Koch's postulates are four criteria that Robert Koch published in 1884, which he said must be fulfilled in order to establish a causal relationship between a parasite and a disease. He applied these to establish the etiology of tuberculosis, but they have been generalized to other diseases.
- The organism must be found in all animals suffering from the disease, but not in healthy animals.
- The organism must be isolated from a diseased animal and grown in pure culture.
- The cultured organism should cause disease when introduced into a healthy animal.
- The organism must be reisolated from the experimentally infected animal.