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Koch’s Postulates
Koch’s Postulates

Koch’s Postulates

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In 1884, German scientist Robert Koch devised a set of logic-based criteria that needed to be met in order to prove a specific pathogen caused a disease. By 1890, he had refined and published them. At the time, Koch’s criteria developed for bacteria as “viruses” were unknown and were not officially “discovered” until 1892 with the Tobacco Mosaic “virus” for plants. The four original Postulates were:

  1. The microorganism must be found in abundance in all cases of those suffering from the disease, but should not be found in healthy subjects.
  2. The microorganism must be isolated from a diseased subject and grown in pure culture.
  3. The cultured microorganism should cause the exact same disease when introduced into a healthy subject.
  4. The microorganism must be reisolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.

Pdf of Koch’s Postulates report (German)

By 1937, it was very clear that virologists were unable to satisfy any of Koch’s Postulates in order to prove invisible particles assumed to be “viruses” existed and could cause disease. Even Robert Koch himself had difficulty with his own Postulates which led him to wiggle around some of them in attempts to “prove” pathogenicity of certain bacteria. Instead of accepting that the Postulates, as originally stated, worked and disproved the Germ Theory, virologists looked to various indirect immunological methods to prove their claims.

Thomas Rivers

This led to Thomas Rivers and his own attempts to water down Koch’s Postulates by revising them to allow virologists even more wiggle room and expanding the 4 Postulates to 6. Unfortunately for all of virology, Koch had unintentionally trapped them in a logical prison for which they still can not free themselves from. If virologists deny Koch’s original Postulates, they are denying logic itself. Presented below are highlights from River’s attempted revision:


“Diseases at one time were thought to be caused by wrath of the gods, configuration of stars or miasmas. After a real struggle that occurred not so many years ago, certain maladies were shown to be induced either by small animals or minute plants, e.g., protozoa, fungi, bacteria and spirochetes. Indeed, the victory was so great that most workers in time began to consider that all infectious diseases, including those whose incitants had not been discovered, must be caused by agents similar to those already recognized. According to them, there could be no infections that were not caused by protozoa, fungi, bacteria or spirochetes, and to intimate that some infectious agents might be inanimate constituted heresy of the first order. Even at the present time, the cause of certain diseases is said by some individuals to be unknown or undiscovered, because no cultivable bacterium or visible protozoan parasite of etiological significance has been demonstrated in them. For instance, a few years ago Cowie made the statement in a scientific paper that the etiological agent of poliomyelitis is unknown, and in the recent book, An American Doctor’s Odyssey, Heiser remarked that “the microbe which causes smallpox has never been discovered.

In spite of the general acceptance of the idea that all infectious diseases are caused by protozoa, fungi, bacteria or spirochetes, some workers have always contended that there might exist other infectious agents incapable of classification with those already known. Furthermore, very early in the bacteriological era a few discerning individuals appreciated the fact that there was no reason, except analogy, for assuming that all infectious agents must be living autonomous organisms. Through the activities of these investigators a group of disease-producing agents, known as viruses, has gradually become recognized. The exact nature of these agents is not known; some may be the midgets of the microbial universe, others may represent forms of life unfamiliar to us, while still others may be inanimate incitants of disease. Regardless of lack of complete knowledge of their nature, it is decidedly incorrect to say that these agents are unknown.”

Microorganisms were known to exist long before their relation to disease was appreciated. After the discovery of this relation it was not uncommon for more than one kind of organism to be accredited with the ability of producing the same malady. This fact is not surprising in view of the almost universal distribution of microbes. As early as 1840, before the specific relation of microorganisms to disease was accepted, Jacob Henle stated the conditions that should be met before an agent could be considered the proved cause of an infectious malady. Unfortunately, investigators were not guided by Henle’s remarks, and it was necessary for Robert Koch to restate and emphasize them 40 years later.

In an article on the etiology of tuberculosis Koch in 1884 made the following statement:

The facts obtained in this manner can in every possible way serve as proof to which only extreme skepticism can still raise the objection that the organisms found are not the cause but only concurrent phenomena of the disease. To be sure this objection often has a real justification and therefore it is not sufficient to establish only the concomitant occurrence of disease and parasite but the parasite must be shown to be the real cause. This can be done only by fully isolating the parasite from the body and all products of disease which might be considered as having a deleterious effect and producing the disease again with all its characteristics by the introduction of the isolated organisms into a normal host. (Author’s translation.)

In 1890, speaking of bacteriological research before the Tenth International Congress of Medicine in Berlin, Koch expressed the same ideas in the following less mandatory manner:

However, if it can be proved: first that the parasite occurs in every case of the disease in question, and under circumstances which can account for the pathological changes and clinical course of the disease; secondly, that it occurs in no other disease as a fortuitous and nonpathogenic parasite; and thirdly, that it, after being fully isolated from the body and repeatedly grown in pure culture, can induce the disease anew; then the occurrence of the parasite in the disease can no longer be accidental, but in this case no other relation between it and
the disease except that the parasite is the cause of the disease can be considered. (Author’s translation.)

The above conditions laid down for the proof of the etiological relation of a microorganism to a disease constitute what are now known as Koch’s postulates. His dictum has had a profound influence on workers investigating infectious maladies and for many years an infectious agent was not accepted as the cause of a disease unless the postulates had been satisfied. With the development of the science of immunology, however, immunological reactions added much to the knowledge of the specific relation of microbes to disease, and now it is possible to bring excellent evidence that an organism is the cause of a malady without the complete satisfaction of the postulates. In spite of this fact, there are certain workers who still refuse to agree that the cause of an infectious disease has been discovered unless all the conditions originally laid down by Koch have been met. This is particularly true regarding the viral maladies, the etiological agents of which have not been cultivated on ordinary lifeless media.”

“Koch’s postulates are responsible for some odd conclusions regarding the cause of certain viral maladies. For example, a few investigators have claimed that streptococci are the inciting agent of poliomyelitis. Such claims, according to them, are based on the fact that Koch’s rules have been satisfied. That is, streptococci have been found associated with the disease, they have been obtained in pure cultures from patients with the malady, they produce paralysis when injected into monkeys and rabbits, and they have been recovered in pure cultures from the experimental hosts. Furthermore, individuals recovering from poliomyelitis possess antibodies against the streptococci. To those unacquainted with the viral field and particularly to cliniicians and bacteriologists unfamiliar with the pathological picture of poliomyelitis, these claims seem valid. Consequently, they wonder why streptococci are not more generally accepted as the cause of infantile paralysis. The reason for lack of general acceptance is a simple one; the disease produced in the experimental animals is not poliomyelitis. Paralysis is not a characteristic sign of a single disease, and the pathological picture observed in the experimental hosts is quite different from that seen in human beings dead of infantile paralysis.

It is obvious that Koch’s postulates have not been satisfied in viral diseases. Moreover, it is equally evident that proof of the etiological significance of viruses has been obtained without their satisfaction. Such a statement, however, does not imply that certain conditons do not have to be met before the specific relation of a virus to a disease is established. The conditions are: (a) A specific virus must be found associated with a disease with a degree of regularity. (b) The virus must be shown to occur in the sick individual not as an incidental or accidental finding but as the cause of the disease under investigation.

In many respects the conditions just stated for viral maladies are similar to those of Koch for the proof of the specific relation of bacteria to disease. Nevertheless, there are certain differences. In the first place, it is not obligatory to demonstrate the presence of a virus in every case of the disease produced by it. Secondly, the existence of virus carriers is recognized. Finally, it is not essential that a virus be grown on lifeless media or in modified tissue cultures.

How does one go about proving that a virus is the cause of a disease? Viruses, regardless of whether they are parasites or the fabrications of autocatalytic processes, are intimately associated with host cells and, therefore, should always be found at the proper time in specific lesions. In addition, viruses, as is the case with bacteria, may be found also in the blood stream, not necessarily multiplying there but appearing frequently only as a phenomenon of overflow from lesions in the tissues. With these facts in mind, tissues with lesions, exudate from such lesions, and blood are collected aseptically and inoculated into a susceptible experimental host of the same or different species. The material should be free from ordinary microbes; if not, the microbes should be killed or removed in a proper manner, e.g., by filtration. If the inoculated animals become sick or die in a characteristic manner, and, if the disease in them can be transmitted from animal to animal by means of inoculations with blood or emulsions of involved tissues free from ordinary microbes or rickettsiae, one is fairly confident that the malady in the experimental animals is induced by a virus. On the other hand, such findings do not necessarily indicate that the active agent was present in the original material used for inoculation of experimental hosts.

When a natural disease under investigation exhibits characteristic features, e.g., paralysis or intracellular inclusions, they are sought for in the experimental malady. If one finds them, one is encouraged, but proof is still lacking that the virus operating in the experimental hosts was present in the material taken from the individual with the natural infection. Not infrequently several viruses produce the same clinical and pathological pictures, and at times the same virus does not induce similar changes in different hosts. Consequently, regardless of the disease picture produced in the experimental animals, one is still faced with the problem of demonstrating that the virus causing it was present in the material used for inoculation of the first group of animals.”

Under at least two sets of conditions a virus of no etiological significance in certain diseases may occur in patients suffering from them. First, patients who have been affected previously by a viral disease continue as carriers after recovery to harbor the agent. Under such conditions they would possess antibodies against this virus at the beginning of their new illness as well as during convalescence. Secondly, it is conceivable that a virus might gain entrance into an individual and remain there only a short time causing little or no reaction. Under these circumstances, the virus, although capable of causing disease in experimental animals, would not incite the production of antibodies in the patients with the result that their serum would be devoid of antibodies both at the beginning and end of their illness. Some may doubt that this state of affairs occurs naturally. Nevertheless, it has been encountered not infrequently in experimental work.

If a virus is the actual cause of a disease, immune substances are usually absent from the patients’ serum at the onset of illness and make their appearance during the period of recovery. However, this is not universally true, inasmuch as recovery sometimes takes place without the development of antibodies, and occasionally an individual possessing antibodies against a virus succumbs to a disease caused by it.

Although the absence of antibodies for a virus at the onset of an illness and their appearance later in the course of the disease or during convalescence constitute highly suggestive evidence that the virus is responsible for the malady, they alone should not be accepted as incontrovertible proof that such is the case.

To summarize, it can be said that the cause of viral diseases is known and that Koch’s postulates as proposed by him do not have to be fulfilled in order to prove that a virus is the cause of a disease. However, the spirit of his rules of proof still holds in that a worker must demonstrate that a virus is not only associated with a disease but that it is actually the cause. The methods of doing this are different from the ones used by Koch but are equally efficient. At the present time, this is accomplished by the production with a degree of regularity of a transmissible infection in susceptible experimental hosts by means of inoculation of material, free from ordinary microbes or rickettsiae, obtained from patients with the natural disease, and by the demonstration through the use of proper controls and immunological studies described above that the virus was neither fortuitously present in the patients nor accidentally picked up in the experimental animals. Changes, notably the more extensive use of tissue-culture technics and serological reactions, will in the future undoubtedly occur in the methods of establishing the specific relation of viruses to disease; the number of changes will be limited only by the amount of ingenuity of investigators. To obtain the best results, however, this ingenuity must be tempered by the priceless attributes of common sense, proper training and sound reasoning.”

In Summary:

  • There were people in the field who disagreed that “viruses” were the true cause of disease
  • Cowie made the claim that the agent responsible for Polio had yet to be discovered
  • Heiser remarked that a microbe causing Smallpox had never been discovered
  • Some workers have always contended that there might exist other infectious agents incapable of classification with those already known
  • There was a lack of complete knowledge of the nature of “viruses
  • It was not uncommon for more than one microbe/organism to be claimed as the cause of the same disease
  • For many years, it was accepted that Koch’s Postulates must be fulfilled in order to prove an infectious agent causes disease
  • Rivers claims that due to (indirect) immunological evidence, it is possible to provide evidence an agent causes disease without fulfilling all of Koch’s Postulates
  • He admits that many are unwilling to accept this evidence without the Postulates being fulfilled
  • A few investigators have claimed that streptococci are the inciting agent of poliomyelitis as it satisfied Koch’s Postulates and patients had antibodies to streptococcus
  • These researchers wonder why streptococci are not more generally accepted as the cause of infantile paralysis
  • Rivers argues that the reason for lack of general acceptance is a simple one:
    1. The disease produced in the experimental animals is not poliomyelitis.
    2. Paralysis is not a characteristic sign of a single disease
    3. The pathological picture observed in the experimental hosts is quite different from that seen in human beings dead of infantile paralysis.
  • Rivers admits that it is obvious Koch’s Postulates have not been satisfied for “viral” diseases
  • Rivers proposes his own revisions and states while they are similar to Koch’s Postulates, they are different for three reasons:
    1. He allows for the “virus” not to be found in every case of disease
    2. He introduces the concept of virus” carriers
    3. He states that “viruses” do not need to be grown in culture
  • Rivers admits that “viruses” could be fabrications of an autocatalytic process
  • He says that the sample must be free of other microbes and if not, they should be removed or killed by filtration
  • He believes that if an animal becomes sick or dies from inoculation of blood/emulsified tissues and then their blood/emulsified tissues produces disease/death in further inoculated animals, one can be fairly confident a “virus” is present
  • However, Rivers says that this does not necessarily mean the agent that produced disease/death in the inoculated animals was the same as what was in the original sample
  • He claims that not infrequently, several “viruses” produce the same clinical and pathological pictures, and at times the same “virus’ does not induce similar changes in different hosts
  • Rivers states two sets of conditions a “virus” of no etiological significance in certain diseases may occur in patients suffering from them:
    1. Patients who have been affected previously by a “viral” disease continue as carriers after recovery to harbor the agent
    2. It is conceivable that a “virus” might gain entrance into an individual and remain there only a short time causing little or no reaction thus generating no antibodies (which raises the question, how did they clear the “virus” then?)
  • He concedes that some may doubt that this state of affairs occurs naturally however Rivers claims it has been encountered not infrequently in experimental work (which would indicate it does not occur naturally)
  • Rivers admits that even if they can reproduce the characteristics of a disease by experimentation in a lab, that still is not proof that what caused disease in the experiment was in the original sample from the sick patient or animal
  • He states it is a problem to show that what caused illness in subsequent animal inoculations was in the original inoculated animal
  • Part of Rivers revisions stem from using immune response experiments as proof yet he admits that the presence/absence of antibodies is not universal and that people can recover without antibodies and can succumb to disease even with antibodies
  • He admits the the presence/absence of antibodies alone is not incontrovertible proof of a “virus
  • Rivers concludes that “viruses” have been proven and that Koch’s Postulates do not need to be fulfilled as originally proposed
  • Rivers states that his revisions still hold the spirit of Koch’s Postulates
  • Rivers admits his Postulates are different than Koch’s based on the methods used
  • Rivers predicts that changes to his criteria in the future will undoubtedly occur and that the number of changes will be limited only by the amount of ingenuity (or imagination) of investigators

These are just a few highlights and I highly recommend reading the full 12 pages as there are many interesting admissions I unfortunately had to leave out for length/editing purposes. It is clear that Rivers revisions of Koch’s Postulates are not the same as those originally proposed by Koch himself. Rivers even admits numerous times that his criteria are different and laid out three main ways that they differ:

  1. He allows for the “virus” not to be found in every case of disease
  2. He introduces the concept of virus” carriers
  3. He states that “viruses” do not need to be grown in culture

All Rivers did was deliberately weaken Koch’s Postulates in order to make life easier for virologists to skirt around established rules of logic. Anyone claiming that they fulfilled Koch’s Postulates by using the criteria laid forth by Rivers are outright lying and being intentionally fraudulent…which in all honesty, sums up virology to a T.

Source: ViroLIEgy