Characterisation of a novel #chicken-derived #H3N3 avian #influenza virus detected in #China in 2023: Pathogenicity and immunogenicity

 

Abstract

The poultry industry faces a constant threat from the mutation and transmission of avian influenza viruses (AIVs). While waterfowl and wild birds are natural hosts of H3N3 AIV, reports of H3N3 infections in chickens are limited. However, in 2023, a decline in egg production among laying hens in the Yancheng Region of Jiangsu Province prompted a study. This research aimed to diagnose the aetiology in laying hens through molecular virological methods and characterise the biological properties of the causative pathogens. An H3N3 AIV subtype strain, A/chicken/China/YC01/2023(H3N3), was isolated from chickens exhibiting lesions. Genome sequencing and analysis revealed a novel genetic makeup: the HA gene originated from an H3N8 AIV, the NA gene from an H10N3 AIV, and the internal genes from an H9N2 AIV, all circulating in China. Chickens experimentally infected with the isolate showed signs of Harderian gland haemorrhage, nasal mucus, tracheal circumferential bleeding, and lung bleeding and localised necrosis. Histopathological examination confirmed nasal mucosal and tracheal inflammation, lung capillary congestion, liver cell damage, and sparse splenic lymphocytes. Viral shedding was significantly higher in the oropharyngeal cavity, peaking 2–6 days post-infection, compared to the cloaca. For the first time, the immunogenicity of a novel chicken-derived H3N3 subtype AIV was assessed in specific pathogen-free chickens. An inactivated vaccine, prepared from the isolated strain, resulted in antibody titres peaking at 9.6 log2 four weeks after immunization. Furthermore, challenges with either the isolated strain or a duck-origin BZ01/2023(H3N3) strain after immunisation did not cause clinical signs or viral shedding on day 4. In conclusion, the isolate H3N3 AIV can replicate in chickens, leading to organ damage and pathogenicity. Crucially, the inactivated vaccine derived from this isolate is highly immunogenic and provides cross-protection against the duck-derived strain.

Source: PLoS One, https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0332213

____

#Assessment of public #health #risk of novel #reassortant #H3N3 avian #influenza viruses that emerged in #chickens

ABSTRACT

Influenza A (H3N2) viruses are historically responsible for the 1968 Hong Kong flu pandemic. Since then, H3N2 has continued to circulate as a seasonal influenza virus in humans. Public health concerns were raised in 2022 when human infections with novel reassortant H3N8 influenza viruses originating from chickens were first reported in China. Here, we conducted a systematic surveillance of H3 avian influenza viruses (AIVs) circulating in poultry and assessed the public health risk of emergent H3 reassortants. We found that H3 AIVs were prevalent in both ducks and chickens. Notably, in December 2022, a novel chicken-derived H3N3 subtype virus was identified, which gradually replaced the previously predominant H3N8 virus and became prevalent in chickens. Genetic analysis demonstrated that the novel H3N3 virus is a triple-reassortment strain with the H3 gene segment from chicken H3N8 virus, the N3 gene segment from the H10N3 virus, and internal gene segments derived from H9N2 viruses. Compared with chicken H3N8 and duck H3N3 viruses, the novel chicken H3N3 viruses produced higher yields and induced greater pathogenicity in human respiratory epithelial cells and mammalian models (mouse and ferret). Importantly, the chicken H3N3 viruses could be transmitted efficiently between ferrets through direct contact. The polymerase activity of the chicken H3N3 viruses in mammalian cells was markedly increased by the PA gene originating from the H9N2 virus. Our findings indicate that the circulation of novel chicken H3N3 viruses poses a threat to both the poultry industry and human public health.

Source: mBio, https://journals.asm.org/doi/10.1128/mbio.00677-25

____

Characterization of emerging #H3N3 avian #influenza viruses in #poultry in #China

Abstract

Avian influenza viruses continue to challenge poultry and human health; therefore, careful surveillance and evaluation of emerging viruses are important for animal disease control and human influenza pandemic preparedness. In this study, we detected a series of H3N3 subtype avian influenza viruses in chickens, pigeons, and ducks during our routine surveillance and diagnosis between September 2022 and May 2023. We performed extensive analyses to fully understand the origins of these viruses and their risk to animals and humans. We found that the viruses were complex reassortants; the viruses from chickens and pigeons carry genes mainly derived from H3N8 viruses and H10N3 viruses, whereas the two duck viruses were reassortants of duck and wild bird viruses. The chicken and pigeon, but not duck, viruses replicated in multiple organs of chickens and were shed for up to 13 days, but none caused disease or death. Six of the viruses tested all bound to both avian- and human-type receptors. Seventeen viruses were tested in mice and most replicated efficiently but were not lethal. Six viruses were tested in guinea pigs, and four of them transmitted efficiently via respiratory droplets. Our study thus identified novel H3N3 avian influenza viruses and revealed their zoonotic potential, thereby emphasizing the importance of careful monitoring and control of H3 viruses in animals.

Source: Emerging Microbes and Infections, https://www.tandfonline.com/doi/full/10.1080/22221751.2025.2509748#

____

#Pathogenicity of Novel #H3 Avian #Influenza Viruses in #Chickens and Development of a Promising #Vaccine

Abstract

Since 2022, three cases of human infections of novel H3N8 avian influenza viruses (AIVs) have been confirmed in China. Given the potential for significant public health implications, the prompt detection and containment of the virus is particularly important. Comprehensive analyses were conducted of the complete viral gene sequences of five H3 subtype AIVs that were isolated from chickens, pigeons, and geese in live poultry markets in China in 2023. Four strains exhibited a high degree of homology with the H3N8 viruses responsible for human infections in 2022 and 2023. A subsequent study was conducted to investigate the pathogenicity differences among multiple subtypes of the H3 AIVs in chickens. The study revealed that all infected chickens exhibited clinical signs and viral shedding. Notably, two H3N8 viruses, which were highly homologous to human strains, demonstrated significant differences in adaptability to chickens. The goose-derived H3N5 strain displayed high adaptability to chickens and could replicate in multiple organs, with the highest titer in the cloaca. Additionally, a potential vaccine strain, designated CK/NT308/H3N3, was successfully developed that provided complete clinical protection and effectively prevented viral shedding against both H3N3 and H3N8 viruses. In conclusion, CK/NT308/H3N3 presents a promising vaccine candidate.

Source: Viruses, https://www.mdpi.com/1999-4915/17/3/288

____

Evidence of an emerging triple- #reassortant #H3N3 avian #influenza virus in #China

Abstract

The H3 subtype of avian influenza virus (AIV) stands out as one of the most prevalent subtypes, posing a significant threat to public health. In this study, a novel triple-reassortant H3N3 AIV designated A/chicken/China/16/2023 (H3N3), was isolated from a sick chicken in northern China. The complete genome of the isolate was determined using next-generation sequencing, and the AIV-like particles were confirmed via transmission electron microscopy. Subsequent phylogenetic analyses revealed that HA and NA genes of the H3N3 isolate clustered within the Eurasian lineage of AIVs, exhibiting the closest genetic relationship with other H3N3 AIVs identified in China during 2023. Interestingly, the HA and NA genes of the nove H3N3 isolate were originated from H3N8 and H10N3 AIVs, respectively, and the six internal genes originated from prevalent H9N2 AIVs. These findings indicated the novel H3N3 isolate possesses a complex genetic constellation, likely arising from multiple reassortment events involving H3N8, H9N2, and H10N3 subtype influenza viruses. Additionally, the presence of Q226 and T228 in the HA protein suggests the H3N3 virus preferentially binds to α-2,3-linked sialic acid receptors. The HA cleavage site motif (PEKQTR/GIF) and the absence of E627K and D701N mutations in PB2 protein classify the virus as a characteristic low pathogenicity AIV. However, several mutations in internal genes raise concerns about potential increases in viral resistance, virulence, and transmission in mammalian hosts. Overall, this study provides valuable insights into the molecular and genetic characterization of the emerging triple-reassortant H3N3 AIVs, and continued surveillance of domestic poultry is essential for monitoring the H3N3 subtype evolution and potential spread.

Source: BMC Genomics, https://bmcgenomics.biomedcentral.com/articles/10.1186/s12864-024-11152-x

_____