Influenza A Virus in Sparrows

Since its emergence in China in February 2013, avian influenza A(H7N9) virus has resulted in more and more cases and fatalities. The virus and its pandemic potential have caused global concern. Although the epidemic declined with the arrival of spring in April 2013, new cases in humans have reemerged since October 2013. The number of new cases has increased sharply during the wintery period in China.

Sequence data indicated that the hemagglutinin gene of this novel subtype H7N9 virus might originate from a subtype H7N3 virus in ducks and that the neuraminidase gene probably originated from a subtype H7N9 virus in wild birds[1] or ducks or chickens[2,3]. These data suggest that wild birds might play a role in the emergence of subtype H7N9 viruses, similar to the role they played in the geographic spread of avian subtype H5N1 viruses[4].

However, although avian influenza A(H7N9) viruses have been isolated from chickens and pigeons, none have been isolated from wild birds.

[Image: www.nationalgeographic.nl]

The high similarity of genes from the avian influenza A(H7N9) virus from an apparently healthy tree sparrow in Shanghai and influenza A(H7N9) viruses from humans and poultry in this region indicate that avian influenza A(H7N9) virus might be transmitted from poultry to tree sparrows or vice versa. A serologic survey also suggested that rates of influenza A virus infection were high among sparrows[5].

Tree sparrows are abundant and widely distributed in China. They are frequently in contact with humans and poultry. Prevalence of avian influenza viruses among tree sparrows could increase opportunities for them to carry influenza viruses from aquatic birds to domestic farms and even to humans. Hence, such expansion of influenza A(H7N9) virus host ranges undoubtedly increased the seriousness of the threat of this novel subtype.

Isolation[6] of novel influenza A(H7N9) virus in a tree sparrow emphasizes the need to expand influenza surveillance to not only domestic birds but also wild and terrestrial birds.

[1] Liu et al: Origin and diversity of novel avian influenza A H7N9 viruses causing human infection: phylogenetic, structural, and coalescent analyses in The Lancet -2013
[2] Lam et al: The genesis and source of the H7N9 influenza viruses causing human infections in China in Nature - 2013
[3] Lee et al: A new piece in the puzzle of the novel avian-origin influenza A (H7N9) virus in Biology Direct - 2013
[4] Fang et al: Environmental factors contributing to the spread of H5N1 avian influenza in mainland China in PLoS ONE - 2008
[5] Arenas et al: Type A influenza viruses in birds in southern Spain: serological survey by enzyme-linked immunosorbent assay and haemagglutination inhibition tests in Avian Pathology - 1990
[6] Baihui et al: Novel Avian Influenza A(H7N9) Virus in Tree Sparrow, Shanghai, China, 2013 in Emerging Infectious Diseases - 2014