Ehrlichiosis
Ehrlichiosis is caused by rickettsial-like bacteria of the genus Ehrlichia transmitted to humans by ticks. Symptoms resemble rocky mountain spotted fever except that a rash is present in only a minority of patients.
Patients have an abrupt onset of illness with fever, chills, headache, and malaise.
Etiology and Epidemiology.
Ehrlichia are obligate,intracellular bacteria that appear as small cytoplasmic inclusions in lymphocytes and neutrophils.
Infections are transmitted to humans via tick bites,sometimes via contacts with animals that carry the brown dog tick or deer tick.
Most cases have been identified in the southeastern and south – central parts of US.
Three species of Ehrlichia are humen pathogens in the US:E. chaffeensis causes human monocytic ehrlichiosis, Anaplasma phagocytophila (formely E.phagocytophila) and E.ewingii cause human granulocytic ehrlichiosis.
The difference in the primary target cell results in only minor differences in clinical manifestations
Symptoms and Signs
Although some infections are asymptomatic,most cause an abrupt onset of illness with fever, chills, headache, and malaise, usually beginning about 12 days after the tick bite.
Some patient develops a maculopapular or petechial rash involving the trunk and extremities, although rash is rare with E.ewingii.
Abdominal pain, vomiting and diarrhea, disseminated intravascular coagulation, seizures, and coma may occur
Diagnosis and treatment
Diagnostic serologic tests are available, but PCR from blood is more sensitive and specific and can render an early diagnosis.
Cytoplasmic ehrlichial inclusions in monocytes or neutrophils may occur. Hematologic and hepatic abnormalities include leucopenia, thrombocytopenia, and abnormal liver function tests, especially elevated levels of transaminases.
Treatment is best started before laboratory results return. When treatment is started early, patients generally respond rapidly and well.
When treatment is delayed ,serious complications may follow, including viral and fungal super infections and death in 2 to 5 % .
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