Volume 5 Supplement 1
Transmissibility of pandemic H1N1 and genetically related swine influenza viruses in ferrets
© Yen et al; licensee BioMed Central Ltd. 2011
Published: 10 January 2011
Zoonotic infections with swine influenza viruses have occurred sporadically in the past. However, sustained human-to-human transmission of a swine virus did not occur until the emergence of the 2009 pandemic H1N1 (H1N1pdm) virus. H1N1pdm possesses a unique gene combination with gene segments derived from the North America triple reassortant (PB2, PB1, PA, HA, NP, and NS) and the Eurasian avian-like (NA and M) swine influenza viruses.
To identify molecular determinants that enable sustained human-to-human transmission, we compared the direct contact and aerosol transmission efficiency of the pandemic viruses with related swine influenza viruses in ferrets. The transmission potential of seasonal H3N2 [A/Wuhan/359/95 (Wuhan95)], H1N1pdm [A/California/4/09 (CA04) and A/HK/415742/09 (HK415742)], and genetically related swine influenza viruses [A/sw/HK/4167/99 (H1N1) (swHK4167), A/sw/Arkansas/2976/ 02 (H1N2) (swAR2976), A/sw/HK/915/04 (H1N2) (swHK915) and A/sw/HK/201/ 10 (H1N1) (swHK201)] were studied. Ferrets were inoculated with 105 TCID50 of the virus. Naïve direct contact and aerosol contact ferrets were introduced at 1day post-inoculation (dpi). Transmission was defined by detection of virus from nasal washes and/ or seroconversion.
We observed direct contact transmission from inoculated donor ferrets to their cage-mates was observed for all viruses studied, albeit at different efficiency. Classical swine-like swHK4167 showed least efficient contact transmission as virus could be detected from all (3/3) direct contacts only at 6 dpi while viral shedding was detected at 4 dpi in other direct contact groups. Aerosol transmission was detected with human seasonal influenza virus Wuhan95 (2/3), H1N1pdm influenza virus CA04 (3/3), HK415742 (2/3), and swine precursor virus swHK915 (1/3). Transmission of Wuhan95 or CA04 to aerosol contacts was detected at 4 or 6 dpi, while transmission of swHK915 was detected later at 8 dpi. While the swine influenza viruses studied were able to transmit via the direct contact route, only swHK915 which shares a common genetic derivation for 7 genes with H1N1pdm possessed capacity for aerosol transmission, albeit of moderate efficiency. SwHK915 differed from swine triple reassortant viruses in the origins of its M gene. It is possible that the M gene derived from Eurasian avian-like swine viruses contributes to the aerosol transmissibility of H1N1pdm influenza viruses.
This article is published under license to BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.