18 Jun 2010

A group of microbiologists in The University of Hong Kong Li Ka Shing Faculty of Medicine identified that the pandemic H1N1 2009 virus has transmitted back to pigs and undergone genetic reassortment to give rise to a novel H1N1 virus that has genes from the pandemic H1N1/2009 virus and other pig influenza viruses. These findings were found through the systematic long-term surveillance of swine influenza in Hong Kong carried out by HKU in collaboration with the HKSAR government. Since such events may give rise to novel viruses of concern for public health, HKU urges heightened global surveillance of influenza viruses in swine. The research is just published in one of the most prestigious international scientific journals, “Science”.

Key research findings:

The pandemic H1N1/2009 virus was not detected in pigs prior to October 2009 but has been detected on four occasions in the period October 2009 – January 2010, demonstrating the repeated transmission of this pandemic virus from humans to pigs. Such findings have also been reported from a number of other countries, including Canada, USA, Australia and Singapore.

In January 2010, the HKU influenza research team found a reassortant (i.e. hybrid) virus that had acquired gene segments from the North American Triple reassortant swine viruses, Eurasian swine viruses and the pandemic H1N1/2009 virus, showing that the pandemic virus can genetically reassort with influenza viruses of pigs, thereby giving rise to novel influenza viruses. Swine experimentally infected with this reassortant did not develop overt clinical illness but could transmit infection to other pigs.

Research Implications:

The findings demonstrate that the H1N1/2009 pandemic virus may change in unpredictable ways in pigs; such viruses may have relevance to global public health. While there is no indication that the particular reassortant virus HKU detected poses an immediate threat to humans, it emphasizes the need for systematic surveillance of influenza viruses in pigs worldwide. Such events are very likely occurring in many other parts of the world. The detection of the virus in Hong Kong therefore probably reflects the intensive surveillance of swine influenza carried out here rather than this being an event that is geographically unique.

Suggestions:

As the H1N1/2009 pandemic virus very likely emerged from pigs, there was the possibility that this virus will in turn easily transmit back from humans to pigs. Pigs are considered a “mixing vessel” for influenza viruses of swine, human and avian origin. Systematic surveillance of pigs for influenza viruses is therefore important to understand how the 2009 pandemic emerged and also to understand the possible future evolution of the pandemic H1N1 virus.

Professor Guan Yi, Professor of the Department of Microbiology, The University of Hong Kong Li Ka Shing Faculty of Medicine says, “The Influenza Research Team at HKU, in collaboration with the Food and Environmental Hygiene Department of the HKSAR government, has been carrying out systematic surveillance of influenza viruses in pigs for the past 12 years. This provides unique information to understand the evolution of influenza viruses in pigs, to understand global movements of pig influenza viruses and reassortment between different lineages of swine influenza viruses. Our long term studies demonstrate the occurrence of many reassortment events in pigs and provide insights into how such a pandemic virus may have arisen on the American continent.”

Another key researcher, Professor Malik Peiris, Tam Wah-Ching Professor in Medical Science, of the Department of Microbiology, The University of Hong Kong Li Ka Shing Faculty of Medicine and the HKU-Pasteur Research Centre reminds the public not to panic about eating pork and says, “The Food and Agriculture Organization (FAO) and the World Health Organization (WHO) have clearly stated that, provided good hygiene measures are maintained and pork is well cooked, pigs and pork products do not pose an influenza-threat to humans. Our findings do not provide reason to change this advice. Our findings do emphasize the need for animal and public health authorities to work closely together to maintain surveillance of influenza viruses in pigs so that any unexpected changes in these viruses are rapidly detected and their significance rapidly evaluated.”

About the HKU Research team:

This research was led by Professor Guan Yi, and Professor Malik Peiris, Tam Wah-Ching Professor in Medical Science, of the Department of Microbiology, The University of Hong Kong Li Ka Shing Faculty of Medicine, with the contribution from a group of researchers from their Department and the State Key Laboratory of Emerging Infectious Diseases, HKU. The HKU influenza research team continues making contribution for combating emerging infectious diseases.