Evaluation of Coronavirus Re-infection and the Transmissibility of Emerging Influenza Viruses
Restricted (Penn State Only)
- Author:
- Field, Cassandra
- Graduate Program:
- Molecular, Cellular, and Integrative Biosciences (PHD)
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 08, 2024
- Committee Members:
- Melissa Rolls, Program Head/Chair
Anthony Schmitt, Major Field Member
Moriah Szpara, Outside Unit & Field Member
Girish Kirimanjeswara, Major Field Member
Troy Sutton, Chair & Dissertation Advisor - Keywords:
- virology
influenza virus
coronavirus
pandemic
respiratory virus
viral transmission
ferret
hamster
emerging viruses - Abstract:
- Influenza viruses and coronaviruses are respiratory pathogens that have caused several pandemics throughout the 20th and 21st centuries. However, our understanding of how these viruses emerge and transmit remains limited. In order to better predict and prepare for future pandemics, this thesis evaluates several attributes of both influenza viruses and coronaviruses. In Aim 1 we evaluated the durability of protection against SARS-CoV-2 re-infection in the Syrian hamster model. While antibody responses to endemic coronaviruses are known to wane over time, the longevity of protection against SARS-CoV-2 re-infection was unknown. Therefore, we established the Syrian golden hamster as a model for SARS-CoV-2 infection, and then inoculated hamsters at several intervals post-primary infection to determine the length of protection. Hamsters infected with SARS-CoV-2 exhibit body weight loss, viral replication in the nasal turbinate and lung, and histopathological features in the lung that model COVID-19. Infected animals mount a robust antibody response that is maintained for at least 6 months, and were protected against clinical illness upon re-infection. However, breakthrough infection did occur despite high titers of antibodies, indicating that antibody titers may not be indicative of sterilizing immunity. In Aim 2 we evaluated the relationship between donor inoculation dose of influenza virus and transmission to respiratory contacts. Because transmission in animal models is a key component of the risk assessment of emerging influenza viruses, it is important that animal models accurately model the physiology of transmission in humans. We inoculated donor ferrets with 10 to 100-fold decreasing doses of influenza virus and then measured the dose which resulted in transmission to 50% of respiratory contacts to determine the transmissible dose 50% (TD50). The 2009 H1N1 and 1968 H3N2 pandemic viruses transmitted at low inoculation doses while a zoonotic avian virus, H7N9, maintained transmission to 75% of contacts at high to moderate doses. Evaluating the TD50 of these viruses allows us to shift to a risk assessment model in which emerging influenza viruses can be described on a scale of transmissibility as opposed to a binary model of transmissible or not transmissible. Finally, in Aim 3 we evaluated the contribution of influenza virus polymerase activity to replication and airborne transmission. We report that the 1968 H3N2 virus has significantly higher polymerase activity than the 2009 H1N1 virus, despite growing to lower titers in vitro and in vivo. To delineate why two pandemic influenza viruses would have significantly different polymerase activity, we interchanged the polymerase segments (PB2, PB1, PA, and NP) between these two viruses. Viruses with the interchanged polymerases were found to have attenuated viral growth in vitro, and reduced or abolished airborne transmission in ferrets. Subsequently, we generated single gene reassortant viruses to assess compatibility between the polymerase and the HA, NA, M, and NS segments. Interchanging the NS segment between the 2009 H1N1 and 1968 H3N2 viruses was found to be attenuating, as well as introducing the HA from the H1N1 virus in the H3N2 virus background. However, re-introducing the NS and/or HA segments to the viruses with an interchanged polymerase did not restore viral replication. Therefore, the reduction in viral replication and airborne transmission that resulted from interchanging polymerases, cannot be directly attributed to incompatibility with the functionality of the polymerase, but is likely due to other gene segment interactions. Collectively, this thesis examines several properties of pandemic respiratory viruses that provide insight to the risk assessment of emerging influenza viruses and coronaviruses. Therefore, these studies can help the public health and research communities to better prepare for and mitigate the impact of future influenza and coronavirus pandemics.