In a recent study published in Emerging Infectious Diseases, researchers identified 10 avian influenza A (H5N6) viruses in poultry from four Chinese provinces, with immune evasion and potential for complex genetic recombination. Because of this, H5N6 clade 2.3.4.4b viruses pose a significant threat of causing infections in humans.
Studio: Novel Avian Reassorting Influenza A (H5N6) Virus, China, 2021. Image Credit: pinkeyes / Shutterstock
Fund
There were 26 cases of laboratory-confirmed human infections with the influenza A (H5N6) virus in China between 2014 and 2020. However, these sporadic infections attracted attention only in 2021, when the figures of cases exceeded the accumulated figures of the previous seven years in China. barely eight months and caused deaths.
There is the availability of highly effective H5N6 vaccines, which reduce the likelihood of serious clinical disease and the spread of the virus in poultry; however, sporadic H5N6 infections occur in waterfowl. These birds have become a weak link to prevent influenza A virus. In addition, they have caused the uncontrolled spread of the H5Nx subtype of highly pathogenic avian influenza (HPAI) to poultry in China.
Due to strict immunization policies for poultry in China, the H5N8 virus was rapidly eliminated, but re-emerged in 2020, causing a serious threat of endemic and subsequent zoonotic spillage to humans. Since the increase in cases of influenza A (H5N6) in humans, the prevalence and mode of restocking of H5N8 are of great concern.
About the study
In the present study, researchers identified a new rearranging avian influenza A (H5N6) virus present in China’s poultry industry; which also caused an increase in human infections. They isolated an H5N6 virus from a sick duck from a poultry farm in Chengdu, Sichuan, China, in June 2021, and another from a dead chicken in the home of a human patient in Chongqing in July 2021. In addition, they isolated two H5N6 viruses. in August and September 2021 of chicken and goose farms in two Chinese provinces. Finally, in October 2021, they detected five H5N6 viruses from Guangdong Province, three from ducks, one from a goose and one more from the environment.
According to the protocol of the World Health Organization (WHO), the researchers sequenced the genomes of the 10 H5N6 viruses and then constructed a high-probability phylogenetic tree to classify them into epidemic clades. All 10 H5N6 viruses belonged to the hemagglutinin (HA) clade 2.3.4.4b, with similar HA genes of 99.1% to 100%.
The researchers used Chongqing bird strains as representative viruses with human-derived virus sequences. He shared multiple similarities between the PB2, acid polymerase, and nonstructural flu virus (H3N2) genes. The authors observed that this new virus regrouped with the H3N2 virus, deriving the basic polymerase (PB) 1 gene from the influenza A (H1N2) virus. The HA genes and the matrix, with 99.2% and 99.9% similarity to H5N8, pointed to the origin of H5N8. Because it shared a similar neuraminidase gene with the H5N6 virus, it is also possible that the new H5N6 virus is a regrouping of the H5N8 and H5N6 viruses. Another speculation is that the involvement of other low pathogenic avian influenza viruses in the clustering made the internal genes of all strains appear complex but inconsistent.
In addition, Bayesian analysis revealed that these viruses formed different clades based on the geographic regions of origin. Current vaccine strains are ineffective against new strains of circulating H5N6 virus, suggesting the urgent need to update vaccines to prevent further transmission. In fact, in January 2022, the Chinese government introduced new strains of H5-Re14 and rHN5801 vaccine to fight poultry infection with the H5N6 virus.
Several H5N6 viral infections in humans occurred during the non-influenza season in southern China in a short time, indicating that their viral load has increased over time. In addition, the researchers collected a viral specimen of a wastewater swab at a Dongguan live poultry market, indicating its presence in the environment. This further increases the likelihood of H5N6 infections in humans.
Conclusions
The current study identified 10 new strains of H5N6 virus from a reassortment of poultry and the surrounding environment that resembled H5N6 viral strains of human origin. The viral strains identified at the onset of the endemic were later grouped into three geographically characterized subclades. However, they all had susceptibility mutations in similar mammals, including T33K, L89V, and G309D, to their PB2 gene. Antigenic differences between vaccine antiserums and these viruses could have implications for the risk of transmission.
Magazine reference:
- Junhong Chen, Lingyu Xu, Tengfei Liu, Shumin Xie, Ke Li, Xiao Li, Mengmeng Zhang, Yifan Wu, Xinkai Wang, Jinfeng Wang, Keyi Shi, Beibei Niu, Ming Liao and Weixin Jia, Novel reassortant avian flu A (H5N6) ) virus, China, 2021. Emerging Infectious Diseases. two: