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Volume 39, Number 4, August 2006

Sequence comparison between two quasi strains of H6N1 with different pathogenicity from a single parental isolates

Chieh-Ning Hsu, Ching-Ho Wang
Department of Veterinary Medicine, National Taiwan University, Taipei, Taiwan

Received: June 25, 2005    Revised: November 22, 2005    Accepted: December 18, 2005   


Corresponding author:

Ching-Ho Wang, Department of Veterinary Medicine, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan. E-mail: This e-mail address is being protected from spam bots, you need JavaScript enabled to view it


Background and purpose: 

Relationships between gene change and virulence for hemagglutinin (HA) subtypes of avian influenza virus remain inconclusive. In this study, sequences of these nearly identical virus strains were obtained in order to elucidate the relationship between molecular determinants and virulence.




Two strains, with different virulence, of an H6N1 avian influenza virus were isolated from an infected chicken flock. Complete 8-gene fragments from the 2 strains were cloned and sequenced. Putative amino acid sequences were compared.




Comparisons of the sequences from the 2 strains showed 0.65%, 0.79%, 0.28%, 1.41%, 0.80%, 0.20%, 0.43%, and 0.83% differences in PB2, PB1, PA, HA, NP, neuraminidase (NA), NS1 and NS2 proteins, respectively. The M1, M2, and PB1-F2 protein sequences from the strains were identical. The HA cleavage site of both strains contained a single R, despite their difference in virulence. Thus, the difference in virulence might be due to sequences other than the HA cleavage site. Most of the changes were in the HA2 part. The sequence immediately after the HA cleavage site was GILR in the non-virulent strain and GIFG in the virulent strain. The change from E to G at position 106 in the HA, near the receptor binding site, might influence the virulence. Other sequence changes likely to influence virulence were from K to R at position 391 (K391R) in NP protein and from P to T at position 201 (P201T) in NA protein.




The amino acid changes identified in this study may be important in the virulence of influenza viruses.



Key words:

Amino acid sequence, chickens, influenza A virus, molecular sequence data, virulence



J Microbiol Immunol Infect 2006;39:292-296