Evidence of H10N8 influenza virus infection among swine in southern China and its infectivity and transmissibility in swine

Swine Influenza Viruses Isolated from 2019 to 2022 in Shandong Province, China, Exemplify the Dominant Genotype

Swine influenza viruses (SIVs) have been circulating in swine globally and are potential threats to human health. During the surveillance of SIVs in Shandong Province, China, from 2019 to 2022, 21 reassortant G4 genotype Eurasian avian-like (EA) H1N1 subtypes containing genes from the EA H1N1 (HA and NA), 2009 pandemic (pdm/09) H1N1 virus (PB2, PB1, PA, NP, and M), and classical swine (CS) H1N1 (NS) lineages were isolated. The analysis of the key functional amino acid sites in the isolated viruses showed that two mutation sites (190D and 225E) that preferentially bind to the human α2-6 sialic acid receptor were found in HA. In PB2, three mutation sites (271A, 590S, and 591R) that may increase mammalian fitness and a mutation site (431M) that increases pathogenicity in mice were found. A typical human signature marker that may promote infection in humans, 357K, was found in NP. The viruses could replicate efficiently in mouse lungs and turbinates, and one of the H1N1 isolates could replicate in mouse kidneys and brains without prior adaption, which indicates that the viruses potentially pose a threat to human health. Histopathological results showed that the isolated viruses caused typical bronchopneumonia and encephalitis in mice. The results indicate that G4 genotype H1N1 has potential transmissibility to humans, and surveillance should be enhanced, which could provide important information for assessing the pandemic potential of the viruses.

Genetic characterization and pathogenicity of a Eurasian avian-like H1N1 swine influenza reassortant virus

BACKGROUND

Swine influenza viruses (SIV), considered the "mixing vessels" of influenza viruses, posed a significant threat to global health systems and are dangerous pathogens. Eurasian avian-like H1N1(EA-H1N1) viruses have become predominant in swine populations in China since 2016.

METHODS

Lung tissue samples were obtained from pregnant sows with miscarriage and respiratory disease in Heilongjiang province, and pathogens were detected by Next-generation sequencing (NGS) and PCR. The nucleic acid of isolates was extracted to detect SIV by RT-PCR. Then, SIV-positive samples were inoculated into embryonated chicken eggs. After successive generations, the isolates were identified by RT-PCR, IFA, WB and TEM. The genetic evolution and pathogenicity to mice of A/swine/Heilongjiang/GN/2020 were analyzed.

RESULTS

The major pathogens were influenza virus (31%), Simbu orthobunyavirus (15%) and Jingmen tick virus (8%) by NGS, while the pathogen that can cause miscarriage and respiratory disease was influenza virus. The SIV(A/swine/Heilongjiang/GN/2020) with hemagglutination activity was isolated from lung samples and was successfully identified by RT-PCR, IFA, WB and TEM. Homology and phylogenetic analysis showed that A/swine/Heilongjiang/GN/2020 is most closely related to A/swine/Henan/SN/10/2018 and belonged to EA-H1N1. Pathogenicity in mice showed that the EA-H1N1 could cause lethal or exhibit extrapulmonary virus spread and cause severe damage to respiratory tracts effectively proliferating in lung and trachea.

CONCLUSION

A/swine/Heilongjiang/GN/2020 (EA-H1N1) virus was isolated from pregnant sows with miscarriage and respiratory disease in Heilongjiang province, China. Clinical signs associated with influenza infection were observed during 14 days with A/swine/Heilongjiang/GN/2020 infected mice. These data suggest that A/swine/Heilongjiang/GN/2020 (EA-H1N1) had high pathogenicity and could be systemic spread in mice.

Effect of serial in vivo passages on the adaptation of H1N1 avian influenza virus to pigs

Introduction

The lack of proofreading activity of the viral polymerase and the segmented nature of the influenza A virus (IAV) genome are responsible for the genetic diversity of IAVs and for their ability to adapt to a new host. We tried to adapt avian IAV (avIAV) to the pig by serial passages in vivo and assessed the occurrence of point mutations and their influence on viral fitness in the pig’s body.

Material and Methods

A total of 25 in vivo avIAV passages of the A/duck/Bavaria/77 strain were performed by inoculation of 50 piglets, and after predetermined numbers of passages 20 uninoculated piglets were exposed to the virus through contact with inoculated animals. Clinical signs of swine influenza were assessed daily. Nasal swabs and lung tissue were used to detect IAV RNA by real-time RT-PCR and isolates from selected passages were sequenced.

Results

Apart from a rise in rectal temperature and a sporadic cough, no typical clinical signs were observed in infected pigs. The original strain required 20 passages to improve its replication ability noticeably. A total of 29 amino-acid substitutions were identified. Eighteen of them were detected in the first sequenced isolate, of which 16 were also in all other analysed strains. Additional mutations were detected with more passages. One substitution, threonine (T) 135 to serine (S) in neuraminidase (NA), was only detected in an IAV isolate from a contact-exposed piglet.

Conclusion

Passaging 25 times allowed us to obtain a partially swine-adapted IAV. The improvement in isolate replication ability was most likely related to S654 to glycine (G) substitution in the basic protein (PB) 1 as well as to aspartic acid (D) 701 to asparagine (N) and arginine (R) 477 to G in PB2, glutamic acid (E) 204 to D and G239E in haemagglutinin and T135S in NA.

The Emergence and Zoonotic Transmission of H10Nx Avian Influenza Virus Infections

Avian influenza viruses pose a continuous threat to both poultry and human health, with significant economic impact. The ability of viruses to reassort and jump the species barrier into mammalian hosts generates a constant pandemic threat. H10Nx avian viruses have been shown to replicate in mammalian species without prior adaptation and have caused significant human infection and fatalities. They are able to rapidly reassort with circulating poultry strains and go undetected due to their low pathogenicity in chickens. Novel detections of both human reassortant strains and increasing endemicity of H10Nx poultry infections highlight the increasing need for heightened surveillance and greater understanding of the distribution, tropism, and infection capabilities of these viruses. In this minireview, we highlight the gap in the current understanding of this subtype and its prevalence across a vast range of host species and geographical locations.

Pathogenicity of novel reassortant Eurasian avian-like H1N1 influenza virus in pigs

Reassortant Eurasian avian-like (EA) H1N1 virus, possessing 2009 pandemic (pdm/09) and triple-reassortant (TR)-derived internal genes, namely G4 genotype, has replaced the G1 genotype EA H1N1 virus (all the genes were of EA origin) and become predominant in swine populations in China. Understanding the pathogenicity of G4 viruses in pigs is of great importance for disease control. Here, we conducted comprehensive analyses of replication and pathogenicity of G4 and G1 EA H1N1 viruses in pigs. G4 virus exhibited enhanced replication, increased duration of virus shedding, and caused more severe respiratory lesions in pigs compared with G1 virus. G4 virus, with viral ribonucleoprotein (vRNP) complex genes of pdm/09 origin, exhibited higher levels of nuclear accumulation and higher polymerase activity, which is essential for improved replication of G4 virus. These findings indicate that G4 virus poses a great threat to both swine industry and public health, and control measures should be urgently implemented.