Latent form of Scrapie virus: a new factor in slow-virus disease.

Scrapie is an unusual slow-virus disease of sheep which is very much like kuru and Creutzfeldt-Jakob disease, both fatal, slow neuological diseases of man. In mice, scrapie usually has an incubation period of about 6 months. Intraperitoneal inoculation of virus particles into newborn mice caused no disease, and there was no detectable virus replication for 1 year, but high titers of scrapie were present in the spleen and brain at 18 months. Virus replication occurred in mice injected from 4 days after birth by all inoculation routes, wheter or not they were injected with scrapie virus on day 0. The results suggest that scrapie virus replicates peripherally only in thymocytes, which are not present in mice until a few days after birth. The latent state suggests that the comparable human diseases could appear in later life as a result of perinatal infection. In some respects these diseases resemble premature senility.