Table 4.

Variation of “conserved” residues in the receptor-binding sites of hemagglutinins of H9N2 viruses

Virus	Amino acid residue*
	183	190	226
A/HK/1073/99	H	E	L
Qa/HK/G1/97†	H	E	L
Ck/HK/G9/97†	N	A	L
Dk/HK/Y280/97†	N	T	L
Ck/Beij/1/94†	N	V	Q
Dk/HK/Y439/97†	H	E	Q
Ty/Wis/1/66	H	E	Q
Human H3N2	H	E/D	L
Human H1N1	H	D (N/V)	Q

^*Numbering according to H3. 

^†Different phylogenetic subgroups of H9N2 viruses (13).