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
  • There is no vaccine.
  • Avoid tick habitat and contact with tick-infested vegetation (see E-243-W "The Biology of Indiana Ticks").
  • Wear clothing consisting of a long sleeved shirt, long pants, and boots.
  • Use a repellent recommended by CDC and treat clothing with permethrin.