XK and infection: A H5N1 virus that caused human infections in Hong Kong in 1997 was a reassortant virus that acquired HA from a Gs/GD/1/96 (H5N1)-like virus, NA from a A/teal/Hong Kong/W312/97(H6N1)-like virus, and internal genes from a A/quail/Hong Kong/G1/97(H9N2)-like virus or A/teal/Hong Kong/W312/97 (H6N1)-like virus (Guan et al., 2002; Puthavathana et al., 2005; Gutiérrez et al., 2009).