Koch's postulates are used to establish the infectious agent that causes a particular infectious disease. in 1937, thomas rivers modified koch's postulates so that they could be applied to viral pathogens.

which of koch's postulates was modified by rivers?

a. the pathogen must be present in every case of the disease.

b. the pathogen must be grown in pure culture.

c. the pathogen must cause the same disease when introduced into experimental animal hosts.

d. the pathogen must be recovered from the diseased experimental lab animals.

B. The pathogen must be grown in pure culture.

Explanation:

Virus, and also some bacteria can not be cultured in "lifeless media". In the case of bacteria, we refer to the obligate intracellular ones, and all virus. Thus, this postulate can not be fulfilled in all cases. Virus can be propagated on tissue cultures, but certainly this was not considered by Koch. Moreover, these methods often result in spontaneous genetic alterations, which leads to adaptation and even attenuation in animal models of disease, so, the cultured virus perhaps does not induce the same disease when introduced to another specimen.

what? are the statements?