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Transmissible spongiform encephalopathies (TSEs) also known as prion diseases,[1] are a group of progressive, incurable, and fatal conditions that are associated with prions and affect the brain and nervous system of many animals, including humans, cattle, and sheep. According to the most widespread hypothesis, they are transmitted by prions, though some other data suggest an involvement of a Spiroplasma infection.[2] Mental and physical abilities deteriorate and many tiny holes appear in the cortex causing it to appear like a sponge when brain tissue obtained at autopsy is examined under a microscope. The disorders cause impairment of brain function, including memory changes, personality changes and problems with movement that worsen chronically.[citation needed]
Unlike other kinds of infectious disease, which are spread by agents with a DNA or RNA genome (such as virus or bacteria), the infectious agent in TSEs is believed to be a prion, thus being composed solely of protein material. Misshapened prion proteins carry the disease between individuals and cause deterioration of the brain. TSEs are unique diseases in that their aetiology may be genetic, sporadic, or infectious via ingestion of infected foodstuffs and via iatrogenic means (e.g., blood transfusion).[6] Most TSEs are sporadic and occur in an animal with no prion protein mutation. Inherited TSE occurs in animals carrying a rare mutant prion allele, which expresses prion proteins that contort by themselves into the disease-causing conformation. Transmission occurs when healthy animals consume tainted tissues from others with the disease. In the 1980s and 1990s, bovine spongiform encephalopathy spread in cattle in an epidemic fashion. This occurred because cattle were fed the processed remains of other cattle, a practice now banned in many countries. In turn, consumption (by humans) of bovine-derived foodstuff which contained prion-contaminated tissues resulted in an outbreak of the variant form of Creutzfeldt–Jakob disease in the 1990s and 2000s.[7]
Prions cannot be transmitted through the air, through touching, or most other forms of casual contact. However, they may be transmitted through contact with infected tissue, body fluids, or contaminated medical instruments. Normal sterilization procedures such as boiling or irradiating materials fail to render prions non-infective. However, treatment with strong, almost undiluted bleach and/or sodium hydroxide, or heating to a minimum of 134°C, does destroy prions.[8]
Classification
Differences in shape between the different prion protein forms are poorly understood.
The degenerative tissue damage caused by human prion diseases (CJD, GSS, and kuru) is characterised by four features: spongiform change (the presence of many small holes), the death of neurons, astrocytosis (abnormal increase in the number of astrocytes due to the destruction of nearby neurons), and amyloid plaque formation. These features are shared with prion diseases in animals, and the recognition of these similarities prompted the first attempts to transmit a human prion disease (kuru) to a primate in 1966, followed by CJD in 1968 and GSS in 1981. These neuropathological features have formed the basis of the histological diagnosis of human prion diseases for many years, although it was recognized that these changes are enormously variable both from case to case and within the central nervous system in individual cases.[13]
The clinical signs in humans vary, but commonly include personality changes, psychiatric problems such as depression, lack of coordination, and/or an unsteady gait (ataxia). Patients also may experience involuntary jerking movements called myoclonus, unusual sensations, insomnia, confusion, or memory problems. In the later stages of the disease, patients have severe mental impairment (dementia) and lose the ability to move or speak.[14]
Early neuropathological reports on human prion diseases suffered from a confusion of nomenclature, in which the significance of the diagnostic feature of spongiform change was occasionally overlooked. The subsequent demonstration that human prion diseases were transmissible reinforced the importance of spongiform change as a diagnostic feature, reflected in the use of the term "spongiform encephalopathy" for this group of disorders.
Prions appear to be most infectious when in direct contact with affected tissues. For example, Creutzfeldt–Jakob disease has been transmitted to patients taking injections of growth hormone harvested from human pituitary glands, from cadaver dura allografts and from instruments used for brain surgery (Brown, 2000) (prions can survive the "autoclave" sterilization process used for most surgical instruments). It is also believed[by whom?] that dietary consumption of affected animals can cause prions to accumulate slowly, especially when cannibalism or similar practices allow the proteins to accumulate over more than one generation. An example is kuru, which reached epidemic proportions in the mid-20th century in the Fore people of Papua New Guinea, who used to consume their dead as a funerary ritual.[15] Laws in developed countries now ban the use of renderedruminant proteins in ruminant feed as a precaution against the spread of prion infection in cattle and other ruminants.[citation needed]
There exists evidence that prion diseases may be transmissible by the airborne route.[16]
Note that not all encephalopathies are caused by prions, as in the cases of PML (caused by the JC virus), CADASIL (caused by abnormal NOTCH3 protein activity), and Krabbe disease (caused by a deficiency of the enzyme galactosylceramidase). Progressive Spongiform Leukoencephalopathy (PSL)—which is a spongiform encephalopathy—is also probably not caused by a prion, although the adulterant that causes it among heroin smokers has not yet been identified.[17][18][19][20] This, combined with the highly variable nature of prion disease pathology, is why a prion disease cannot be diagnosed based solely on a patient's symptoms.
Mutations in the PRNPgene cause prion disease. Familial forms of prion disease are caused by inherited mutations in the PRNP gene. Only a small percentage of all cases of prion disease run in families, however. Most cases of prion disease are sporadic, which means they occur in people without any known risk factors or gene mutations. In rare circumstances, prion diseases also can be transmitted by exposure to prion-contaminated tissues or other biological materials obtained from individuals with prion disease.
The PRNP gene provides the instructions to make a protein called the prion protein (PrP). Under normal circumstances, this protein may be involved in transporting copper into cells. It may also be involved in protecting brain cells and helping them communicate. 24[citation needed] Point-Mutations in this gene cause cells to produce an abnormal form of the prion protein, known as PrPSc. This abnormal protein builds up in the brain and destroys nerve cells, resulting in the signs and symptoms of prion disease.
Familial forms of prion disease are inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. In most cases, an affected person inherits the altered gene from one affected parent.
In some people, familial forms of prion disease are caused by a new mutation in the PRNP gene. Although such people most likely do not have an affected parent, they can pass the genetic change to their children.
Protein-only hypothesis
Protein could be the infectious agent, inducing its own replication by causing conformational change of normal cellular PrPC into PrPSc. Evidence for this hypothesis:
Infectivity titre correlates with PrPSc levels. However, this is disputed.[21]
PrPC depletion in the neural system of mice with established neuroinvasive prion infection reverses early spongeosis and behavioural deficits, halts further disease progression and increases life-span[24]
While not containing a nucleic acid genome, prions may be composed of more than just a protein. Purified PrPC appears unable to convert to the infectious PrPSc form, unless other components are added, such as RNA and lipids.[25] These other components, termed cofactors, may form part of the infectious prion, or they may serve as catalysts for the replication of a protein-only prion.
Viral hypothesis
This hypothesis postulates that an as of yet undiscovered infectious viral agent is the cause of the disease. Evidence for this hypothesis is as follows:
Strain variation of different isolates of PrPSc[26]
An increasing titre of PrPSc as the disease progresses suggests a replicating agent.
Diagnosis
There continues to be a very practical problem with diagnosis of prion diseases, including BSE and CJD. They have an incubation period of months to decades during which there are no symptoms, even though the pathway of converting the normal brain PrP protein into the toxic, disease-related PrPSc form has started. At present, there is virtually no way to detect PrPSc reliably except by examining the brain using neuropathological and immunohistochemical methods after death. Accumulation of the abnormally folded PrPSc form of the PrP protein is a characteristic of the disease, but it is present at very low levels in easily accessible body fluids like blood or urine. Researchers have tried to develop methods to measure PrPSc, but there are still no fully accepted methods for use in materials such as blood.[citation needed]
In 2010, a team from New York described detection of PrPSc even when initially present at only one part in a hundred billion (10−11) in brain tissue. The method combines amplification with a novel technology called Surround Optical Fiber Immunoassay (SOFIA) and some specific antibodies against PrPSc. After amplifying and then concentrating any PrPSc, the samples are labelled with a fluorescent dye using an antibody for specificity and then finally loaded into a micro-capillary tube. This tube is placed in a specially constructed apparatus so that it is totally surrounded by optical fibres to capture all light emitted once the dye is excited using a laser. The technique allowed detection of PrPSc after many fewer cycles of conversion than others have achieved, substantially reducing the possibility of artefacts, as well as speeding up the assay. The researchers also tested their method on blood samples from apparently healthy sheep that went on to develop scrapie. The animals' brains were analysed once any symptoms became apparent. The researchers could therefore compare results from brain tissue and blood taken once the animals exhibited symptoms of the diseases, with blood obtained earlier in the animals' lives, and from uninfected animals. The results showed very clearly that PrPSc could be detected in the blood of animals long before the symptoms appeared.[27][28]
Epidemiology
Transmissible spongiform encephalopathies (TSE) are very rare but can reach epidemic proportions.[clarification needed] It is very hard to map the spread of the disease due to the difficulty of identifying individual strains of the prions. This means that, if animals at one farm begin to show the disease after an outbreak on a nearby farm, it is very difficult to determine whether it is the same strain affecting both herds—suggesting transmission—or if the second outbreak came from a completely different source.
Classic Creutzfeldt-Jakob disease (CJD) was discovered in 1920. It occurs sporadically over the world but is very rare. It affects about one person per million each year. Typically, the cause is unknown for these cases. It has been found to be passed on genetically in some cases. 250 patients contracted the disease through iatrogenic transmission (from use of contaminated surgical equipment).[29] This was before equipment sterilization was required in 1976, and there have been no other iatrogenic cases since then. In order to prevent the spread of infection, the World Health Organization created a guide to tell health care workers what to do when CJD appears and how to dispose of contaminated equipment.[30] The Centers for Disease Control and Prevention (CDC) have been keeping surveillance on CJD cases, particularly by looking at death certificate information.[31]
Chronic wasting disease (CWD) is a prion disease found in North America in deer and elk. The first case was identified as a fatal wasting syndrome in the 1960s. It was then recognized as a transmissible spongiform encephalopathy in 1978. Surveillance studies showed the endemic of CWD in free-ranging deer and elk spread in northeastern Colorado, southeastern Wyoming and western Nebraska. It was also discovered that CWD may have been present in a proportion of free-ranging animals decades before the initial recognition. In the United States, the discovery of CWD raised concerns about the transmission of this prion disease to humans. Many apparent cases of CJD were suspected transmission of CWD, however the evidence was lacking and not convincing.[32]
In the 1980s and 1990s, bovine spongiform encephalopathy (BSE or "mad cow disease") spread in cattle at an epidemic rate. The total estimated number of cattle infected was approximately 750,000 between 1980 and 1996. This occurred because the cattle were fed processed remains of other cattle. Then human consumption of these infected cattle caused an outbreak of the human form CJD. There was a dramatic decline in BSE when feeding bans were put in place. On May 20, 2003, the first case of BSE was confirmed in North America. The source could not be clearly identified, but researchers suspect it came from imported BSE-infected cow meat. In the United States, the USDA created safeguards to minimize the risk of BSE exposure to humans.[33]
Variant Creutzfeldt-Jakob disease (vCJD) was discovered in 1996 in England. There is strong evidence to suggest that vCJD was caused by the same prion as bovine spongiform encephalopathy.[34] A total of 231 cases of vCJD have been reported since it was first discovered. These cases have been found in a total of 12 countries with 178 in the United Kingdom, 27 in France, five in Spain, four in Ireland, four in the United States, three in the Netherlands, three in Italy, two in Portugal, two in Canada, and one each in Japan, Saudi Arabia, and Taiwan.[35]
History
In the 5th century BCE, Hippocrates described a disease like TSE in cattle and sheep, which he believed also occurred in man.[36]Publius Flavius Vegetius Renatus records cases of a disease with similar characteristics in the 4th and 5th centuries AD.[37] In 1755, an outbreak of scrapie was discussed in the British House of Commons and may have been present in Britain for some time before that.[38] Although there were unsupported claims in 1759 that the disease was contagious, in general it was thought to be due to inbreeding and countermeasures appeared to be successful. Early-20th-century experiments failed to show transmission of scrapie between animals, until extraordinary measures were taken such as the intra-ocular injection of infected nervous tissue. No direct link between scrapie and disease in man was suspected then or has been found since. TSE was first described in man by Alfons Maria Jakob in 1921.[39]Daniel Carleton Gajdusek's discovery that Kuru was transmitted by cannibalism accompanied by the finding of scrapie-like lesions in the brains of Kuru victims strongly suggested an infectious basis to TSE.[40] A paradigm shift to a non-nucleic infectious entity was required when the results were validated with an explanation of how a prion protein might transmit spongiform encephalopathy.[41] Not until 1988 was the neuropathology of spongiform encephalopathy properly described in cows.[42] The alarming amplification of BSE in the British cattle herd heightened fear of transmission to humans and reinforced the belief in the infectious nature of TSE. This was confirmed with the identification of a Kuru-like disease, called new variant Creutzfeldt–Jakob disease, in humans exposed to BSE.[43] Although the infectious disease model of TSE has been questioned in favour of a prion transplantation model that explains why cannibalism favours transmission,[44] the search for a viral agent was, as of 2007, being continued in some laboratories.[45][46]
Creutzfeldt–Jakob disease (CJD), also known as subacute spongiform encephalopathy or neurocognitive disorder due to prion disease, is a fatal degenerative brain disorder. Early symptoms include memory problems, behavioral changes, poor coordination, and visual disturbances. Later symptoms include dementia, involuntary movements, blindness, weakness, and coma. About 70% of people die within a year of diagnosis. The name Creutzfeldt–Jakob disease was introduced by Walther Spielmeyer in 1922, after the German neurologists Hans Gerhard Creutzfeldt and Alfons Maria Jakob.
A prion is a misfolded protein that can induce misfolding of normal variants of the same protein and trigger cellular death. Prions cause prion diseases known as transmissible spongiform encephalopathies (TSEs) that are transmissible, fatal neurodegenerative diseases in humans and animals. The proteins may misfold sporadically, due to genetic mutations, or by exposure to an already misfolded protein. The consequent abnormal three-dimensional structure confers on them the ability to cause misfolding of other proteins.
Scrapie is a fatal, degenerative disease affecting the nervous systems of sheep and goats. It is one of several transmissible spongiform encephalopathies (TSEs), and as such it is thought to be caused by a prion. Scrapie has been known since at least 1732 and does not appear to be transmissible to humans. However, it has been found to be experimentally transmissible to humanised transgenic mice and non-human primates.
Chronic wasting disease (CWD), sometimes called zombie deer disease, is a transmissible spongiform encephalopathy (TSE) affecting deer. TSEs are a family of diseases thought to be caused by misfolded proteins called prions and include similar diseases such as BSE in cattle, Creutzfeldt–Jakob disease (CJD) in humans and scrapie in sheep. Natural infection causing CWD affects members of the deer family. In the United States, CWD affects mule deer, white-tailed deer, red deer, sika deer, elk, caribou, and moose. Experimental transmission of CWD to other species such as squirrel monkeys and genetically modified (humanized) mice has been shown.
Gerstmann–Sträussler–Scheinker syndrome (GSS) is an extremely rare, always fatal neurodegenerative disease that affects patients from 20 to 60 years in age. It is exclusively heritable, and is found in only a few families all over the world. It is, however, classified with the transmissible spongiform encephalopathies (TSE) due to the causative role played by PRNP, the human prion protein. GSS was first reported by the Austrian physicians Josef Gerstmann, Ernst Sträussler and Ilya Scheinker in 1936.
Transmissible mink encephalopathy (TME) is a rare sporadic disease that affects the central nervous system of ranch-raised adult mink. It is a transmissible spongiform encephalopathy, caused by proteins called prions.
Protein misfolding cyclic amplification (PMCA) is an amplification technique to multiply misfolded prions originally developed by Soto and colleagues. It is a test for spongiform encephalopathies like chronic wasting disease (CWD) or bovine spongiform encephalopathy (BSE).
Major prion protein (PrP) is encoded in the human body by the PRNP gene also known as CD230. Expression of the protein is most predominant in the nervous system but occurs in many other tissues throughout the body.
Laura Manuelidis is a physician and neuropathologist at Yale University.
John Mark Purdey was an English organic farmer who came to public attention in the 1980s, when he began to circulate his own theories regarding the causes of bovine spongiform encephalopathy.
Variant Creutzfeldt–Jakob disease (vCJD), commonly referred to as "mad cow disease" or "human mad cow disease" to distinguish it from its BSE counterpart, is a fatal type of brain disease within the transmissible spongiform encephalopathy family. Initial symptoms include psychiatric problems, behavioral changes, and painful sensations. In the later stages of the illness, patients may exhibit poor coordination, dementia and involuntary movements. The length of time between exposure and the development of symptoms is unclear, but is believed to be years to decades. Average life expectancy following the onset of symptoms is 13 months.
Kuru is a rare, incurable, and fatal neurodegenerative disorder that was formerly common among the Fore people of Papua New Guinea. Kuru is a form of transmissible spongiform encephalopathy (TSE) caused by the transmission of abnormally folded proteins (prions), which leads to symptoms such as tremors and loss of coordination from neurodegeneration.
Bovine spongiform encephalopathy (BSE), commonly known as mad cow disease, is an incurable and invariably fatal neurodegenerative disease of cattle. Symptoms include abnormal behavior, trouble walking, and weight loss. Later in the course of the disease, the cow becomes unable to function normally. There is conflicting information about the time between infection and onset of symptoms. In 2002, the World Health Organization (WHO) suggested it to be approximately four to five years. Time from onset of symptoms to death is generally weeks to months. Spread to humans is believed to result in variant Creutzfeldt–Jakob disease (vCJD). As of 2018, a total of 231 cases of vCJD had been reported globally.
Surround optical-fiber immunoassay (SOFIA) is an ultrasensitive, in vitro diagnostic platform incorporating a surround optical-fiber assembly that captures fluorescence emissions from an entire sample. The technology's defining characteristics are its extremely high limit of detection, sensitivity, and dynamic range. SOFIA's sensitivity is measured at the attogram level (10−18 g), making it about one billion times more sensitive than conventional diagnostic techniques. Based on its enhanced dynamic range, SOFIA is able to discriminate levels of analyte in a sample over 10 orders of magnitude, facilitating accurate titering.
Frank O. Bastian is an American physician and neuropathologist, who previously worked at Louisiana State University, moved to a university in New Orleans in 2019. He specializes in the transmissible spongiform encephalopathies (TSEs), which include, but are not limited to, Bovine spongiform encephalopathy (BSE) "Mad cow disease" in cattle, scrapie in sheep and goats, and Creutzfeldt–Jakob disease (CJD) in humans.
The United Kingdom was afflicted with an outbreak of Bovine spongiform encephalopathy, and its human equivalent variant Creutzfeldt–Jakob disease (vCJD), in the 1980s and 1990s. Over four million head of cattle were slaughtered in an effort to contain the outbreak, and 178 people died after contracting vCJD through eating infected beef. A political and public health crisis resulted, and British beef was banned from export to numerous countries around the world, with some bans remaining in place until as late as 2019.
Real-time quaking-induced conversion (RT-QuIC) is a highly sensitive assay for prion detection.
Michael Coulthart is a Canadian microbiologist who is employed as the head of the Canadian Creutzfeldt–Jakob Disease Surveillance System (CJDSS) within the Public Health Agency of Canada (PHAC), which terms CJD a zoonotic and infectious disease. In 2006, a working group named "classic CJD" as well as Variant Creutzfeldt–Jakob disease as two notifiable diseases. It is unknown whether PHAC tracks in an official capacity other transmissible spongiform encephalopathies (TSE), but Coulthart is on the Advisory Committee of the Center for Infectious Disease Research and Policy for Chronic Wasting Disease of cervidae.
The Creutzfeldt-Jakob Disease Surveillance System (CJDSS) is a unit of the Public Health Agency of Canada. It studies the various variants of Creutzfeldt-Jakob Disease, and at least as of 2017, assisted "with DNA sequencing, autopsy and case confirmation". As of 2014, the CJDSS conducted "prospective national surveillance for all types of human prion disease in Canada. The main purposes of the CJDSS [were then] to better understand the epidemiology of human prion diseases, to improve the options available for their rapid and accurate diagnosis, and ultimately to protect the health of Canadians by reducing risks of prion disease transmission."
↑ Brown P, Preece M, Brandel JP, Sato T, McShane L, Zerr I, Fletcher A, Will RG, Pocchiari M, Cashman NR, d'Aignaux JH, Cervenakova L, Fradkin J, Schonberger LB, Collins SJ (2000). "Iatrogenic Creutzfeldt–Jakob disease at the millennium". Neurology. 55 (8): 1075–81. doi:10.1212/WNL.55.8.1075. PMID11071481. S2CID25292433.
↑ Colle, JG; Bradley, R; Libersky, PP (2006). "Variant CJD (vCJD) and bovine spongiform encephalopathy (BSE): 10 and 20 years on: part 2". Folia Neuropatholica. 44 (2): 102–110. PMID16823692.
↑ Nitrini R, Rosemberg S, Passos-Bueno MR, da Silva LS, Iughetti P, Papadopoulos M, Carrilho PM, Caramelli P, Albrecht S, Zatz M, LeBlanc A (August 1997). "Familial spongiform encephalopathy associated with a novel prion protein gene mutation". Annals of Neurology. 42 (2): 138–46. doi:10.1002/ana.410420203. PMID9266722. S2CID22600579.
↑ Jeffrey M, Goodbrand IA, Goodsir CM (1995). "Pathology of the transmissible spongiform encephalopathies with special emphasis on ultrastructure". Micron. 26 (3): 277–98. doi:10.1016/0968-4328(95)00004-N. PMID7788281.
↑ Collins S, McLean CA, Masters CL (2001). "Gerstmann-Straussler-Scheinker syndrome, fatal familial insomnia, and kuru: a review of these less common human transmissible spongiform encephalopathies". J Clin Neurosci. 8 (5): 387–97. doi:10.1054/jocn.2001.0919. PMID11535002. S2CID31976428.
↑ Hope J, Reekie LJ, Hunter N, Multhaup G, Beyreuther K, White H, Scott AC, Stack MJ, Dawson M, Wells GA.; Reekie; Hunter; Multhaup; Beyreuther; White; Scott; Stack; Dawson; etal. (Nov 1988). "Fibrils from brains of cows with new cattle disease contain scrapie-associated protein". Nature. 336 (6197): 390–2. Bibcode:1988Natur.336..390H. doi:10.1038/336390a0. PMID2904126. S2CID4351199.{{cite journal}}: CS1 maint: multiple names: authors list (link)
↑ Will RG, Ironside JW, Zeidler M, Cousens SN, Estibeiro K, Alperovitch A, Poser S, Pocchiari M, Hofman A, Smith PG.; Ironside; Zeidler; Cousens; Estibeiro; Alperovitch; Poser; Pocchiari; Hofman; Smith (April 1996). "A new variant of Creutzfeldt–Jakob disease in the UK". Lancet. 347 (9006): 921–5. doi:10.1016/S0140-6736(96)91412-9. PMID8598754. S2CID14230097.{{cite journal}}: CS1 maint: multiple names: authors list (link)
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