Scrapie See prion diseases

scrapie agent A prion which causes a natural disease of sheep and goats, mainly in the northern hemisphere. Affected animals are usually about 3 years old and have intense pruritis and ataxia, which becomes severe before death. They scratch themselves by scraping against fences, hence the name. Recovery in mild cases may be explained by misdiagnosis, which, to be certain, is by histological examination of the brain post-mortem. Mode of transmission is not clear, but probably often vertical. In primates causes a condition similar to Creutzfeldt-Jakob disease. Chimpanzees are not susceptible, and there is no evidence of infection in humans. Goats are more uniformly susceptible to experimental disease than sheep. Injections of brain tissue extract by any route will transmit the disease, but the shortest incubation period (6-9 months) follows i.c. injection. Mice and hamsters can be infected, the virus replicating first in lym-phoid tissue, then in the brain. Injection into mink causes a disease similar to transmissible mink encephalopathy, but the agent so passed will not reinfect mice. Different strains of agent cause slightly different signs and symptoms. Infectivity appears to reside in a small proteinaceous infectious particle called a 'prion'. Prions can be recovered from scrapie-infected brain as a 27-30kDa protein called PrPsc. They appear to be isoforms of a cellular protein of the same amino acid sequence called PrPc. The sequence of the PrPsc gene has been determined. It is believed that the PrPsc, which in contrast to PrPc is highly resistant to proteolysis, can undergo autocatalytic replication without the involvement of nucleic acid. See prion.

Chesebro BW (Editor) (1991) Curr Top Microbiol Immun 172, 228 pp

Prusiner SB (editor) (1999) Prion Biology and Diseases. Cold Spring Harbor Laboratory Monograph 38, New York: Cold Spring Harbor Laboratory Press

Prusiner SB (1999) In Encyclopedia of Virology, Second edition, edited by A Granoff and RG Webster. London: Academic Press, p. 1388

scrum-pox A contagious disease of the facial skin of rugby players. Etiology variable but Human herpesvirus 1 and Vaccinia virus have been implicated. Almost exclusively confined to forwards.

A survey of 30 rugby clubs identified 48 infected players, of whom 47 were forwards and one a scrum-half. Of the 47 forwards, 32 played in the front row, 8 in the second row and 7 in the back row of the scrum. 23 of them reported direct contact with opponents who had obvious facial lesions; 34 had similar contacts within their own teams. Some of the cases were treated with idoxuridine. See also Norwalk virus.

Synonyms: herpes gladiatorum; herpes rugbeiorum; herpes venatorum; prop-pox

SDAV Sialodacryoadenitis virus. See Rat coronavirus.

SDS Sodium dodecyl sulfate, an anionic detergent.

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