Identification of the source of A (H10N8) virus causing human infection

Abstract

A novel H10N8 influenza A virus has been detected in three humans in China since December 2013. Although this virus was hypothesized to be a novel reassortant among influenza viruses from wild birds and domestic poultry, its evolutionary path leading to human infection is unknown. Sporadic surveillance at the live poultry market (LPM) suspected to be the source of infection for the first H10N8 patient has shown a gradual increase in influenza virus prevalence culminating with a predominance of H10N8 viruses. Influenza viruses detected in the LPM up to 8 months prior to human infection contributed genetic components to the zoonotic virus. These H10N8 viruses have continued to evolve within this LPM subsequent to the human infection, and continuous assessments of these H10N8 viruses will be necessary. Serological surveillance showed that the virus appears to have been present throughout the LPM system in Nanchang, China. Reduction of the influenza virus burden in LPMs is essential in preventing future emergence of novel influenza viruses with zoonotic and pandemic potential.

Keywords: Avian influenza virus; H10N8; Human infection; Live poultry market.

Figure 1. Phylogenetic analysis of H10 (A) and N8 (B) genes recovered from the samples collected from the LPM which the index patient visited

The phylogenetic analyses were performed using maximum likelihood by GARLI (Gutell and Jansen, 2006) and bootstrap resampling analyses using PAUP* 4.0 Beta (Wilgenbusch and Swofford, 2003) to apply a neighborhood joining method, as described earlier (Wan et al., 2008). The genes from this surveillance are marked in red, and those from the human H10N8 isolate in green. The bootstrap values for representative lineages are marked.

Figure 2. Phylogenetic analysis of PB2 (A), PB1 (B), PA (C), NP (D), MP (E), and NS (F) genes recovered from the samples collected from the LPM which the index patient visited

The details of these genes are shown in Supplementary Table S2. The genes from this surveillance are marked in red, and those from the human H10N8 isolate in green. The bootstrap values for representative lineages are marked.

Figure 3. Distribution of H10 seropositive samples collected from February 25 to March 27, 2014 and across five LPMs in Nanchang city

The seropositive samples were determined by hemagglutination inhibition assays with a H10N8 virus isolated from the surveillance described above and a cutoff of 1:20. LPM A was the one that the first index H10N8 patient visited in November 2013. The highest H10 positive percentile in a single sampling period was marked for each LPM.