Respiratory Viruses

Acute respiratory disease, including the common cold, influenza-like illness, croup, bronchiolitis, and viral pneumonia, can be caused by a wide variety of viral and non-viral agents. Among the viruses, those with RNA genomes tend to play a more prominent role, particularly among immunologically intact individuals. DNA viruses are also associated with respiratory disease. The characteristics of the viruses most often associated with respiratory disease are described briefly in the chapter. Three distinct types of influenza viruses are recognized, influenza A virus, influenza B virus, and influenza C virus, based on antigenic differences in the nucleoprotein and matrix proteins. All three viruses share certain characteristics, including the presence of a viral envelope containing glycoproteins important for viral entry and egress from cells, and a segmented genome. The standard nomenclature for influenza viruses includes the influenza type, place of initial isolation, strain designation, and year of isolation.