Avian Influenza Infections Increasing in China

摘要

Assessment of the current epidemic virus’s traits indicates a moderate to high risk for pandemicity. There have now been five annual epidemics in China caused by the novel avian influenza virus A(H7N9) since 2013 involving a total of 1258 people. During the first four epidemics, pneumonia occurred in 88% of infected patients, and 41 % of patients died. The ongoing fifth epidemic, which began in October 2016, has thus far resulted in 460 human infections, more than in any of the previous four epidemics. Most infections in the epidemics were related to poultry exposure, but some nonsustained human-to-human transmissions have occurred. In the fifth epidemic, two distinct genetic lineages have been identified: the Yangtze River Delta lineage, for which 93% of 74 hemagglutinin (HA) gene sequences have been analyzed, and the Pearl River Delta lineage. Antigenic analysis of the Yangtze River Delta lineage viruses showed diminished cross-reactivity between these isolates and candidate vaccine viruses (CVV) developed from prior influenza A (H7N9) epidemics. Genetic analysis indicates that 7% to 9% of neuraminidase genes from Yangtze River Delta isolates have markers for reduced sensitivity to neuraminidase inhibitory drugs. Isolates from the fifth epidemic contain a four-amino acid insertion in the HA protein protease cleavage site associated with increased virulence. Assessment of the current epidemic virus’s traits indicate a moderate to high risk for pandemicity.