DO search about Koch's postulates and answer the following question; What are the main limitations of Koch's postulates?...

Koch postulates tell whether any particular disease is caused by a particular organism or not.

These postulates are not applicable on viruses because they can not be cultured artificially.

Limitations of Koch's postulates -

• These are not applicable on viruses. 
• These are not applicable on asymptomatic carriers.
• Some disease causing organisms cannot be artificially cultured.
• There are chances where a single organism may cause several diseases.
•  Every pathogen has different effect on every organism.