|A newly discovered virus, human metapneumovirus (hemp), responsible for respiratory disease in young children, is closely related to subgroup C isolates of the prototype metapneumovirus, avian pneumovirus (APV). APV is a major cause of significant economic losses in the poultry industry in Europe. Current diagnostic techniques cannot detect these metapneumoviruses and as a result the significance and distribution of hemp subgroup C APV are not known. Thus the burden of disease from these agents cannot be assessed. The proposal addresses these problems by generating new, standardised, detection and characterisation assays, developed for commercial use. Using reverse genetics techniques for both hemp and APV, the molecular biology, aspects of pathogen city and host specificity will be analysed This will also generate recombinant viruses which will be the foundation for future rational vaccine design.