parasitic micro-organism, 1919, from German, coined 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, + abstract noun ending -ia. 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.