Epidemiological analysis of H4N6 viruses isolated from wild ducks and domestic ducks in Taiwan
Date Issued
2009
Date
2009
Author(s)
Lin, Yu-tsun
Abstract
Wild birds were considered as natural reservoir of influenza A viruses. Hence, they always play important roles in the issue for epidemiology of avian influenza. This study sought to understand the transmission of H4N6 viruses between wild birds and domestic birds in Taiwan. We sequenced total of eight genome segments of ten H4N6 viruses isolated from wild ducks in Taiwan between 1998 and 2007 and twelve H4N6 viruses isolated from domestic ducks in Taiwan in 1999, 2006 and 2007. Sequences mentioned above are analyzed and compared with the sequences of H4N6 viruses, Taiwanese isolates and H5 subtype viruses available in the public database. All of Taiwanese domestic duck isolates, part or all of eight genome sequences are classified in the same sublineage with the sequences of Taiwanese wild duck isolates in phylogenetic trees. The similarity of H4 and N6 nucleotide sequences between wild duck and domestic duck isolates can be as high as 99.9 % (range from 87.1 to 99.9 %). These analyses indicated that the transmission of H4N6 viruses between wild ducks and domestic ducks in Taiwan might exist. Therefore, the domestic duck will be exposed to the risk of influenza virus infection when the wild ducks carrying viruses pass through. In H4 phylogenetic tree, the Taiwanese domestic isolates isolated in the year of 2006 and 2007 did not fall under the same sublineage, which is probably due to the fact that the virus had already disappeared in domestic duck populations in 2006. All Taiwanese H4N6 isolates were found in the sublineages with Eurasian isolates, not form an independent sublineage. In recombination analysis, the rate of recombination of Taiwanese H4N6 isolates was 4/169 (2.4%). In serology survey in Taiwan, we found that some chicken serum samples (7/8403; 0.08 %) have low HI antibody titers ( 16X ~ 32X ) for H4. It indicated that chicken in Taiwan might have been exposed to H4 virus but without significant inter-species transmission. Besides, positive-selection analyses were performed by using codon-based substitution models and found residues 285 and 287 of N6 gene and residue 105 of NP gene are possible positive selection sites. These specific codons detected might be helpful in clarifying the driving force of wild duck and domestic duck influenza virus evolution and in selecting specific targets for selective pressure.
Subjects
H4N6 subtype
inter-species transmission
phylogenetic analysis
recombination
serological survey
Type
thesis
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