The ecology and adaptive evolution of influenza A interspecies transmission

Pigs are highly susceptible to but do not transmit mink-derived highly pathogenic avian influenza virus H5N1 clade 2.3.4.4b

ABSTRACTRapid evolution of highly pathogenic avian influenza viruses (HPAIVs) is driven by antigenic drift but also by reassortment, which might result in robust replication in and transmission to mammals. Recently, spillover of clade 2.3.4.4b HPAIV to mammals including humans, and their transmission between mammalian species has been reported. This study aimed to evaluate the pathogenicity and transmissibility of a mink-derived clade 2.3.4.4b H5N1 HPAIV isolate from Spain in pigs. Experimental infection caused interstitial pneumonia with necrotizing bronchiolitis with high titers of virus present in the lower respiratory tract and 100% seroconversion. Infected pigs shed limited amount of virus, and importantly, there was no transmission to contact pigs. Notably, critical mammalian-like adaptations such as PB2-E627 K and HA-Q222L emerged at low frequencies in principal-infected pigs. It is concluded that pigs are highly susceptible to infection with the mink-derived clade 2.3.4.4b H5N1 HPAIV and provide a favorable environment for HPAIV to acquire mammalian-like adaptations.

Emergence of Eurasian Avian-Like Swine Influenza A (H1N1) virus in a child in Shandong Province, China

BACKGROUND

Influenza A virus infections can occur in multiple species. Eurasian avian-like swine influenza A (H1N1) viruses (EAS-H1N1) are predominant in swine and occasionally infect humans. A Eurasian avian-like swine influenza A (H1N1) virus was isolated from a boy who was suffering from fever; this strain was designated A/Shandong-binzhou/01/2021 (H1N1). The aims of this study were to investigate the characteristics of this virus and to draw attention to the need for surveillance of influenza virus infection in swine and humans.

METHODS

Throat-swab specimens were collected and subjected to real-time fluorescent quantitative polymerase chain reaction (RT‒PCR). Positive clinical specimens were inoculated onto Madin-Darby canine kidney (MDCK) cells to isolate the virus, which was confirmed by a haemagglutination assay. Then, whole-genome sequencing was carried out using an Illumina MiSeq platform, and phylogenetic analysis was performed with MEGA X software.

RESULTS

RT‒PCR revealed that the throat-swab specimens were positive for EAS-H1N1, and the virus was subsequently successfully isolated from MDCK cells; this strain was named A/Shandong-binzhou/01/2021 (H1N1). Whole-genome sequencing and phylogenetic analysis revealed that A/Shandong-binzhou/01/2021 (H1N1) is a novel triple-reassortant EAS-H1N1 lineage that contains gene segments from EAS-H1N1 (HA and NA), triple-reassortant swine influenza H1N2 virus (NS) and A(H1N1) pdm09 viruses (PB2, PB1, PA, NP and MP).

CONCLUSIONS

The isolation and analysis of the A/Shandong-binzhou/01/2021 (H1N1) virus provide further evidence that EAS-H1N1 poses a threat to human health, and greater attention should be given to the surveillance of influenza virus infections in swine and humans.

Molecular characterization of the whole genome of H9N2 avian influenza virus isolated from Egyptian poultry farms

H9N2 avian influenza viruses (AIVs) affect both poultry and humans on a global level, and they are especially prevalent in Egypt. In this study, we sequenced the entire genome of AIV H9N2 isolated from chickens in Egypt in 2021, using next-generation sequencing (NGS) technology. Phylogenetic analysis of the resulting sequences showed that the studied strain was generally monophyletic and grouped within the G1 sublineage of the Eurasian lineage. Four segments (polymerase basic 2 [PB2], polymerase basic 1 [PB1], polymerase acidic [PA], and non-structural [NS]) were related to Egyptian genotype II, while the nucleoprotein (NP), neuraminidase (NA), matrix (M), and haemagglutinin (HA) segments were related to Egyptian genotype I. Molecular analysis revealed that HA protein contained amino acid residues (191H and 234L) that suggested a predilection for attaching to human-like receptors. The antigenic sites of HA had two nonsynonymous mutations: V194I at antigenic site A and M40K at antigenic site B. Furthermore, the R403W and S372A mutations, which have been observed in H3N2 and H2N2 strains that caused human pandemics, were found in the NA protein of the detected strain. The internal proteins contained virulence markers: 504V in the PB2 protein, 622G, 436Y, 207K, and 677T in the PB1 protein, 127V, 550L, and 672L in PA protein, and 64F and 69P in the M protein. These results show that the detected strain had undergone intrasubtype reassortment. Furthermore, it contains changes in the viral proteins that make it more likely to be virulent, raising a question about the tendency of AIV H9N2 to become highly pathogenic in the future for both poultry and humans.

Diversity and prevalence of zoonotic infections at the animal-human interface of primate trafficking in Peru

Wildlife trafficking creates favorable scenarios for intra- and inter-specific interactions that can lead to parasite spread and disease emergence. Among the fauna affected by this activity, primates are relevant due to their potential to acquire and share zoonoses - infections caused by parasites that can spread between humans and other animals. Though it is known that most primate parasites can affect multiple hosts and that many are zoonotic, comparative studies across different contexts for animal-human interactions are scarce. We conducted a multi-parasite screening targeting the detection of zoonotic infections in wild-caught monkeys in nine Peruvian cities across three contexts: captivity (zoos and rescue centers, n = 187); pet (households, n = 69); and trade (trafficked or recently confiscated, n = 132). We detected 32 parasite taxa including mycobacteria, simian foamyvirus, bacteria, helminths, and protozoa. Monkeys in the trade context had the highest prevalence of hemoparasites (including Plasmodium malariae/brasilianum, Trypanosoma cruzi, and microfilaria) and enteric helminths and protozoa were less common in pet monkeys. However, parasite communities showed overall low variation between the three contexts. Parasite richness (PR) was best explained by host genus and the city where the animal was sampled. Squirrel (genus Saimiri) and wooly (genus Lagothrix) monkeys had the highest PR, which was ~2.2 times the PR found in tufted capuchins (genus Sapajus) and tamarins (genus Saguinus/Leontocebus) in a multivariable model adjusted for context, sex, and age. Our findings illustrate that the threats of wildlife trafficking to One Health encompass exposure to multiple zoonotic parasites well-known to cause disease in humans, monkeys, and other species. We demonstrate these threats continue beyond the markets where wildlife is initially sold; monkeys trafficked for the pet market remain a reservoir for and contribute to the translocation of zoonotic parasites to households and other captive facilities where contact with humans is frequent. Our results have practical applications for the healthcare of rescued monkeys and call for urgent action against wildlife trafficking and ownership of monkeys as pets.

Nanomaterial-based biosensors for avian influenza virus: A new way forward

Avian influenza virus (AIV) is a zoonotic virus that can be transmitted from animals to humans. Although human infections are rare, the virus has a high mortality rate when contracted. Appropriate detection methods are thus crucial for combatting this pathogen. There is a growing demand for rapid, selective, and accurate methods of identifying the virus. Numerous biosensors have been designed and commercialized to detect AIV. However, they all have considerable shortcomings. Nanotechnology offers a new way forward. Nanomaterials produce more eco-friendly, rapid, and portable diagnostic systems. They also exhibit high sensitivity and selectivity while achieving a low detection limit (LOD). This paper reviews state-of-the-art nanomaterial-based biosensors for AIV detection, such as those composed of quantum dots, gold, silver, carbon, silica, nanodiamond, and other nanoparticles. It also offers insight into potential trial protocols for creating more effective methods of identifying AIV and discusses key issues associated with developing nanomaterial-based biosensors.

Phylodynamic approaches to studying avian influenza virus

Avian influenza viruses can cause severe disease in domestic and wild birds and are a pandemic threat. Phylodynamics is the study of how epidemiological, evolutionary, and immunological processes can interact to shape viral phylogenies. This review summarizes how phylodynamic methods have and could contribute to the study of avian influenza viruses. Specifically, we assess how phylodynamics can be used to examine viral spread within and between wild or domestic bird populations at various geographical scales, identify factors associated with virus dispersal, and determine the order and timing of virus lineage movement between geographic regions or poultry production systems. We discuss factors that can complicate the interpretation of phylodynamic results and identify how future methodological developments could contribute to improved control of the virus.

Comparative analysis of PB2 residue 627E/K/V in H5 subtypes of avian influenza viruses isolated from birds and mammals

Avian influenza viruses (AIVs) are naturally found in wild birds, primarily in migratory waterfowl. Although species barriers exist, many AIVs have demonstrated the ability to jump from bird species to mammalian species. A key contributor to this jump is the adaption of the viral RNA polymerase complex to a new host for efficient replication of its RNA genome. The AIV PB2 gene appears to be essential in this conversion, as key residues have been discovered at amino acid position 627 that interact with the host cellular protein, acidic nuclear phosphoprotein 32 family member A (ANP32A). In particular, the conversion of glutamic acid (E) to lysine (K) is frequently observed at this position following isolation in mammals. The focus of this report was to compare the distribution of PB2 627 residues from different lineages and origins of H5 AIV, determine the prevalence between historical and contemporary sequences, and investigate the ratio of amino acids in avian vs. mammalian AIV sequences. Results demonstrate a low prevalence of E627K in H5 non-Goose/Guangdong/1996-lineage (Gs/GD) AIV samples, with a low number of mammalian sequences in general. In contrast, the H5-Gs/GD lineage sequences had an increased prevalence of the E627K mutation and contained more mammalian sequences. An approximate 40% conversion of E to K was observed in human sequences of H5 AIV, suggesting a non-exclusive requirement. Taken together, these results expand our understanding of the distribution of these residues within different subtypes of AIV and aid in our knowledge of PB2 mutations in different species.

Efficacy of oseltamivir treatment in influenza virus-infected obese mice

Obesity has been epidemiologically and empirically linked with more severe diseases upon influenza infection. To ameliorate severe disease, treatment with antivirals, such as the neuraminidase inhibitor oseltamivir, is suggested to begin within days of infection especially in high-risk hosts. However, this treatment can be poorly effective and may generate resistance variants within the treated host. Here, we hypothesized that obesity would reduce oseltamivir treatment effectiveness in the genetically obese mouse model. We demonstrated that oseltamivir treatment does not improve viral clearance in obese mice. While no traditional variants associated with oseltamivir resistance emerged, we did note that drug treatment failed to quench the viral population and did lead to phenotypic drug resistance in vitro. Together, these studies suggest that the unique pathogenesis and immune responses in obese mice could have implications for pharmaceutical interventions and the within-host dynamics of the influenza virus population. IMPORTANCE Influenza virus infections, while typically resolving within days to weeks, can turn critical, especially in high-risk populations. Prompt antiviral administration is crucial to mitigating these severe sequalae, yet concerns remain if antiviral treatment is effective in hosts with obesity. Here, we show that oseltamivir does not improve viral clearance in genetically obese or type I interferon receptor-deficient mice. This suggests a blunted immune response may impair oseltamivir efficacy and render a host more susceptible to severe disease. This study furthers our understanding of oseltamivir treatment dynamics both systemically and in the lungs of obese mice, as well as the consequences of oseltamivir treatment for the within-host emergence of drug-resistant variants.

Ribavirin inhibits the replication of infectious bursal disease virus predominantly through depletion of cellular guanosine pool

Introduction

The antiviral activity of different mutagens against single-stranded RNA viruses is well documented; however, their activity on the replication of double-stranded RNA viruses remains unexplored. This study aims to investigate the effect of different antivirals on the replication of a chicken embryo fibroblast-adapted Infectious Bursal Disease virus, FVSKG2. This study further explores the antiviral mechanism utilized by the most effective anti-IBDV agent.

Methods

The cytotoxicity and anti-FVSKG2 activity of different antiviral agents (ribavirin, 5-fluorouracil, 5-azacytidine, and amiloride) were evaluated. The virus was serially passaged in chicken embryo fibroblasts 11 times at sub-cytotoxic concentrations of ribavirin, 5-fluorouracil or amiloride. Further, the possible mutagenic and non-mutagenic mechanisms utilized by the most effective anti-FVSKG2 agent were explored.

Results and Discussion

Ribavirin was the least cytotoxic on chicken embryo fibroblasts, followed by 5-fluorouracil, amiloride and 5-azacytidine. Ribavirin inhibited the replication of FVSKG2 in chicken embryo fibroblasts significantly at concentrations as low as 0.05 mM. The extinction of FVSKG2 was achieved during serial passage of the virus in chicken embryo fibroblasts at ≥0.05 mM ribavirin; however, the emergence of a mutagen-resistant virus was not observed until the eleventh passage. Further, no mutation was observed in 1,898 nucleotides of the FVSKG2 following its five passages in chicken embryo fibroblasts in the presence of 0.025 mM ribavirin. Ribavarin inhibited the FVSKG2 replication in chicken embryo fibroblasts primarily through IMPDH-mediated depletion of the Guanosine Triphosphate pool of cells. However, other mechanisms like ribavirin-mediated cytokine induction or possible inhibition of viral RNA-dependent RNA polymerase through its interaction with the enzyme's active sites enhance the anti-IBDV effect. Ribavirin inhibits ds- RNA viruses, likely through IMPDH inhibition and not mutagenesis. The inhibitory effect may, however, be augmented by other non-mutagenic mechanisms, like induction of antiviral cytokines in chicken embryo fibroblasts or interaction of ribavirin with the active sites of RNA-dependent RNA polymerase of the virus.

Monoclonal antibody targeting a novel linear epitope on nucleoprotein confers pan-reactivity to influenza A virus

Nucleoprotein (NP) functions crucially in the replicative cycle of influenza A virus (IAV) via forming the ribonucleoprotein complex together with PB2, PB1, and PA proteins. As its high conservation, NP ranks one of the hot targets for design of universal diagnostic reagents and antiviral drugs for IAV. Here, we report an anti-NP murine monoclonal antibody (mAb) 5F10 prepared from traditional lymphocyte hybridoma technique with the immunogen of a clade 2.3.4.4 H5N1 subtype avian influenza virus. The specificity of mAb 5F10 to NP protein was confirmed by immunofluorescence assay and western blotting, and the mAb 5F10 could be used in immunoprecipitation and immunohistochemistry assays. Importantly, mAb 5F10 possessed broad-spectrum reactivity against H1~H11 subtypes of avian influenza viruses, including various HA clades of H5Nx subtype. In addition, mAb 5F10 also showed good affinity with H1N1 and H3N2 subtype influenza viruses of swine and human origin. Furthermore, the recognized antigenic epitope of mAb 5F10 was identified to consist of the conserved amino acid motif ⁸¹EHPSA⁸⁵ in the second flexible loop region of NP protein through screening the phage display peptide library. Collectively, the mAb 5F10 which recognizes the novel universal NP linear B-cell epitope of IAV with diverse origins and subtypes will be a powerful tool for NP protein-based structural, functional, and mechanistic studies, as well as the development of detection methods and universal vaccines for IAV. KEY POINTS: • A broad-spectrum mAb against various subtypes and sources of IAV was developed • The mAb possessed good reactivity in IFA, western blot, IP, and IHC assays • The mAb targeted a novel conserved linear B-cell epitope involving ⁸¹EHPSA⁸⁵ on NP protein.

Antiviral Potential of the Genus Panax: An updated review on their effects and underlying mechanism of action

Viral infections are known as one of the major factors causing death. Ginseng is a medicinal plant that demonstrated a wide range of antiviral potential, and saponins are the major bioactive ingredients in the genus Panax with vast therapeutic potential. Studies focusing on the antiviral activity of the genus Panax plant-derived agents (extracts and saponins) and their mechanisms were identified and summarized, including contributions mainly from January 2016 until January 2022. P. ginseng, P. notoginseng, and P. quinquefolius were included in the review as valuable medicinal herbs against infections with 14 types of viruses. Reports from 9 extracts and 12 bioactive saponins were included, with 6 types of protopanaxadiol (PPD) ginsenosides and 6 types of protopanaxatriol (PPT) ginsenosides. The mechanisms mainly involved the inhibition of viral attachment and replication, the modulation of immune response by regulating signaling pathways, including the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway, cystathionine γ-lyase (CSE)/hydrogen sulfide (H₂S) pathway, phosphoinositide-dependent kinase-1 (PDK1)/ protein kinase B (Akt) signaling pathway, c-Jun N-terminal kinase (JNK)/activator protein-1 (AP-1) pathway, and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathway. This review includes detailed information about the mentioned antiviral effects of the genus Panax extracts and saponins in vitro and in vivo, and in human clinical trials, which provides a scientific basis for ginseng as an adjunctive therapeutic drug or nutraceutical.

Infectivity and transmissibility of an avian H3N1 influenza virus in pigs

In 2019 a low pathogenic H3N1 avian influenza virus (AIV) caused an outbreak in Belgian poultry farms, characterized by an unusually high mortality in chickens. Influenza A viruses of the H1 and H3 subtype can infect pigs and become established in swine populations. Therefore, the H3N1 epizootic raised concern about AIV transmission to pigs and from pigs to humans. Here, we assessed the replication efficiency of this virus in explants of the porcine respiratory tract and in pigs, using virus titration and/or RT-qPCR. We also examined transmission from directly, intranasally inoculated pigs to contact pigs. The H3N1 AIV replicated to moderate titers in explants of the bronchioles and lungs, but not in the nasal mucosa or trachea. In the pig infection study, infectious virus was only detected in a few lung samples collected between 1 and 3 days post-inoculation. Virus titers were between 1.7 and 4.8 log₁₀ TCID₅₀. In line with the ex vivo experiment, no virus was isolated from the upper respiratory tract of pigs. In the transmission experiment, we could not detect virus transmission from directly inoculated to contact pigs. An increase in serum antibody titers was observed only in the inoculated pigs. We conclude that the porcine respiratory tract tissue explants can be a useful tool to assess the replication efficiency of AIVs in pigs. The H3N1 AIV examined here is unlikely to pose a risk to swine populations. However, continuous risk assessment studies of emerging AIVs in pigs are necessary, since different virus strains will have different genotypic and phenotypic traits.

Research progress on the antiviral activities of natural products and their derivatives: Structure–activity relationships

Viruses spread rapidly and are well-adapted to changing environmental events. They can infect the human body readily and trigger fatal diseases. A limited number of drugs are available for specific viral diseases, which can lead to non-efficacy against viral variants and drug resistance, so drugs with broad-spectrum antiviral activity are lacking. In recent years, a steady stream of new viral diseases has emerged, which has prompted development of new antiviral drugs. Natural products could be employed to develop new antiviral drugs because of their innovative structures and broad antiviral activities. This review summarizes the progress of natural products in antiviral research and their bright performance in drug resistance issues over the past 2 decades. Moreover, it fully discusses the effect of different structural types of natural products on antiviral activity in terms of structure–activity relationships. This review could provide a foundation for the development of antiviral drugs.

Full-Length Genome of the Equine Influenza A Virus Subtype H3N8 from 2019 Outbreak in Saudi Arabia

Simple Summary

Equine influenza is a highly contagious respiratory viral disease. The current study is the first to provide a description of the full-length genome sequence and surveillance of recent exposure to the equine influenza virus (EIV) during the 2019 epidemic in Saudi Arabia. This epidemic was benign, since it resulted in low case fatality (0.45%, 1/224). The viruses detected in the current study were found to be related to subtype H73N8 clade 1 of the Florida sublineage. Full-length genome sequencing revealed no evidence of major genetic changes or of reassortment among the eight segments of the viral genome. However, the Saudi strains showed a considerable number of amino acid substitutions in the signal peptide (2 amino acid substitutions), HA1 (10 amino acid substitutions) and HA2 (4 amino acid substitutions) in the haemagglutinin glycoprotein in comparison to clade 1 Florida sublineage vaccinal strains. These findings should be considered during selection of the equine influenza vaccine strains approved for use in Saudi Arabia.

Abstract

Equine influenza is a major cause of respiratory infections in horses and can spread rapidly despite the availability of commercial vaccines. This study aimed to screen the incidence of equine influenza virus (EIV) and molecularly characterize the haemagglutinin and neuraminidase from positive EIV field samples collected from Saudi Arabia. Six-hundred twenty-one horses from 57 horse barns were screened for the presence of the clinical signs, suggestive for equine influenza, from different parts of Saudi Arabia. Nasopharyngeal swabs were collected from each horse showing respiratory distress. Samples from the same horse barn were pooled together and screened for the presence of the influenza A virus using quantitative real time reverse transcriptase polymerase chain reaction (qRT-PCR). Selective positive samples were subjected to full-length genome sequencing using MiSeq Illumina. Out of the total 57 pools, 39 were found positive to EIV using qRT-PCR. Full-length gene sequences were compared with representative EIV strains selected from the GenBank database. Phylogenetic analysis of the HA and NA genes revealed that the identified virus strains belong to H3N8 clade 1 of the Florida sublineage and were very similar to viruses identified in USA in 2019, with no current evidence for reassortment. This is one of the first reports providing detailed description and characterization of EIVs in Saudi Arabia. Detailed surveillance and genetic information sharing could allow genetic evolution of equine influenza viruses to be monitored more effectively on a global basis and aid in refinement of vaccine strain selection for EIV.

Increased virulence of a novel reassortant H1N3 avian influenza virus in mice as a result of adaptive amino acid substitutions

In this study, a novel multiple-gene reassortant H1N3 subtype avian influenza virus (AIV) (A/chicken/Zhejiang/81213/2017, CK81213) was isolated in Eastern China, whose genes were derived from H1 (H1N3), H7 (H7N3 and H7N9), and H10 (H10N3 and H10N8) AIVs. This AIV belongs to the avian Eurasian-lineage and exhibits low pathogenicity. Serial lung-to-lung passages of CK81213 in mice was performed to study the amino acid substitutions potentially related to the adaptation of H1 AIVs in mammals. And the mouse-adapted H1N3 virus showed greater virulence than wild-type H1N3 AIV in mice and the genomic analysis revealed a total of two amino acid substitutions in the PB2 (E627K) and HA (L67V) proteins. Additionally, the results of the animal study indicate that CK81213 could infect mice without prior adaption and become highly pathogenic to mice after continuous passage. Our findings show that routine surveillance of H1 AIVs is important for the prediction of influenza epidemics.

Characterization of an intracellular humanized single-chain antibody to matrix protein (M1) of H5N1 virus

We developed a human intracellular antibody based on the M1 protein from avian influenza virus H5N1 (A/meerkat/Shanghai/SH-1/2012) and then characterized the properties of this antibody. The M1 protein sequence was amplified by RT-PCR using the cDNA of the H5N1 virus as a template, expressed in bacterial expression system BL21 (DE3) and purified. A human strain, high affinity, and single chain antibody (HuScFv) against M1 protein was obtained by phage antibody library screening using M1 as an antigen. A recombinant TAT-HuScFv protein was expressed by fusion with the TAT protein transduction domain (PTD) gene of HIV to prepare a human intracellular antibody against avian influenza virus. Further analysis demonstrated that TAT-HuScFv could inhibit the hemagglutination activity of the 300 TCID50 H1N1 virus, thus providing preliminary validation of the universality of the antibody. After two rounds of M1 protein decomposition, the TAT-HuScFv antigen binding site was identified as Alanine (A) at position 239. Collectively, our data describe a recombinant antibody with high binding activity against the conserved sequences of avian influenza viruses. This intracellular recombinant antibody blocked the M1 protein that infected intracellular viruses, thus inhibiting the replication and reproduction of H5N1 viruses.

Diversity and evolution of the animal virome

The COVID-19 pandemic has given the study of virus evolution and ecology new relevance. Although viruses were first identified more than a century ago, we likely know less about their diversity than that of any other biological entity. Most documented animal viruses have been sampled from just two phyla - the Chordata and the Arthropoda - with a strong bias towards viruses that infect humans or animals of economic and social importance, often in association with strong disease phenotypes. Fortunately, the recent development of unbiased metagenomic next-generation sequencing is providing a richer view of the animal virome and shedding new light on virus evolution. In this Review, we explore our changing understanding of the diversity, composition and evolution of the animal virome. We outline the factors that determine the phylogenetic diversity and genomic structure of animal viruses on evolutionary timescales and show how this impacts assessment of the risk of disease emergence in the short term. We also describe the ongoing challenges in metagenomic analysis and outline key themes for future research. A central question is how major events in the evolutionary history of animals, such as the origin of the vertebrates and periodic mass extinction events, have shaped the diversity and evolution of the viruses they carry.

Three-Dimensional Cell Culture Models to Study Respiratory Virus Infections Including COVID-19

Respiratory viral infections, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), are among the most common illnesses and a leading cause of morbidity and mortality worldwide. Due to the severe effects on health, the need of new tools to study the pathogenesis of respiratory viruses as well as to test for new antiviral drugs and vaccines is urgent. In vitro culture model systems, such as three-dimensional (3D) cultures, are emerging as a desirable approach to understand the virus host interactions and to identify novel therapeutic agents. In the first part of the article, we address the various scaffold-free and scaffold-based 3D culture models such as hydrogels, bioreactors, spheroids and 3D bioprinting as well as present their properties and advantages over conventional 2D methods. Then, we review the 3D models that have been used to study the most common respiratory viruses including influenza, parainfluenza, respiratory syncytial virus (RSV) and coronaviruses. Herein, we also explain how 3D models have been applied to understand the novel SARS-CoV-2 infectivity and to develop potential therapies.

Molecular Analysis of the Avian H7 Influenza Viruses Circulating in South Korea during 2018-2019: Evolutionary Significance and Associated Zoonotic Threats

Avian influenza virus (AIV) subtypes H5 and H7, possessing the ability to mutate spontaneously from low pathogenic (LP) to highly pathogenic (HP) variants, are major concerns for enormous socio-economic losses in the poultry industry, as well as for fatal human infections. Through antigenic drift and shift, genetic reassortments of the genotypes pose serious threats of increased virulence and pathogenicity leading to potential pandemics. In this study, we isolated the H7-subtype AIVs circulating in the Republic of Korea during 2018–2019, and perform detailed molecular analysis to study their circulation, evolution, and possible emergence as a zoonotic threat. Phylogenetic and nucleotide sequence analyses of these isolates revealed their distribution into two distinct clusters, with the HA gene sharing the highest nucleotide identity with either the A/common teal/Shanghai/CM1216/2017, isolated from wild birds in Shanghai, China, or the A/duck/Shimane/2014, isolated from Japan. Mutations were found in HA (S138A (H3 numbering)), M1 (N30D and T215A), NS1 (P42S), PB2 (L89V), and PA (H266R and F277S) proteins—the mutations had previously been reported to be related to mammalian adaptation and changes in the virulence of AIVs. Taken together, the results firmly put forth the demand for routine surveillance of AIVs in wild birds to prevent possible pandemics arising from reassortant AIVs.

Analysis of the Genetic Diversity Associated With the Drug Resistance and Pathogenicity of Influenza A Virus Isolated in Bangladesh From 2002 to 2019

The subtype prevalence, drug resistance- and pathogenicity-associated mutations, and the distribution of the influenza A virus (IAV) isolates identified in Bangladesh from 2002 to 2019 were analyzed using bioinformatic tools. A total of 30 IAV subtypes have been identified in humans (4), avian species (29), and environment (5) in Bangladesh. The predominant subtypes in human and avian species are H1N1/H3N2 and H5N1/H9N2, respectively. However, the subtypes H5N1/H9N2 infecting humans and H3N2/H1N1 infecting avian species have also been identified. Among the avian species, the maximum number of subtypes (27) have been identified in ducks. A 3.56% of the isolates showed neuraminidase inhibitor (NAI) resistance with a prevalence of 8.50, 1.33, and 2.67% in avian species, humans, and the environment, respectively, the following mutations were detected: V116A, I117V, D198N, I223R, S247N, H275Y, and N295S. Prevalence of adamantane-resistant IAVs was 100, 50, and 30.54% in humans, the environment, and avian species, respectively, the subtypes H3N2, H1N1, H9N2, and H5N2 were highly prevalent, with the subtype H5N1 showing a comparatively lower prevalence. Important PB2 mutations such D9N, K526R, A588V, A588I, G590S, Q591R, E627K, K702R, and S714R were identified. A wide range of IAV subtypes have been identified in Bangladesh with a diversified genetic variation in the NA, M2, and PB2 proteins providing drug resistance and enhanced pathogenicity. This study provides a detailed analysis of the subtypes, and the host range of the IAV isolates and the genetic variations related to their proteins, which may aid in the prevention, treatment, and control of IAV infections in Bangladesh, and would serve as a basis for future investigations.

Emergence of a novel reassortant avian influenza virus (H10N3) in Eastern China with high pathogenicity and respiratory droplet transmissibility to mammals

Decades have passed since the first discovery of H10-subtype avian influenza virus (AIV) in chickens in 1949, and it has been detected in many species including mammals such as minks, pigs, seals and humans. Cases of human infections with H10N8 viruses identified in China in 2013 have raised widespread attention. Two novel reassortant H10N3 viruses were isolated from chickens in December 2019 in eastern China during routine surveillance for AIVs. The internal genes of these viruses were derived from genotype S (G57) H9N2 and were consistent with H5N6, H7N9 and H10N8, which cause fatal infections in humans. Their viral pathogenicity and transmissibility were further studied in different animal models. The two H10N3 isolates had low pathogenicity in chickens and were transmitted between chickens via direct contact. These viruses were highly pathogenic in mice and could be transmitted between guinea pigs via direct contact and respiratory droplets. More importantly, these viruses can bind to both human-type SAα-2,6-Gal receptors and avian-type SAα-2,3-Gal receptors. Asymptomatic shedding in chickens and good adaptability to mammals of these H10N3 isolates would make it easier to transmit to humans and pose a threat to public health.

Survey on the Presence of Viruses of Economic and Zoonotic Importance in Avifauna in Northern Italy

Wild birds play an important role in the circulation and spread of pathogens that are potentially zoonotic or of high economic impact on zootechnical production. They include, for example, West Nile virus (WNV), Usutu virus (USUV), avian influenza virus (AIV), and Newcastle disease virus (NDV), which, despite having mostly an asymptomatic course in wild birds, have a strong impact on public health and zootechnical production. This study investigated the presence of these viruses in several wild bird species from North Italy during the biennium 2019-2020. Wild birds derived from 76 different species belonging to 20 orders. Out of 679 birds, 27 were positive for WNV (lineage 2) with a prevalence of 4%; all birds were negative for USUV; one gull was positive for H13N6 influenza virus, and 12 samples were positive for NDV with a prevalence of 2%. Despite the low prevalence observed, the analyses performed on these species provide further data, allowing a better understanding of the diffusion and evolution of diseases of both economic and zoonotic importance.

Complement Decay-Accelerating Factor is a modulator of influenza A virus lung immunopathology

Clearance of viral infections, such as SARS-CoV-2 and influenza A virus (IAV), must be fine-tuned to eliminate the pathogen without causing immunopathology. As such, an aggressive initial innate immune response favors the host in contrast to a detrimental prolonged inflammation. The complement pathway bridges innate and adaptive immune system and contributes to the response by directly clearing pathogens or infected cells, as well as recruiting proinflammatory immune cells and regulating inflammation. However, the impact of modulating complement activation in viral infections is still unclear. In this work, we targeted the complement decay-accelerating factor (DAF/CD55), a surface protein that protects cells from non-specific complement attack, and analyzed its role in IAV infections. We found that DAF modulates IAV infection in vivo, via an interplay with the antigenic viral proteins hemagglutinin (HA) and neuraminidase (NA), in a strain specific manner. Our results reveal that, contrary to what could be expected, DAF potentiates complement activation, increasing the recruitment of neutrophils, monocytes and T cells. We also show that viral NA acts on the heavily sialylated DAF and propose that the NA-dependent DAF removal of sialic acids exacerbates complement activation, leading to lung immunopathology. Remarkably, this mechanism has no impact on viral loads, but rather on the host resilience to infection, and may have direct implications in zoonotic influenza transmissions.

Exacerbated complement activation and immune deregulation are at the basis of several pathologies induced by respiratory viruses. Here, we report that complement decay-accelerating factor (DAF), which inhibits complement activation in healthy cells, increases disease severity upon influenza A virus (IAV) infection. Remarkably, DAF interaction with IAV proteins, hemagglutinin (HA) and neuraminidase (NA), resulted in excessive complement activation and recruitment of innate and adaptive immune cells, without affecting viral loads. Furthermore, we observed that viral NA directly cleaves DAF and promotes complement activation, providing a possible link between IAV-DAF interaction and pathology. Therefore, our results unveil a novel pathway that could modulate disease severity, which may help to understand the increased pathogenicity of zoonotic and pandemic IAV infections.

Influenza Virus and SARS-CoV-2 Vaccines

Seasonal influenza and the current COVID-19 pandemic represent looming global health challenges. Efficacious and safe vaccines remain the frontline tools for mitigating both influenza virus and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-induced diseases. This review will discuss the existing strategies for influenza vaccines and how these strategies have informed SARS-CoV-2 vaccines. It will also discuss new vaccine platforms and potential challenges for both viruses.

Avian Influenza in Wild Birds and Poultry: Dissemination Pathways, Monitoring Methods, and Virus Ecology

Avian influenza is one of the largest known threats to domestic poultry. Influenza outbreaks on poultry farms typically lead to the complete slaughter of the entire domestic bird population, causing severe economic losses worldwide. Moreover, there are highly pathogenic avian influenza (HPAI) strains that are able to infect the swine or human population in addition to their primary avian host and, as such, have the potential of being a global zoonotic and pandemic threat. Migratory birds, especially waterfowl, are a natural reservoir of the avian influenza virus; they carry and exchange different virus strains along their migration routes, leading to antigenic drift and antigenic shift, which results in the emergence of novel HPAI viruses. This requires monitoring over time and in different locations to allow for the upkeep of relevant knowledge on avian influenza virus evolution and the prevention of novel epizootic and epidemic outbreaks. In this review, we assess the role of migratory birds in the spread and introduction of influenza strains on a global level, based on recent data. Our analysis sheds light on the details of viral dissemination linked to avian migration, the viral exchange between migratory waterfowl and domestic poultry, virus ecology in general, and viral evolution as a process tightly linked to bird migration. We also provide insight into methods used to detect and quantify avian influenza in the wild. This review may be beneficial for the influenza research community and may pave the way to novel strategies of avian influenza and HPAI zoonosis outbreak monitoring and prevention.

Hemagglutinin Stability and Its Impact on Influenza A Virus Infectivity, Pathogenicity, and Transmissibility in Avians, Mice, Swine, Seals, Ferrets, and Humans

Genetically diverse influenza A viruses (IAVs) circulate in wild aquatic birds. From this reservoir, IAVs sporadically cause outbreaks, epidemics, and pandemics in wild and domestic avians, wild land and sea mammals, horses, canines, felines, swine, humans, and other species. One molecular trait shown to modulate IAV host range is the stability of the hemagglutinin (HA) surface glycoprotein. The HA protein is the major antigen and during virus entry, this trimeric envelope glycoprotein binds sialic acid-containing receptors before being triggered by endosomal low pH to undergo irreversible structural changes that cause membrane fusion. The HA proteins from different IAV isolates can vary in the pH at which HA protein structural changes are triggered, the protein causes membrane fusion, or outside the cell the virion becomes inactivated. HA activation pH values generally range from pH 4.8 to 6.2. Human-adapted HA proteins tend to have relatively stable HA proteins activated at pH 5.5 or below. Here, studies are reviewed that report HA stability values and investigate the biological impact of variations in HA stability on replication, pathogenicity, and transmissibility in experimental animal models. Overall, a stabilized HA protein appears to be necessary for human pandemic potential and should be considered when assessing human pandemic risk.

Insights into RNA-dependent RNA Polymerase Inhibitors as Antiinfluenza Virus Agents

BACKGROUND

Influenza is a seasonal disease that affects millions of people every year and has a significant economic impact. Vaccines are the best strategy to fight this viral pathology, but they are not always available or administrable, prompting the search for antiviral drugs. RNA-dependent RNA polymerase (RdRp) recently emerged as a promising target because of its key role in viral replication and its high conservation among viral strains.

DISCUSSION

This review presents an overview of the most interesting RdRp inhibitors that have been discussed in the literature since 2000. Compounds already approved or in clinical trials and a selection of inhibitors endowed with different scaffolds are described, along with the main features responsible for their activity.

RESULTS

RdRp inhibitors are emerging as a new strategy to fight viral infections and the importance of this class of drugs has been confirmed by the FDA approval of baloxavir marboxil in 2018. Despite the complexity of the RdRp machine makes the identification of new compounds a challenging research topic, it is likely that in the coming years, this field will attract the interest of a number of academic and industrial scientists because of the potential strength of this therapeutic approach.

Ambient hydrogen sulfide exposure increases the severity of influenza A virus infection in swine

Hydrogen sulfide (H₂S) is common in concentrated pig feed operations from the decomposition of manure. Ambient H₂S is a respiratory tract irritant and an environmental stressor for caretakers and pigs. Influenza A virus (IAV), a zoonotic pathogen, has caused prior pandemics. The effects of H₂S or IAV alone on the respiratory system have been investigated, but their interaction has not. We hypothesized that exposure to environmentally-relevant H₂S concentrations increases the pathogenicity of IAV infection in swine. Thirty-five, three-week old pigs of mixed sex were exposed to breathing air or H₂S via inhalation 6 hours daily for 12 days. After 7 days, pigs were inoculated with H3N2 IAV (or a placebo). Results showed that ambient H₂S increased the severity of respiratory distress and lung pathology. H₂S also suppressed IL-IL-1β, IL-6 and IL-8 cytokine response in BALF and increased viral loads and nasal shedding.

Nucleic Acid-Based Sensing Techniques for Diagnostics and Surveillance of Influenza

Influenza virus poses a threat to global health by causing seasonal outbreaks as well as three pandemics in the 20th century. In humans, disease is primarily caused by influenza A and B viruses, while influenza C virus causes mild disease mostly in children. Influenza D is an emerging virus found in cattle and pigs. To mitigate the morbidity and mortality associated with influenza, rapid and accurate diagnostic tests need to be deployed. However, the high genetic diversity displayed by influenza viruses presents a challenge to the development of a robust diagnostic test. Nucleic acid-based tests are more accurate than rapid antigen tests for influenza and are therefore better candidates to be used in both diagnostic and surveillance applications. Here, we review various nucleic acid-based techniques that have been applied towards the detection of influenza viruses in order to evaluate their utility as both diagnostic and surveillance tools. We discuss both traditional as well as novel methods to detect influenza viruses by covering techniques that require nucleic acid amplification or direct detection of viral RNA as well as comparing advantages and limitations for each method. There has been substantial progress in the development of nucleic acid-based sensing techniques for the detection of influenza virus. However, there is still an urgent need for a rapid and reliable influenza diagnostic test that can be used at point-of-care in order to enhance responsiveness to both seasonal and pandemic influenza outbreaks.

MD simulation of the interaction between sialoglycans and the second sialic acid binding site of influenza A virus N1 neuraminidase

The neuraminidases (NAs) of avian influenza viruses (IAVs) contain a second sialic acid-binding site (2SBS), historically known as the hemadsorption site, which is separated from the sialyl-hydrolase catalytic site and serves to facilitate NA catalytic activity towards multivalent sialyl-capped glycoconjugates. Transmission and adaptation of avian IAVs to humans decreases hemadsorption and catalytic activities of the NA. Here, we report the molecular recognition features of the NA 2SBS of two pandemic H1N1 IAVs, A/Brevig Mission /1/1918 (BM18) and A/California/04/2009 (CA09), differing by their 2SBS activity. Using explicit solvent MD simulation, molecular mechanics, and glycosidic conformation analysis we initially analyzed the interactions of BM18 2SBS with two sialyllacto-N-tetraose pentasaccharides, 3'SLN-LC and 6'SLN-LC, which are models for the glycan receptors of IAVs in birds and humans, respectively. These studies characterize the binding specificity of BM18 2SBS towards human-type and avian-type receptors and identifies the key amino acids that affects binding. We next compared the interactions of the 2SBSs of BM18 and CA09 with 6'SLN-LC, revealing the critical effect of amino acid 372 on binding. Our results expand the current knowledge of the molecular features of NA 2SBSs and its alteration during the adaptation of avian IAVs to humans.

Immunoinformatics approach for a novel multi-epitope subunit vaccine design against various subtypes of Influenza A virus

Vaccination is the best strategy for the control and prevention of contagious diseases caused by Influenza A viruses. Extraordinary genetic variability and continual evolvability are responsible for the virus having survival and adaptation to host cell immune response, thus rendering the current influenza vaccines with suboptimal effectiveness.Therefore, in the present study, using a novel immunoinformatics approach, we have designed a universal influenza subunit vaccine based on the highly conserved epitopic sequences of rapidly evolving (HA), a moderately evolving (NP) and slow evolving (M1) proteins of the virus. The vaccine design includes 2 peptide adjuvants, 26 CTL epitopes, 9 HTL epitopes, and 7 linear BCL epitopes to induce innate, cellular, and humoral immune responses against Influenza A viruses. We also analyzed the physicochemical properties of the designed construct to validate its thermodynamic stability, hydrophilicity, PI, antigenicity, and allergenicity. Furthermore, we predicted a highly stable tertiary model of the designed subunit vaccine, wherein additional disulfide bonds were incorporated to enhance its stability. The molecular docking and molecular dynamics simulations of the refined vaccine model with TLR3, TLR7, TLR8, MHC-I and MHC-II showed stable vaccine and receptors complexes, thus confirming the immunogenicity of the designed vaccine. Collectively, these findings suggest that our multi-epitope vaccine construct may confer protection against various strains of influenza A virus subtypes, which could prevent the need for annual reformulation of vaccine and alleviate disease burden.

Gaps in Serologic Immunity against Contemporary Swine-Origin Influenza A Viruses among Healthy Individuals in the United States

Influenza A Viruses (IAV) in domestic swine (IAV-S) are associated with sporadic zoonotic transmission at the human–animal interface. Previous pandemic IAVs originated from animals, which emphasizes the importance of characterizing human immunity against the increasingly diverse IAV-S. We analyzed serum samples from healthy human donors (n = 153) using hemagglutination-inhibition (HAI) assay to assess existing serologic protection against a panel of contemporary IAV-S isolated from swine in the United States (n = 11). Age-specific seroprotection rates (SPR), which are the proportion of individuals with HAI ≥ 1:40, corresponded with lower or moderate pandemic risk classifications for the multiple IAV-S examined (one H1-δ1, one H1-δ2, three H3-IVA, one H3-IVB, one H3-IVF). Individuals born between 2004 and 2013 had SPRs of 0% for the five classified H3 subtype IAV-S, indicating youth may be particularly predisposed to infection with these viruses. Expansion of existing immunologic gaps over time could increase likelihood of future IAV-S spillover to humans and facilitate subsequent sustained human-to-human transmission resulting in disease outbreaks with pandemic potential.

Avian influenza H5N1: still a pandemic threat?

Highly pathogenic avian influenza H5N1 viruses have become endemic in global poultry populations over the past 25 years and pose an ongoing public health threat. Although the incidence of human cases has declined, viruses from the H5N1 lineage can now be found in poultry throughout Asia, the Middle East and Africa, in addition to causing outbreaks in Europe and the Americas. The recent emergence and spread of reassortant H5Nx viruses, resulting in regional poultry outbreaks, has increased the risk for further evolution of these viruses and possible avian-to-human transmission. Ongoing surveillance and pandemic preparedness for H5N1 and other avian influenza viruses of public health concern are warranted.

Crossroads of highly pathogenic H5N1: overlap between wild and domestic birds in the Black Sea-Mediterranean impacts global transmission

Understanding transmission dynamics that link wild and domestic animals is a key element of predicting the emergence of infectious disease, an event that has highest likelihood of occurring wherever human livelihoods depend on agriculture and animal trade. Contact between poultry and wild birds is a key driver of the emergence of highly pathogenic avian influenza (HPAI), a process that allows for host switching and accelerated reassortment, diversification, and spread of virus between otherwise unconnected regions. This study addresses questions relevant to the spillover of HPAI at a transmission hotspot: what is the nature of the wild bird-poultry interface in Egypt and adjacent Black Sea-Mediterranean countries and how has this contributed to outbreaks occurring worldwide? Using a spatiotemporal model of infection risk informed by satellite tracking of waterfowl and viral phylogenetics, this study identified ecological conditions that contribute to spillover in this understudied region. Results indicated that multiple ducks (Northern Shoveler and Northern Pintail) hosted segments that shared ancestry with HPAI H5 from both clade 2.2.1 and clade 2.3.4 supporting the role of Anseriformes in linking viral populations in East Asia and Africa over large distances. Quantifying the overlap between wild ducks and H5N1-infected poultry revealed an increasing interface in late winter peaking in early spring when ducks expanded their range before migration, with key differences in the timing of poultry contact risk between local and long-distance migrants.

Molecular identification and phylogenetic characterization of influenza A virus at a wildlife-livestock interface in Mexico

Influenza A virus (IAV) outbreaks constitute a constant threat to public health and pose a remarkable impact on socio-economic systems worldwide. Interactions between wild and domestic birds, humans and swine can lead to spillover events. Backyard livestock systems in proximity to wetlands represent high-risk areas for viral spread. However, some gaps remain in our knowledge of IAV transmission at the wildlife-livestock interface in Mexico. Hence, the study aimed at molecular identification and phylogenetic characterization of IAV in the wild duck-backyard livestock interface at a wetland of Mexico. A total of 875 animals were tested by real-time RT-PCR (qRT-PCR). We detected IAV in 3.68% of the wild ducks sampled during the winter season 2016-2017. Nonetheless, the samples obtained from backyard poultry and swine tested negative. The highest IAV frequency (11.10%) was found in the Mexican duck (Anas diazi). Subtypes H1N1, H3N2 and H5N2 were detected. Phylogenetic analyses revealed that IAV detected in wild birds from the Lerma wetlands was mostly related to swine and poultry IAV strains previously isolated in the United States and Mexico. Except, the UIFMVZ377/H5N2 related to North American waterbirds. In conclusion, the co-circulation of three IAV subtypes in wild ducks close to backyard farms in Mexico, as well as the local identification of influenza viruses genetically related to Mexican and North American IAV strains, highlights the importance of the Lerma marshes for influenza surveillance given the close interaction among wild birds, poultry, pigs and humans.

Tissue Tropisms of Avian Influenza A Viruses Affect Their Spillovers from Wild Birds to Pigs

Wild aquatic birds maintain a large, genetically diverse pool of influenza A viruses (IAVs), which can be transmitted to lower mammals and, ultimately, humans. Through phenotypic analyses of viral replication efficiency, only a small set of avian IAVs were found to replicate well in epithelial cells of the swine upper respiratory tract, and these viruses were shown to infect and cause virus shedding in pigs. Such a phenotypic trait of the viral replication efficiency appears to emerge randomly and is distributed among IAVs across multiple avian species and geographic and temporal orders. It is not determined by receptor binding preference but is determined by other markers across genomic segments, such as those in the ribonucleoprotein complex. This study demonstrates that phenotypic variants of viral replication efficiency exist among avian IAVs but that only a few of these may result in viral shedding in pigs upon infection, providing opportunities for these viruses to become adapted to pigs, thus posing a higher potential risk for creating novel variants or detrimental reassortants within pig populations.IMPORTANCE Swine serve as a mixing vessel for generating pandemic strains of human influenza virus. All hemagglutinin subtypes of IAVs can infect swine; however, only sporadic cases of infection with avian IAVs are reported in domestic swine. The molecular mechanisms affecting the ability of avian IAVs to infect swine are still not fully understood. From the findings of phenotypic analyses, this study suggests that the tissue tropisms (i.e., in swine upper respiratory tracts) of avian IAVs affect their spillovers from wild birds to pigs. It was found that this phenotype is determined not by receptor binding preference but is determined by other markers across genomic segments, such as those in the ribonucleoprotein complex. In addition, our results show that such a phenotypic trait was sporadically and randomly distributed among IAVs across multiple avian species and geographic and temporal orders. This study suggests an efficient way for assessment of the risk posed by avian IAVs, such as in evaluating their potentials to be transmitted from birds to pigs.

Equine-Like H3 Avian Influenza Viruses in Wild Birds, Chile

Since their discovery in the United States in 1963, outbreaks of infection with equine influenza virus (H3N8) have been associated with serious respiratory disease in horses worldwide. Genomic analysis suggests that equine H3 viruses are of an avian lineage, likely originating in wild birds. Equine-like internal genes have been identified in avian influenza viruses isolated from wild birds in the Southern Cone of South America. However, an equine-like H3 hemagglutinin has not been identified. We isolated 6 distinct H3 viruses from wild birds in Chile that have hemagglutinin, nucleoprotein, nonstructural protein 1, and polymerase acidic genes with high nucleotide homology to the 1963 H3N8 equine influenza virus lineage. Despite the nucleotide similarity, viruses from Chile were antigenically more closely related to avian viruses and transmitted effectively in chickens, suggesting adaptation to the avian host. These studies provide the initial demonstration that equine-like H3 hemagglutinin continues to circulate in a wild bird reservoir.

Quantifying between-Host Transmission in Influenza Virus Infections

The error-prone replication and life cycle of influenza virus generate a diverse set of genetic variants. Transmission between hosts strictly limits both the number of virus particles and the genetic diversity of virus variants that reach a new host and establish an infection. This sharp reduction in the virus population at transmission--the transmission bottleneck--is significant to the evolution of influenza virus and to its epidemic and pandemic potential. This review describes transmission bottlenecks and their effect on the diversity and evolution of influenza virus. It also reviews the methods for calculating and predicting bottleneck sizes and highlights the host and viral determinants of influenza transmissibility.

A case of reassortant seasonal influenza A(H1N2) virus, Denmark, April 2019

A reassortant influenza A subtype H1N2 virus with gene segments from seasonal A(H1N1)pdm09 virus (HA, MP, NP, NS, PA, PB1 and PB2) and seasonal A(H3N2) virus (NA) was identified in a routine surveillance sample in Denmark. The patient recovered fully. This is the second reassortant influenza A(H1N2) virus identified in Europe in the 2018/19 influenza season, with the first case being detected December 2018 in Sweden.

Full-length genome sequences of the first H9N2 avian influenza viruses isolated in the Northeast of Algeria

Background

H9N2 avian influenza viruses (AIV) has a worldwide geographic distribution and affects poultry of different types of production. H9N2 AIV was first reported in the Northeast of Algeria in April 2017, following an outbreak associated with high mortality, in broiler flocks. In the present study, we report full-length genome sequences of AIV H9N2, and the detailed phylogeny and molecular genetic analyses.

Methods

Ten AIV H9N2 strains, collected in broiler flocks, were amplified in 9-day-old embryonated specific pathogen free (SPF) chicken eggs. Their full-length genomes were successfully sequenced and phylogenetic and molecular characterizations were conducted.

Results

Phylogenetic analysis showed that the isolates were monophyletic, grouped within the G-1 lineage and were very close to Moroccan and Algerian strains identified in 2016 and 2017, respectively. The low pathogenicity of the strains was confirmed by the sequence motif (335RSSR/GLF341) at the hemagglutinin (HA) cleavage site. An exclusive substitution (T197A) that had not been previously reported for H9N2 viruses; but, conserved in some pandemic H1N1 viruses, was observed. When compared to the G1-like H9N2 prototype, the studied strains showed one less glycosylation site in HA, but 2–3 additional ones in the stalk of the neuraminidase (NA). The HA protein harbored the substitution 234 L, suggesting binding preference to human-like receptors. The NA protein harbored S372A and R403W substitutions, previously detected in H9N2 from Asia and the Middle East, and especially in H2N2 and H3N2 strains that caused human pandemics. Different molecular markers associated with virulence and mammalian infections have been detected in the viral internal proteins. The matrix M2 protein possessed the S31N substitution associated with drug resistance. The non-structural 1 (NS1) protein showed the “GSEV” PDZ ligand (PL) C-terminal motif and no 80–84 deletion.

Conclusion

Characterized Algerian AIV isolates showed mutations that suggest increased zoonotic potential. Additional studies in animal models are required to investigate the pathogenicity of these H9N2 AIV strains. Monitoring their evolution in both migratory and domestic birds is crucial to prevent transmission to humans. Implementation of adequate biosecurity measures that limit the introduction and the propagation of AIV H9N2 in Algerian poultry farm is crucial.

Controlling Avian Influenza Virus in Bangladesh: Challenges and Recommendations

Avian influenza virus (AIV) remains a huge challenge for poultry production with negative repercussions for micro- and macro-economy and public health in Bangladesh. High (HP) H5N1 and low pathogenicity (LP) H9N2 AIV are currently endemic in poultry, and both have been reported to infect humans sporadically. Multiple virus introductions of different clades of HPAIV H5N1, reassorted genotypes, and on-going diversification of LPAIV H9N2 create a highly volatile virological environment which potentially implicates increased virulence, adaptation to new host species, and subsequent zoonotic transmission. Allotropy of poultry rearing systems and supply chains further increase the risk of virus spreading, which leads to human exposure and fosters the emergence of new potentially pre-pandemic virus strains. Here, we review the epidemiology, focusing on (i) risk factors for virus spreading, (ii) viral genetic evolution, and (iii) options for AIV control in Bangladesh. It is concluded that improved control strategies would profit from the integration of various intervention tools, including effective vaccination, enhanced biosecurity practice, and improved awareness of producers and traders, although widespread household poultry rearing significantly interferes with any such strategies. Nevertheless, continuous surveillance associated with rapid diagnosis and thorough virus characterization is the basis of such strategies.

Staphylococcus aureus Lipase 1 Enhances Influenza A Virus Replication

Influenza A virus (IAV) causes annual epidemics and sporadic pandemics of respiratory disease. Secondary bacterial coinfection by organisms such as Staphylococcus aureus is the most common complication of primary IAV infection and is associated with high levels of morbidity and mortality. Here, we report the first identified S. aureus factor (lipase 1) that enhances IAV replication during infection via positive modulation of virus budding. The effect is observed in vivo in embryonated hen’s eggs and greatly enhances the yield of a vaccine strain, a finding that could be applied to address global shortages of influenza vaccines.

Influenza A virus (IAV) causes annual epidemics of respiratory disease in humans, often complicated by secondary coinfection with bacterial pathogens such as Staphylococcus aureus. Here, we report that the S. aureus secreted protein lipase 1 enhances IAV replication in vitro in primary cells, including human lung fibroblasts. The proviral activity of lipase 1 is dependent on its enzymatic function, acts late in the viral life cycle, and results in increased infectivity through positive modulation of virus budding. Furthermore, the proviral effect of lipase 1 on IAV is exhibited during in vivo infection of embryonated hen’s eggs and, importantly, increases the yield of a vaccine strain of IAV by approximately 5-fold. Thus, we have identified the first S. aureus protein to enhance IAV replication, suggesting a potential role in coinfection. Importantly, this activity may be harnessed to address global shortages of influenza vaccines.

Epidemiology of bacteria and viruses in the respiratory tract of humans and domestic pigs

Bacteria and viruses were analysed in the upper respiratory tract of symptomatic pig farmers and their domestic pigs. Eighty six human nasal and 495 (50 pools) porcine snout swabs were collected in Schleswig-Holstein, Germany. Staphylococcus (S.) aureus (62.8%, 54/86), human rhino- and coronaviruses (HRV, 29.1%, 25/86; HCoV, 16.3%, 14/86) were frequently detected in humans, while Haemophilus parasuis (90.0%, 45/50), Mycoplasma hyorhinis (78.6%, 11/14), Enterovirus G (EV-G, 56.0%, 28/50) and S. aureus (36.0%, 18/50), respectively, were highly prevalent in pigs. The detection of S. aureus in human follow-up samples indicates a carrier status. The methicillin-resistant phenotype (MRSA) was identified in 33.3% (18/54) of nasal swabs and in one of 18 (5.6%) pooled snout swabs that were tested positive for S. aureus. Strains were indicative of the livestock-associated clonal complex CC398, with t011 being the most common staphylococcal protein A type. Enterobacterales and non-fermenters were frequently isolated from swabs. Their detection in follow-up samples suggests a carrier status. All were classified as being non-multiresistant. There was no example for cross-species transmission of viruses. In contrast, transmission of S. aureus through occupational contact to pigs seems possible. The study contributes to the 'One Health' approach.

Insertion of Basic Amino Acids in the Hemagglutinin Cleavage Site of H4N2 Avian Influenza Virus (AIV)-Reduced Virus Fitness in Chickens is Restored by Reassortment with Highly Pathogenic H5N1 AIV

Highly pathogenic (HP) avian influenza viruses (AIVs) are naturally restricted to H5 and H7 subtypes with a polybasic cleavage site (CS) in hemagglutinin (HA) and any AIV with an intravenous pathogenicity index (IVPI) ≥ 1.2. Although only a few non-H5/H7 viruses fulfill the criteria of HPAIV; it remains unclear why these viruses did not spread in domestic birds. In 2012, a unique H4N2 virus with a polybasic CS ³²²PEKRRTR/G³²⁹ was isolated from quails in California which, however, was avirulent in chickens. This is the only known non-H5/H7 virus with four basic amino acids in the HACS. Here, we investigated the virulence of this virus in chickens after expansion of the polybasic CS by substitution of T³²⁷R (³²²PEKRRRR/G³²⁹) or T³²⁷K (³²²PEKRRKR/G³²⁹) with or without reassortment with HPAIV H5N1 and H7N7. The impact of single mutations or reassortment on virus fitness in vitro and in vivo was studied. Efficient cell culture replication of T³²⁷R/K carrying H4N2 viruses increased by treatment with trypsin, particularly in MDCK cells, and reassortment with HPAIV H5N1. Replication, virus excretion and bird-to-bird transmission of H4N2 was remarkably compromised by the CS mutations, but restored after reassortment with HPAIV H5N1, although not with HPAIV H7N7. Viruses carrying the H4-HA with or without R³²⁷ or K³²⁷ mutations and the other seven gene segments from HPAIV H5N1 exhibited high virulence and efficient transmission in chickens. Together, increasing the number of basic amino acids in the H4N2 HACS was detrimental for viral fitness particularly in vivo but compensated by reassortment with HPAIV H5N1. This may explain the absence of non-H5/H7 HPAIV in poultry.

Vaccination with Consensus H7 Elicits Broadly Reactive and Protective Antibodies against Eurasian and North American Lineage H7 Viruses

H7 subtype avian influenza viruses have caused outbreaks in poultry, and even human infection, for decades in both Eurasia and North America. Although effective vaccines offer the best protection against avian influenza viruses, antigenically distinct Eurasian and North American lineage subtype H7 viruses require the development of cross-protective vaccine candidates. In this study, a methodology called computationally optimized broadly reactive antigen (COBRA) was used to develop four consensus H7 antigens (CH7-22, CH7-24, CH7-26, and CH7-28). In vitro experiments confirmed the binding of monoclonal antibodies to the head and stem domains of cell surface-expressed consensus HAs, indicating display of their antigenicity. Immunization with DNA vaccines encoding the four antigens was evaluated in a mouse model. Broadly reactive antibodies against H7 viruses from Eurasian and North American lineages were elicited and detected by binding, inhibition, and neutralizing analyses. Further infection with Eurasian H7N9 and North American H7N3 virus strains confirmed that CH7-22 and CH7-24 conferred the most effective protection against hetero-lethal challenge. Our data showed that the consensus H7 vaccines elicit a broadly reactive, protective response against Eurasian and North American lineage H7 viruses, which are suitable for development against other zoonotic influenza viruses.

Influenza A Virus Infection in Cats and Dogs: A Literature Review in the Light of the "One Health" Concept

Influenza A viruses are amongst the most challenging viruses that threaten both human and animal health. Constantly evolving and crossing species barrier, the emergence of novel zoonotic pathogens is one of the greatest challenges to global health security. During the last decade, considerable attention has been paid to influenza virus infections in dogs, as two canine H3N8 and H3N2 subtypes caused several outbreaks through the United States and Southern Asia, becoming endemic. Cats, even though less documented in the literature, still appear to be susceptible to many avian influenza infections. While influenza epidemics pose a threat to canine and feline health, the risks to humans are largely unknown. Here, we review most recent knowledge of the epidemiology of influenza A viruses in dogs and cats, existing evidences for the abilities of these species to host, sustain intraspecific transmission, and generate novel flu A lineages through genomic reassortment. Such enhanced understanding suggests a need to reinforce surveillance of the role played by companion animals-human interface, in light of the “One Health” concept and the potential emergence of novel zoonotic viruses.

Antigenic characterization of novel H1 influenza A viruses in swine

Novel H1N2 influenza A viruses (IAVs) in swine have been identified in Chile co-circulating with pandemic H1N1 2009-like (A(H1N1)pdm09-like) viruses. The objective of this study was to characterize antigenically the swine H1 IAVs circulating in Chile. Genetic analysis based on the HA1 domain and antigenic analysis by hemagglutination inhibition assay were carried out. Three antigenic clusters were identified, named Chilean H1 A (ChH1A), Chilean H1 B (ChH1B), and A(H1N1)pdm09-like. The antigenic sites of ChH1A and ChH1B strains were 10–60% distant from those of commercial vaccine strains at the amino acid sequence level. Antigenic variants were identified within the clusters ChH1A and A(H1N1)pdm09-like. Substitutions in the main antigenic sites (E153G in Sa, Q193H in Sb, D168N in Ca1, P137S in Ca2, and F71L in Cb) were detected in variants from the ChH1A cluster, whereas only a single substitution in antigenic site Sa (G155E) was detected in variants from A(H1N1)pdm09-like cluster, which confirms the importance to carrying out antigenic analyses in addition to genetic analyses to evaluate control measures such as vaccination. These results highlight the need to update vaccines for swine in Chile and the importance of continued surveillance to determine the onward transmission of antigenic variants in Chilean pig populations.

Bearing the brunt: Mongolian khulan (Equus hemionus hemionus) are exposed to multiple influenza A strains

The majority of influenza A virus strains are hosted in nature by avian species in the orders of Anseriformes and Charadriformes. A minority of strains have been able to cross species boundaries and establish themselves in novel non-avian hosts. Influenza viruses of horses, donkeys, and mules represent such successful events of avian to mammal influenza virus adaptation. Mongolia has over 3 million domestic horses and is home to two wild equids, the Asiatic wild ass or khulan (Equus hemionus hemionus), and Przewalski's horse (Equus ferus przewalskii). Domestic and wild equids are sympatric across most of their range in Mongolia. Epizootic influenza A virus outbreaks among Mongolian domestic horses have been frequently recorded. However, the exposure, circulation and relation to domestic horse influenza A virus outbreaks among wild equids is unknown. We evaluated serum samples of Asiatic wild asses in Mongolia for antibodies against influenza A viruses, using modified protein microarray technique. We detected antibodies against hemagglutinin (H) H1, H3, H5, H7, H8 and H10 influenza A viruses. Asiatic wild asses may represent a previously unidentified influenza A virus reservoir in an ecosystem shared with populations of domestic horses in which influenza strains circulate.