Developing an in vitro approach to study transmission of respiratory viruses

A key area of current influenza research attempts to understand the genetic basis of transmissibility. We do not know why the particular swine influenza virus that emerged in Mexico in 2008/9 caused a pandemic where as other swine influenza viruses, to which humans are exposed, did not. However the large number of experiments currently performed with ferrets use small animal numbers and crude readouts, and do not adequately measure difference in transmissibility between different viruses that might have large epidemiological impacts. For example, the length of contagiousness is not measured. Instead of using many more sentinel animals, we propose to develop methodology whereby sentinel animals are replaced by cultures of human airway epithelium that recapitulate the innate barriers that respiratory viruses must overcome before they initiate infection.

The project will use the H1N1 2009 pandemic strain of influenza A virus as a model because we and others already have a body of results generated in ferrets to compare and validate the in vitro alternative. The idea is to allow infected donor ferrets to breathe into a chamber as if in a small room or confined space. We will ask whether the air breathed out will and initiate infection on a cell culture placed downstream. The days on which infected animals are contagious will be compared for different viruses to measure increases or decreases in transmission.

Once methodology is established, we will move to replacing the infected donor animals with infected airway cultures to assess the environmental conditions that affect transmission of different respiratory viruses through the air. Experiments showing influenza virus transmission to be optimal at dry and cold conditions are often used to explain the winter seasonality of influenza. But parainfluenza virus outbreaks occur in summer, so we aim to assess the effect of humidity and temperature on transmission of PIV and other respiratory pathogens through the air.

• The 3Rs across Europe webinar series 2020: Reducing the use of animals for studying transmission of respiratory viruses
• 2019 Research Review: Ferrets and flu transmission studies
• Further Funding: NC3Rs Project Grant, Highly differentiated cultures of ferret airway epithelium for the study of respiratory viruses, including influenza, April 2011, £125,349