Transmissible spongiform encephalopathy
This article needs attention from an expert in Medicine. The specific problem is: "Cause" section is in fairly bad shape with undue weight. may be able to help recruit an expert. (January 2022) |
Transmissible spongiform encephalopathy | |
---|---|
Other names | Prion disease |
Gerstmann-Sträussler-Scheinker syndrome, feline spongiform encephalopathy, transmissible mink encephalopathy, exotic ungulate encephalopathy | |
Causes | Prion |
Risk factors | Contact with infected fluids, ingestion of infected flesh, having one or two parents that have the disease (in case of fatal familial insomnia) |
Diagnostic method | Currently there is no way to reliably detect prions except at post-mortem |
Prevention | Varies |
Treatment | Palliative care |
Prognosis | Invariably fatal |
Frequency | Rare |
Transmissible spongiform encephalopathies (TSEs) also known as prion diseases,
TSEs of humans include
TSEs in non-human mammals include
Unlike other kinds of infectious disease, which are spread by agents with a
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.
ICTVdb Code[9] | Disease name | Natural host | Prion name | PrP isoform
|
Ruminant |
---|---|---|---|---|---|
Non-human mammals | |||||
90.001.0.01.001. | Scrapie | Sheep and goats | Scrapie prion | PrPSc | Yes |
90.001.0.01.002. | Transmissible mink encephalopathy (TME) | Mink | TME prion | PrPTME | No |
90.001.0.01.003. | Chronic wasting disease (CWD) | Elk, white-tailed deer, mule deer and red deer | CWD prion | PrPCWD | Yes |
90.001.0.01.004. | Bovine spongiform encephalopathy (BSE) commonly known as "mad cow disease" |
Cattle | BSE prion | PrPBSE | Yes |
90.001.0.01.005. | Feline spongiform encephalopathy (FSE) | Cats | FSE prion | PrPFSE | No |
90.001.0.01.006. | Exotic ungulate encephalopathy (EUE) | greater kudu
|
EUE prion | PrPEUE | Yes |
Camel spongiform encephalopathy (CSE)[10] | Camel | PrPCSE | Yes | ||
Human diseases | |||||
90.001.0.01.007. | Kuru | Humans | Kuru prion | PrPKuru | No |
90.001.0.01.008. | Creutzfeldt–Jakob disease (CJD) | CJD prion | PrPsCJD | No | |
Variant Creutzfeldt–Jakob disease (vCJD, nvCJD) | vCJD prion[11] | PrPvCJD | |||
90.001.0.01.009. | Gerstmann-Sträussler-Scheinker syndrome (GSS)
|
GSS prion | PrPGSS | No | |
90.001.0.01.010. | Fatal familial insomnia (FFI)
|
FFI prion | PrPFFI | No | |
Familial spongiform encephalopathy[12] |
Features
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
The clinical signs in humans vary, but commonly include personality changes, psychiatric problems such as
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
There exists evidence that prion diseases may be transmissible by the airborne route.[16]
Note that not all
Cause
Genetics
Mutations in the
The PRNP gene provides the instructions to make a protein called the
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]
- PrPSc is an isomer of PrPC
- Denaturing PrP removes infectivity[22]
- PrP-null mice cannot be infected[23]
- 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]
Multi-component hypothesis
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:
- Incubation time is comparable to a lentivirus
- 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
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
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
See also
References
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- ^ "Variant Creutzfeldt-Jakob disease". World Health Organization. Retrieved 2017-04-25. February 2012. Archived from the original on December 20, 2002.
- ^ "Variant Creutzfeldt-Jakob disease > Relationship with BSE (Mad Cow Disease)". Centers for Disease Control and Prevention. Retrieved 2017-04-25. 10 February 2015.
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- ^ "Prion Disinfection Options - Biosafety & Occupational Health". University of Minnesota. 17 November 2017.
- ^ "ICTVdB : the universal virus database of the International Committee on Taxonomy of Viruses - NLM Catalog - NCBI". www.ncbi.nlm.nih.gov. Retrieved 23 April 2023.
- ^ "Deux chercheurs algériens découvrent la maladie du "chameau fou" à Ouargla". 2018-05-09. Archived from the original on 2018-06-17. Retrieved 2019-03-13.
- ^ Believed to be identical to the BSE prion.
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- ^ "Detecting Prions in Blood" (PDF). Microbiology Today.: 195. August 2010. Archived from the original (PDF) on 2012-03-31. Retrieved 2011-08-21.
- ^ "SOFIA: An Assay Platform for Ultrasensitive Detection of PrPSc in Brain and Blood" (PDF). SUNY Downstate Medical Center. Retrieved 2011-08-19.
- ^ "Transmissible Spongiform Encephalopathies (TSEs), also known as prion diseases | Anses - Agence nationale de sécurité sanitaire de l'alimentation, de l'environnement et du travail". www.anses.fr. 18 February 2013. Retrieved 2017-11-09.
- ^ "Infection Control | Creutzfeldt-Jakob Disease, Classic (CJD) | Prion Disease | CDC". www.cdc.gov. Retrieved 2017-11-09.
- ^ "Surveillance for vCJD | Variant Creutzfeldt-Jakob Disease, Classic (CJD) | Prion Disease | CDC". www.cdc.gov. Retrieved 2017-11-09.
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- ^ "Variant Creutzfeldt-Jakob disease". World Health Organization. Archived from the original on December 20, 2002. Retrieved 2017-11-09.
- ^ "Risk for Travelers | Variant Creutzfeldt-Jakob Disease, Classic (CJD) | Prion Disease". www.cdc.gov. Retrieved 2017-11-09.
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- This entry incorporates public domain text originally from the National Institute of Neurological Disorders and Stroke, U.S. National Library of Medicine [2]
External links
- Transmissible spongiform encephalopathy at Curlie