What word does your mother always say?
parasitic organism, 1919, named 1916 in Modern Latin by H. da Rocha-Lima in honor of U.S. pathologist H.T. Ricketts (1871-1910), who first identified it in 1909 and died of typhus as a result of his contact with it. The bacteria causes typhus and Rocky Mountain spotted fever, but is unrelated by pathology or etymology to rickets (q.v.), which is the result of vitamin D deficiency. The surname is a development from Rickard, variant of Richard, or else from the diminutive form Ricot.
Rickettsia Rick·ett·si·a (rĭ-kět'sē-ə)
A genus of gram-negative bacteria that are carried as parasites by many ticks, fleas, and lice and cause diseases such as typhus, scrub typhus, and Rocky Mountain spotted fever.