An overview of animal prion diseases

Abstract

Prion diseases are transmissible neurodegenerative conditions affecting human and a wide range of animal species. The pathogenesis of prion diseases is associated with the accumulation of aggregates of misfolded conformers of host-encoded cellular prion protein (PrPC). Animal prion diseases include scrapie of sheep and goats, bovine spongiform encephalopathy (BSE) or mad cow disease, transmissible mink encephalopathy, feline spongiform encephalopathy, exotic ungulate spongiform encephalopathy, chronic wasting disease of cervids and spongiform encephalopathy of primates. Although some cases of sporadic atypical scrapie and BSE have also been reported, animal prion diseases have basically occurred via the acquisition of infection from contaminated feed or via the exposure to contaminated environment. Scrapie and chronic wasting disease are naturally sustaining epidemics. The transmission of BSE to human has caused more than 200 cases of variant Cruetzfeldt-Jacob disease and has raised serious public health concerns. The present review discusses the epidemiology, clinical neuropathology, transmissibility and genetics of animal prion diseases.

Bovine spongiform encephalopathy and food safety

“…There is no evidence that BSE can be transmitted between living cattle. This is in marked contrast to the horizontal infectivity of scrapie in sheep and CWD in deer [16][17][18] .…”

“…At the peak of the epidemic 1,000 cases were being diagnosed each week in the UK 18 . The feeding of MBM to cattle was banned in the UK in 1988, but because of the long incubation period and initially ineffective implementation of the feed ban, clinical incidence continued to rise, peaking in 1992.…”

“…Cases of TSE were also diagnosed in two domestic goats 20 and a number of domestic cats 8,18 . All these cases were attributed to ingestion of BSE prions in beef or processed feed.…”

Neurobehavioral Testing in Prion Disease Studies

“…Similar to sheep, discrete clinical phenotypes have been identified in goat scrapie, namely a "scratching syndrome" characterized principally by pruritus and a "drowsy syndrome" characterized by decreased activity and depression absent pruritus [21,45,46]. However additional features have been reported, including teeth grinding, irritability, and heightened alertness [42]. Additional noted differences between scrapie-infected sheep and goats include hyperesthesia in goats (as opposed to hypoesthesia in sheep) and nibbling of the body in goats (as opposed to rubbing of the body in sheep) [21].…”

“…Accordingly, three profiles of clinical disease have been described, namely (1) a pruritic form, (2) a paralytic form (which lack pruritus), and (3) an atypical cerebellar (Nor98) form [41]. The neurologic signs of scrapie are wide-ranging, and include mentation abnormalities (e.g., hyperresponsiveness), motor deficits (e.g., incoordination, exaggerated gait, hypermetria, ataxia, tremors), visual deficits (including nystagmus and blindness), loss of the menace response, dysphagia, and dysphonia [42,43]. Although not always the case, deficits in locomotion, including hypotonia, proprioceptive deficits, reduced withdrawal reflex, and ataxia, are reported to occur later in disease [27,43].…”