14th ICID - Poster Abstracts - International Society for Infectious ...

When citing these abstracts please use the following reference:
Author(s) of abstract. Title of abstract [abstract]. Int J Infect Dis 2010;14S1: Abstract number.
Please note that the official publication of the International Journal of Infectious Diseases 2010, Volume 14, Supplement 1
is available electronically on http://www.sciencedirect.com
Final Abstract Number: 28.001
Session: Influenza
Date: Wednesday, March 10, 2010
Time: 12:30-13:30
Room: Poster & Exhibition Area/Ground Level
Type: Poster Presentation
The new North American strain of influenza A virus (H1N1) may not be a novel variant of H1
subtype
Y.-H. Lu, L.-W. Ju, C.-Y. Jiang, Y.-J. Zheng, Q.-W. Jiang
School of Public Health, Fudan University, Shanghai, China
Background: The current influenza A virus (H1N1) epidemic raises a serious concern about the
nature of the virus. The transmissibility was substantially higher for this virus compared with
seasonal flu viruses and close to those from previous influenza pandemics. It’s reported that the
virus had been already evolving for some time.
Methods: The present study was based on HA (hemagglutinin) fragment. A total of 558 H1 fulllength
sequences collected since 1930 were selected from the GenBank, including 76 H1N1
isolates from 2009 outbreak, 439 H1N1 and 48 H1N2 sequences collected previously. If there
were many sequences isolated simultaneously in the same area, three were randomly included.
A Bayesian approach (http://beast.bio.ed.ac.uk/) was used to construct genetic phylogeny and to
explore evolutionary history with incorporation of a time-scale.
Results: All the H1 sequences were classified into 5 main clusters. There was a little diversity
within Swine 1 (swine H1 in the US, Canada, Japan, Korea, Thailand, Philippines, China
Mainland and Taiwan) and Swine 2 (swine H1 in Europe and China Mainland). Swine 2 was more
close to clusters Avian 1 (avian H1 in the US and Canada) and Avian 2 (avian H1 in other areas)
phylogenetically. Cluster Human consisted of human H1 worldwide with a similar identity. Further
research revealed that the time to most recent common ancestor (tMRCA) of animal H1
sequences was 93.6 years ago and that of human H1 sequences was 91.6 years ago.
The H1 isolates in 2009 outbreak remarkably clustered within Swine 1 with tMRCA being 9.1
years ago. It was noted that there were other 7 human H1 sequences clustered within Swine 1.
Among them, six were isolated in the US with the earliest isolation time of 1976.
Phylogenetic tree of HA fragment produced with posterior probability
Conclusion: The present study suggested that H1 virus was originally circulating in human and
animals simultaneously and separately. In addition there was marked spatial clustering in the
evolution of H1 in animals.
It’s likely that there was a long-term cross-species circulation of swine-origin H1 virus in the US
and that the current outbreak was attributable to an accumulated genetic mutation induced by
zoonosis rather than a novel variation.