Human granulocytic anaplasmosis (HGA) is an infectious disease caused by the bacterium Anaplasma phagocytophilum. It is primarily transmitted to humans through the bite of infected ticks, particularly the black-legged tick and the western black-legged tick. Symptoms of HGA can include fever, chills, headache, muscle aches, and fatigue. Diagnosis is typically made through blood tests that identify the presence of the bacteria or antibodies. Treatment usually involves antibiotics, such as doxycycline, which are effective in clearing the infection. If left untreated, HGA can lead to more severe health complications.