Prescott's Microbiology 8th Edition by Joanne Willey, Linda Sherwood, Christopher J. Woolverton, Lansing Prescott, John Harley, Donald Klein

Exercise 4

Some individuals can be infected by a pathogen yet not develop disease. In fact, some become chronic carriers of the pathogen. How does this observation affect Koch's postulates? How might the postulates be modified to account for the existence of chronic carriers?

Step 1 of 3

Koch’s postulates cannot be applied to all cases of disease. There are instances where individuals may harbor a microbe but not have any disease. One famous example of this is “Typhoid Mary”. She carried Salmonella typhimurium, which causes typhoid fever. She never had any symptoms but passed it to many of her customers. Typhoid Mary is an example of an asymptomatic carrier of disease.