Isolation of ortho- and paramyxoviruses from domestic poultry in Hong Kong between November 1977 and October 1978 and comparison with isolations made in the preceding two years.

Regular surveillance of domestic poultry from Hong Kong and southern China for influenza A viruses was conducted in Hong Kong from November 1977 to October 1978. Tracheal or cloacal swabs taken from 2844 ducks, geese and fowls yielded 141 influenza viruses of which 135 were derived from ducks. The isolation rate from ducks was twice as high from the cloaca (12.1 per cent) as from the trachea (5.8 per cent). The overall frequency of isolation was 10.3 per cent and 2.3 per cent for poultry originating from southern China and Hong Kong, respectively. Fourteen of the influenza antigenic combinations recorded in this period of surveillance had been obtained in the previous two years while five were new--H2N2, H2Nav6, Hav5N2, Hav6Nav1 and Hav7Nav4. The number of combinations recorded over three years was 39, the most frequent being Hav4Nav1 which comprised one fifth of the total. All the combinations found in geese and fowl isolates, apart from Hav7Nav6 found in a fowl, have been recorded in duck isolates. Faecal/oral transmission of virus from infected pond water was thought to be an important factor in the high incidence of influenza in ducks. The existence of a large number of combinations of haemagglutinin and neuraminidase antigens and the isolation of two viruses from the cloaca suggest that recombination is occurring in these birds. Reasons for the limited isolation of some antigenic combinations are considered. The paramyxoviruses, Newcastle disease virus and the Hong Kong avian paramyxovirus, were also isolated. Over the three year period the isolation rate of influenza and paramyxoviruses from ducks appeared to be cyclical and seasonal. Influenza was found mainly in the summer and paramyxoviruses in the winter.