Epidemiology, Evolution, and Recent Outbreaks of Avian Influenza Virus in China

Abstract

Novel reassortants of H7N9, H10N8, and H5N6 avian influenza viruses (AIVs) are currently circulating in China's poultry flocks, occasionally infecting humans and other mammals. Combined with the sometimes enzootic H5N1 and H9N2 strains, this cauldron of genetically diverse AIVs pose significant risks to public health. Here, we review the epidemiology, evolution, and recent outbreaks of AIVs in China, discuss reasons behind the recent increase in the emergence of novel AIVs, and identify warning signs which may point to the emergence of a potentially virulent and highly transmissible AIV to humans. This review will be useful to authorities who consider options for the detection and control of AIV transmission in animals and humans, with the goal of preventing future epidemics and pandemics.

FIG 1

Emergence and distribution of avian influenza viruses in China. (A) Distribution of AIVs found in China (from the NCBI database [http://www.ncbi.nlm.nih.gov/genomes/FLU/FLU.html] and various news reports). Various colors depict different HA subtypes. Yellow stars indicate provinces with confirmed H7N9 human infections. The shaded regions represent the emergence of AIV cases in humans. (B) Schematic for the emergence of novel AIVs in China. The eight bars, from top to bottom, represent the PB2, PB1, PA, HA, NP, NA, M, and NS gene segments. Different colors represent different genetic origins.

FIG 2

Live-poultry markets and live-animal markets in China. (A to C) Photographs taken from a typical LPM in China; (D to F) photographs representative of a live-animal market in Guangdong Province; (G) proposed ecosystem model for the production and cross-species transmission of novel reassortant AIV in China. The cycles represent different regions in China.