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Ehrlichiosis

Clinical Features

  • Fever, headache, malaise are common.
  • Rash occurs in less than one third of patients.
  • Laboratory findings include thrombocytopenia and elevated liver enzymes.

Etiologic Agent

Ehrlichia chaffeensis causes monocytic ehrlichiosis (HME) and a second Ehrlichia species causes granulocytic ehrlichiosis (HGE) in the United States

Incidence

  • Unknown.
  • Studies suggest that the HME occurs at an incidence rate at or above Rocky Mountain spotted fever (3-5/100,000) in endemic locations.
  • Approximately 200 cases of HGE and 400 cases of HME have been confirmed.

Sequelae

Fatalities have been reported for HME and HGE (~3-10%).

Cost

Unknown.
Medical costs include hospitalization in severe cases.

Transmission

Approximately, 70% of cases reported bites by ticks Evidence suggests that Amblyomma americanum, the Lone Star tick, is a vector of monocytic ehrlichiosis, and Ixodes scapularis, the black legged tick, is a vector of granulocytic ehrlichiosis.

Risk Groups

  • The risk of clinical or severe ehrlichiosis may be greater in older persons.
  • The larger proportion of male cases may reflect the increased risk of tick exposure.
  • Occupational (military) and recreational (golf) risks have been identified.

Surveillance

  • Neither disease is nationally reportable.
  • CDC provides serologic and genetic testing for HME and HGE.

Trends

  • Unknown but increasingly recognized as a threat.
  • Geographic range of known cases of HGE and HME increasing.

Challenges

  • Improve the rapid diagnostic capabilities and identify the incidence of disease and the ratio of clinical illness to infection.
  • Establish epidemiology and maintenance cycles for human ehrlichioses.

Opportunities

  • Rapid diagnosis leads to appropriate antibiotic therapy and reduced morbidity and mortality.
  • The natural history and epizootiology of the ehrlichiae are poorly understood.

Research Priorities

  • Develop a rapid diagnostic test for ehrlichiosis.
  • Further characterize the spectrum of the disease.
  • Investigate the relative incidence of ehrlichiosis among tick-borne diseases.
  • Conduct field and laboratory studies aimed at understanding the complex relationships of the agents with their vectors and vertebrate reservoirs to form prevention strategies.

January 1996
Courtesy of the Centers for Disease Control and Prevention