Ehrlichioses are tick-borne infections that cause fever, chills, headache, and a general feeling of illness (malaise). These symptoms begin suddenly.
Ehrlichia bacteria, like rickettsiae, can live only inside the cells of an animal or a person. However, unlike rickettsiae, Ehrlichia bacteria inhabit white blood cells (such as granulocytes and monocytes). Different species inhabit different types of white blood cells.
Ehrlichioses are most common in the southeastern and south central United States. They also occur in Europe. They 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 brown dog tick or deer tick.
Symptoms usually begin 1 to 2 weeks after a tick bite. The first symptoms are fever, chills, severe headache, body aches, and malaise. As the infection progresses, other symptoms may develop:
Rash is much less common than in rickettsial infections. Death is uncommon but can occur in people with a weakened immune system or who are not treated soon enough.
Diagnosis and Treatment
Doctors do blood tests, which may detect a low white blood cell count, a low platelet count (thrombocytopenia), 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. Polymerase chain reaction (PCR) testing 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. The presence of morulae confirms the diagnosis of ehrlichiosis.
If people who may have been exposed to infected ticks have typical symptoms, treatment is usually started based on the person's symptoms before test results are available. Doxycycline, chloramphenicol, and tetracycline are all effective. 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.
Last full review/revision November 2007 by William A. Petri, Jr., MD, PhD