[Significance of hemagglutinins for the pathogenicity of avian influenza viruses].

In addition to acute viral diseases, persistent infections have attained considerable interest in recent years. Such persistent infections are characterized by extended time periods in which the infecting virus remains within the organism before the eventual appearance of manifest symptoms. These infections may be evoked by a variety of virus species resulting in a diversity of pathogenic reactions and clinical manifestations. The mechanisms of viral persistence, where known, also appear to be quite diverse. As far as space permits, some examples of persistent infections will be presented and the mechanisms of the pathogenesis of the resulting diseases will be discussed.