Genetic relatedness of hemagglutinins of the H1 subtype of influenza A viruses isolated from swine and birds.

The hemagglutinin (HA) gene of the influenza virus subtype H1N1 isolated from pigs and birds has been analyzed by the hybridization technique. According to the RNase protection data the HA genes of recent isolates from pigs in Northern Europe are genetically more closely related to those of isolates from birds in Europe and North America than to those of isolates from pigs in the United States, Taiwan, and Italy. Thus, two different H1N1 subtypes are circulating in the pig population. The results are consistent with the view that H1N1 viruses can be transmitted from birds to pigs and/or vice versa.