Viral load of the highly pathogenic avian influenza H5N1 virus in infected human tissues

Efficacy and safety of single-dose antiviral drugs for influenza treatment: A systematic review and network meta-analysis

To conduct network meta-analysis (NMA) of clinical efficacy and safety of single-dose antiviral drugs, grouped by dosage, in treatment of influenza. Systematic retrievals were conducted in databases, including Pubmed, Embase, Web of Science, the Cochrane Register of Clinical Trials and from the website ClinicalTrials.gov, for clinical trials recorded between the interception of the databases and March 31, 2021. Randomized controlled trials (RCTs) of influenza treatment in which single-dose antiviral drugs were administered were selected according to preset inclusion and exclusion criteria by two researchers who screened the literature independently from each other. The quality of the included studies was assessed using the Cochrane bias risk assessment tool. Software such as Stata 16.0 and Review Manager 5.3 was adopted for statistical analysis. Pairwise meta-analysis and NMA were carried out under the random-effects model. For both binary and continuous variables, odds ratio (OR), mean difference (MD) and their 95% confidence intervals (CI) were used to rank treatment efficiencies and analyze the differences. A total of 12 RCTs involving 7296 participants were included in the analysis. According to the NMA results, peramivir 300 mg (MD = -17.68, 95% CI: [-34.05, -1.32]), peramivir 600 mg (MD = -16.15, 95% CI: [-29.35, -2.95]), baloxavir (MD = -14.67, 95% CI: [-26.75, -2.58]) and laninamivir 40 mg (MD = -12.42, 95% CI: [-22.53, -2.31]) remarkably outperformed laninamivir 20 mg in time to alleviation of symptoms (TTAS). However, no intervention statistically outperform others in antipyretic time, virus titer variations against the baseline 24 and 48 h after medication and adverse events (AEs). The efficacy rankings were: peramivir 300 mg (the surface under the cumulative ranking curve [SUCRA] = 80.3%) > peramivir 600 mg (SUCRA = 76.2%) > baloxavir (SUCRA = 68.4%) > laninamivir 40 mg (SUCRA = 55.0%) > laninamivir 20 mg (SUCRA = 16.6%) for TTAS; baloxavir (SUCRA = 76.3%) > peramivir 600 mg (SUCRA = 67.8%) > laninamivir 40 mg (SUCRA = 47.2%) > laninamivir 20 mg (SUCRA = 40.0%) for antipyretic time; baloxavir (SUCRA = 96.7%) > peramivir 300 mg (SUCRA = 64.5%) ≈ peramivir 600 mg (SUCRA = 63.2%), baloxavir (SUCRA = 93.2%) > peramivir 600 mg (SUCRA = 64.0%) ≈ peramivir 300 mg (SUCRA = 55.0%), for virus titer variations against the baseline 24 and 48 h after medication, respectively; and baloxavir (SUCRA = 83.4%) > peramivir 300 mg (SUCRA = 71.4%) > laninamivir 20 mg (SUCRA = 62.4%) > peramivir 600 mg (SUCRA = 56.2%) > laninamivir 40 mg (SUCRA = 36.8%) for adverse events. Among the single-dose anti-influenza virus drugs compared, peramivir is superior to baloxavir and laninamivir in TTAS, whereas baloxavir has the best efficacy in antipyretic time, virus titer variations against the baseline 24 and 48 h after medication and AEs. This study has been registered in the International Prospective Register of Systematic Reviews (PROSPERO), with a registration number of CRD42021238220.

Full Genomic Sequences of H5N1 Highly Pathogenic Avian Influenza Virus in Human Autopsy Specimens Reveal Genetic Variability and Adaptive Changes for Growth in MDCK Cell Cultures

The entire H5N1 highly pathogenic avian influenza viral genomes were identified in the frozen autopsy specimens: the trachea, lung, colon, and intestinal feces from a patient who died of the disease in 2006. Phylogenetic analysis of the viral genomes showed that these viruses belonged to clade 1 and were the reassortants generated from the reassortment of the viruses within the same clade. The sequencing data from the autopsy specimens revealed at least 8 quasispecies of the H5N1 viruses across all 4 specimen types. These sequences were compared to those derived from the virus isolates grown in Madin Darby canine kidney (MDCK) cells. The virus isolates from the trachea, lung, and fecal specimens showed 27 nucleotide substitutions, leading to the changes of 18 amino acid residues. However, there was no change in the amino acid residues that determined the viral virulence. The changes were more commonly observed in the lung, particularly in the HA and NA genes. Our study suggested that the adaptation changes for the viral fitness to survive in a new host species (MDCK cells) might involve many genes, for example, the amino acid substitution 177G or 177W adjacent to the receptor-binding residues in the HA1 globular head and the substitution M315I in PB2. However, a mutation changes near the receptor binding domain may play an important role in determining the cell tropism and is needed to be further explored.

Silent Infection of B and CD8+ T Lymphocytes by Influenza A Virus in Children with Tonsillar Hypertrophy

Influenza A viruses (IAVs) cause more than 2 million annual episodes of seasonal acute respiratory infections (ARI) and approximately 500,000 deaths worldwide. Depending on virus strain and host immune status, acute infections by IAV may reach sites other than the respiratory tract. In the present study, IAV RNA and antigens were searched for in tissues of palatine tonsils and adenoids removed from patients without ARI symptoms. A real-time reverse transcriptase PCR (RT-PCR) screening revealed that 8 tissue samples from 7 patients out of 103 were positive for IAV. Positive samples were subjected to next-generation sequencing (NGS) and 3 of 8 tissues yielded complete IAV pH1N1 genomes, whereas in 5 samples, the PB1 gene was not fully assembled. Phylogenetic analysis placed tonsil-derived IAV in clusters clearly segregated from contemporaneous Brazilian viruses. Flow cytometry of dispersed tissue fragments and serial immunohistochemistry of paraffin-embedded sections of naturally infected biopsies indicated that CD20⁺ B lymphocytes, CD8⁺ T lymphocytes, and CD11c⁺ cells are susceptible to IAV infection. We sought to investigate whether these lymphoid tissues could be sites of viral replication and sources of viable virus particles. MDCK cells were inoculated with tissue lysates, enabling recovery of one IAV isolate confirmed by immunofluorescence, reverse transcriptase quantitative PCR (RT-qPCR), and NGS. The data indicate that lymphoid tissues not only harbor expression of IAV proteins but also contain infectious virus. Asymptomatic long-term infection raises the possibility of IAV shedding from tonsils, which may have an impact on host-to-host transmission.IMPORTANCE Influenza A virus (IAV) infections are important threats to human health worldwide. Although extensively studied, some aspects of virus pathogenesis and tissue tropism remain unclear. Here, by different strategies, we describe the asymptomatic infection of human lymphoid organs by IAV in children. Our results indicate that IAV was not only detected and isolated from human tonsils but displayed unique genetic features in comparison with those of contemporaneous IAVs circulating in Brazil and detected in swabs and nasal washes. Inside the tissue microenvironment, immune cells were shown to be carrying IAV antigens, especially B and T CD8⁺ lymphocytes. Taken together, these results suggest that human lymphoid tissues can be sites of silent IAV infections with possible impact on virus shedding to the population.

Complete Genomic Sequences of Highly Pathogenic H5N1 Avian Influenza Viruses Obtained Directly from Human Autopsy Specimens

The complete genomic sequences of H5N1 highly pathogenic avian influenza (HPAI) viruses were directly obtained from lung, trachea, and colon tissues and an intestinal fecal sample of a patient by using the next-generation sequencing technique. This is the first report on complete H5N1 viral genomes from human autopsy specimens.

The complete genomic sequences of H5N1 highly pathogenic avian influenza (HPAI) viruses were directly obtained from lung, trachea, and colon tissues and an intestinal fecal sample of a patient by using the next-generation sequencing technique. This is the first report on complete H5N1 viral genomes from human autopsy specimens.

Taiwan's Public Health National Laboratory System: Success in Influenza Diagnosis and Surveillance

Taiwan's National Laboratory System is one of the action packages of the Global Health Security Agenda, which was launched by the World Health Organization (WHO) to promote health security as an international priority and to encourage progress toward full implementation of the WHO International Health Regulations (IHR) 2005. The mission of each national laboratory system is to conduct real-time biosurveillance and effective laboratory-based diagnostics, as measured by a nationwide laboratory system able to reliably conduct diagnoses on specimens transported properly to designated laboratories from at least 80% of the regions in the country. In Taiwan, the national laboratory system for public health is well-established and coordinated by the Taiwan Centers for Disease Control (CDC), which is the government authority in charge of infectious disease prevention and intervention. Through the national laboratory system, Taiwan CDC effectively detects and characterizes pathogens that cause communicable diseases across the entire country, including both known and novel threats, and also conducts epidemiologic analyses of infectious diseases. In this article, we describe the national laboratory system for public health in Taiwan. We provide additional information on the national influenza laboratory surveillance network to demonstrate how our national laboratory systems work in practice, including descriptions of long-term seasonal influenza characterization and successful experiences identifying novel H7N9 and H6N1 influenza viruses.

C-Reactive Protein Mediating Immunopathological Lesions: A Potential Treatment Option for Severe Influenza A Diseases

Severe influenza diseases with high mortality have been frequently reported, especially in those patients infected with avian influenza A (H5N1, H7N9 or H10N8) or during a pandemic. Respiratory distress, which is attributed to alveolar damage associated with immunopathological lesions, is the most common cause of death. There is a wealth of information on pathogenesis or treatment options. In this study, we showed that high levels of C-reactive protein (CRP) were induced and correlated with complement activation in patients infected with severe influenza A (H5N1, H7N9 or H10N8), and higher levels were induced in fatal patients than in survivors. CRP treatment enhanced the phagocytosis of monocytes THP-1 to H5N1 virus as well as the expression of proinflammatory cytokines or apoptosis-associated genes in THP-1 cells or pneumocytes A-549 respectively. CRP may link to proinflammatory mediators contributing to activation of complement and boosting inflammatory response in severe influenza infections. Compound 1,6-bis(phosphocholine)-hexane improved the severity and mortality of mice infected with lethal influenza virus significantly. These observations showed that CRP is involved in deterioration of severe influenza diseases, and indicated a substantial candidate molecule for immunotherapy of severe influenza diseases.

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CRP induces exacerbated immunoresponse toward overt pulmonary inflammation in severe influenza infections.

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CRP may link to proinflammatory mediators contributing to activation of complement and boosting inflammatory response.

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CRP stabilizer can alleviate the immunopathological lesions and mortality in mice infected with lethal influenza virus.

Severe influenza diseases with high mortality have been frequently reported, especially in those patients infected with avian influenza A (H5N1, H7N9, or H10N8) or during a pandemic. Respiratory distress associated with immunopathological lesions is the most common cause of death in patients infected by these viruses. In this study, we found that CRP may be linked to exacerbated immunoresponse toward overt pulmonary inflammation, which led to alveolar damage and respiratory failure in severe influenza infection. Our data identified that CRP stabilizer can be used to alleviate the immunopathological lesions and mortality in mice infected with lethal influenza virus.

Two Genetically Similar H9N2 Influenza A Viruses Show Different Pathogenicity in Mice

H9N2 Avian influenza virus has repeatedly infected humans and other mammals, which highlights the need to determine the pathogenicity and the corresponding mechanism of this virus for mammals. In this study, we found two H9N2 viruses with similar genetic background but with different pathogenicity in mice. The A/duck/Nanjing/06/2003 (NJ06) virus was highly pathogenic for mice, with a 50% mouse lethal dose (MLD₅₀) of 10^2.83 50% egg infectious dose (EID₅₀), whereas the A/duck/Nanjing/01/1999 (NJ01) virus was low pathogenic for mice, with a MLD₅₀ of >10^6.81 EID₅₀. Further studies showed that the NJ06 virus grew faster and reached significantly higher titers than NJ01 in vivo and in vitro. Moreover, the NJ06 virus induced more severe lung lesions, and higher levels of inflammatory cellular infiltration and cytokine response in lungs than NJ01 did. However, only 12 different amino acid residues (HA-K157E, NA-A9T, NA-R435K, PB2-T149P, PB2-K627E, PB1-R187K, PA-L548M, PA-M550L, NP-G127E, NP-P277H, NP-D340N, NS1-D171N) were found between the two viruses, and all these residues except for NA-R435K were located in the known functional regions involved in interaction of viral proteins or between the virus and host factors. Summary, our results suggest that multiple amino acid differences may be responsible for the higher pathogenicity of the NJ06 virus for mice, resulting in lethal infection, enhanced viral replication, severe lung lesions, and excessive inflammatory cellular infiltration and cytokine response in lungs. These observations will be helpful for better understanding the pathogenic potential and the corresponding molecular basis of H9N2 viruses that might pose threats to human health in the future.

Predicting Disease Severity and Viral Spread of H5N1 Influenza Virus in Ferrets in the Context of Natural Exposure Routes

Although avian H5N1 influenza virus has yet to develop the capacity for human-to-human spread, the severity of the rare cases of human infection has warranted intensive follow-up of potentially exposed individuals that may require antiviral prophylaxis. For countries where antiviral drugs are limited, the World Health Organization (WHO) has developed a risk categorization for different levels of exposure to environmental, poultry, or human sources of infection. While these take into account the infection source, they do not account for the likely mode of virus entry that the individual may have experienced from that source and how this could affect the disease outcome. Knowledge of the kinetics and spread of virus after natural routes of exposure may further inform the risk of infection, as well as the likely disease severity. Using the ferret model of H5N1 infection, we compared the commonly used but artificial inoculation method that saturates the total respiratory tract (TRT) with virus to upper respiratory tract (URT) and oral routes of delivery, those likely to be encountered by humans in nature. We show that there was no statistically significant difference in survival rate with the different routes of infection, but the disease characteristics were somewhat different. Following URT infection, viral spread to systemic organs was comparatively delayed and more focal than after TRT infection. By both routes, severe disease was associated with early viremia and central nervous system infection. After oral exposure to the virus, mild infections were common suggesting consumption of virus-contaminated liquids may be associated with seroconversion in the absence of severe disease.

IMPORTANCE

Risks for human H5N1 infection include direct contact with infected birds and frequenting contaminated environments. We used H5N1 ferret infection models to show that breathing in the virus was more likely to produce clinical infection than swallowing contaminated liquid. We also showed that virus could spread from the respiratory tract to the brain, which was associated with end-stage disease, and very early viremia provided a marker for this. With upper respiratory tract exposure, infection of the brain was common but hard to detect, suggesting that human neurological infections might be typically undetected at autopsy. However, viral spread to systemic sites was slower after exposure to virus by this route than when virus was additionally delivered to the lungs, providing a better therapeutic window. In addition to exposure history, early parameters of infection, such as viremia, could help prioritize antiviral treatments for patients most at risk of succumbing to infection.

Quantifying the risk of pandemic influenza virus evolution by mutation and re-assortment

Large outbreaks of zoonotic influenza A virus (IAV) infections may presage an influenza pandemic. However, the likelihood that an airborne-transmissible variant evolves upon zoonotic infection or co-infection with zoonotic and seasonal IAVs remains poorly understood, as does the relative importance of accumulating mutations versus re-assortment in this process. Using discrete-time probabilistic models, we determined quantitative probability ranges that transmissible variants with 1-5 mutations and transmissible re-assortants evolve after a given number of zoonotic IAV infections. The systematic exploration of a large population of model parameter values was designed to account for uncertainty and variability in influenza virus infection, epidemiological and evolutionary processes. The models suggested that immunocompromised individuals are at high risk of generating IAV variants with pandemic potential by accumulation of mutations. Yet, both immunocompetent and immunocompromised individuals could generate high viral loads of single and double mutants, which may facilitate their onward transmission and the subsequent accumulation of additional 1-2 mutations in newly-infected individuals. This may result in the evolution of a full transmissible genotype along short chains of contact transmission. Although co-infection with zoonotic and seasonal IAVs was shown to be a rare event, it consistently resulted in high viral loads of re-assortants, which may facilitate their onward transmission among humans. The prevention or limitation of zoonotic IAV infection in immunocompromised and contact individuals, including health care workers, as well as vaccination against seasonal IAVs-limiting the risk of co-infection-should be considered fundamental tools to thwart the evolution of a novel pandemic IAV by accumulation of mutations and re-assortment.

Chimerization and characterization of a monoclonal antibody with potent neutralizing activity across multiple influenza A H5N1 clades

The persistent evolution and circulation of highly pathogenic avian influenza H5N1 viruses pose a serious threat to global heath and hamper pandemic preparedness through conventional vaccine strategies. Combination passive immunotherapy using non-competing neutralizing antibodies has been proposed as a viable alternative to provide broad protection against drift variants. This necessitates the pre-pandemic production and characterization of potently neutralizing monoclonal antibodies (MAbs). One such antibody, MAb 9F4 was shown to provide heterologous protection against multiple H5N1 clade viruses, including one of the recently designated subclades, namely 2.3.4, through binding to a novel epitope, warranting its further development and characterization as a therapeutic candidate. In this study, the conversion of MAb 9F4 from mouse IgG2b to mouse-human chimeric (xi) IgG1 and IgA1 was achieved. These chimeric MAb versions were found to retain high degrees of binding and neutralizing activity against H5N1. The demonstration that xi-IgA1-9F4 retains a fairly high level of neutralizing activity, which is ∼10-fold lower than the corresponding xi-IgG1 isotype, suggests that this MAb could be further developed and engineered for intranasal administration.

Immunomorphologic manifestations in mice liver infected with influenza A/H5N1, A/goose/Krasnoozerskoye/627/05 strain

Highly pathogenic avian influenza H5N1 (HPAI H5N1) viruses can infect mammals, including humans, causing severe systemic disease with the inhibition of the immune system and a high mortality rate. In conditions of lymphoid tissue depletion, the liver plays an important role in host defence against viruses. The changes in mice liver infected with HPAI H5N1 virus A/goose/Krasnoozerskoye/627/05 have been studied. It has been shown that the virus persistence in the liver leads to the expression of proinflammatory cytokines (TNF-α, IL-6) and intracellular proteases (lysozyme, cathepsin D, and myeloperoxidase) by Kupffer cells. Defective antiviral response exacerbates destructive processes in the liver accelerating the development of liver failure.

Experimental infection of macaques with a wild water bird-derived highly pathogenic avian influenza virus (H5N1)

Highly pathogenic avian influenza virus (HPAIV) continues to threaten human health. Non-human primate infection models of human influenza are desired. To establish an animal infection model with more natural transmission and to determine the pathogenicity of HPAIV isolated from a wild water bird in primates, we administered a Japanese isolate of HPAIV (A/whooper swan/Hokkaido/1/2008, H5N1 clade 2.3.2.1) to rhesus and cynomolgus monkeys, in droplet form, via the intratracheal route. Infection of the lower and upper respiratory tracts and viral shedding were observed in both macaques. Inoculation of rhesus monkeys with higher doses of the isolate resulted in stronger clinical symptoms of influenza. Our results demonstrate that HPAIV isolated from a water bird in Japan is pathogenic in monkeys by experimental inoculation, and provide a new method for HPAIV infection of non-human primate hosts, a good animal model for investigation of HPAIV pathogenicity.

Human H7N9 avian influenza virus infection: a review and pandemic risk assessment

China is undergoing a recent outbreak of a novel H7N9 avian influenza virus (nH7N9) infection that has thus far involved 132 human patients, including 37 deaths. The nH7N9 virus is a reassortant virus originating from the H7N3, H7N9 and H9N2 avian influenza viruses. nH7N9 isolated from humans contains features related to adaptation to humans, including a Q226L mutation in the hemagglutinin cleavage site and E627K and D701N mutations in the PB2 protein. Live poultry markets provide an environment for the emergence, spread and maintenance of nH7N9 as well as for the selection of mutants that facilitate nH7N9 binding to and replication in the human upper respiratory tract. Innate immune suppression conferred by the internal genes of H9N2 may contribute to the virulence of nH7N9. The quail may serve as the intermediate host during the adaptation of avian influenza viruses from domestic waterfowl to gallinaceous poultry, such as chickens and related terrestrial-based species, due to the selection of viral mutants with a short neuraminidase stalk. Infections in chickens, common quails, red-legged partridges and turkeys may select for mutants with human receptor specificity. Infection in Ratitae species may lead to the selection of PB2-E627K and PB2-D701N mutants and the conversion of nH7N9 to a highly pathogenic avian influenza virus.

Pathological study of archival lung tissues from five fatal cases of avian H5N1 influenza in Vietnam

Highly pathogenic avian H5N1 influenza virus (H5N1) infection in humans causes acute respiratory distress syndrome, leading to multiple organ failure. Five fatal cases of H5N1 infection in Vietnam were analyzed pathologically to reveal virus distribution, and local proinflammatory cytokine and chemokine expression profiles in formalin-fixed, paraffin-embedded lung tissues. Our main histopathological findings showed diffuse alveolar damage in the lungs. The infiltration of myeloperoxidase-positive and/or CD68 (clone KP-1)-positive neutrophils and monocytes/macrophages was remarkable in the alveolar septa and alveolar spaces. Immunohistochemistry revealed that H5N1 mainly infected alveolar epithelial cells and monocytes/macrophages in lungs. H5N1 replication was confirmed by detecting H5N1 mRNA in epithelial cells using in situ hybridization. Quantitation of H5N1 RNA using quantitative reverse transcription PCR assays revealed that the level of H5N1 RNA was increased in cases during early phases of the disease. We quantified the expression of tumor necrosis factor-alpha (TNF-α), interleukin (IL)-6, IL-8, regulated on activation normal T-cell expressed and secreted (commonly known as RANTES), and interferon-gamma-inducible protein of 10 kDa (IP-10) in formalin-fixed, paraffin-embedded lung sections. Their expression levels correlated with H5N1 RNA copy numbers detected in the same lung region. Double immunofluorescence staining revealed that TNF-α, IL-6, IL-8 and IP-10 were expressed in epithelial cells and/or monocytes/macrophages. In particular, IL-6 was also expressed in endothelial cells. The dissemination of H5N1 beyond respiratory organs was not confirmed in two cases examined in this study.

Highly pathogenic H5N1 influenza A virus strains provoke heterogeneous IFN-α/β responses that distinctively affect viral propagation in human cells

The fatal transmissions of highly pathogenic avian influenza A viruses (IAV) of the H5N1 subtype to humans and high titer replication in the respiratory tract indicate that these pathogens can overcome the bird-to-human species barrier. While type I interferons (IFN-α/β) are well described to contribute to the species barrier of many zoonotic viruses, current data to the role of these antiviral cytokines during human H5N1 IAV infections is limited and contradictory. We hypothesized an important role for the IFN system in limiting productive infection of avian H5N1 strains in human cells. Hence, we examined IFN-α/β gene activation by different avian and human H5N1 isolates, if the IFN-α/β response restricts H5N1 growth and whether the different strains were equally capable to regulate the IFN-α/β system via their IFN-antagonistic NS1 proteins. Two human H5N1 isolates and a seasonal H3N2 strain propagated efficiently in human respiratory cells and induced little IFN-β, whereas three purely avian H5N1 strains were attenuated for replication and provoked higher IFN secretion. Replication of avian viruses was significantly enhanced on interferon-deficient cells, and exogenous IFN potently limited the growth of all strains in human cells. Moreover, IFN-α/β activation by all strains depended on retinoic acid-inducible gene I excluding principal differences in receptor activation between the different viruses. Interestingly, all H5N1 NS1 proteins suppressed IFN-α/β induction comparably well to the NS1 of seasonal IAV. Thus, our study shows that H5N1 strains are heterogeneous in their capacity to activate human cells in an NS1-independent manner. Our findings also suggest that H5N1 viruses need to acquire adaptive changes to circumvent strong IFN-α/β activation in human host cells. Since no single amino acid polymorphism could be associated with a respective high- or low induction phenotype we propose that the necessary adaptations to overcome the human IFN-α/β barrier involve mutations in multiple H5N1 genes.

Cell receptors for influenza a viruses and the innate immune response

The interaction of the hemagglutinin (HA) of the influenza A viruses (IAV) with the cell surface is a key factor for entry of the virus and productive infection of the cell. This glycoprotein has affinity for sialic acids (SA), and different strains present specificity for SA bound through α2,3 or α2,6 linkages to the underlying sugar chain, which is usually related with host and cell tropism. Nucleic acid recognizing receptors (mainly RIG-I and Toll-like receptors) are the most extensively studied pattern recognition receptors for IAV. However, due to the ability of the HA of avian, swine, or human influenza viruses to bind differently linked SA and also to the high levels and variability of glycosylations of their major virion glycoprotein components, HA and NA, IAV interacting proteins on the cell surface could also play an important role in initiating different signaling pathways to elicit the immune response in infected cells. But, at present, these processes are not well understood. In this mini-review we discuss how the interactions of IAV with cell surface receptors on immune cells might be important for the induction of specific innate immune responses and as a result, for pathogenicity in humans.