Can leeches kill people?
It would be very unusual for leeches to kill people, however, they do suck blood, and a person can die from blood loss. In order to lose that much blood, a person would have to be unconscious will leeches are feasting at will.
No leeches are definitely not Mammals. Leeches are annelids comprising the subclass Hirudinea. There are fresh water, terrestrial, and marine leeches. Like the Oligochaeta, they share the presence of a clitellum. Like earthworms, leeches are hermaphrodites. Some, but not all leeches feed on blood. en.wikipedia.org/wiki/Leeches