Late-breaking Poster Asia-Pacific Vaccine and Immunotherapy Congress 2024

Trends in viral replication and lung pathogenesis of influenza A(H1N1)pdm09 viruses from 2009 to 2022 in the ferret model. (#172)

Harry Stannard 1 , Paulina Koszalka 1 , Smitha Georgy 2 , Nikita Deshpande 1 , Saira Hussain 1 , Kanta Subbarao 1 3 , Patrick Reading 1 3 , Ian Barr 1
  1. WHO Collaborating Centre for Reference and Research on Influenza, at the Peter Doherty Institute for Infection and Immunity, Melbourne, VIC, Australia
  2. Melbourne Veterinary School, Faculty of Science, The University of Melbourne, Melbourne, VIC, Australia
  3. Department of Microbiology and Immunology, University of Melbourne, Melbourne, VIC, Australia

Background:

Ferrets are widely considered to be the gold-standard small animal model to study the pathogenesis of influenza viruses, as well as the impact of vaccines and antiviral drugs on influenza infections. This study aims to explore trends in viral replication and lung pathogenesis of A(H1N1)pdm09 viruses from their emergence in 2009 to 2022 using the ferret model. In addition, we aimed to identity contemporary influenza virus strains that demonstrate robust influenza disease, and lower respiratory tract involvement in the ferret, updating the current ferret model for A(H1N1)pdm09 infection.

Methods:

Five cell passaged, plaque-purified human influenza A(H1N1)pdm09 viruses selected from 2009 to 2022 vaccine recommendations (A/California/07/2009, A/Michigan/45/2015, A/Victoria/2570/2019, A/Sydney/5/2021, and A/Victoria/4897/2022) and a A(H3N2) virus, A/Darwin/6/2021 for comparison, were inoculated intranasally into ferrets. At 3- or 5-days post-infection, nasal wash and respiratory tissue (including individual lung lobes) samples were collected to determine viral titres and/or histopathological analysis.

Results:

Our results revealed consistent viral tires in the nasal wash, nasal turbinate, and soft palate tissues of ferrets in all viruses tested. Area under the curve analysis indicated A/Sydney/5/2021 had higher total viral shedding over five days than A/California/07/2009 infected animals. Viral replication in the lung lobes differed between the five strains. A/Sydney/5/2021 also demonstrated the greatest lung tropism at day 5 post infection, with a 1.2, 2.1 and 2.1 log10TCID50 higher mean lung viral titre than the three older strains, although only 0.6 log10TCID50 higher than the most recent A/Victoria/4897/2022 virus. Lung histopathology showed that A/Sydney/5/2021 had significantly higher histopathology scores than earlier strains, with a prominent feature of bronchiolitis and peribronchiolar lymphocyte cuffing. A recent human A(H3N2) virus (A/Darwin/6/2021) in contrast, was not detected in ferret lungs and displayed no histological changes in their lungs.

Conclusions:

While upper respiratory tract viral replication remained similar across the five A(H1N1)pdm09 viruses isolated from 2009 to 2022, the two most recent viruses tested (2021 and 2022) had higher viral titres in the lungs of ferrets and more severe lung pathology compared to the other earlier viruses. This was not observed with a recent A(H3N2) virus (A/Darwin/6/2021), which like other previous A(H3N2) viruses did not replicate in the lungs of ferrets. The A/Sydney/5/2021 ferret infections displayed robust viral loads and histopathology, making it an ideal contemporary virus for exploring the protective efficacy of current and future anti-influenza treatments or vaccines in the ferret model.