Ehrlichiosis & Anaplasmosis

For further information, see CMDT Part 32-13: Other Rickettsial & Rickettsial-Like Diseases

Key Features

Essentials of Diagnosis

• Infection of monocyte or granulocyte by tick-borne gram-negative bacteria

• Nine-day incubation period; clinical disease ranges from asymptomatic to life-threatening

• Malaise, nausea, fever, and headaches

General Considerations

• Human ehrlichiosis and anaplasmosis are endemic in the United States

• Ehrlichiosis typically occurs in men aged 60–69 years; anaplasmosis typically occurs in men over 40 years old

• Ehrlichia chaffeensis

  • Most common species infecting humans

  • Seen primarily in Arkansas, Missouri, Oklahoma and New York

• Ehrlichia ewingii

  • Causes human granulocytic ehrlichiosis similar to anaplasmosis

  • Constitutes almost 10% of ehrlichiosis cases

  • Most cases in the United States are reported from the Midwest and Southeast

• Ehrlichia muris eauclairiensis is seen in the upper Midwestern United States

• Anaplasma phagocytophilum

  • Causes human granulocytic anaplasmosis

  • Most cases in the United States are reported from New England, New York, Minnesota, and Wisconsin

  • Increasingly being reported from Asia, South Korea, Mongolia, China (where a new species [Anaplasma capra] has been identified), and Northern Europe

• CDC reports that the incidences of human monocytic ehrlichiosis, granulocytic ehrlichiosis and, in particular, anaplasmosis are increasing; coinfection may occur

Clinical Findings

• Human monocytic ehrlichiosis

  • Clinical disease ranges from mild to life-threatening

  • Incubation period: 1–2 weeks

  • Prodrome then develops, consisting of malaise, rigors, and nausea, high fever and headache

  • A pleomorphic rash may occur

  • Presentation in immunosuppressed patients and older patients tends to be more severe

• Human granulocytic ehrlichiosis and anaplasmosis

  • Clinical manifestations are similar to those seen with human monocytic ehrlichiosis

  • However, rash is infrequent

  • If a rash is present, coinfection with other tick-borne diseases or an alternative diagnosis should be suspected

  • Persistent fever and malaise are reported to occur for 2 or more years

• Coinfection with anaplasmosis and Lyme disease or babesiosis may occur, but the clinical manifestations (including fever and cytopenias) are more severe with anaplasmosis than with Lyme disease

Differential Diagnosis

• Infection with Borrelia miyamotoi may mimic anaplasmosis in its clinical manifestations

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

Outcome

Complications

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