Sound The Trumpet : The Elusive H7N9 Virus: Chinese Researchers Predict Future Pandemic

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“The Elusive H7N9 Virus: Chinese Researchers Predict Future Pandemic”
by science 2.0
June 20th, 2013

Since February 2013, China experienced an outbreak of the novel H7N9 avian flu, causing 131 cases of infection, and a death toll of 39. This particular H7N9 strain is considered to be one of the most worrisome pathogens since the H5N1 pandemic in 1997; a reputation based on the virus’ ability to spread easily across species and to infect humans. According to the May 23, 2013 Science paper published by the Joint Influenza Research Centre (State Key Laboratory of Emerging Infectious Diseases, Shantou PR, China), Drs. Y. Guan and Y. Shu reported that H7N9 infects the upper respiratory tract of ferrets and pigs, and spreads via direct contact, suggesting that the rapid surge of H7N9 infections are likely caused by human’s direct contact with infected birds.

The source of the H7N9 virus is quite elusive, mainly because birds carrying the H7N9 virus appear to be unharmed by the infection. This is quite unlike the H5N1 outbreak in 1997, where H5N1-infected birds can succumb to the infection, and that the presence of dead ducks and poultry often indicates the presence of the H5N1 virus.

The Elusive Origin of H7N9
To solve the puzzle of H7N9’s origin, a group of scientists lead by Dr. Kwok Yung Yuen (University of Hong Kong) discovered that H7N9 virus was derived from two origins of ducks, a study the was published in the June 1, 2013 issue of the Lancet. The conclusion was based on the sequencing the hemagglutinin (H7) and neuraminidase (N9) viral genes in human patients that were infected with H7N9 (throat swabs, Zhejiang, China), and extensive analysis to determine whether similar H7 and N9 sequences can be found in duck and poultry samples from the Asian wet markets. Using this approach, Yuen reported that the H7 sequence found in domestic ducks in Zhejiang, and the N9 sequence found in wild ducks in Korea, were the closest match to the respective H7 and N9 protein sequences in H7N9-infected patients in Zhejiang. Yuen further highlighted that in contrast to the H7 proteins from domestic ducks, the H7 proteins in H7N9-infected patients carry several amino-acid mutations including the Gln226Leu, Gly186Val substitutions (associated with their ability to infect humans) and PB2 Asp701Asn mutation (associated with mammalian adaptation).

Further extrapolating the origin of H7N9 from an influenza sequence database (Global Initiative on Sharing Avian Influenza Data (GISAID) database), Dr. George Gao at the Chinese Center for Disease Control and Prevention (Beijing) demonstrated that the H7 gene is likely to have evolved from wild migratory ducks in Asia. Gao further found the H7N9 virus also shares internal genes that are similar to what is found in two lineages of H9N2 poultry influenza virus. In his report published in the June 1, 2013 issue of the Lancet, Gao further concluded that the H7N9 in humans is an evolutionary product that is likely created by multiple gene reassortment events between influenza viruses from at least four different migratory ducks and poultry lineages. According to Gao, H7N9 virus transmission and mutations in birds, and potentially in intermediate animals, should be watched closely to minimize the chances of a future pandemic.

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