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Diseases > Ticks > Human Granulocytic Ehrlichiosis


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Human Granulocytic Ehrlichiosis

Human granulocytic ehrlichiosis (HGE) was recognized as a human disease in Missouri in 1999. Additional cases in the U.S. have been reported in patients with a weak immune system. The parasite previously was known only as a cause of disease in dogs and other canines.

Causative agent

  • A bacterium with the scientific name Ehrlichia ewingii.
  • It is an intracellular parasite that undergoes development within white blood cells, especially granulocytes.

Geographical distribution of cases

  • Documented cases have occurred in Missouri and the southern U.S.

Symptoms of infection

  • Fever, headache, joint pain, and muscle ache.
  • Infections usually are mild, but severe cases can result in death in susceptible humans.

Reservoir hosts of Ehrlichia ewingii

  • Coyotes, other wild canines, and dogs.

Vectors of Ehrlichia ewingii

  • Amblyomma americanum, lone star tick.
  • Rhipicephalus sanguineus, brown dog tick.

Modes of transmission

  • From infected ticks (nymphs and adults) to humans via their bite.
  • From infected tick larvae to nymphs to adults via transstadial transmission.
  • NOTE: there is no human-to-human transmission.

Diagnosis of infection

  • Symptoms, together with onset in late spring into summer.

Treatment of infection

  • Antibiotic prescribed by a physician.

Prevention of infection

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