Influenza A virus subtype H9N2

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Lua error in package.lua at line 80: module 'strict' not found. H9N2 is a subtype of the species Influenza A virus (bird flu virus).[1][2]

Over the years the H9N2 influenza strain caused illness in several children aged nine months to 5 years in Hong Kong with the latest occurring in December 2009.[3][4]

Infection in birds

This the most common subtype of influenza viruses in chickens in China. H9N2 also causes a great economic loss for the poultry industry, even under the long-term vaccination programs. Recent human infections with avian influenza virus revealed that H9N2 is the gene donor for H7N9 and H10N8 viruses that are infecting humans too. The crucial role of H9N2 viruses at the animal-human interface is due to the wide host range, adaptation to both poultry and mammals and extensive gene reassortment. In China, which is regarded as an epicenter of avian influenza viruses, the H9N2 virus has been detected in multiple avian species, including chicken, duck, quail, pheasant, partridge, pigeon, silky chicken, chukar and egret.

Epidemiological and genetic studies revealed that the hemagglutinin (HA) gene of the H9N2 influenza viruses could be divided into Eurasian avian and American avian lineages. The Eurasian avian lineage involved three distinct lineages, including A/chicken/Beijing/1/94-like (BJ/94-like), A/quail/Hong Kong/G1/97-like (G1-like), and A/duck/Hong Kong/Y439/97 (Y439-like).[5]

Transmission from chicken to human

The H9N2 influenza virus can be transmitted by air droplet, dust, feed, or water. Chickens usually seemed to be healthy after the infection but some of them do show depression and ruffled feathers. The virus replicates itself in the trachea. It makes chickens more susceptible to secondary infections, especially Escherichia coli infections with a mortality rate of at least 10%. Also, the trachea or bronchi are easily embolized by mucus when the ventilation is poor, leading to severe respiratory disease and death.[5]

Antigenicity

Localization of amino acids related to the antigenicity of H9N2 influenza virus on the three-dimensional map of A/Swine/Hong Kong/9/98. PDB ID is 1JSD. All positions are shown with H9 numbering

H9N2 viruses isolated from chickens in China showed antigenic drift that evolved into distinct antigenic groups. This antigenic drift may have led to immunization failure and may explain the current prevalence of the H9N2 influenza virus in China. The identification of amino acids in H9 antigenic sites revealed different distribution of antigenic areas among other subtypes. Multiple amino acid positions in HA protein related to the antigenicity of H9N2 viruses were identified, most of which located in the distal head of the HA trimer. H9N2 influenza virus has been recognized to reassort with multiple other subtypes, including H6N1, H6N2, and H5N1 viruses. The G1-like H9N2 viruses were the likely donors of the six internal genes of the H5N1 viruses causing the bird flu outbreak which transmitted to humans in Hong Kong in 1997 and the BJ/94-like H9N2 viruses provided the six internal genes to H7N9 and H10N8 viruses which emerged in humans in China since 2013. Moreover, H7N9 influenza viruses continued to reassort with circulating H9N2 viruses, resulting in multiple genotypes of H7N9 viruses. The contribution of H9N2 genes, especially ribonucleoprotein (RNP) genes, to the infection in human needs to be determined.[5]

Sources

  1. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  2. ↑ NAID NIH
  3. ↑ Influenza A (H9N2) infection in a 5-year-old boy
  4. ↑ HK girl infected with rare but mild A/H9N2 flu virus
  5. ↑ 5.0 5.1 5.2 H9N2 influenza virus in China: a cause of concern

Further reading

External links

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