Ehrlichiosis

Key Features

• Tick-borne gram-negative obligate intracellular bacteria

• Two main clinical entities

  • Human granulocytic ehrlichiosis (typically Anaplasma phagocytophilium and, rarely, Ehrlichia ewingii)

  • Human monocytic ehrlichiosis (typically Ehrlichia chaffeensis)

• Bacteria form morulae, intracytoplasmic aggregates within leukocytes

• In the United States, mainly found in mid-Atlantic, southeastern, and central states

• Rare serious sequelae include acute respiratory failure and acute respiratory distress syndrome; neurologic complications, the most common being meningoencephalitis and aseptic meningitis; acute kidney disease (which may mimic thrombotic thrombocytopenic purpura); hemophagocytic syndrome, and multi-organ failure

• May see coinfection with other tick-borne illnesses (eg, Lyme disease or babesiosis)

Clinical Findings

• Clinical disease of human monocytic ehrlichiosis ranges from mild to life threatening

• Incubation period is 1–2 weeks

• Prodrome of malaise, rigors, and nausea, followed by fever, and headache

• Respiratory failure, acute kidney disease, and encephalopathy may ensue in severe cases

Diagnosis

• Leukopenia, absolute lymphopenia, thrombocytopenia, and transaminitis common

• Thrombocytopenia occurs more often than leukopenia in human granulocytic ehrlichiosis

• Examination of peripheral blood with Giemsa stain may reveal characteristic intraleukocytic vacuoles (morulae) in up to 20% of patients

• Polymerase chain reaction assay is most sensitive in the first week of illness and can be used as a confirmatory test

• Indirect fluorescent antibody assay available from the CDC and requires acute and convalescent sera

Treatment

• Treatment for all forms of ehrlichiosis is with doxycycline, 100 mg twice daily (orally or intravenously) for 10–14 days or until 3 days of defervescence

• Rifampin is an alternative in pregnant women