George Charbonneau from South West Ontario Veterinary Services, Swine-Origin H1 IAV Shows Sustained Infectivity in Aerosols

The relative importance of human influenza virus transmission via aerosols is not well understood but some experimental data suggest that aerosol transmission may occur in humans in some cases.  These US Centers for Disease Control (CDC) researchers wanted to evaluate the longevity of influenza viruses in aerosols generated in the laboratory. A panel of H1 viruses that exhibit diverse transmission profiles in the ferret model, including four human isolates of swine origin (referred to as variant) and a seasonal strain were used in the study.

The researchers found the following:

  • Influenza viruses known to transmit efficiently through the air display enhanced stability in an aerosol state for prolonged periods compared to those viruses that do not transmit as efficiently through the air.
  • Ferrets exposed to very low levels of H1 influenza virus (≤17 PFU) in aerosols aged for 15 or 30 min became infected.
  • Ferrets ( 5 of 6) were found to be shedding virus in nasal washes at titers on par with ferrets who inhaled higher doses of unaged influenza virus.

Each time a swine influenza virus transmits to a human, it provides an opportunity for the virus to acquire adaptations needed for sustained human-to-human transmission. These results show that highly transmissible influenza viruses display enhanced stability in an aerosol state compared to viruses that do not transmit as efficiently.

Take Home Message:

  • Public Health officials continue to evaluate the human to human transmission risk of airborne swine-origin influenza viruses.
  • Determination of the molecular markers that affect the longevity of airborne influenza viruses would improve the ability to quickly identify emerging strains that could present a threat to public health.
  • If swine origin IAV strains that affect humans could inherit the ability to transmit from human to human by aerosol over long distances rather than the more common droplet infection they would quickly pose a more significant public health risk.

Ref:  Pulit-Penaloza JA, Belser JA, Tumpey TM, Maines TR.   Swine-Origin H1 Influenza Viruses Isolated from Humans Exhibit Sustained Infectivity in an Aerosol State.  Appl Environ Microbiol. 2019 May 2;85(10). pii: e00210-19. doi: 10.1128/AEM.00210-19. Print 2019 May 15.

Submitted by George Charbonneau DVM