Novel Avian-Origin Influenza A (H7N9) Virus

Posted On 2013-05-21 10:07:22
A recent article in the New England Journal of Medicine discusses clinical presentation and outcome of three patient with the H7N9 virus. (1)

The authors describe that infection of poultry with influenza A subtype H7 viruses occurs worldwide, but that the introduction of this subtype to humans in Asia has not been observed previously. The three urban residents of Shanghai or Anhui, China, presented in March 2013 with rapidly progressing lower respiratory tract infections and were found to be infected with a novel reassortant avian-origin influenza A (H7N9) virus. The authors obtained and analyzed clinical, epidemiologic, and virologic data from these patients. Respiratory specimens were tested for influenza and other respiratory viruses by means of real-time reverse-transcriptase-polymerase-chain-reaction assays, viral culturing, and sequence analyses. 

The authors describe the isolation of a novelreassortant avian-origin influenza A (H7N9) virus from respiratory specimens obtained from all three patients and was identified as H7N9. Sequencing analyses revealed that all the genes from these three viruses were of avian origin, with six internal genes from avian influenza A (H9N2) viruses. Substitution Q226L (H3 numbering) at the 210-loop in the hemagglutinin (HA) gene was found in the A/Anhui/1/2013 and A/Shanghai/2/2013 virus but not in the A/Shanghai/1/2013 virus. A T160A mutation was identified at the 150-loop in the HA gene of all three viruses. A deletion of five amino acids in the neuraminidase (NA) stalk region was found in all three viruses. All three patients presented with fever, cough, and dyspnea. Two of the patients had a history of recent exposure to poultry. Chest radiography revealed diffuse opacities and consolidation. Complications included acute respiratory distress syndrome and multiorgan failure. All three patients died. 

The authors conclude that the novel reassortant H7N9 viruses were associated with severe and fatal respiratory disease in three patients. 

A second paper published in Lances describes the origin and diversity of this virus. (2)

  1. Human Infection with a Novel Avian-Origin Influenza A (H7N9) Virus. Gao R, Cao B, Hu Y, Feng Z, Wang D, Hu W, Chen J, Jie Z, Qiu H, Xu K, Xu X, Lu H, Zhu W, Gao Z, Xiang N, Shen Y, He Z, Gu Y, Zhang Z, Yang Y, Zhao X, Zhou L, Li X, Zou S, Zhang Y, Li X, Yang L, Guo J, Dong J, Li Q, Dong L, Zhu Y, Bai T, Wang S, Hao P, Yang W, Zhang Y, Han J, Yu H, Li D, Gao GF, Wu G, Wang Y, Yuan Z, Shu Y. N Engl J Med. 2013 Apr 11. [Epub ahead of print]
  2. Origin and diversity of novel avian influenza A H7N9 viruses causing human infection: phylogenetic, structural, and coalescent analyses. Liu D, Shi W, Shi Y, Wang D, Xiao H, Li W, Bi Y, Wu Y, Li X, Yan J, Liu W, Zhao G, Yang W, Wang Y, Ma J, Shu Y, Lei F, Gao GF. Lancet. 2013 May 1. doi:pii: S0140-6736(13)60938-1. 10.1016/S0140-6736(13)60938-1. [Epub ahead of print]