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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.

Two types of human ehrlichiosis were identified in the U.S. in the late 1980s: human monocytic ehrlichiosis (HME) and human granulocytic ehrlichiosis (HGE). HME is now referred to as ehrlichiosis, which is caused by one of three Ehrlichia species, primarily E. chaffeensis. HGE is now known as anaplasmosis, which is caused by Anaplasma phagocytophilum (previously known as Ehrlichia phagocytophilum).