Genetic characteristics of avian influenza a viruses isolated from Thai free-grazing ducks and their pathogenicity potential in animal models

Abstract

Influenza A viruses (IAVs) can infect several animal species and humans. In Thailand, free-grazing ducks are reservoir hosts of influenza A virus. The free-grazing ducks are potentially interface with wild birds and domestic birds and subsequently cause interspecies transmission of IAVs. This thesis composes of three study phases. Phase 1 is surveillance of influenza A in free-grazing ducks. Phase 2 is genetic characterization and diversity analysis of influenza A viruses from free-grazing ducks. Phase 3 is challenge of influenza A viruses isolated from free-grazing ducks in animal models. For phase 1, multi-years surveillance of IAVs in free-grazing ducks was conducted in central and lower northern parts of Thailand. Our results found 1.77% of influenza A virus from oropharyngeal swabs (n=2,012) and cloacal swabs (n=2,012), 70.24% of influenza A antibody and 6.40% of specific H5 subtype antibody from serum samples (n=1,959). Of 71 IAV positive samples, 15 subtypes of IAVs could be identified and the predominant subtypes were subtypes H3N8 and H4N6. For phase 2, representative viruses (n=26) were characterized by whole genome sequencing. The results from phylogenetic analysis of 8 genes of Thai influenza viruses revealed new reassortant viruses (n=3) (H11N9, H4N6 and H11N7). While the origin of most Thai IAVs was from Avian Eurasian lineage I. According to the origins of each gene, the gene constellation of 26 representative viruses was identified to 24 patterns. For phase 3, influenza A virus subtype H1N3 (n=1) and H11N9 (n=1) were selected for animal challenge study. Both H1N3 and H11N9 viruses can infect chickens and quails. Chickens and quails can shed the viruses and develop antibody response during the experiment period. The viruses can also transmit to contacted chickens and quails. In summary, our results confirmed that free-grazing ducks are important reservoir hosts of influenza A virus and the H1N3 and H11N9 viruses from free grazing ducks were able to infect and transmit to chickens and quails. Thus, the results from multi-years influenza A surveillance in free-grazing ducks, the genetic characteristics and the pathogenicity of the viruses in animal models provided useful information for influenza prevention and control measures both in animals and humans in the future.