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.

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Extended observations on the secretion of an influenza virus inhibitor in the colostrum of a Caucasian donor.

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Animals↗

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Influenza viruses from avian and porcine sources and their possible role in the origin of human pandemic strains.

Studies on influenza viruses from feral ducks trapped in Canada in August 1976, gave a 26% isolation rate from cloacal samples of juvenile birds. Several different influenza A viruses were isolated, some of which possessed novel hemagglutinin and/or neuraminidase antigens. Influenza A viruses isolated from the rectum of feral ducks replicate in the upper respiratory tract and also in the intestinal tract of feral and domestic ducks. Representative human influenza viruses of the H0N1, H3N2 and Hsw1 N1 subtypes replicate in the upper respiratory tract of ducks but not in the intestinal tract. The A/Hong Kong/68 [H3N2] influenza virus that has not been isolated from man for several years was recently isolated from pigs originating from The People's Republic of China. A/Victoria/3/75-like influenza viruses that are currently circulating in man were also isolated from pigs. Both the A/Hong Kong/68 and the A/Victoria/75-like viruses transmitted readily from pig to pig in experimental studies. The susceptibility of ducks and pigs to infection with human influenza viruses suggests that these animals may play an important role in the ecology of influenza A viruses.

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