Live Poultry Markets Spread Avian Influenza

Research suggests that H7N9 has become established in animals in China, highlighting the need for more stringent controls of the live poultry trade.

AsianScientist (Mar. 18, 2015) – Research published in Nature has revealed the dissemination, divergence and establishment of the avian influenza A (H7N9) virus causing ongoing outbreaks in China.

Since 2013, a total of 622 laboratory-confirmed cases of human infection with avian influenza A virus have been reported globally, with 227 deaths recorded as of March 3, 2015. Human cases were not reported in Guangdong until August 2013, and the autumn of that year saw a dramatic increase of human infections. Guangdong has now become the province with the most H7N9 patients.

Led by Professor Yi Guan from the University of Hong Kong (HKU), the researchers found that the H7N9 viruses have diverged into three geographically distinct clades, with at least 48 different reassortant genotypes.

Multiple introductions of the viruses from East China, e.g. Zhejiang, to Guangdong and the other provinces such as Jiangxi were observed. In the second wave, none of the H7N9 viruses inherited all internal genes from the Wave 1 viruses, indicating marked changes in the genotypes. Fortunately, overt antigenic changes have not been identified in the Wave 2 viruses, thus the candidate vaccine strains recommended by the WHO in 2013 will still be effective.

Following the second H7N9 outbreak wave, the researchers collected samples from the oropharynx and respiratory tracts of chickens and ducks over 15 cities across five provinces in China. In collaboration with local hospitals and Centers for Disease Control and Prevention, the HKU researchers also collected clinical samples from patients with severe pneumonia.

They isolated many influenza viruses and genetically sequenced those of the H7N9 subtype and other related viruses. Advanced phylogenetic methods were used to reconstruct how the H7N9 virus evolved, disseminated and diverged into persistent clades and to determine the origin of the genes

Their study showed that chickens at live-poultry markets are the direct source of H7N9 human infections. The virus was predominantly shed from the respiratory and oropharyngeal tracts of these birds. In Jiangxi, there was a previously unrecognized, but related, H7N6 variant also emerging in chickens in the live poultry markets.

The H7N9 virus has persisted and diversified in chickens and spread across China, most likely due to poultry movement along trade routes. The expansion of its genetic diversity and geographical spread indicates that, unless effective control measures are in place, the H7N9 virus is likely to persist and spread beyond the region.

The researchers suggest that a change in the poultry trading and marketing systems to prevent direct contact of human populations with live poultry, especially chickens, will be key to averting avian-to-human transmission of viruses. Closure of live poultry markets, central husbandry and central slaughtering are the ultimate solutions to this problem.

The article can be found at: Lam et al. (2015) Dissemination, Divergence and Establishment of H7N9 Influenza Viruses in China.

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Source: University of Hong Kong.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

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