Ehrlichiosis

Ehrlichiosis refers to several tick-borne diseases caused by very small organisms called Ehrlichiae, which affect both humans and animals. Ehrlichiae are gram negative bacteria that infect and destroy white blood cells. Two human diseases are caused by varieties of Ehrlichiae found in the U.S.

• Human monocyte ehrlichiosis (HME) infects white cells known as monocytes. More than 1000 cases of HME have been reported since it was first identified in 1986. It is caused by the bacterium Ehrlichiachaffeensis and is carried by the Lone Star tick, found primarily in the southcentral and southeastern U.S.
• Human granulocytic ehrlichiosis (HGE) infects granulocyte white blood cells. It is more likely than HME to be carried by adult Ixodes ticks and so is most often found northeastern and upper midwestern states.

Ehrlichiosis caused by other or unspecified organisms is a new category that was added in 2000 to account for other cases of these bacteria that have been detected.

Text Continues Below

---

Both HGE and HME have been reported in Europe. In fact, a Swedish study reported an almost equal prevalence of ehrlichiosis and Lyme disease in one population group. The European form of HGE appears to be a less severe condition than in the U.S. HME has also been reported in Africa.

Some studies indicate that middle-aged and elderly men are most likely to be infected with either form of ehrlichiosis.

Symptoms of Ehrlichiosis

Ehrlichiosis usually develops rapidly. Patients who are infected with ehrlichiosis will begin to feel symptoms between 3 to 16 days after being bitten by an infected tick. A patient may feel fine early in the day only to experience very severe, debilitating symptoms a few hours later. While ehrlichiosis is often very mild, with only flu-like symptoms, in some cases, symptoms can be severe:

• Rash -- about one-third of HME patients and a smaller proportion of HGE patients develop a rash; the rash does not form a circle as it does in Lyme disease
• Fever