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(er″lik-ē-ō′sĭs) [Paul Ehrlich, Ger. physician, 1854–1915. Awarded Nobel Prize in medicine in 1908] Any of several forms of an infectious disease of monocytes and granulocytes transmitted by exposure to species of Ehrlichia. It was first reported in humans in the U.S. in 1987 and is considered an emerging disease.

CAUSES: There are numerous causes of ehrlichiosis, e.g., 1) E. chaffeensis, which is carried by the Lone Star tick and causes human monocytic (monocytotropic) ehrlichiosis (HME); 2) Anaplasma phagocytophila (formerly called E. phagocytophila), which is carried by Ixodes, e.g., the Western blacklegged tick (I. pacificus), and causes human granulocytic ehrlichiosis (HGE); and 3) E. ewingii, which causes a related syndrome. Other Ehrlichia species include E. canis, E. muris, E. ruminantium, and Panola Moutain Ehrlichia.

Participation in outdoor recreational activities, such as hiking, camping, or hunting are implicated in the tick exposures that lead to ehrlichiosis. More than 30 states have reported cases, but HME is found mostly in the southern U.S., and HGE in the northern U.S. In Japan, E. sennetsu causes a mononucleosis-like illness (Sennetsu fever).

SYMPTOMS AND SIGNS: Both HME and HGE are marked by nonspecific influenza-like symptoms. A high fever with rigors, headache, malaise, myalgia, leukopenia, and thrombocytopenia are most common; a rash may be present in HME. The symptoms last for approx. 3 weeks; it is unclear if a latent infection remains. Complications of renal failure, cardiomegaly, coagulopathies, or coma occur in 16% of patients, mostly in the older adults. Most patients are male.

DIAGNOSIS: Serological tests are used; a polymerase chain reaction applied to whole blood samples can confirm the diagnosis in 24 to 48 hr. The morulae of the infecting organism can sometimes be identified within polymorphonuclear leukocytes on a peripheral blood smear.

PREVENTION: Ticks should be avoided by avoiding grassy areas where they reside, by wearing long pants and light-colored clothing, and by applying tick repellents to clothing before entering grasslands or woodlands. After leaving these areas, exposed clothing should be immediately laundered, and the skin bathed and inspected for the presence of adult ticks and tiny nymphs. Any attached ticks should be promptly removed with tweezers, making certain to remove the entire insect, including the head.

TREATMENT: Doxycycline (or other tetracyclines) is the recommended treatment.

IMPACT ON HEALTH: Although most patients recover, immunosuppressed individuals have a graver prognosis. The mortality rate from infection is about 3%.


Enzyme immunoassay.


[Gr. eikosi, twenty] Prefix used in chemistry to indicate twenty.


(ī-kō′să-noyd″) Any of several autocrine or paracrine cytokines formed from the metabolism of arachidonic acid. They include prostaglandins, thromboxanes, and leukotrienes.

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