25 May 2011

In 2009, a novel Influenza A H1N1 virus (pandemic H1N1/2009 virus) emerged from pigs which caused the first influenza pandemic of the 21st century. Previous studies by virologists from The University of Hong Kong Li Ka Shing Faculty of Medicine and others have highlighted the fact that our understanding on the origins and emergence of the pandemic H1N1/2009 virus is greatly hindered by the lack of global systemic surveillance of swine influenza virus.

In order to fill this important knowledge-gap on pandemic emergence, subsequent to the previous studies, the same HKU research team led by Professor Malik Peiris and Professor Guan Yi analyzed more than 600 swine influenza viruses collected over 30 years from this region the largest and most comprehensive systematic study on swine influenza virus worldwide so far. They found that swine influenza viruses are a highly dynamic population with movement of viruses across continents, leading to genetic reassortment and the emergence of hybrid viruses. The research is just published in one of the most prestigious international scientific journals, Nature.

This study was made possible by the excellent collaboration between government departments (the Food and Environmental Hygiene Department of the HKSAR Government,) the swine industry and university researchers (at HKU), which serves as a model for the world.

Research findings
Dated back to 70s, HKU started to collect swine influenza virus samples from pigs. Since 1998, HKU further developed a systematic surveillance of influenza viruses in pigs. The study analyzed a dataset of over 650 swine isolates and over 800 swine sera obtained from the 12 years of systematic surveillance in Hong Kong, supplemented with samples dating back to 1977.

The results show the swine influenza viruses are a highly dynamic population with movement of viruses across continents. This allows the co-circulation of multiple lineages of swine influenza viruses and genetic reassortment in Asia leading to emergence of hybrid viruses. Such genetic mixing leads to lineage competition and replacement, and to the generation of an antigenically- and genetically-diverse virus population. Results of this work also suggest that increased antigenic drift is associated with reassortment events and offer insights into the processes leading to the emergence of influenza viruses with possible epidemic or pandemic potential in swine and humans.

Implications and suggestions
Since the research team didn’t find any virus sample from the dataset matches with the pandemic H1N1 2009 virus before the outbreak of the 2009 influenza pandemic, it shows that this study has reconfirmed that the 2009 pandemic did not arise in China, a conclusion which has previously suggested by the same research team in a study published in Nature in 2009. However, the evidence of long-distance movement of swine influenza viruses, the co-circulation of multiple virus lineages and genetic reassortment we observed in our study almost certainly occurred in other geographical locations as well. Thus our findings provide an insight into how the 2009 pandemic may have arisen.

None of the viruses collected from this surveillance study posed immediate health threat to humans. This study, however, highlights the fact that similar intensive studies on swine influenza viruses are needed globally so that any unexpected changes in these viruses could be rapidly detected and the significances of such changes could be evaluated in a timely manner.

About the research team
This research was led by Professor Malik Peiris, Tam Wah-ching Professor in Medical Science and Professor Guan Yi, of the Department of Microbiology, The University of Hong Kong Li Ka Shing Faculty of Medicine. Researchers from the Department of Microbiology and the State Key Laboratory of Emerging Infectious Diseases of HKU, Duke-Nus Graduate Medical School Singapore, University of Oxford, UK and St Jude Children’s Research Hospital, USA also contributed to this study.

This work was supported by the "Centers of Excellence for Influenza Research and Surveillance" of the National Institute of Allergy and Infectious Diseases, National Institutes of Health (NIAID contract HHSN266200700005C) and the Area of Excellence Scheme of the University Grants Committee (grant AoE/M-12/06) of the Hong Kong SAR Government.