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Genetic characterization of 2008 reassortant influenza A virus (H5N1), Thailand

Alongkorn Amonsin12*, Jiradej Lapkuntod1, Kamol Suwannakarn6, Pravina Kitikoon13, Sanipa Suradhat15, Rachod Tantilertcharoen1, Supanat Boonyapisitsopa1, Napawan Bunpapong1, Manoosak Wongphatcharachai12, Trong Wisedchanwet1, Apiradee Theamboonlers6, Yong Poovorawan6, Jiroj Sasipreeyajan14 and Roongroje Thanawongnuwech13

Author Affiliations

1 Emerging and Re-emerging Infectious Diseases in Animals, Research Unit, Faculty of Veterinary Science, Chulalongkorn University, Bangkok, Thailand

2 Department of Veterinary Public Health, Faculty of Veterinary Science, Chulalongkorn University, Bangkok, Thailand

3 Department of Pathology, Faculty of Veterinary Science, Chulalongkorn University, Bangkok, Thailand

4 Department of Medicine, Faculty of Veterinary Science, Chulalongkorn University, Bangkok, Thailand

5 Department of Microbiology, Faculty of Veterinary Science, Chulalongkorn University, Bangkok, Thailand

6 Center of Excellence in Clinical Virology, Faculty of Medicine, Chulalongkorn University Bangkok, Thailand

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Virology Journal 2010, 7:233  doi:10.1186/1743-422X-7-233

Published: 16 September 2010


In January and November 2008, outbreaks of avian influenza have been reported in 4 provinces of Thailand. Eight Influenza A H5N1 viruses were recovered from these 2008 AI outbreaks and comprehensively characterized and analyzed for nucleotide identity, genetic relatedness, virulence determinants, and possible sites of reassortment. The results show that the 2008 H5N1 viruses displayed genetic drift characteristics (less than 3% genetic differences), as commonly found in influenza A viruses. Based on phylogenetic analysis, clade 1 viruses in Thailand were divided into 3 distinct branches (subclades 1, 1.1 and 1.2). Six out of 8 H5N1 isolates have been identified as reassorted H5N1 viruses, while other isolates belong to an original H5N1 clade. These viruses have undergone inter-lineage reassortment between subclades 1.1 and 1.2 and thus represent new reassorted 2008 H5N1 viruses. The reassorted viruses have acquired gene segments from H5N1, subclade 1.1 (PA, HA, NP and M) and subclade 1.2 (PB2, PB1, NA and NS) in Thailand. Bootscan analysis of concatenated whole genome sequences of the 2008 H5N1 viruses supported the reassortment sites between subclade 1.1 and 1.2 viruses. Based on estimating of the time of the most recent common ancestors of the 2008 H5N1 viruses, the potential point of genetic reassortment of the viruses could be traced back to 2006. Genetic analysis of the 2008 H5N1 viruses has shown that most virulence determinants in all 8 genes of the viruses have remained unchanged. In summary, two predominant H5N1 lineages were circulating in 2008. The original CUK2-like lineage mainly circulated in central Thailand and the reassorted lineage (subclades 1.1 and 1.2) predominantly circulated in lower-north Thailand. To prevent new reassortment, emphasis should be put on prevention of H5N1 viruses circulating in high risk areas. In addition, surveillance and whole genome sequencing of H5N1 viruses should be routinely performed for monitoring the genetic drift of the virus and new reassorted strains, especially in light of potential reassortment between avian and mammalian H5N1 viruses.