Diseases > Ticks > Human Granulocytic Ehrlichiosis

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 and Medical Importance of Ticks in Indiana" (PDF 757KB)).
• Wear clothing consisting of a long sleeved shirt, long pants, and boots.
• Use a repellent recommended by CDC and treat clothing with permethrin.