摘要：

In 1954, the late Bjorn Sigurdsson drew attention to an unusual class of slow infection distinguished by a prolonged incubation period and a protracted symptomatic phase. Sigurdsson's concept of slow infection resulted from his observations on the natural history of a group of diseases of Icelandic sheep. In this review, the focus is on one of these diseases, visna, as a prototype of slow infections caused by viruses, and as a paradigm of the challenging questions raised by slow infections: the persistence of virus in the face of the host's defensive response, the strikingly slow pace of replication of virus, and the basis of the tissue lesions. Because visna virus is closely related to RNA tumor viruses, these central issues are discussed against the background of the structure and replication of RNA tumor viruses. In particular, the hypothesis is advanced here that the persistence of visna virus is the consequence of its ability, held in common with RNA tumor viruses, to transfer its genetic information to a DNA replica, or provirus, that resides in the cell and allows the virus to elude the host defensive response.

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