How can a virus be determined to cause a disease? From other posts I have read here, humans carry hundreds of different strains of viruses. How is a study structured and carried out to determine that one virus is the cause of a disease, and not any of the other viruses present? Any examples of studies are greatly appreciated as well.
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A modified form of Koch's postulates is used to guide experiments that establish that a particular virus causes disease.
As a specific example of such a study, the SARS-CoV virus was determined to cause the SARS disease by fulfilling these criteria:
- SARS virus is found in people suffering from SARS, and not found in those who are healthy.
- The virus can be isolated from infected people and grown in cell cultures (here, Vero cells).
- Viruses grown in culture can be reisolated and compared with (and found identical to) the suspected pathogenic virus.
- This isolated virus can re-infect people (or infect model organisms; in this case, a species of macaques).
- Virus in reinfected organisms can be isolated, grown in culture, and found identical to the original pathogen.
- The immune system is observed to respond in similar ways to the infection (pneumonia and lung tissue lesions).
answered Mar 21, 2020 at 5:09
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$\begingroup$ That's right, Koch's postulates have undergone adaptations over the years. Still, for some pathogens, the original postulates still succeed in proving causality. Above, I cited some more modern models, such as the Falkow criteria (which you cite as Koch's molecular postulates) and the Bradford Hill criteria; but they are all based on Koch's originals. $\endgroup$ Jul 5, 2021 at 23:08
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$\begingroup$ I'm going to submit an article, from 1996, written by Fredericks and Relman, which presented the most important updates to the original postulates: Sequence-based identification of microbial pathogens: a reconsideration of Koch's postulates. ncbi.nlm.nih.gov/pmc/articles/PMC172879 $\endgroup$ Jul 5, 2021 at 23:08