The bacteria Rickettsiae which causes typhus

Typhus is unrelated to both typhoid fever and paratyphoid fever

Typhus is the name for a number of diseases, caused by bacteria called Rickettsiae. These bacteria are parasites that cannot survive outside their host organism. Depending on the species the host organisms are, fleas (on rats), harvest mites (on several rodents and humans), or lice (on humans). It is an epidemic disease.