scrapie(redirected from scrapie agent)
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, abnormal form of a protein found in mammals, believed to cause a group of diseases known as prion diseases or transmissible spongiform encephalopathies. Well-known prion diseases are Creutzfeldt-Jakob disease (CJD) and kuru in humans, scrapie in sheep, bovine
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a slowly developing infectious disease of sheep that is associated with degenerative changes in the central nervous system and characterized by excitability, severe itching, paralysis, and emaciation. First reported in Great Britain in 1732, scrapie is recorded today in Europe, southern Africa, India, Australia, Canada, the USA, and many other areas.
The nature of the causative agent of scrapie has not been determined. A viral hypothesis has been formulated but not substantiated. Some believe the causative agent to be a protein, whereas others believe it to be a special type of polysaccharide. There also is a membrane hypothesis, which states that the biological activity of the causative agent of scrapie is the function of a modified cell membrane.
The causative agent of scrapie is extraordinarily resistant; it can withstand boiling for three hours, is resistant to chemical agents, and preserves well in desiccated pathological material and at low temperatures. Sheep 18 months of age and older are affected. The causative agent is transmitted when sick and healthy animals are housed together and when animals graze on infected pastures. Sheep of various breeds have different susceptibilities to scrapie. Although the disease has been recorded year-round, it occurs more frequently in winter and spring. Scrapie might be related to such human diseases as multiple sclerosis and parkinsonism. The incubation period lasts one to four years. At first, infected animals are characterized by unusual behavior, increased excitability, tremors, and an abnormal gait. Itching is also a characteristic early symptom. Subsequent symptoms include emaciation, incoordination, and paralysis. The animals die several weeks after the appearance of the first symptoms.
Scrapie is diagnosed according to clinical symptoms and histological examination. A treatment has not been developed. Control and preventive measures include the refusal of entry of sheep from an infected country and the slaughter of infected flocks. Some sheep breeders discontinue hereditary lines of sheep among which scrapie has been discovered.
REFERENCESKukhto, A. F. “Pochesukha ovets: skreipi.” In Bolezni ovets. Moscow, 1963.
Andrewes, C. Virusy pozvonochnykh. Moscow, 1967. (Translated from English.)
Andrewes, C. Estestvennaia istoriia virusov. Moscow, 1969. (Translated from English.)
I. A. BAKULOV