Koch's postulates

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Koch's postulates (or Henle-Koch postulates) are four criteria designed to establish a causal relationship between a causative microbe and a disease. The postulates were formulated by Robert Koch and Friedrich Loeffler in 1884 and refined and published by Koch in 1890. Koch applied the postulates to establish the etiology of anthrax and tuberculosis, but they have been generalized to other diseases.

Contents

[edit] The Postulates

Koch's postulates are:

  1. The organism must be found in all animals suffering from the disease, but not in healthy animals.
  2. The organism must be isolated from a diseased animal and grown in pure culture.
  3. The cultured organism should cause disease when introduced into a healthy animal.
  4. The organism must be reisolated from the experimentally infected animal.

However, it must be noted that Koch abandoned the second part of the first postulate altogether when he discovered asymptomatic carriers of cholera (Koch, 1893) and later, Typhoid Mary. Indeed, asymptomatic carriers of many diseases have since been found, especially viruses such as polio, herpes simplex, HIV and hepatitis C. As a specific example, all doctors and virologists agree that poliovirus causes paralysis in just a few infected subjects, and the success of the polio vaccine in preventing disease supports the conviction that the poliovirus is the causative agent.

The third postulate does not always happen, as Koch himself discovered and stated in regard to both tuberculosis and cholera (Koch, 1884). Indeed, we see this today with diseases such as HIV, where CCR5 Δ32 deletion individuals seem to be resistant to infection with HIV.

[edit] History

Koch's postulates were developed in the 19th century as general guidelines to identify pathogens that could be isolated with the techniques of the day.[1] Even in Koch's time, it was recognized that some infectious agents were clearly responsible for disease in spite of the fact that they did not fulfill all of the postulates.[2] Attempts to rigidly apply Koch's postulates to the diagnosis of viral diseases in the late 19th century, at a time when viruses could not be seen or isolated in culture, may have impeded the early development of the field of virology.[3][4] Currently, a number of infectious agents are accepted as the cause of disease despite their not fulfilling all of Koch's postulates.[5] Therefore, while Koch's postulates retain historical importance and continue to inform the approach to microbiologic diagnosis, fulfillment of all 4 postulates is not required to demonstrate causality.

[edit] Notes

  1. ^ Walker L, Levine H, Jucker M (2006). "Koch's postulates and infectious proteins.". Acta Neuropathol (Berl) 112 (1): 1-4. PMID 16703338.
  2. ^ Koch R. (1884) Mitt Kaiser Gesundh 2, 1-88; Koch R. (1893) J. Hyg. Inf. 14, 319-333
  3. ^ Brock TD (1999) Robert Koch: a life in medicine and bacteriology. American Society of Microbiology Press, Washington
  4. ^ Evans AS (1976) Causation and disease: the Henle-Koch postulates revisited. Yale J Biol Med 49:175–195
  5. ^ Jacomo V, Kelly P, Raoult D (2002). "Natural history of Bartonella infections (an exception to Koch's postulate).". Clin Diagn Lab Immunol 9 (1): 8-18. PMID 11777823.

[edit] References

  • Koch R. Über die Ätiologie der Tuberkulose. In: "Verhandlungen des Kongresses für Innere Medizin. Erster Kongress, Wiesbaden 1882".
  • Koch R. (1884) Mitt Kaiser Gesundh 2, 1-88
  • Koch R. (1893) J. Hyg. Inf. 14, 319-333
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