What are Koch's postulates? Why are they not applicable to viruses?
According to the Koch, there must be four conditions present for an organism to be causative agent of a disease. He gave following postulates for pathogenic diseases and these are:
1. The causative organism must be present in each disease and in case the organism is not present, there is secondary cause of disease.
2. Pathogen must be able to be isolated from the diseased host & grown in pure culture.
3. When the isolated pathogen is introduced in healthy person, it must infect that person.
4. The same organism must be isolated from the person who is experimentally infected.
Viruses do not follow Koch postulates as they cannot be cultured in artificial media.