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Ehrlichiosis and Anaplasmosis

By William A. Petri, Jr, MD, PhD, University of Virginia School of Medicine

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

Ehrlichia and Anaplasma bacteria, like rickettsiae, can live only inside the cells of an animal or a person (see also Overview of Rickettsial Infections). 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. Anaplasmosis occurs in the Northeast, mid-Atlantic states, upper Midwest and West Coast of the United States. Anaplasmosis also occurs in Europe. 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.

Ehrlichiosis is transmitted by the lone star tick (Amblyomma americanum), and anaplasmosis is transmitted by the deer tick (Ixodes species).

Lyme disease and babesiosis are also carried by ticks and are common in the same areas. Consequently, people may get more than one infection if they are bitten by a tick infected with more than one organism.

Because Ehrlichia and Anaplasma bacteria infect white blood cells, which circulate in the bloodstream, these bacteria may be transmitted through blood transfusions or organ transplantation. 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

Symptoms of ehrlichiosis and anaplasmosis 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 and anaplasmosis may cause widespread blood clotting ( disseminated intravascular coagulation), severe malfunction (failure) of several organs, seizures, and coma.

Symptoms of both infections 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 is more likely to occur in people with a weakened immune system or who are not treated soon enough.

Diagnosis

  • Blood tests

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 these test usually cannot detect the antibodies 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.

Treatment

  • Antibiotics

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.

Tick Bite Prevention

Preventing tick access to skin includes

  • Staying on paths and trails

  • Tucking trousers into boots or socks

  • Wearing long-sleeved shirts

  • Applying repellents with diethyltoluamide (DEET) to skin surfaces

DEET should be used cautiously in very young children because toxic reactions have been reported. Permethrin on clothing effectively kills ticks. Frequent searches for ticks, particularly in hairy areas and on children, are essential in endemic areas.

Engorged ticks should be removed with care and not crushed between the fingers because crushing the tick may result in disease transmission. The tick’s body should not be grasped or squeezed. Gradual traction on the head with a small forceps dislodges the tick. The point of attachment should be swabbed with alcohol. Petroleum jelly, lit matches, and other irritants are not effective ways to remove ticks and should not be used.

No practical means are available to rid entire areas of ticks, but tick populations may be reduced in endemic areas by controlling small-animal populations.

* This is the Consumer Version. *