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What is ehrlichiosis?
Ehrlichiosis was first described in dogs in 1935 and was not recognized as a human disease until the last half of the 20th century. Bacteria of the genus Ehrlichia cause a variety of diseases, both in humans and animals. Scientists continue to discover new species and to recognize different ways they cause disease. The bacteria are spread to humans through tick bites.

What are the symptoms of ehrlichiosis? What does ehrlichiosis cause?
Regardless of the species causing the infection, the symptoms and signs are similar. The diseases range anywhere from no symptoms, to an illness so mild that no medical attention is sought, to a severe, life-threatening condition. Most cause an abrupt onset of illness with fever, chills, headache, and malaise (a general ill feeling), usually beginning about 12 days after the tick bite. Patients may also experience confusion, nausea, vomiting, and joint pain. Some patients develop a rash involving the trunk and limbs.

Severely ill patients can develop abnormally low numbers of white blood cells, abnormally low numbers of platelets, and kidney failure.

Since 1986, two types of human ehrlichiosis have been identified in the U.S.: human monocytic ehrlichiosis (HME) and human granulocytic ehrlichiosis (HGE). The illnesses differ in the types of white blood cells the bacteria attack. In the U.S., HME has so far been concentrated in the southeastern and south central regions (including Texas). HGE has been found mainly in the upper Midwestern and northeastern states, but also in northern California.

How common is ehrlichiosis?
In Texas, ehrlichiosis is a rare disease with fewer than 10 cases of ehrlichiosis reported each year. However, since many people with ehrlichiosis infections have no symptoms and do not seek medical care and other cases may have been misdiagnosed, it is difficult to know how common it really is.

Who is likely to get ehrlichiosis?
Anyone can get ehrlichiosis, although the majority of known cases have been in adults. People who spend time outdoors in tick-infested areas, usually from April until October, are at greatest risk for exposure.

How is ehrlichiosis spread?
Ehrlichiosis is spread through the bite of an infected tick. Evidence suggests that the lone star tick transmits HME and that the deer tick transmits HGE.

How do I protect myself from ehrlichiosis?
No vaccine is available to protect humans against ehrlichiosis. You can reduce your risk by taking these precautions against tick bites:

  • During outside activities, wear long sleeves and long pants tucked into socks. Wear a hat, and tie hair back.
  • Use chemicals to repel or kill ticks. When using any of these chemicals, follow label directions carefully, paying close attention to whether they can be applied to the skin or to clothing. Be especially cautious when using them on children.
  • After outdoor activities, check yourself for ticks, with the help of a friend. Check body areas where ticks are commonly found: behind the knees, between the fingers and toes, under the arms, in and behind the ears, and on the neck, hairline, and top of the head. Check places where clothing presses on the skin.
  • Remove attached ticks immediately. Use tweezers, and grab as closely to the skin as possible. Do not remove ticks by squeezing them, coating them with petroleum jelly, or burning them with a match. If attached ticks are removed within 36 hours, the risk of infection is minimal.

What do I do if I think I have ehrlichiosis?
Contact your healthcare provider, and mention your exposure to ticks.

How are ehrlichiosis infections diagnosed?
Ehrlichiosis is difficult to diagnose. Often, it is initially confused with Rocky Mountain spotted fever (RMSF). The main difference is that the rash in ehrlichiosis occurs less frequently and is less pronounced than in RMSF. Because diagnostic tests are not widely available, the diagnosis of ehrlichiosis is usually based on symptoms and a history of exposure to ticks. Certain laboratory test results (such as low white blood cell count, low platelet count, and elevated liver enzymes) can suggest a diagnosis of ehrlichiosis.

How are ehrlichiosis infections treated?
When treatment with antibiotics is started early, patients generally respond quickly and well.

Should I worry about ehrlichiosis when I travel out of the country?
In addition to the southeastern and south central regions of U.S., HME has been reported in Europe and Africa. HGE has been more frequently reported in Europe than HME. A very rare, related illness, Sennetsu fever, occurs in Malaysia and Japan.

Observe the usual tick precautions when participating in outdoor activities in grassy or wooded areas (e.g., trekking, camping, or going on safari).

Last updated March 29, 2019