Ticks that transmit Borrelia burgdorferi to humans can also carry and transmit several other parasites, such as Theileria microti and Anaplasma phagocytophilum, which cause the diseases babesiosis and human granulocytic anaplasmosis, respectively.
Dermacentor variabilis may also carry Anaplasma phagocytophilum, the causative agent of HGE (human granulocytic ehrlichiosis), and Ehrlichia chaffeensis, the causative agent of HME (human monocytic ehrlichiosis).