Abstract
Among the different strains of avian paramyxoviruses isolated from migrating feral ducks, two were identified as Newcastle disease viruses (NDV) and the five others would correspond to a new serotype for which we suggest the name of Duck/Mississippi/75 virus. The characteristics of this new serotype are as follows: (1) Duck/Mississippi/75 virus is able to grow as well in allantoic as in amniotic cavities of embryonated hen's eggs; (2) the haemagglutinin and haemolytic activities can be detected with hen red blood cells; (3) the neuraminidase hydrolyses the alpha 2 leads to 3 bonds of the fetuin substrate and its pH activity could be species specific. Antigenically, this serotype is different from all human and animal paramyxoviruses, in spite of an antigenic relationship with NDV.