Yours, Etc.: Origins and Uses of 8 Sign-Offs
A person likely to cause a disaster; from Mary Mallen, an Irish woman in the United States who was discovered to be a carrier of typhoid fever.
Note: The term is often applied to the carrier of a contagious disease, or, more generally, to anyone who brings bad luck: “The last three insurance companies I had policies with folded. I feel like Typhoid Mary.”