Among unconventional agents and unclassified viruses the contributions to this volume focused on prion-related diseases, with special emphasis on bovine spongiform encephalopathy and human spongiform encephalopathies, and Borna disease virus, an agent known since long time to be pathogenic for horses and sheep, which is now discussed as a potential pathogen for humans. Additionally, the volume contains articles about newly discovered viruses like porcine respiratory and reproductive syndrome virus and viruses that are classified only provisionally like African swine fever virus, hepatitis C and E viruses, or the arteriviruses.

Original Papers.- Molecular characterization of hepatitis C and E viruses.- Molecular organization and replication of hepatitis E virus (HEV).- Variability of the envelope regions of HCV in European isolates and its significance for diagnostic tools.- Molecular characterization of positive-strand RNA viruses: pestiviruses and the porcine reproductive and respiratory syndrome virus (PRRSV).- Serological and antigenical findings indicating pestivirus in man.- Molecular analysis of the human coronavirus (strain 229E) genome.- Toroviruses - members of the coronavirus superfamily?.- Molecular biology and evolution of filoviruses.- Borna disease virus: nature of the etiologic agent and significance of infection in man.- Biology and neurobiology of Borna disease viruses (BDV), defined by antibodies, neutralizability and their pathogenic potential.- Pathogenesis of Borna disease.- Brain cell lesions in Borna disease are mediated by T cells.- Borna Disease virus infection and affective disorders in man.- Virus-host interactions in African swine fever: the attachment to cellular receptors.- African swine fever virus genome content and variability.- The biology and molecular biology of scrapie-like diseases.- Analysis of nucleic acids in purified scrapie prion preparations.- Prions and molecular chaperones.- Epidemiology of bovine spongiform encephalopathy and related diseases.- Bovine spongiform encephalopathy: a new disease of cattle?.- Human prion diseases (spongiform encephalopathies).- Brief Reports.- Distribution of cytopathogenic and noncytopathogenic bovine virus diarrhea virus in tissues from a calf with experimentally induced mucosal disease using antigenic and genetic markers.- Establishment of cell lines from bovine brain.