Human ehrlichiosis.

Human ehrlichiosis is a newly emergent, tick-borne, zoonotic infection caused by members of the genus Ehrlichia. These rickettsia-like, obligate intracellular, gram-negative bacteria produce two similar yet distinct diseases. Human monocytic ehrlichiosis is caused by Ehrlichia chaffeensis. Human granulocytic ehrlichiosis is caused by an organism closely related to Ehrlichia equi. The most common initial clinical findings include fever, malaise, myalgia, headaches and rigors, while the most common laboratory findings are thrombocytopenia, leukopenia, anemia and elevated liver enzyme levels. Both diseases can produce intracytoplasmic morulae, in either monocytes or neutrophils, which may be visible on Wright-stained peripheral smears. Treatment consists of tetracycline or doxycycline. Rifampin or chloramphenicol can be tried when tetracycline is absolutely contraindicated. Treatment should never be delayed pending serologic or polymerase chain reaction confirmation of the diagnosis because of the 5 to 10 percent mortality rate.