Koch’s postulates

Koch’s postulates must be satisfied in order to state that a particular microbe causes a specific infectious disease. They include the following: (i) The parasite occurs in every case of the disease in question and under circumstances which can account for the pathological changes and clinical course of the disease. (ii) The parasite occurs in no other disease as a fortuitous and non-pathogenic parasite. (iii) After being fully isolated from the body and repeatedly grown in pure culture, the parasite can induce the disease anew (Fredricks and Relman, 1996; Koch, 1891; Rivers, 1937).