Viral pathogenesis: mechanism of acute and persistent infections with paramyxoviruses.

Paramyxoviruses are a group of infectious agents that cause a variety of diseases in man and animals, such as mumps, measles, respiratory infections in infants, Newcastle disease in chickens, and canine distemper. Besides these acute diseases, the viruses of this group are known to often induce long-term persistent infections and have long been suspected to be involved in chronic neurological diseases such as subacute sclerosing panencephalitis and multiple sclerosis. Viral pathogenesis, the way in which a virus produces a disease, involves a complex interaction between the virus and the infected organism. Thus, it is, in general, not easy to define the molecular basis for pathogenesis with any given virus. A virus is pathogenic for a particular host if it can infect the host and produce signs and symptoms of disease. A virus strain is said to be more virulent than another if it regularly produces more severe signs or disease in a host in which both strains are pathogenic. Thus, one way to study such a difficult problem as pathogenesis is to define the factors responsible for the differences in virulence. In this context, Newcastle disease virus (NDV) provides a good research model since it comprises a wide variety of well-characterized strains which differ markedly in virulence but are indistinguishable from each other by conventional serology. The processes of diseases in long-term persistent infections are even more complicated. Therefore, efforts have mainly concentrated on elucidation of the mechanism of induction of persistent infections in cultured cells. Of the paramyxoviruses, Sendai virus (hemagglutinating virus of Japan, HVJ) has probably been best studied in this respect. In this article, we illustrate our recent attempts to answer the questions related to acute and persistent infections with NOV and Sendai virus as well as those reported by other authors for different viruses.