from PLoS ONE:
South Asia has experienced regular outbreaks of H5N1 avian influenza virus since its first detection in India and Pakistan in February, 2006. Till 2009, the outbreaks in this region were due to clade 2.2 H5N1 virus. In 2010, Nepal reported the first outbreak of clade 2.3.2 virus in South Asia. In February 2011, two outbreaks of H5N1 virus were reported in the State of Tripura in India. The antigenic and genetic analyses of seven H5N1 viruses isolated during these outbreaks were carried out. Antigenic analysis confirmed 64 to 256-fold reduction in cross reactivity compared with clade 2.2 viruses. The intravenous pathogenicity index of the isolates ranged from 2.80–2.95 indicating high pathogenicity to chickens. Sequencing of all the eight gene-segments of seven H5N1 viruses isolated in these outbreaks was carried out. The predicted amino acid sequence analysis revealed high pathogenicity to chickens and susceptibility to the antivirals, amantadine and oseltamivir. Phylogenetic analyses indicated that these viruses belong to clade 18.104.22.168 and were distinct to the clade 22.214.171.124 viruses isolated in Nepal. Identification of new clade 2.3.2 H5N1 viruses in South Asia is reminiscent of the introduction of clade 2.2 viruses in this region in 2006/7. It is now important to monitor whether the clade 126.96.36.199 is replacing clade 2.2 in this region or co-circulating with it. Continued co-circulation of various subclades of the H5N1 virus which are more adapted to land based poultry in a highly populated region such as South Asia increases the risk of evolution of pandemic H5N1 strains.
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Shanmuga Nagarajan1*, Chakradhar Tosh1, David K. Smith3, Joseph Sriyal Malik Peiris2, Harshad Vinayakrao Murugkar1, Rajangam Sridevi1, Manoj Kumar1, Megha Katare1, Rajlaxmi Jain1, Zohra Syed1, Padmanava Behera1, Chung L. Cheung2, Rekha Khandia1, Sushil Tripathi1, Yi Guan2, Shiv Chandra Dubey1
1 High Security Animal Disease Laboratory, Indian Veterinary Research Institute, Anand Nagar, Bhopal, India, 2 State Key Laboratory for Emerging Infectious Diseases, The University of Hong Kong, Hong Kong Special Administrative Region, 3 State Key Laboratory of Emerging Infectious Diseases, Li Ka Shing Faculty of Medicine, University of Hong Kong, International Institute of Infection and Immunity, Shantou University Medical School, Shantou, People's Republic of China