| Summary: | 碩士 === 國立臺灣大學 === 獸醫學研究所 === 95 === To investigate avian influenza viruses in domestic ducks in Taiwan and possible roles of domestic ducks in transmission chain and cross-species infection of avian influenza, virological and serological surveillance have been conducted on live bird markets and avian farms during 2002-2007. Six viruses of H4N6 subtype were isolated and identified from 3 sources whereas none of the other HA subtypes were found. In total, 16 viral isolates included those 6 H4N6 viruses and the other 10 H4 viruses isolated from migratory and domestic ducks during the period of 1998 to 2006, which kindly provided from the Animal Health Research Institute, Council of Agriculture and the Graduate Institute of Epidemiology College of Public Health, National Taiwan University, were subject to genome sequencing. After sequence comparisons, the divergence of 0.4-14.5% was observed among all 8 individual corresponding genes of H4 viruses from different species and isolation dates. The results revealed further that H4N6 subtype viruses in Taiwanese poultry are genetically diverse and migratory duck might be the one of sources of H4N6 viruses isolated from domestic ducks. HA sequence comparisons showed that only one basic amino acid residues was found around proteolytic cleavage site in HA. It suggested that all 16 H4 isolates were low or non- pathogenic. The deletion of 8 amino acid residues over a region of aa 52-72 in deduced NA sequence was found in A/Duck/Changhua/0648/06 (H4N6), compared to the remaining Taiwanese H4N6 viruses as well. The impact of truncated NA on virus is unclear and awaited for further analyses. Phylogenetic relationships based on all 8 individual corresponding genes among the 16 H4 viruses and reference viruses have indicated that all Taiwanese H4 isolates were distributed into 4 small clusters in Eurasian lineages. The domestic and migratory duck H4 viruses isolated from the same year were grouped together, distingnished separated from the other isolates from different years. It implies that at least 4 invasions of H4N6 viruses from migratory ducks to domestic ones were independently occurred in different years in Taiwan and migratory duck viruses might have not perpetuated and disseminated in the infected domestic duck population. To investigate the prevalence of H4 virus in Taiwanese poultry, serum from several species of domestic poultry collected during 2002-2007 were subjected to hemagglutination-inhibition assays using A/DK/Changhua/5911/2006 (H4N6). Low seroprevalences were observed as the following: 0.38% in chicken (7/1826) over 7.4% of chicken flocks (6/81), 0% in quail (0/96), 0% in duck (0/857), 0% in goose (0/266), respectively. These results showed that H4 subtype virus is not prevalent in poultry in Taiwan. Conclusively, even though Taiwanese H4N6 viruses are quite diverse with each others, all are in Eurasian lineages regardless of their species origins. Furthermore, the finding from this investigation implies that H4N6 viruses might transmit from migratory birds to domestic poultry in Taiwan but might not be disseminated stably and efficiently in new hosts after cross-species infections.
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