Discovery of disease-causing pathogens
Many viruses, bacteria, protozoa, fungi, helminths (parasitic worms), and prions are identified as a confirmed or potential pathogen.
In the United States, a Centers for Disease Control and Prevention program, begun in 1995, identified over a hundred patients with life-threatening illnesses that were considered to be of an infectious cause but that could not be linked to a known pathogen.
[1] The association of pathogens with disease can be a complex and controversial process, in some cases requiring decades or even centuries to achieve.
Factors which have been identified as impeding the identification of pathogens include the following: Vibrio cholerae bacteria are transmitted through contaminated water.
[4] Whilst John Snow's epidemiological maps were well recognized and led to the removal of the Broad Street pump handle (e.g., the 1854 Broad Street cholera outbreak), in 1874, scientific representatives from 21 countries voted unanimously to resolve that cholera was caused by environmental toxins from miasmata, or clouds of unhealthy substances which float in the air.
His conclusions were based upon the constant finding of the peculiar "comma bacillus" in the stools of cholera patients, and the failure to demonstrate this organism in the feces of other persons.
At the time the "germ theory" of disease had not yet obtained general acceptance, and Koch's announcement was received with considerable skepticism, particularly after it was found that similar "comma bacilli" could be found at times in the feces of persons not suffering from cholera, and often in all sorts of other environments - well and river waters, cheese, etc.
Attesting to its increasing importance in the United States, a symposium on Giardiasis, sponsored by the Environmental Protection Agency, was held in the fall of 1978.
His experiments were described at the EPA Symposium on Waterborne Transmission of Giardiasis in 1978: [...] we also included Giardia lamblia, which at that time was not generally believed to be an invasive pathogenic parasite of man.
Giardia was thought in the 1950's to cause occasional problems of diarrhea in children but its appearance was so common and, in adults so lacking in clinical symptomatology, that most considered it a non-pathogen.
The communication was re-published in the Proceedings of the EPA Symposium on Waterborne Transmission of Giardiasis in 1979, and that version included the following quote from the Director of the Oregon State Board of Health, suggesting that diarrhea from Giardia was still being attributed to other causes by health authorities in 1954: While an unidentified virus seems the most likely etiologic agent, the unusual prevalence of Giardia lamblia cysts in stools of patients seems worthy of record.
The discovery is generally credited to Australian gastroenterologists Dr. Barry Marshall and Dr. J. Robin Warren, who published their findings in 1983.
[3] Although the theory has no scientific basis, it would become a stumbling block for scientists, discouraging them for searching for infective causes of stomach ulcers.
Stone Freeberg and Dr. Louis E. Barron published a paper describing a spiral bacteria found in about half of their gastroenterology patients who had stomach ulcers.
[3] Lykoudis' experience was followed in 1975 by a further publication in Gut magazine that included spiral bacteria living on the borders of duodonal ulcers.
[25] Publications regarding variants of E. coli which cause disease appeared regularly in medical journals throughout the 1950s, '60s, and '70s,[26][27][28][29][30] with fatalities being reported in humans and infants starting in the 1970s.
[31][32][33] Despite the earlier reports, pathogenic E. coli did not rise to public prominence until 1983, when a CDC researcher published a paper identifying ETEC as the cause of a series of outbreaks of unexplained hemorrhagic gastrointestinal illness.
[42] It is established that HIV-2 originated from the sooty mangabey (Cercocebus atys), an Old World monkey of Guinea Bissau, Gabon, and Cameroon.
The discovery of the cause was made by Mr. Ramachandran Rajah, the head of a medical clinic's laboratory in Kathmandu, Nepal.
[49] As with newly discovered pathogens before them, researchers are reporting that these organisms may be responsible for illnesses for which no clear cause has been found, such as irritable bowel syndrome.
[50][51][52] Dientamoeba fragilis is a single-celled parasite which infects the large intestine causing diarrhea, gas, and abdominal pain.
A study in Denmark identified a high incidence Dientamoeba fragilis infection in a group of patients suspected of having gastrointestinal illness of an infectious nature.
[49] An additional study found that many IBS patients from whom Blastocystis could not be identified showed a strong antibody reaction to the organism, which is a type of test used to diagnose certain difficult-to-detect infections.
