A parasitic ectoparasitic infectious disease that involves parasitic infestation by members of the subclass Hirudinea. The leeches remain attached to their hosts and feed on blood until they become full, at which point they fall off to digest. While feeding, they release an anesthetic and use a combination of mucus and suction to stay attached and secrete an anti-clotting enzyme, hirudin, into the host's blood stream.