Low genetic mixing between avian influenza viruses of different geographic regions.

The degree of genetic relatedness of vRNA segments 1, 2, and 3 of avian influenza A viruses was investigated by molecular hybridization. The results indicate that avian influenza A viruses isolated within a given geographic region are genetically more closely related than strains from different regions, irrespective of the year of isolation and the species from which the virus was isolated. Studies on RNA segment 4 of viruses within the subtype H7 isolated in different regions gave similar results. Thus the genetic composition of avian influenza A viruses appears to be maintained to a rather high degree within a given geographic region and the intrusion of genes from "foreign regions" appears to be taking place with low frequency. The results are discussed with respect to the worldwide distribution of influenza virus genes by migrating birds.