Recombination as a mechanism in the evolution of influenza viruses: a two-year study of ducks in Hong Kong.

An analysis was made of 149 influenza A viruses isolated from ducks in Hong Kong during the period of November 1975 through October 1977. The viruses were isolated five times more frequently from ducks raised in the People's Republic of China than from those raised in Hong Kong. The isolation rate fo viruses was higher from the cloaca than it was from the trachea, but this pattern varied over the two years of investifation. The large number of different combinations (30) of hemagglutinin and neuraminidase genes suggests that recombination of viruses was taking place. Analysis of these combinations showed that their distribution was not random and that certain combinations occured more frequently, and others less frequently, than was expected. The recombination of influenza viruses and the excess or restriction of certain combinations may have implications for the evolution of pandemic strains of influenza virus in humans.