Ehrlichiosis History

Ehrlichiosis is one of a number of bacterial tickborne diseases that occur in the United States. The most common by far is Lyme disease, but others include Rocky Mountain spotted fever, tularemia and ehrlichiosis. In the United States ticks can also be responsible for transmitting parasites and viruses, which may cause illness (81).

There are numerous ehrlichial species that can infect humans and animals worldwide, five of which are known to infect humans. However, this section will focus on those species that cause clinical illness in humans in the United States. Ehrlichia sennetsu, the cause of sennetsu fever in the far east, is not known to exist in the United States. Ehrlichia canis, the cause of canine monocytic ehrlichiosis, does occur in the US, but has only rarely been documented to infect persons in other countries (81).

Ehrlichiosis is considered an emerging zoonotic pathogen based on the fact that both conditions affecting humans in the United States are newly identified and not fully characterized. Ehlichiosis was initially characterized as a condition of dogs in the 1930s. E. canis was identified as a pathogen causing illness in military working dogs in Vietnam in the 1960s. Human ehrlichiosis is a newly recognized disease in the United States and was first identified in 1986. The agent of human monocytic ehrlichiosis (HME), Ehrlichia chaf-feensis, was first identified in 1991. The name is derived from Fort Chaffee Arkansas, where the Ehrlichia species was first isolated from an ill soldier. Human granulocytic ehrlichiosis (HGE) was first recognized in a series of patients from Minnesota and Wisconsin in the early 1990s (82-84).

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