rick·ett·si·a 
(rĭ-kĕtsē-ə)
(rĭ-kĕtsē-ə)n. pl. rick·ett·si·ae (-sē-ē′)
Any of various bacteria of the genus Rickettsia, carried as parasites by many ticks, fleas, and lice, that cause diseases such as typhus and Rocky Mountain spotted fever in humans.
[New Latin Rickettsia, genus name, after Howard Taylor Ricketts (1871-1910), American pathologist.]
rick·ettsi·al adj.