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Ehrlichiosis describes several tick-borne
bacterial infections originally known to only affect dogs and
livestock in the United States, although human disease has been
reported in the Far East since the 1950s. Since the mid-1980s,
however, bacteria of the genus Ehrlichia have increasingly
infected humans in the United States. In June 1999, the Centers
for Disease Control and Prevention began listing ehrlichiosis as a
reportable disease (see
surveillance criteria); 302 cases were reported in 1999.
Ehrlichia bacteria live inside the cells of infected individuals
and cause two major diseases in the U.S. human population. Human
granulocytic ehrlichiosis (HGE) occurs when the bacteria infect
granulocytes, specific cells involved in immune responses and
allergies. Human monocytic ehrlichiosis (HME) occurs when a
different Ehrlichia species infects macrophages, another type of
immune cell.
HGE and HME differ, but their symptoms overlap. Both often cause
fever, headaches, and aches and pains, but a rash is not as common
as with Rocky Mountain spotted fever or Lyme disease. HGE and HME
can be treated with antibiotics if the infection is detected
early. No vaccine is available.
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