History of emerging infectious diseases
Encyclopedia
The discovery of disease
-causing pathogen
s is an important activity in the field of medical science, as many virus
es, bacteria
, protozoa
, fungi, helminthes and prion
s are identified as a confirmed or potential pathogen. A Center for Disease Control program begun in 1995 identified over a hundred patients, with life threatening illnesses which were considered to be of an infectious
cause, but could not be linked to a known pathogen. The association of pathogens with disease can be a complex and controversial process, in some cases requiring decades or even centuries to achieve.
, which is transmitted through contaminated water. Once ingested, the bacteria colonizes the intestinal tract of the host and produces a toxin which causes body fluids to flow across the lining of the intestine. Death can result in 2–3 hours from dehydration if no treatment is provided.
Prior to the discovery of an infectious cause, the symptoms of Cholera
were thought to be caused by an excess of bile in the patient. The disease Cholera
gets its name from the Greek word choler meaning bile. This was consistent with medical thought at the time, which held that four liquids or humors controlled health, and lead to such medical practices as bloodletting as a method of curing illnesses. The bacteria was first reported in 1849 by M. Gabriel Pouchet, who discovered it in stools from patients with Cholera
. But he did not appreciate its significance. The first scientist to understand the significance of Vibrio cholerae
was an Italian anatomist Filippo Pacini
, who published detailed drawings of the organism in "Microscopical observations and pathological deductions on cholera" in 1854. He would go onto publish additional papers in 1866, 1871, 1876 and 1880, all of which were ignored by the scientific community. He correctly described how the bacteria caused diarrhea, and developed treatments that were found to be effective. But his findings did not influence medical opinion. In 1874, scientific representatives from 21 countries voted unanimously to resolve that Cholera was caused by environmental toxins from miasmatas
, or clouds of unhealthy substances which float in the air. In 1884, Robert Koch
re-discovered Vibrio cholerae
as a causal element in Cholera
. Some scientists opposed the new theory, and even drank Cholera
cultures to disprove it:
Von Pettenkofer considered his experience proof that Vibrio cholerae
was harmless, as he did not develop Cholera from consuming the culture. Between 1849 when Pouchet discovered Vibrio cholerae
and 1891, over a million people died in Cholera
epidemics in Europe and Russia. In 1995, researchers published a study in Science Magazine
explaining why some persons are able to be infected with Cholera
without symptoms, possibly explaining why Pettenkofer did not get sick. The study showed that a series of genetic mutations in some people provide resistance to Cholera
toxin. However, these mutations come with a price. If too many of them occur in a person, they will develop Cystic Fibrosis
, an incurable and often fatal genetic disorder.
. Infection with Giardia
can produce diarrhea, gas, and abdominal pain in some people. If untreated, infection can be chronic. In children, chronic Giardia
infection can cause stunting (stunted growth) and lowered intelligence, Infection with Giardia
is now universally recognized as a disease, and treated by physicians with anti-protozoal drugs. Since 2002, Giardia
cases must be reported to the Center for Disease Control, according to the CDC’s Reportable Disease Spreadsheet. The United States National Institutes of Health
Gastrointestinal Parasites Lab studies Giardia
almost exclusively.
However, Giardia
experienced an extraordinarily long term of emergence, from its discovery in 1681, until the 1970s when it was fully accepted that infection with Giardia
was a treatable cause of chronic diarrhea:
Some of the first evidence in modern times of Giardia's pathogenicity came during World War II
when soldiers were treated for malaria
with the antiprotozoal Quinacrine
, and their diarrhea disappeared, as did the Giardia
from their stool samples. In 1954, Dr. R.C. Rendtorff performed experiments on prisoner volunteers, infecting them with Giardia
. In the experiment, although some prisoners experienced changes in stool habits, he concluded that these could not be conclusively linked to Giardia infection, and also indicated that all prisoners experienced spontaneous clearance of Giardia. His experiments were described in the EPA Symposium on Waterborne Transmission of Giardiasis in 1979:
In 1954-55, an outbreak of Giardia
infection occurred in Oregon
(US), sickening 50,000 people. This was documented in a communication by Dr. Lyle Veazie, which wasn't published until 15 years later in the New England Journal of Medicine
. In the communication, Veazie notes that he was unable to find a publisher for his account of the epidemic. The communication was re-published in 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:
is the cause of most stomach ulcers. The discovery is generally credited to Australian gastroenterologists Dr. Barry Marshall
and Dr. J Robin Warren, who published their findings in 1983. The pair received the Nobel Prize in 2005 for their work. Before this, nobody really knew what caused stomach ulcers, though a popular belief was that the "stress" played a role. Some researchers suggested that ulcers were a psychosomatic illness.
In H Pylori Pioneers, Dr. Marshall noted that other physicians had produced evidence of H. pylori infection as early as 1892. Marshall writes that earlier reports were disregarded because they conflicted with existing belief. The first description of H. Pylori came in 1892 from Giulio Bizzozero, who identified acid-tolerant bacteria living in a dog’s stomach. Later, a theory would be developed that no bacteria could live in the stomach. 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. In 1940, two physicians, Dr. A. 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. Dr. John Lykoudis
, a Greek physician, was one of the first physicians to treat stomach ulcers as an infectious disease. Between 1960 and 1970, he treated over 10,000 ulcer patients in Athens with antibiotics. Lykoudis tried to publish a paper on his findings, but they conflicted with traditional theory, and his work was never published. Lykoudis' experience was followed in 1975 by a further publication in Gut magazine that included spiral bacteria living on the borders of duodonal ulcers. The medical significance of Steer’s findings was disregarded, but he “continued to publish papers on H. Pylori, mostly as a hobby."
H. pylori can infect the stomach of some people without causing stomach ulcers. In investigating asymptomatic carriers of H. pylori, researchers identified a genetic trait called Interleuik-1 beta-31 which causes increased production of stomach acid, resulting in ulcers if patients become infected with H. pylori. Patients without the trait do not develop stomach ulcers in response to H. pylori infection, but instead have increased risk from stomach cancer if they become infected. Investigation into other gastrointestinal infections has also shown that the symptoms are the result of interaction between the infection and specific genetic mutations in the host.
(ETEC) is a type found to cause illness in humans, possessing gene
that allows it to manufacture a substance toxic to humans. Cattle are immune to its effects but when people eat food contaminated with cattle feces, the organism can cause disease. Reports of pathogenic E. coli appear in medical literature as early as 1947. Publications regarding variants of E. coli which cause disease appeared regularly in medical journals throughout the 1950s, 60s, and 70s, with fatalities being reported in humans and infants starting in the 1970s. Despite the earlier reports, pathogenic E. coli did not rise to public prominence until 1983, when a Center for Disease Control researcher published a paper identifying ETEC as the cause of a series of outbreaks of unexplained hemorrhagic gastrointestinal illness. Despite the earlier publication of pathogenic variants of E. coli, researchers encountered significant difficulties in establishing ETEC as a pathogen.
recorded a cluster of Pneumocystis carinii pneumonia (now still classified as PCP but known to be caused by Pneumocystis jirovecii) in five homosexual men in Los Angeles
. The discovery of the virus took several years of research, and was announced in 1984 by Dr. Gallo of the National Cancer Institute, Dr. Luc Montagnier at the Pasteur Institute in Paris, and Dr. Jay Levy at the University of California, San Francisco.
However, HIV existed long before the 1981 CDC report. Three of the earliest known instances of HIV infection are as follows:
Two species of HIV infect humans: HIV-1 and HIV-2. HIV-1 is more virulent and more easily transmitted. HIV-1 is the source of the majority of HIV infections throughout the world, while HIV-2 is not as easily transmitted and is largely confined to West Africa
. Both HIV-1 and HIV-2 are of primate
origin. The origin of HIV-1 is the Central Common Chimpanzee
(Pan troglodytes troglodytes) found in southern Cameroon
. It is established that HIV-2 originated from the Sooty Mangabey
(Cercocebus atys), an Old World monkey
of Guinea Bissau, Gabon
, and Cameroon.
Most experts believe that HIV probably transferred to humans as a result of direct contact with primates, for instance during hunting or butchery.
is a gastrointestinal pathogen that causes fever, diarrhea, vomiting, and severe weight loss. Outbreaks of the disease occurred in Chicago
in 1989 and other areas in the United States. But investigation by the Center for Disease Control could not identify an infectious cause. The discovery of the cause was made by Mr. Ramachandran Rajah, the head of a medical clinic's laboratory in Katmandu, Nepal. Mr. Rajah was trying to discover why local residents and visitors were becoming ill every summer. He identified an unusual looking organism in stool samples from patients who were sick. But when the clinic sent slides of the organism to the Center for Disease Control, it was identified as Blue-Green algae, which is harmless. Many pathologists had seen the same thing before, but dismissed it as irrelevant to the patient's disease. Later, the organism would be identified as a special kind of parasite, and treatment would be developed to help patients with the infection. In the United States, Cyclospora
infection must be reported to the Center for Disease Control according to the CDC's Reportable Disease Chart
Many recently emerged pathogens infect the gastrointestinal tract
. For example, there are three gastrointestinal protozoal infections which must be reported to the Center for Disease Control.
They are Giardia
, Cyclospora
and Cryptosporidium
, and none of them were known to be significant pathogens in the 1970s.
Figure 1 shows the prevalence of gastrointestinal protozoa in studies from the United States
and Canada
. The most prevalent protozoa in these studies are considered emerging infectious diseases by some researchers, because a consensus does not yet exist in the medical and public health spheres concerning their importance in the role of human disease. Researchers have suggested that their treatment may be complicated by differing opinions regarding pathogenicity, lack of reliable testing procedures, and lack of reliable treatments. 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
.
. Their symptoms resolved following treatment. A study in Denmark identified a high incidence Dientamoeba fragilis
infection in a group of patients suspected of having gastrointestinal illness of an infectious cause. The study also suggested special methods may be required to identify infection.
Disease
A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...
-causing pathogen
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
s is an important activity in the field of medical science, as many virus
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
es, bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
, protozoa
Protozoa
Protozoa are a diverse group of single-cells eukaryotic organisms, many of which are motile. Throughout history, protozoa have been defined as single-cell protists with animal-like behavior, e.g., movement...
, fungi, helminthes and prion
Prion
A prion is an infectious agent composed of protein in a misfolded form. This is in contrast to all other known infectious agents which must contain nucleic acids . The word prion, coined in 1982 by Stanley B. Prusiner, is a portmanteau derived from the words protein and infection...
s are identified as a confirmed or potential pathogen. A Center for Disease Control program begun in 1995 identified over a hundred patients, with life threatening illnesses which were considered to be of an infectious
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
cause, but could not be linked to a known pathogen. The association of pathogens with disease can be a complex and controversial process, in some cases requiring decades or even centuries to achieve.
Factors impairing identification of pathogens
Factors which have been identified as impeding the identification of pathogens include the following:- 1. Lack of animal models: Experimental infection in animals has been used as a criterion to demonstrate an organism's disease-causing ability, but for some pathogens (such as Vibrio choleraeVibrio choleraeVibrio cholerae is a Gram-negative, comma-shaped bacterium. Some strains of V. cholerae cause the disease cholera. V. cholerae is facultatively anaerobic and has a flagella at one cell pole. V...
, which cause disease only in humans) animal models do not exist. In cases where animal models were not available, scientists have sometimes infected themselves or others to determine an organism's disease causing ability.
- 2. Pre-existing theories of disease: Before a pathogen is well-recognized, scientists may attribute the symptoms of infection to other causes, such as toxicologicalToxicologyToxicology is a branch of biology, chemistry, and medicine concerned with the study of the adverse effects of chemicals on living organisms...
, psychologicalPsychosomatic illnessPsychosomatic medicine is an interdisciplinary medical field studying the relationships of social, psychological, and behavioral factors on bodily processes and well-being in humans and animals...
, or geneticGeneticsGenetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
causes. Once a pathogen has been associated with an illness, researchers have reported difficulty displacing these pre-existing theories.
- 3. Variable pathogenicity: Infection with pathogens can produce varying responses in hosts, complicating the process of showing a relationship between infection and the pathogen. In some infectious diseases, the severity of symptoms has been shown to be dependent on specific genetic traits of the host.
- 4. Organisms that look alike but behave differently: In some cases a harmless organism exists which looks identical to a disease causing organism with a microscope, which complicates the discovery process.
- 5. Lack of research effort: Slow progress has been attributed to the small numbers of researchers working on a pathogen.
Vibrio cholerae (1849-1884)
Cholera is a sometimes fatal disease caused by infection with the bacteria Vibrio choleraeVibrio cholerae
Vibrio cholerae is a Gram-negative, comma-shaped bacterium. Some strains of V. cholerae cause the disease cholera. V. cholerae is facultatively anaerobic and has a flagella at one cell pole. V...
, which is transmitted through contaminated water. Once ingested, the bacteria colonizes the intestinal tract of the host and produces a toxin which causes body fluids to flow across the lining of the intestine. Death can result in 2–3 hours from dehydration if no treatment is provided.
Prior to the discovery of an infectious cause, the symptoms of Cholera
Cholera
Cholera is an infection of the small intestine that is caused by the bacterium Vibrio cholerae. The main symptoms are profuse watery diarrhea and vomiting. Transmission occurs primarily by drinking or eating water or food that has been contaminated by the diarrhea of an infected person or the feces...
were thought to be caused by an excess of bile in the patient. The disease Cholera
Cholera
Cholera is an infection of the small intestine that is caused by the bacterium Vibrio cholerae. The main symptoms are profuse watery diarrhea and vomiting. Transmission occurs primarily by drinking or eating water or food that has been contaminated by the diarrhea of an infected person or the feces...
gets its name from the Greek word choler meaning bile. This was consistent with medical thought at the time, which held that four liquids or humors controlled health, and lead to such medical practices as bloodletting as a method of curing illnesses. The bacteria was first reported in 1849 by M. Gabriel Pouchet, who discovered it in stools from patients with Cholera
Cholera
Cholera is an infection of the small intestine that is caused by the bacterium Vibrio cholerae. The main symptoms are profuse watery diarrhea and vomiting. Transmission occurs primarily by drinking or eating water or food that has been contaminated by the diarrhea of an infected person or the feces...
. But he did not appreciate its significance. The first scientist to understand the significance of Vibrio cholerae
Vibrio cholerae
Vibrio cholerae is a Gram-negative, comma-shaped bacterium. Some strains of V. cholerae cause the disease cholera. V. cholerae is facultatively anaerobic and has a flagella at one cell pole. V...
was an Italian anatomist Filippo Pacini
Filippo Pacini
Filippo Pacini was an Italian anatomist, posthumously famous for isolating the cholera bacillus Vibrio cholerae in 1854, well before Robert Koch's more widely accepted discoveries thirty years later....
, who published detailed drawings of the organism in "Microscopical observations and pathological deductions on cholera" in 1854. He would go onto publish additional papers in 1866, 1871, 1876 and 1880, all of which were ignored by the scientific community. He correctly described how the bacteria caused diarrhea, and developed treatments that were found to be effective. But his findings did not influence medical opinion. In 1874, scientific representatives from 21 countries voted unanimously to resolve that Cholera was caused by environmental toxins from miasmatas
Miasma theory of disease
The miasma theory held that diseases such as cholera, chlamydia or the Black Death were caused by a miasma , a noxious form of "bad air"....
, or clouds of unhealthy substances which float in the air. In 1884, Robert Koch
Robert Koch
Heinrich Hermann Robert Koch was a German physician. He became famous for isolating Bacillus anthracis , the Tuberculosis bacillus and the Vibrio cholerae and for his development of Koch's postulates....
re-discovered Vibrio cholerae
Vibrio cholerae
Vibrio cholerae is a Gram-negative, comma-shaped bacterium. Some strains of V. cholerae cause the disease cholera. V. cholerae is facultatively anaerobic and has a flagella at one cell pole. V...
as a causal element in Cholera
Cholera
Cholera is an infection of the small intestine that is caused by the bacterium Vibrio cholerae. The main symptoms are profuse watery diarrhea and vomiting. Transmission occurs primarily by drinking or eating water or food that has been contaminated by the diarrhea of an infected person or the feces...
. Some scientists opposed the new theory, and even drank Cholera
Cholera
Cholera is an infection of the small intestine that is caused by the bacterium Vibrio cholerae. The main symptoms are profuse watery diarrhea and vomiting. Transmission occurs primarily by drinking or eating water or food that has been contaminated by the diarrhea of an infected person or the feces...
cultures to disprove it:
Von Pettenkofer considered his experience proof that Vibrio cholerae
Vibrio cholerae
Vibrio cholerae is a Gram-negative, comma-shaped bacterium. Some strains of V. cholerae cause the disease cholera. V. cholerae is facultatively anaerobic and has a flagella at one cell pole. V...
was harmless, as he did not develop Cholera from consuming the culture. Between 1849 when Pouchet discovered Vibrio cholerae
Vibrio cholerae
Vibrio cholerae is a Gram-negative, comma-shaped bacterium. Some strains of V. cholerae cause the disease cholera. V. cholerae is facultatively anaerobic and has a flagella at one cell pole. V...
and 1891, over a million people died in Cholera
Cholera
Cholera is an infection of the small intestine that is caused by the bacterium Vibrio cholerae. The main symptoms are profuse watery diarrhea and vomiting. Transmission occurs primarily by drinking or eating water or food that has been contaminated by the diarrhea of an infected person or the feces...
epidemics in Europe and Russia. In 1995, researchers published a study in Science Magazine
Science Magazine
Science Magazine was a half-hour television show produced by the Canadian Broadcasting Corporation from 1975 to 1979.The show was hosted by geneticist David Suzuki, who previously hosted the daytime youth programme Suzuki On Science...
explaining why some persons are able to be infected with Cholera
Cholera
Cholera is an infection of the small intestine that is caused by the bacterium Vibrio cholerae. The main symptoms are profuse watery diarrhea and vomiting. Transmission occurs primarily by drinking or eating water or food that has been contaminated by the diarrhea of an infected person or the feces...
without symptoms, possibly explaining why Pettenkofer did not get sick. The study showed that a series of genetic mutations in some people provide resistance to Cholera
Cholera
Cholera is an infection of the small intestine that is caused by the bacterium Vibrio cholerae. The main symptoms are profuse watery diarrhea and vomiting. Transmission occurs primarily by drinking or eating water or food that has been contaminated by the diarrhea of an infected person or the feces...
toxin. However, these mutations come with a price. If too many of them occur in a person, they will develop Cystic Fibrosis
Cystic fibrosis
Cystic fibrosis is a recessive genetic disease affecting most critically the lungs, and also the pancreas, liver, and intestine...
, an incurable and often fatal genetic disorder.
Giardia lamblia (1681-1975)
Giardiasis is a disease caused by infection with the protozoan Giardia lambliaGiardia lamblia
Giardia lamblia is a flagellated protozoan parasite that colonizes and reproduces in the small intestine, causing giardiasis. The giardia parasite attaches to the epithelium by a ventral adhesive disc, and reproduces via binary fission...
. Infection with Giardia
Giardia
Giardia is a genus of anaerobic flagellated protozoan parasites of the phylum Metamonada in the supergroup "Excavata" that colonise and reproduce in the small intestines of several vertebrates, causing giardiasis, commonly known as Beaver fever...
can produce diarrhea, gas, and abdominal pain in some people. If untreated, infection can be chronic. In children, chronic Giardia
Giardia
Giardia is a genus of anaerobic flagellated protozoan parasites of the phylum Metamonada in the supergroup "Excavata" that colonise and reproduce in the small intestines of several vertebrates, causing giardiasis, commonly known as Beaver fever...
infection can cause stunting (stunted growth) and lowered intelligence, Infection with Giardia
Giardia
Giardia is a genus of anaerobic flagellated protozoan parasites of the phylum Metamonada in the supergroup "Excavata" that colonise and reproduce in the small intestines of several vertebrates, causing giardiasis, commonly known as Beaver fever...
is now universally recognized as a disease, and treated by physicians with anti-protozoal drugs. Since 2002, Giardia
Giardia
Giardia is a genus of anaerobic flagellated protozoan parasites of the phylum Metamonada in the supergroup "Excavata" that colonise and reproduce in the small intestines of several vertebrates, causing giardiasis, commonly known as Beaver fever...
cases must be reported to the Center for Disease Control, according to the CDC’s Reportable Disease Spreadsheet. The United States National Institutes of Health
National Institutes of Health
The National Institutes of Health are an agency of the United States Department of Health and Human Services and are the primary agency of the United States government responsible for biomedical and health-related research. Its science and engineering counterpart is the National Science Foundation...
Gastrointestinal Parasites Lab studies Giardia
Giardia
Giardia is a genus of anaerobic flagellated protozoan parasites of the phylum Metamonada in the supergroup "Excavata" that colonise and reproduce in the small intestines of several vertebrates, causing giardiasis, commonly known as Beaver fever...
almost exclusively.
However, Giardia
Giardia
Giardia is a genus of anaerobic flagellated protozoan parasites of the phylum Metamonada in the supergroup "Excavata" that colonise and reproduce in the small intestines of several vertebrates, causing giardiasis, commonly known as Beaver fever...
experienced an extraordinarily long term of emergence, from its discovery in 1681, until the 1970s when it was fully accepted that infection with Giardia
Giardia
Giardia is a genus of anaerobic flagellated protozoan parasites of the phylum Metamonada in the supergroup "Excavata" that colonise and reproduce in the small intestines of several vertebrates, causing giardiasis, commonly known as Beaver fever...
was a treatable cause of chronic diarrhea:
Some of the first evidence in modern times of Giardia's pathogenicity came during World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
when soldiers were treated for malaria
Malaria
Malaria is a mosquito-borne infectious disease of humans and other animals caused by eukaryotic protists of the genus Plasmodium. The disease results from the multiplication of Plasmodium parasites within red blood cells, causing symptoms that typically include fever and headache, in severe cases...
with the antiprotozoal Quinacrine
Quinacrine
Quinacrine is a drug with a number of different medical applications. It is related to mefloquine.-Uses:Its main effects are as an antiprotozoal, antirheumatic and an intrapleural sclerosing agent....
, and their diarrhea disappeared, as did the Giardia
Giardia
Giardia is a genus of anaerobic flagellated protozoan parasites of the phylum Metamonada in the supergroup "Excavata" that colonise and reproduce in the small intestines of several vertebrates, causing giardiasis, commonly known as Beaver fever...
from their stool samples. In 1954, Dr. R.C. Rendtorff performed experiments on prisoner volunteers, infecting them with Giardia
Giardia
Giardia is a genus of anaerobic flagellated protozoan parasites of the phylum Metamonada in the supergroup "Excavata" that colonise and reproduce in the small intestines of several vertebrates, causing giardiasis, commonly known as Beaver fever...
. In the experiment, although some prisoners experienced changes in stool habits, he concluded that these could not be conclusively linked to Giardia infection, and also indicated that all prisoners experienced spontaneous clearance of Giardia. His experiments were described in the EPA Symposium on Waterborne Transmission of Giardiasis in 1979:
In 1954-55, an outbreak of Giardia
Giardia
Giardia is a genus of anaerobic flagellated protozoan parasites of the phylum Metamonada in the supergroup "Excavata" that colonise and reproduce in the small intestines of several vertebrates, causing giardiasis, commonly known as Beaver fever...
infection occurred in Oregon
Oregon
Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...
(US), sickening 50,000 people. This was documented in a communication by Dr. Lyle Veazie, which wasn't published until 15 years later in the New England Journal of Medicine
New England Journal of Medicine
The New England Journal of Medicine is an English-language peer-reviewed medical journal published by the Massachusetts Medical Society. It describes itself as the oldest continuously published medical journal in the world.-History:...
. In the communication, Veazie notes that he was unable to find a publisher for his account of the epidemic. The communication was re-published in 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
Giardia
Giardia is a genus of anaerobic flagellated protozoan parasites of the phylum Metamonada in the supergroup "Excavata" that colonise and reproduce in the small intestines of several vertebrates, causing giardiasis, commonly known as Beaver fever...
was still being attributed to other causes by health authorities in 1954:
Helicobacter pylori (1892-1982)
Infection with the bacteria Helicobacter pyloriHelicobacter pylori
Helicobacter pylori , previously named Campylobacter pyloridis, is a Gram-negative, microaerophilic bacterium found in the stomach. It was identified in 1982 by Barry Marshall and Robin Warren, who found that it was present in patients with chronic gastritis and gastric ulcers, conditions that were...
is the cause of most stomach ulcers. The discovery is generally credited to Australian gastroenterologists Dr. Barry Marshall
Barry Marshall
Barry James Marshall, AC, FRS, FAA is an Australian physician, Nobel Prize laureate in Physiology or Medicine, and Professor of Clinical Microbiology at the University of Western Australia. Marshall is well-known for proving that the bacterium Helicobacter pylori Barry James Marshall, AC, FRS, FAA...
and Dr. J Robin Warren, who published their findings in 1983. The pair received the Nobel Prize in 2005 for their work. Before this, nobody really knew what caused stomach ulcers, though a popular belief was that the "stress" played a role. Some researchers suggested that ulcers were a psychosomatic illness.
In H Pylori Pioneers, Dr. Marshall noted that other physicians had produced evidence of H. pylori infection as early as 1892. Marshall writes that earlier reports were disregarded because they conflicted with existing belief. The first description of H. Pylori came in 1892 from Giulio Bizzozero, who identified acid-tolerant bacteria living in a dog’s stomach. Later, a theory would be developed that no bacteria could live in the stomach. 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. In 1940, two physicians, Dr. A. 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. Dr. John Lykoudis
John Lykoudis
John Lykoudis was a general practitioner in Greece who treated patients suffering from peptic ulcer disease with antibiotics long before it was commonly recognized that bacteria were a dominant cause for the disease....
, a Greek physician, was one of the first physicians to treat stomach ulcers as an infectious disease. Between 1960 and 1970, he treated over 10,000 ulcer patients in Athens with antibiotics. Lykoudis tried to publish a paper on his findings, but they conflicted with traditional theory, and his work was never published. Lykoudis' experience was followed in 1975 by a further publication in Gut magazine that included spiral bacteria living on the borders of duodonal ulcers. The medical significance of Steer’s findings was disregarded, but he “continued to publish papers on H. Pylori, mostly as a hobby."
H. pylori can infect the stomach of some people without causing stomach ulcers. In investigating asymptomatic carriers of H. pylori, researchers identified a genetic trait called Interleuik-1 beta-31 which causes increased production of stomach acid, resulting in ulcers if patients become infected with H. pylori. Patients without the trait do not develop stomach ulcers in response to H. pylori infection, but instead have increased risk from stomach cancer if they become infected. Investigation into other gastrointestinal infections has also shown that the symptoms are the result of interaction between the infection and specific genetic mutations in the host.
Pathogenic variants of Escherichia coli (1947-1983)
There are different types of E. coli, some of which are found in humans and are harmless. Enterotoxigenic Escherichia coliEnterotoxigenic Escherichia coli
Enterotoxigenic Escherichia coli is a type of Escherichia coli and the leading bacterial cause of diarrhea in the developing world, as well as the most common cause of traveler's diarrhea. Each year, approximately 210 million cases and 380,000 deaths occur, mostly in children, from ETEC...
(ETEC) is a type found to cause illness in humans, possessing gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
that allows it to manufacture a substance toxic to humans. Cattle are immune to its effects but when people eat food contaminated with cattle feces, the organism can cause disease. Reports of pathogenic E. coli appear in medical literature as early as 1947. Publications regarding variants of E. coli which cause disease appeared regularly in medical journals throughout the 1950s, 60s, and 70s, with fatalities being reported in humans and infants starting in the 1970s. Despite the earlier reports, pathogenic E. coli did not rise to public prominence until 1983, when a Center for Disease Control researcher published a paper identifying ETEC as the cause of a series of outbreaks of unexplained hemorrhagic gastrointestinal illness. Despite the earlier publication of pathogenic variants of E. coli, researchers encountered significant difficulties in establishing ETEC as a pathogen.
Human Immunodeficiency Virus (1959-1984)
AIDS was first reported June 5, 1981, when the U.S. Centers for Disease Control and PreventionCenters for Disease Control and Prevention
The Centers for Disease Control and Prevention are a United States federal agency under the Department of Health and Human Services headquartered in Druid Hills, unincorporated DeKalb County, Georgia, in Greater Atlanta...
recorded a cluster of Pneumocystis carinii pneumonia (now still classified as PCP but known to be caused by Pneumocystis jirovecii) in five homosexual men in Los Angeles
Los Ángeles
Los Ángeles is the capital of the province of Biobío, in the commune of the same name, in Region VIII , in the center-south of Chile. It is located between the Laja and Biobío rivers. The population is 123,445 inhabitants...
. The discovery of the virus took several years of research, and was announced in 1984 by Dr. Gallo of the National Cancer Institute, Dr. Luc Montagnier at the Pasteur Institute in Paris, and Dr. Jay Levy at the University of California, San Francisco.
However, HIV existed long before the 1981 CDC report. Three of the earliest known instances of HIV infection are as follows:
- A plasma sample taken in 1959 from an adult male living in what is now the Democratic Republic of the Congo.
- HIV found in tissue samples from a 15 year old African-American teenager who died in St. Louis in 1969.
- HIV found in tissue samples from a NorwegianNorwayNorway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...
sailor who died around 1976.
Two species of HIV infect humans: HIV-1 and HIV-2. HIV-1 is more virulent and more easily transmitted. HIV-1 is the source of the majority of HIV infections throughout the world, while HIV-2 is not as easily transmitted and is largely confined to West Africa
West Africa
West Africa or Western Africa is the westernmost region of the African continent. Geopolitically, the UN definition of Western Africa includes the following 16 countries and an area of approximately 5 million square km:-Flags of West Africa:...
. Both HIV-1 and HIV-2 are of primate
Primate
A primate is a mammal of the order Primates , which contains prosimians and simians. Primates arose from ancestors that lived in the trees of tropical forests; many primate characteristics represent adaptations to life in this challenging three-dimensional environment...
origin. The origin of HIV-1 is the Central Common Chimpanzee
Common Chimpanzee
The common chimpanzee , also known as the robust chimpanzee, is a great ape. Colloquially, the common chimpanzee is often called the chimpanzee , though technically this term refers to both species in the genus Pan: the common chimpanzee and the closely related bonobo, formerly called the pygmy...
(Pan troglodytes troglodytes) found in southern Cameroon
Cameroon
Cameroon, officially the Republic of Cameroon , is a country in west Central Africa. It is bordered by Nigeria to the west; Chad to the northeast; the Central African Republic to the east; and Equatorial Guinea, Gabon, and the Republic of the Congo to the south. Cameroon's coastline lies on the...
. It is established that HIV-2 originated from the Sooty Mangabey
Sooty Mangabey
The sooty mangabey is an Old World monkey found in forests from Senegal east to Ghana. It is famous for being believed to be the monkey that HIV-2 might have originated in before jumping species...
(Cercocebus atys), an Old World monkey
Old World monkey
The Old World monkeys or Cercopithecidae are a group of primates, falling in the superfamily Cercopithecoidea in the clade Catarrhini. The Old World monkeys are native to Africa and Asia today, inhabiting a range of environments from tropical rain forest to savanna, shrubland and mountainous...
of Guinea Bissau, Gabon
Gabon
Gabon , officially the Gabonese Republic is a state in west central Africa sharing borders with Equatorial Guinea to the northwest, Cameroon to the north, and with the Republic of the Congo curving around the east and south. The Gulf of Guinea, an arm of the Atlantic Ocean is to the west...
, and Cameroon.
Most experts believe that HIV probably transferred to humans as a result of direct contact with primates, for instance during hunting or butchery.
Cyclospora (1995)
CyclosporaCyclospora
Cyclospora is a genus of apicomplexan parasites. It includes the species Cyclospora cayetanensis, the causative agent of Cyclosporiasis....
is a gastrointestinal pathogen that causes fever, diarrhea, vomiting, and severe weight loss. Outbreaks of the disease occurred in Chicago
Chicago
Chicago is the largest city in the US state of Illinois. With nearly 2.7 million residents, it is the most populous city in the Midwestern United States and the third most populous in the US, after New York City and Los Angeles...
in 1989 and other areas in the United States. But investigation by the Center for Disease Control could not identify an infectious cause. The discovery of the cause was made by Mr. Ramachandran Rajah, the head of a medical clinic's laboratory in Katmandu, Nepal. Mr. Rajah was trying to discover why local residents and visitors were becoming ill every summer. He identified an unusual looking organism in stool samples from patients who were sick. But when the clinic sent slides of the organism to the Center for Disease Control, it was identified as Blue-Green algae, which is harmless. Many pathologists had seen the same thing before, but dismissed it as irrelevant to the patient's disease. Later, the organism would be identified as a special kind of parasite, and treatment would be developed to help patients with the infection. In the United States, Cyclospora
Cyclospora
Cyclospora is a genus of apicomplexan parasites. It includes the species Cyclospora cayetanensis, the causative agent of Cyclosporiasis....
infection must be reported to the Center for Disease Control according to the CDC's Reportable Disease Chart
Present day discoveries
The process of identifying new infectious agents continues. One study has suggested there are a large number of pathogens already causing illness in the population, but they have not yet been properly identified.Gastrointestinal pathogens
Gastrointestinal tract
The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....
. For example, there are three gastrointestinal protozoal infections which must be reported to the Center for Disease Control.
They are Giardia
Giardia
Giardia is a genus of anaerobic flagellated protozoan parasites of the phylum Metamonada in the supergroup "Excavata" that colonise and reproduce in the small intestines of several vertebrates, causing giardiasis, commonly known as Beaver fever...
, Cyclospora
Cyclospora
Cyclospora is a genus of apicomplexan parasites. It includes the species Cyclospora cayetanensis, the causative agent of Cyclosporiasis....
and Cryptosporidium
Cryptosporidium
Cryptosporidium is a protozoan that can cause gastro-intestinal illness with diarrhea in humans.Cryptosporidium is the organism most commonly isolated in HIV positive patients presenting with diarrhea...
, and none of them were known to be significant pathogens in the 1970s.
Figure 1 shows the prevalence of gastrointestinal protozoa in studies from the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
and Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
. The most prevalent protozoa in these studies are considered emerging infectious diseases by some researchers, because a consensus does not yet exist in the medical and public health spheres concerning their importance in the role of human disease. Researchers have suggested that their treatment may be complicated by differing opinions regarding pathogenicity, lack of reliable testing procedures, and lack of reliable treatments. 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
Irritable bowel syndrome
Irritable bowel syndrome is a diagnosis of exclusion. It is a functional bowel disorder characterized by chronic abdominal pain, discomfort, bloating, and alteration of bowel habits in the absence of any detectable organic cause. In some cases, the symptoms are relieved by bowel movements...
.
Dientamoeba fragilis
Dientamoeba fragilis is a single-celled parasite which infects the large intestine causing diarrhea, gas, and abdominal pain. An Australian study identified patients with symptoms of IBS who were actually infected with Dientamoeba fragilisDientamoeba fragilis
Dientamoeba fragilis is a single celled parasite found in the gastrointestinal tract of some humans, pigs and gorillas. In some people it causes gastrointestinal upset while in others it does not...
. Their symptoms resolved following treatment. A study in Denmark identified a high incidence Dientamoeba fragilis
Dientamoeba fragilis
Dientamoeba fragilis is a single celled parasite found in the gastrointestinal tract of some humans, pigs and gorillas. In some people it causes gastrointestinal upset while in others it does not...
infection in a group of patients suspected of having gastrointestinal illness of an infectious cause. The study also suggested special methods may be required to identify infection.