Typhus is any of several similar
diseases caused by
Rickettsia bacteria. The name comes from the
Greek typhos (τύφος) meaning smoky or hazy, describing the state of mind of those affected with typhus. The causative organism
Rickettsia is an
obligate intracellular parasitic bacterium that cannot survive for long outside living cells. It is transmitted to humans via external
parasites such as
lice,
fleas and
ticks. While "typhoid" means "typhus-like", typhus and
typhoid fever are distinct diseases caused by different
genera of bacteria.