Ehrlichiosis
Key points
- Erhlichiosis is an infectious disease transmitted by the bite of a tick.
- Ehrlichiosis is a disease caused by Ehrlichia organisms.
- The incubation period for ehrlichiosis is approximately 9 days from the time of tick bite.
- Rickettsial diseases, in general, are often responsive to a group of antibiotics belonging to the tetracyclines.
Definition
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.
Symptoms
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.
Symptoms
- fever
- chills
- headache
- nausea
- muscle aches
- malaise
- rash, maculopapular
- rash, petechial (fine pinhead-sized hemorrhages in the skin)
Signs and tests
Written and revised by
David Cohen, M.D.
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