press; Trifonov et al., 2009; Garten et al., in press and http://influenza.bio.ed.ac.uk; CDC, 2009a; Shortridge et al., 1977).
Given that S-OIV contains genes of Eurasian origin, we included in our phylogenetic analyses 15 newly sequenced swine influenza viruses from Hong Kong, sampled in the course of a surveillance program conducted since the early 1990s. The viruses were a mixture of seven H1N1 and eight H1N2 subtypes, and viruses belonging to the classical, Eurasian avian-like, and triple-reassortant swine lineages were all present. Both Eurasian and triple-reassortant strains were isolated in Hong Kong in 2009. Extensive reassortment among these three virus lineages was also observed from the Hong Kong surveillance data (Supplementary Table A14-3), with reassortment between Eurasian avian-like and triple-reassortant swine lineages occurring as early as 2003 (for example, Sw/HK/78/2003).