Myxoviruses.

Myxoviruses can be divided into 2 groups, orthomyxoviruses and paramyxoviruses. the former comprise the influenza group which is subdivided into types A,B and C. Influenza B and C are purely human pathogens but influenza A, which includes a large number of antigenic subtypes, occurs in nature in pigs, horses, birds and man. All influenza A viruses irrespective of origin are chemically, biologically and genetically related. The epidemics which they cause are curious and puzzling and are an important cause of morbidity. Paramyxoviruses consist of human and animal parainfluenza viruses. The former comprise parainfluenza types 1,2,3 and 4 and mumps viruses, and, rather less certainly, measles and respiratory syncytial virus. The main animal paramyxoviruses are parainfluenza 3 (agent of shipping fever) in cattle; NDV (cause of fowl pest) and Yucaipavirus in birds; Sendai and PVM in mice; Nariva virus in rodents; possibly bovinerespiratory syncytial virus; and SV5 and SV41 in monkeys. The viruses and their place in nature will be reviewed.