Human granulocytic anaplasmosis (HGA), formerly referred to as human granulocytic ehrlichiosis (HGE), is caused by the bacterium Anaplasma phagocytophilum. Recent studies in New Jersey have shown the infection prevalence in the blacklegged tick vector to be between 6% and 17%. The white-footed mouse is the probable reservoir. Non-specific symptoms, which normally occur within 1 to 2 weeks following tick bite, may be mild to severe and include fever, chills, malaise, headache, muscle aches and pain, and nausea. Although reportable in New Jersey since 1995, the first case of HGA was not reported until 1997 and about 5 cases are reported annually.