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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:

  1. SARS virus is found in people suffering from SARS, and not found in those who are healthy.
  2. The virus can be isolated from infected people and grown in cell cultures (here, Vero cells).
  3. Viruses grown in culture can be reisolated and compared with (and found identical to) the suspected pathogenic virus.
  4. This isolated virus can re-infect people (or infect model organisms; in this case, a species of macaques).
  5. Virus in reinfected organisms can be isolated, grown in culture, and found identical to the original pathogen.
  6. The immune system is observed to respond in similar ways to the infection (pneumonia and lung tissue lesions).
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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. $\endgroup$ – Lambert macuse Jul 5 at 23:08
  • $\begingroup$ 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 $\endgroup$ – Lambert macuse Jul 5 at 23:08

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