Erhlichiosis is an infectious disease transmitted by the bite of a tick.

Causes, incidence, and risk factors

Ehrlichiosis is a disease caused by Ehrlichia organisms. It was first described in 1990. The two specific organisms that have been implicated are Ehrlichia chaffeensis and granulocytic Ehrlichia.

The Ehrlichia bacteria belong to the family Rickettsiae. Rickettsial organisms are responsible for a number of serious diseases with worldwide distribution such as Rocky Mountain spotted fever, typhus, murine typhus, scrub typhus, Queensland tick typhus, Boutonneuse fever, North Asian tick-borne rickettsiosis, rickettsial pox, and others. All of these diseases require an insect (tick, flea, mite) to transmit them to humans or other animals.

The infectious organism of ehrlichiosis is transmitted to humans by the bite of a tick. Rickettsiae are often associated with a specific tick. Ehrlichia inhabit the Lone Star tick (Amblyomma americanum), the American dog tick (Dermacentor variabilis), and the deer ticks (Ixodes dammini and Ixodes scapularis). (NOTE: the deer tick is also the carrier of Lyme disease.).

In the U.S., ehrlichiosis is found mainly in the southern central states and the Southeast. It has recently also been reported in the upper midwestern and Northeast.

Risk factors for ehrlichiosis include living in an area with a lot of ticks, activities in high grasses, and owning a pet that may bring a tick home.


The incubation period for ehrlichiosis is approximately 9 days from the time of tick bite. Ehrlichiosis begins with fever, chills, headache, muscle pain, and nausea. A rash appears in over half the cases and the disease may be mistaken for Rocky Mountain spotted fever. The symptoms are often quite general, but the infected individual is sometimes sick enough to seek medical attention.

Surveys show that the majority of people exposed do not seek treatment and likely never knew they were infected. Ehrlichiosis can be fatal. The organism is sensitive to antibiotics and treatment results in improvement in 24 to 48 hours. Recovery takes 3 weeks.


  • fever  
  • chills  
  • headache  
  • nausea  
  • muscle aches  
  • malaise  
  • rash, maculopapular  
  • rash, petechial (fine pinhead-sized hemorrhages in the skin)

Signs and tests

  • CBC shows decreased white blood cells (leukopenia), decreased platelets (thrombocytopenia)  
  • a granulocyte stain shows clumps of bacteria inside white blood cells  
  • the platelet count shows decreased platelets (thrombocytopenia)  
  • liver enzymes show elevated transaminase  
  • a fluorescent antibody test may turn positive for E. chaffeensis or granulocytic Ehrlichia


Rickettsial diseases, in general, are often responsive to a group of antibiotics belonging to the tetracyclines. Treatment with tetracycline or doxycycline produces rapid improvement. Note: Oral tetracycline is usually not prescribed for children until after all the permanent teeth have erupted; it can permanently discolor teeth that are still forming.

Expectations (prognosis)

With treatment full recovery is expected.


Infection may damage many organ systems but typically the lungs and kidney are involved. Several cases have resulted in death.

Calling your health care provider

Call your health care provider if you have had a recent tick bite or exposure to tick-infested areas and have developed symptoms suggestive of ehrlichiosis. Be sure to mention the tick exposure to the health care provider.


Ehrlichiosis is spread by tick bites. Preventing tick bites will prevent Ehrlichiosis and other tick-borne diseases. Common measures include the use of insect repellent, appropriate clothing, sticking to trails and avoiding dense brush when hiking, and not standing under overhanging foliage. After hiking or outings in the woods it is a good idea to examine yourself for ticks and remove any that may be found.

Studies suggest that a tick must be attached for at least 24 hours in order to cause disease, so early removal will prevent infection. The date and time of a tick bite should be recorded as the incubation period of some tick-borne diseases is long enough (the incubation period for Lyme disease is up to 1 month) that the event could be forgotten.

Johns Hopkins patient information

Last revised: December 2, 2012
by Arthur A. Poghosian, M.D.

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