Theses and Dissertations


Yifei Xu

Issuing Body

Mississippi State University


Wan, Xiu-Feng (Henry)

Committee Member

Hanson, Larry

Committee Member

Perkins, Andy D.

Committee Member

Hoffmann, Federico G.

Committee Member

Zhao, Nan (Alan)

Date of Degree


Document Type

Dissertation - Open Access


Veterinary Medical Sciences

Degree Name

Doctor of Philosophy


College of Veterinary Medicine


Veterinary Medical Science Program


Periodic introductions of influenza A viruses (IAVs) from wild birds contribute to emergence of novel strains that infect domestic poultry, lower mammals, and humans, but the mechanisms of emergence are unclear. The objectives of this dissertation research are to infer the genesis of two emerging IAVs, low pathogenic avian influenza (LPAI) H10N8 and highly pathogenic avian influenza (HPAI) H7N8 viruses, and to characterize the antigenic diversity and genetic evolution of contemporary H7 avian influenza viruses (AIVs) from North America. First, AIVs that are genetically close to the human H10N8 isolate were recovered at the live poultry market (LPM) visited by the first H10N8 patient. High seroprevalence of H10 virus was observed in ducks and chickens from five LPMs in the region. These findings suggested that LPM was the most probable source of human infection with the H10N8 virus, and this virus appeared to be present throughout the LPM system in the city. Second, the novel H7N8 virus most likely circulated among diving ducks in the Mississippi flyway during autumn 2015 and was subsequently introduced to Indiana turkey, in which it evolved from LPAI into HPAI. H4N8 IAVs from diving ducks possess a gene constellation comprising five H7N8–like gene segments. These findings suggest that viral gene constellations circulating among diving ducks could contribute towards the emergence of IAVs that can affect poultry. Diving ducks may serve as a unique reservoir, contributing to the maintenance, diversification, and transmission of IAVs in wild birds. Third, antigenic and genetic characterization of 93 H7 AIVs from North America showed limited antigenic diversity. Gradual accumulation of nucleotide and amino acid substitutions in the H7 gene of AIVs from wild and domestic birds caused a wide genetic diversity. These findings suggested that continuous genetic evolution has not led to significant antigenic diversity for contemporary H7 AIVs isolated from wild and domestic birds in North America. In summary, these findings not only improve our understanding of the ecology and evolution of IAVs but also provide information for formulation of effective disease prevention and control strategies.