Molecular Epidemiology of Avian Influenza H5N1 in Thailand

Yong Poovorawan*

ABSTRACT: Avian influenza H5N1 epidemics have been reported in Asia since 2003. Early in 2004, this virus emerged in Thailand, which necessitated the culling of nearly one hundred million domestic poultry. The distinctive feature of this virus is that it can cross from avian species to humans. Molecular characterization of Avian influenza virus H5N1 from this outbreak showed evidence of HPAI on the cleavage site of the H gene (poly basic amino acids in HA), a 20 codon deletion in the neuraminidase gene (stalk region), a 5 codon deletion in the NS gene and mutations or polymorphisms in the M2 gene leading to Amantadine resistance. Our group analyzed the entire genome sequences from multiple virus isolates in Thailand between 2004 and 2007 and concluded that H5N1 can be divided into two clades. The avian influenza outbreaks appeared to emerge in five major episodes between 2004 and 2007 with the first three waves caused by genotype Z, clade I. During the last two waves in Thailand in 2006-2007, two genotypes, V and Z, clades 1 and 2, subclade 3 predominated with surveillance still in progress. The resulting data might be crucial for developing preventive measures, such as an efficient vaccine in order to prepare the population for the potential occurrence of a pandemic of avian influenza.

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Center of Excellence in Clinical Virology, Department of Pediatrics, Faculty of Medicine, Chulalongkorn University, Bangkok 10330, Thailand.

* Corresponding author, E-mail: Yong.P@chula.ac.th