Ehrlichioses
Ehrlichioses are tick-borne infections that cause an abrupt onset of fever, chills, headache, and a general feeling of illness (malaise).
Ehrlichiae are very similar to rickettsiae: they are bacteria that can live only inside the cells of an animal or person. Unlike rickettsiae, however, ehrlichiae inhabit white blood cells (such as granulocytes and monocytes). Different species of ehrlichiae inhabit different types of white blood cells. In general, however, ehrlichioses are very similar in the symptoms they produce and in the way they are diagnosed and treated.
Ehrlichioses occur in the United States and Europe, but are most common in the midwestern, southeastern, and south-central United States. Ehrlichioses are most likely to develop between spring and late fall, when ticks are most active.
Symptoms, Diagnosis, and Treatment
Ehrlichioses begin 1 to 2 weeks after a tick bite. The first symptoms are fever, severe headache, body aches, and malaise. As the illness progresses, vomiting and diarrhea may develop, along with confusion and even coma. Sometimes cough and difficulty breathing develop. Skin rash is much less common than in rickettsial disease. Death is uncommon, but can occur in people with a poorly functioning immune system or in those who are not treated soon enough.
A person with an ehrlichial infection may have a low white blood cell count, a low blood count (anemia), and abnormal blood clotting, but these findings occur in many other illnesses. Blood tests for antibodies to ehrlichiae may be helpful, but usually do not give positive results until several weeks after the beginning of the illness. Polymerase chain reaction (PCR), a test that identifies the organism's DNA in the person's blood, may be more useful. Sometimes the person's white blood cells contain characteristic spots (morulae) that can be seen under a microscope. The presence of morulae confirms the diagnosis of ehrlichiosis, but they are often not visible.
Treatment is usually started based on the person's symptoms. Tetracycline, doxycycline, and chloramphenicol are all effective against ehrlichioses.
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