Koch's Postulates

Robert Koch is a German bacteriologist, one of the founders of modern microbiology and epidemiology. He was the first who isolated a pure culture of anthrax pathogen and proved its ability to spore formation. In 1905, Robert Koch was awarded the Nobel Prize in Physiology and Medicine for the discovery and allocation of Mycobacterium tuberculosis (Daniel 2000). Koch’s postulates are another achievement of the scientist formulated in relation to bacteria that can cause the development of the disease. The postulates were stated by Friedrich Loeffler and Robert Koch in 1884 and revised and published by Koch in 1890 (Daniel 2000). In such a way, in the 19th century, an outstanding bacteriologist, Robert Koch, formulated four conditions under which certain microbes or bacteria can be regarded as the cause of a particular disease.

Koch’s postulates are four criteria of the establishment of the causal relationship between bacteria and disease. “Koch’s postulates, or rules of proof, define the criteria for establishing a causal relationship between a suspect pathogen and a disease” (Zourob, Elwary & Turner 2008, p. 43). The scientist applied the postulates to establish the etiology of anthrax and tuberculosis. However, they were later applicable to other diseases. Nevertheless, Koch admitted that in some cases, it is impossible to fulfill all postulates. “Although Koch successfully used these postulates to establish the cause of anthrax, they were not applicable to all diseases” (Zourob, Elwary & Turner 2008, p. 43). This bacterium has to be present in every case of the disease and absent in a healthy person. It can be isolated from the patient and grown in artificial conditions – in vitro. It is possible to inject this microbe in another person and, thereby, infect him/her with this disease. The same microbe can again be isolated from the experimentally infected host (Kumar 2012). However, this theory does not satisfy the first postulate. It is associated with the fact that on the one hand, the microbes that are causative agents of certain diseases successfully live in healthy people without causing any symptoms. On the other hand, many people with a particular disease are not carriers of the microbe recognized as its agent. It should be noted that Robert Koch completely withdrew the second part of the first postulate when he found asymptomatic carriers of fever and cholera. Indeed, asymptomatic carriers of many diseases, in particular viral including herpes, hepatitis C, HIV, and polio were later found. One example lies in the fact that most of virologists and doctors state that poliovirus causes paralysis in only a few infected, and only the success of treatment with poliomyelitis vaccine supports the proposition that poliovirus is the causative agent of the disease (Kumar 2012). “Koch’s postulates have been difficult to fulfill for most bacterial diseases and even more difficult for viral diseases, in which the causative cannot be grown in pure culture” (Riegelman 2012, p. 58). The third postulate does not always occur, as Koch found for both tuberculosis and cholera. Indeed, today, it can be seen with such a disease as HIV, where individuals with a missing gene CCR5 32, seems to be resistant to HIV infection (Kumar 2012). “Subsequently, an additional fifth criterion introduced states that specific antibodies to the organism should be demonstrable in the serum of patients suffering from the disease” (Kumar 2012, p. 7).

Nowadays, Koch’s postulates regularly appear in the debates about whether HIV causes AIDS. Some scientists state that HIV does not satisfy these postulates, and, therefore, the link between HIV and AIDS cannot be proved. However, modern researchers have extensive evidence that proves the relevance of Koch’s postulates in respect to HIV. The first postulate states that the microorganism is detected in all cases of the disease. United States Centers for Disease Control and Prevention identifies a condition called idiopathic CD4+ T-lymphocytopenia (Chin 2007). This condition is diagnosed when the amount of CD4+ in blood is below 300/mm3 or less than 20% of the total number of T-lymphocytes and if HIV or another known cause of immunodeficiency is not detected (Chin 2007). HIV dissidents call this state HIV-negative AIDS. In 1993, a special commission published an exhaustive review of ICL in the United States (Chin 2007). 230,179 cases similar to AIDS were examined (Chin 2007). It was reported about 47 accurately established and 127 doubtful cases since 1983 (Chin 2007). All other people with AIDS had positive results when testing for HIV (Chin 2007). In addition, the commission reviewed in detail the ICL cases and discovered that they did not conform to the characteristics peculiar to AIDS. There were 29 men and 18 women among them (Chin 2007). 39 of them were white while 4 others were of the Asian origin (Chin 2007). In 29 cases, the researchers were unable to include gays, hemophiliacs, injecting drug users, and sex partners to the traditional risk groups for AIDS (Chin 2007). Regardless of these 47 cases, they cannot be considered as typical cases of the AIDS epidemic (Chin 2007).

Survey data on ICL correspond to the data of large-scale controlled studies including multicenter AIDS cohort study (Chin 2007). During this study, the scientists observed the health of 2,713 gay and bisexual men who had a negative result in the study of antibodies to HIV (Chin 2007). Only one of these men continuously had the low level of CD4 + cells for several years (Chin 2007). It was associated with the fact that he was undergoing treatment for cancer depressing his immune system. Similar results were found among the donors and recipients of blood and blood products, intravenous drug users, and other groups (Chin 2007). In fact, pronounced immunosuppression was not among those people whose HIV test was negative.

A fairly large number of people in the United States, especially in the early 80-ies of the 20th century, was diagnosed with AIDS (Chin 2007). It was despite the fact that they had never held an HIV test (Chin 2007). Nobody knows whether these people were HIV-positive (Chin 2007). However, Koch’s first postulate has certainly been satisfied on the basis of a much larger sample of people who were tested. The only way, in which HIV dissidents managed to find a significant number of cases of AIDS without HIV, is the use of extremely loose interpretations of the AIDS concept. Such interpretations include many people with moderate immune deficiency, which generally is not fatal.

The second postulate states that the microorganism should be isolated from the host and grown as a pure culture. This determines that the third and fourth postulates can be checked properly. This fact should ensure that the disease is generated by the suspected organism and not by something else. Many viruses are allocated from cell tissues and fluids of the patient infected by the viral disease. In such a way, it is simple to take a pure sample and compare it with the known samples. There were many reports of HIV isolation (Chin 2007). In 1983, Luc Montagnier and his colleagues from France reported the isolation of a virus called LAV, which infected and killed CD4 + T-cells (Chin 2007). A year later, an American scientist, Robert Gallo, announced that he allocated a virus called HTLV-III and found a way of its cultivation (Chin 2007). Later, it was found that both open viruses were identical (Chin 2007). They were given the common name – HIV. The researchers were able to isolate HIV from most AIDS patients whom they have learned and cultivate it in them and other patients with antibodies to HIV (Chin 2007). They isolated the virus from the cells and blood plasma, lymph nodes, semen, vaginal secretions, amniotic fluid, marrow and brain, spinal fluid, intestine, breast milk, saliva, and urine and cultivated it in various cell types (Chin 2007). The images obtained with the help of electron microscopy have shown virus-like particles that by density, shape, size, behavior structure, and proteins are typical of retroviruses. Methods developed in the mid-90s made the selection and study of the sequence of the entire genetic material of the virus easier (Chin 2007). Nowadays, there are hundreds of complete genomes of HIV around the world, each of which contains all of the same nine genes (Chin 2007). On the basis of genetic similarities and differences, these sequences were used to identify types, groups, and subtypes of HIV, as well as recombinant forms. Using PCR analysis, full or partial genomes of HIV have been found in many patients with HIV/AIDS (Chin 2007). Nearly all individuals positive for HIV genetic material also give a positive result for antibodies to HIV. People who have been infected from the same source have genetically extremely similar HIV strains.

The scientists used the method of molecular cloning to get purified HIV (Chin 2007). The material extracted with the usage of PCR and other methods has been introduced in the bacteria which produce a plurality of exact copies of the viral genes (Chin 2007). In the case when cloned genomes are inserted into cells of a person, they can cause a new generation of infectious of HIV particles free from contamination. Virtually all experts agree that HIV has been isolated according to the most rigorous standards of modern virology (Chin 2007). It means that Koch’s second postulate is satisfied.

The third postulate states that the microorganism introduced into a susceptible host should be able to cause the original disease. The last postulate states that the microorganism has to be detected in the infected host. In respect to HIV, the third and fourth postulates are the most difficult to prove. It is required that the disease could be reproduced by the introduction of the intended micro agent to an uninfected person. However, intentional contamination of someone with HIV culture is considered unethical. In such a way, this experiment was never implemented properly. Nevertheless, there is no reason to believe that the transfer must necessarily be intentional. There are three reports on the development of immunodeficiency in the laboratory staff after they accidentally exposed themselves to the impact of cloned and purified culture of HIV. “Koch’s postulate number 3 has been fulfilled in tragic incidents involving three laboratory workers with no other risk factors who have developed AIDS or severe immunosuppression after accidental exposure to concentrated cloned HIV in the laboratory” (Chin 2007, p. 51). As it was mentioned above, such a grown culture of the virus is free from all contaminants from the source. None of these people were at risk of HIV infection (Chin 2007). In all cases, HIV was isolated and genetically sequenced. “In all three cases, HIV was isolated from the infected individual, sequenced, and shown to be the infecting strain of virus” (Chin 2007, p. 51). It was found that it was the same strain of the virus to which these people were exposed. In one of the employees, pneumocystis pneumonia was developed, and the level of CD4 + cells was less than 50 before antiretroviral therapy (Chin 2007).

Other examples include animal studies. In some studies, in chimpanzees that were artificially infected with HIV-1, symptoms peculiar to AIDS were developed (Chin 2007). However, it was rare. A similar effect was observed in baboons while infecting them with HIV-2 (Chin 2007). In rhesus monkeys, AIDS developed after infection with a hybrid virus called SHID, which contained HIV genes (Chin 2007). In mice of a special line derived by genetic engineering with an immune system similar to human, viral replication occurred exactly as in the body of the infected people (Chin 2007).

Moreover, there is an example of people infected with crude HIV (Chin 2007). Such cases at least give reasons to assume that AIDS is a contagious disease, although it does not exclude the possibility of the involvement of other microorganisms. Scientists have documented numerous cases of AIDS in humans after HIV infection through blood transfusion, drug use, vertical transmission from mother to child, occupational exposure, and sexual transmission (Chin 2007). In these cases, the researchers documented the formation of antibodies to HIV using a study of blood samples before the development of AIDS (Chin 2007). It is often accompanied by a slight influenza-like illness or hyperplasia of the tonsils. Until the mid-90s of the 20th century, no one claimed that the last two Koch’s postulates were performed in respect to HIV (Chin 2007). Even for today, the evidence of Koch’s postulates is far from perfect. However, most scientists still believe that the evidence is strong enough to dispel all doubts.

In the late 19th century, the great scientist Robert Koch became known in Germany. He began his activity as a bacteriologist. The scientist concentrated his efforts on the study of the animal disease – anthrax. Subsequently, Robert Koch detected the cause of tuberculosis, cholera, and other diseases. In 1905, the scientist received the Nobel Prize for the detection of tuberculosis sticks. Robert Koch formulated the so-called Koch’s postulates. They are the conditions that must be met for the recognition of pathogen microorganisms. However, now, these postulates are rejected by many doctors and virologists. Despite this fact, Koch’s postulates still have not lost their relevance and are fundamental tenets of microbiology and infectious pathology, compliance with which is a necessary condition for the study of the hypothesis about infectious etiology of any disease.