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).

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.

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.

[14] 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.

[15] 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.

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.

A total of 721 cases of scrapie were detected in small ruminants in the 27 Member States and in the United Kingdom in respect of Northern Ireland: 538 in sheep (557 in 2022) and 183 in goats (224 in 2022).Surveillance of TSE in cervids is voluntary in the.

[21][22] Protein could be the infectious agent, inducing its own replication by causing conformational change of normal cellular PrPC into PrPSc.

Purified PrPC appears unable to convert to the infectious PrPSc form, unless other components are added, such as RNA and lipids.

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.

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.

[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.

[clarification needed] It is very hard to map the spread of the disease due to the difficulty of identifying individual strains of the prions.

[36] The Centers for Disease Control and Prevention (CDC) have been keeping surveillance on CJD cases, particularly by looking at death certificate information.

Surveillance studies showed the endemic of CWD in free-ranging deer and elk spread in northeastern Colorado, southeastern Wyoming and western Nebraska.

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.

[46] 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.

[48] 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.