Emergence and evolution of H10 subtype influenza viruses in poultry in China

Abstract

The cases of human infections with H10N8 viruses identified in late 2013 and early 2014 in Jiangxi, China, have raised concerns over the origin, prevalence, and development of these viruses in this region. Our long-term influenza surveillance of poultry and migratory birds in southern China in the past 12 years showed that H10 influenza viruses have been introduced from migratory to domestic ducks over several winter seasons at sentinel duck farms at Poyang Lake, where domestic ducks share their water body with overwintering migratory birds. H10 viruses were never detected in terrestrial poultry in our survey areas until August 2013, when they were identified at live-poultry markets in Jiangxi. Since then, we have isolated 124 H10N8 or H10N6 viruses from chickens at local markets, revealing an ongoing outbreak. Phylogenetic analysis of H10 and related viruses showed that the chicken H10N8 viruses were generated through multiple reassortments between H10 and N8 viruses from domestic ducks and the enzootic chicken H9N2 viruses. These chicken reassortant viruses were highly similar to the human isolate, indicating that market chickens were the source of human infection. Recently, the H10 viruses further reassorted, apparently with H5N6 viruses, and generated an H10N6 variant. The emergence and prevalence of H10 viruses in chickens and the occurrence of human infections provide direct evidence of the threat from the current influenza ecosystem in China.

Importance: After the outbreak of avian-origin H7N9 influenza viruses in China, fatal human infections with a novel H10N8 virus were reported. Utilizing data from 12 years of influenza surveillance in southern China, we showed that H10 viruses were regularly introduced by migratory ducks to domestic ducks on Poyang Lake, a major aggregative site of migratory birds in Asia. The H10 viruses were maintained and amplified in domestic ducks and then transmitted to chickens and reassorted with enzootic H9N2 viruses, leading to an outbreak and human infections at live-poultry markets. The emergence of the H10N8 virus, following a pathway similar to that of the recent H7N9 virus, highlights the role of domestic ducks and the current influenza ecosystem in China that facilitates influenza viruses moving from their reservoir hosts through the live-poultry system to cause severe consequences for public health.

FIG 1

Isolation of H10 influenza A viruses from migratory and domestic birds in Jiangxi during 2012 to 2014. If two sampling occasions fell within 1 week, this is indicated. LPM, live-poultry market.

FIG 2

Maximum likelihood phylogenies of the surface genes. Sequences obtained in this study are labeled in blue, green, and purple for isolates from chickens, domestic ducks, and migratory ducks, respectively, in the phylogenetic trees of Eurasian H10 (n = 70) (A), North American N8 (n = 44) (B), and Eurasian N6 (n = 36) (C). The human H10N8 virus is marked in red, and the JX346-like sublineage is indicated by a dark blue bar. Introductions of H10 viruses from migratory to domestic ducks are indicated by asterisks in the H10 phylogeny. Intercontinental introductions of N8 viruses from North America to Eurasia are indicated by triangles in the N8 phylogeny. Bootstrap support values (percentages) from 1,000 pseudoreplicates are shown for selected lineages. Ck, chicken; Dk, duck; Gs, goose; Pg, pigeon; Mdk, migratory duck; Md, mallard; JX, Jiangxi; ST, Shantou; DG, Dongguan; SZ, Shenzhen.

FIG 3

Maximum likelihood phylogenies of the PB1 gene (n = 76). Isolates that contained mixed infections are indicated by “-a” and “-b” after the strain name in the PB1 tree (see Materials and Methods). The ZJ-HJ-07 lineage nominal virus is highlighted in yellow. Abbreviations are described in the legend of Fig. 2.

FIG 4

Genesis and evolutionary pathway of H10 viruses in Jiangxi. Either independent H10 and N8 viruses (dotted light blue lines) or an undetected H10N8 precursor in ducks (solid dark blue lines) was introduced to chickens and reassorted with enzootic H9N2 viruses. Reassortment of H10N8 viruses with N6 viruses is indicated by orange lines. Virus particles are indicated by ovals containing bars for the eight gene segments (PB2, PB1, PA, HA, NP, M, and NS, from top to bottom), colored by their source. NA stalk deletions are indicated by a broken line in segment 6.

FIG 5

The current ecosystem of avian influenza viruses in China. The diversity of avian influenza viruses is maintained primarily in the classic gene pool viruses of wild waterfowl (green circle). Industrial poultry farming (blue and pink circles) largely separates species, but wild and domestic ducks may interact and transmit viruses. Trading in live-poultry markets (funnel) brings different types of poultry together to facilitate the sharing and mixing of viruses, favoring the emergence of novel AIVs and interspecies transmission of viruses (arrows). The markets are the major contact point between humans and live poultry, and this leads to the transmission of viruses to humans. Improper management may lead to the transfer of viruses from chickens in LPMs to those in farms. The stroke weight of an arrow indicates the frequency of transmissions between different hosts, arrowheads show the direction, and dashed lines indicate sporadic transmissions.