots (morulae) that can be seen under a microscope. These spots occur in 20 to 80% of people with anaplasmosis and can help confirm the diagnosis. They rarely occur in ehrlichiosis.


If people who may have been exposed to infected ticks have typical symptoms, treatment is usually started before test results are available. When treatment is started early, most people respond rapidly and well. A delay in treatment may lead to serious complications, including death in 2 to 5% of people.

Doxycycline is usually used, People take this antibiotic until they improve and have had no fever for 24 to 48 hours, but they must take it for at least 7 days. Some people continue to have headaches and feel weak and generally unwell for weeks after treatment.

To prevent these disorders, people should take measures to prevent tick bites (see Preventing Tick Bites).

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