Determination of Scrapie Agent Titer from Incubation Period Measurements in Hamsters

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Abstract
One of the most distinctive and remarkable features of slow virus infections is the prolonged incubation period during which the host is free of disease (1). These long incubation periods terminate with the onset of clinical disease which progresses to death in a relatively short time. Considerable interest has surrounded the mechanisms regulating the length of the incubation periods of the spongiform encephalopathies: scrapie of sheep and goats, transmissible encephalopathy of mink, and kuru and Creutzfeldt-Jakob disease (CJD) of humans (2,3). Factors controlling the length of the incubation period in scrapie include: the dose of agent, the genetic background of the host, the strain and passage history of the agent, the lymphoid system of the host, and the metabolic and endocrinological state of the host (4, 5). The shortest incubation periods are found in scrapie, where hamsters develop clinical disease in two months, while the longest incubation periods approach three decades in kuru and probably CJD (6–8).