Persistent Paramyxovirus Infections in Vitro and in Vivo

Abstract

Epidemic disease based on a chain of virus transmission between acutely infected individuals is of a relatively recent origin. Prior to the existence of societies including in excess of tens of thousands of people a continued virus perseverance required persistence in individuals of the infectious agent in the absence of obvious signs of disease. Thus not many millenia ago viruses only occurred in the form of persistent infections. This talent for persistence has remained with most different kinds of viruses till today. Persistence of viruses of different nature infer various forms of virus-cell interactions. DNA viruses or retroviruses may sequester into forms of DNA which persist in an episomal state or integrated into host cell DNA. RNA viruses lacking a reverse transcriptase only can persist under conditions when the expression of the genome is quantitatively or qualitatively limited so that the lytic destruction of cells is suppressed. In addition these viruses in spite of their continued replication should not reveal their presence in cells by any introduction of changes of antigens in the cytoplasmic membrane. If such changes occurred a normally functioning immune surveillance system could identify and possibly remove infected cells. The persistence of a lytically replicating virus under conditions of a yielding immunity represents a special situation which will not be discussed in this article. However in some of the conditions to be presented the virus initiates an infection in the central nervous system of an immature individual.