Date of Award


Document Type


Degree Name

Master of Science (MS)


Biomedical Sciences


Microbiology, Immunology, and Biochemistry

Research Advisor

Richard J. Webby, Ph.D.


Kui Li, Ph.D.; James Patrick Ryan, Ph.D.


A(H1N1), BEAST, Influenza, Pandemic, Phylogenetics, Zoonosis


The 2009 pandemic influenza A(H1N1)pdm09 virus emerged from the swine population. Despite frequent zoonotic events, swine influenza viruses had not become established in humans previously and little is known about host-barriers which prevent swine influenza viruses from efficiently infecting humans. Thus, the emergence of the H1N1pdm09 viruses in humans and the subsequent reverse zoonoses back to swine offered an extremely valuable opportunity to expand current knowledge. We used our active swine farm surveillance platform in combination with viruses from the USDA surveillance program to look for evidence of interspecies transmission of H1N1pdm09 viruses in the US. We found phylogenetic evidence for multiple human to swine transmission events, all of which were transient suggesting that the human adapted viruses of swine origin had lost some fitness for swine. Based on our phylogenetic analysis we selected representative H1N1pdm09 viruses from the tips of swine and human sub-lineages for further study. Intriguingly, we found that after being re-introduced into the swine population, the human H1N1pdm09 viruses rapidly lost replicative fitness in human cells. Together these data provide support for a model where transmission of viruses from human to swine leads to rapid adaptation for the swine host which comes at the expense of optimal fitness for human.




2019-019-Darnell-DOA.pdf (360 kB)
Declaration of Authorship