05.02.2014

H9N2 origin

In December, 2013, Chinese health officials confirmed the first human case of avian influenza A H10N8 virus infection. The virus - designated as A/Jiangxi-Donghu/346/2013(H10N8), henceforth JX346 - was identified by sequencing of tracheal aspirate samples obtained 1 week after illness onset. Preliminary phylogenetic analysis of the retrieved sequences suggests that JX346 originated through reassortment of H9N2 strains circulating in poultry and recorded in environmental samples from Jiangxi, with one or two viruses contributing haemagglutinin and neuraminidase genes. The data suggest that JX346 arose by reassortment events in domestic birds. JX346 has avian-like receptor specificity, which might contribute to the fatal outcome of infection. So far, only two H10N8 viruses have been reported in China: one environmental isolate from a water sample in Hunan province, China, in 2007, and one from a live poultry market in southern China in 2012. However, phylogenetic analysis shows that JX346 is different from these previously identified viruses. Sequence analysis of the JX346 haemagglutinin gene shows no indications for a multibasic cleavage site, suggesting low pathogenicity in poultry.

As for the newly emerged avian influenza A H7N9 virus, this low pathogenicity will make surveillance efforts substantially more difficult.
JX346 is the third virus strain generated by reassortment in avian species that are transmitted to people, and all internal gene segments (PB2, PB1, PA, NP, M, and NS) are derived from H9N2 viruses. The 1997 avian influenza A H5N1 viruses and the H7N9 isolates from China both carried all internal genes from H9N2. This gene cassette might thus be a genetic platform for new strains with zoonotic potential.
So far, only one additional human case of avian influenza A H10N8 virus infection has been reported: on Jan 26, 2014, health authorities announced infection in a 55-year-old woman in Nanchang, Jiangxi province. This patient developed flu-like symptoms after visiting an agricultural market, and was admitted to hospital 1 week after onset of illness.