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Q&A: China’s control strategy for H7N9 flu virus
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In 2013, China experienced the first outbreak of avian influenza A(H7N9).
Since then, the country has implemented many interventions to control the transmission of H7N9 from chickens to humans. The risk for human infection was reduced with the temporary closing of live poultry markets, but transmission of the virus among poultry was not prevented, eventually leading to more human cases.
However, the mass vaccination of poultry in 2017 has effectively prevented H7N9 virus infection among humans and poultry, leading to a sharp decline in cases.
In Open Forum Infectious Diseases, Gregory C. Gray MD, MPH, FIDSA, an infectious disease epidemiologist and professor at Duke University, and colleagues explained that highly pathogenic H7N9 and H7N2 viruses have emerged in unimmunized ducks, leading them to ask the question, “Will China’s H7N9 control strategy continue to be effective?”
Infectious Disease News spoke with Gray about the current status of control strategies in China, remaining gaps in control measures and what more China can do to effectively contain the highly pathogenic viruses. – by Marley Ghizzone
Why are novel strains of H7N9 emerging and spreading so rapidly among poultry in mainland China, and what risk do they pose to global public health?
In a relatively short period of approximately 5 years, H7N9 avian influenza A viruses have spread among poultry in most regions of China and infected more than 1,500 persons. This transmission reflects the relative ease at which the virus has moved between poultry flocks, weaknesses in farm biosecurity and human behaviors that increase risk of H7N9 infection in poultry and man.
What is the pandemic potential of H7N9 compared with other pathogens?
Considering currently circulating viruses, the CDC ranks the H7N9 viruses in China as being of the highest pandemic risk and importance for research by their [influenza risk assessment tool] instrument. However, I have argued that, in general, the swine reservoired viruses (variant influenza A viruses) seem more likely to routinely infect man than avian viruses. This impression is based upon my gestalt of case reports, sero-epidemiological studies, archeo-epidemiological studies, environmental studies and historical observations.
How have control strategies — like aggressively vaccinating chickens with inactivated vaccine, or the closure of live poultry markets — impacted the spread of H7N9?
Various interventions have demonstrated some limited and transient success in reducing the prevalence of H7N9 among poultry and also infections in man, but of marked recent success has been the administration of bivalent H5/H7 inactivated vaccine to chickens. This intervention has markedly reduced the H7N9 problem among both poultry and humans.
What are the remaining gaps in control measures, and how do they impact disease transmission?
Although there are gaps in avian influenza virus surveillance and control, especially in countries with poor public health and veterinary health infrastructure, there is considerable avian influenza virus surveillance. I am more concerned with the lack of surveillance for novel influenza A viruses that might emerge from pigs.
How can China contain H7N9 more effectively?
Because a novel avian influenza virus H5, H7, or other H-type virus could emerge in China and undermine the H5/H7 vaccination program, continued periodic surveillance for novel emergent avian influenza strains among poultry must be continued. Additionally, because ducks, geese and other poultry were largely spared vaccination, we recommend expanding the current H5/H7 chicken vaccination program to include other such avian species.
Reference:
Wang GL, et al. Open Forum Infect Dis. 2019;doi:10.1093/ofid/ofz258.
Disclosures: The authors report no relevant financial disclosures.