Cocirculation of avian H9N2 and contemporary "human" H3N2 influenza A viruses in pigs in southeastern China: Potential for genetic reassortment?

Pigs are permissive to both human and avian influenza viruses and have been proposed to be an intermediate host for the genesis of pandemic influenza viruses through reassortment or adaptation of avian viruses. Prospective vi rological surveillance carried out between March 1998 and June 2000 in Hong Kong, Special Administrative Region, People's Republic of China, on pigs i mported from southeastern China, provides the first evidence of interspecie s transmission of avian H9N2 viruses to pigs and documents their cocirculat ion with contemporary human H3N2 (A/Sydney/5/97-like, Sydney97-like) viruse s. All gene segments of the porcine H9N2 viruses were closely related to vi ruses similar to chicken/Beijing/1/94 (H9N2), duck/Hong KongIY280/97 (H9N2) , and the descendants of the latter virus lineage. Phylogenetic analysis su ggested that repeated interspecies transmission events bad occurred from th e avian host to pigs. The Sydney97-like (H3N2) viruses isolated from pigs w ere related closely to contemporary human H3N2 viruses in all gene segments and had not undergone genetic reassortment. Cocirculation of avian H9N2 an d human H3N2 viruses in pigs provides an opportunity for genetic reassortme nt leading to the emergence of viruses with pandemic potential.