Sequences of the hemagglutinin (HA) gene of H9N2 isolates, A/chicken/Shandong/1/02(H9N2), A/chicken/Hebei/1/01(H9N2), and A/chicken/Beijing/1/00(H9N2), from Shandong Province, Hebei Province, and Beijing in Peoples Republic of China have become available at GenBank. They show evidence of recombination with earlier H9N2 isolates.
Recombination in HA is important because it contains the receptor binding domain wich is a regognition sequence used for facilitate entry into a cell. Swapping of the human binding domain with a virulent avian strain is a likely mechanism for generation of a pandemic bird flu virus. H9N2 is the most prevalent bird flu subtype in China and some isolates have a human receptor binding domain.
Recombination in HA of human H3N2 isolates from Korea has also been observed. The 5´ end of the gene comes from earlier H3N2 isolates, while the 3´ end is Fujian-like
Recent H9N2 Korean swine isolates, A/swine/Korea/S81/2004(H9N2), A/swine/Korea/S83/2004(H9N2), A/swine/Korea/S109/2004(H9N2), and A/swine/Korea/S190/2004(H9N2) also have extensive recombination in the neuraminidase (NA) gene. These isolates also have human WSN/33 genes from 1933 and two have PB2 recombination, where half of the gene is human and half is avian.
The extensive amount of recombination in HA and NA as well as recombination between human and avian sequences, is cause for concern that H5N1, which has genes that have reassorted with H9N2 genes in both H9N2 and H5N1 isolates, will soon gain efficient human to human transmission and significant pandemic potential.
*the isolates of H9N2 in recent years in China need a closer look, researchers can find the Chinese version of Vet Journals in F.I.C´s article service*