Emergence and pandemic potential of swine-origin H1N1 influenza virus

Analytical performance determination and clinical validation of the novel Roche RealTime Ready Influenza A/H1N1 Detection Set

The emergence of a novel pandemic human strain of influenza A (H1N1/09) virus in April 2009 has demonstrated the need for well-validated diagnostic tests that are broadly applicable, rapid, sensitive, and specific. The analytical performance and clinical validity of results generated with the novel Roche RealTime Ready Influenza A/H1N1 Detection Set using the LightCycler 2.0 instrument were characterized. Analytical performance was assessed by processing respiratory samples spiked with H1N1/09 and seasonal influenza A virus, a set of seasonal influenza A virus subtypes, and samples containing common viral and bacterial respiratory pathogens. The clinical validity of results was assessed in comparison to other assays by analyzing 359 specimens at three clinical sites and one reference laboratory. Direct sequencing was used to resolve samples with discrepant results. The assay detected virus concentrations down to <50 RNA copies per reverse transcription (RT)-quantitative PCR (qPCR). Various influenza A virus subtypes were covered. The analytical specificity was 100%. High clinical validity was demonstrated by the 99% positive agreement between seasonal influenza A viruses, 98% positive agreement between H1N1/09 viruses, and 88% agreement between negative results. The analytical sensitivity was compared to those of three other RT-qPCR assays and was found to be equivalent. The novel Roche RealTime Ready Influenza A/H1N1 Detection Set can be utilized on the widely used LightCycler platform. We demonstrate its usefulness for the rapid detection and surveillance of pandemic H1N1/09 influenza A virus infections.

Autopsy findings in eight patients with fatal H1N1 influenza

A novel H1N1 influenza A virus emerged in April 2009, and rapidly reached pandemic proportions. We report a retrospective observational case study of pathologic findings in 8 patients with fatal novel H1N1 infection at the University of Michigan Health Systems (Ann Arbor) compared with 8 age-, sex-, body mass index-, and treatment-matched control subjects. Diffuse alveolar damage (DAD) in acute and organizing phases affected all patients with influenza and was accompanied by acute bronchopneumonia in 6 patients. Organizing DAD with established fibrosis was present in 1 patient with preexisting granulomatous lung disease. Only 50% of control subjects had DAD. Peripheral pulmonary vascular thrombosis occurred in 5 of 8 patients with influenza and 3 of 8 control subjects. Cytophagocytosis was seen in all influenza-related cases. The autopsy findings in our patients with novel H1N1 influenza resemble other influenza virus infections with the exception of prominent thrombosis and hemophagocytosis. The possibility of hemophagocytic syndrome should be investigated in severely ill patients with H1N1 infection.

Human antibodies reveal a protective epitope that is highly conserved among human and nonhuman influenza A viruses

Influenza remains a serious public health threat throughout the world. Vaccines and antivirals are available that can provide protection from infection. However, new viral strains emerge continuously because of the plasticity of the influenza genome, which necessitates annual reformulation of vaccine antigens, and resistance to antivirals can appear rapidly and become entrenched in circulating virus populations. In addition, the spread of new pandemic strains is difficult to contain because of the time required to engineer and manufacture effective vaccines. Monoclonal antibodies that target highly conserved viral epitopes might offer an alternative protection paradigm. Herein we describe the isolation of a panel of monoclonal antibodies derived from the IgG(+) memory B cells of healthy, human subjects that recognize a previously unknown conformational epitope within the ectodomain of the influenza matrix 2 protein, M2e. This antibody binding region is highly conserved in influenza A viruses, being present in nearly all strains detected to date, including highly pathogenic viruses that infect primarily birds and swine, and the current 2009 swine-origin H1N1 pandemic strain (S-OIV). Furthermore, these human anti-M2e monoclonal antibodies protect mice from lethal challenges with either H5N1 or H1N1 influenza viruses. These results suggest that viral M2e can elicit broadly cross-reactive and protective antibodies in humans. Accordingly, recombinant forms of these human antibodies may provide useful therapeutic agents to protect against infection from a broad spectrum of influenza A strains.

Mapping the risk of avian influenza in wild birds in the US

BACKGROUND

Avian influenza virus (AIV) is an important public health issue because pandemic influenza viruses in people have contained genes from viruses that infect birds. The H5 and H7 AIV subtypes have periodically mutated from low pathogenicity to high pathogenicity form. Analysis of the geographic distribution of AIV can identify areas where reassortment events might occur and how high pathogenicity influenza might travel if it enters wild bird populations in the US. Modelling the number of AIV cases is important because the rate of co-infection with multiple AIV subtypes increases with the number of cases and co-infection is the source of reassortment events that give rise to new strains of influenza, which occurred before the 1968 pandemic. Aquatic birds in the orders Anseriformes and Charadriiformes have been recognized as reservoirs of AIV since the 1970s. However, little is known about influenza prevalence in terrestrial birds in the order Passeriformes. Since passerines share the same habitat as poultry, they may be more effective transmitters of the disease to humans than aquatic birds. We analyze 152 passerine species including the American Robin (Turdus migratorius) and Swainson's Thrush (Catharus ustulatus).

METHODS

We formulate a regression model to predict AIV cases throughout the US at the county scale as a function of 12 environmental variables, sampling effort, and proximity to other counties with influenza outbreaks. Our analysis did not distinguish between types of influenza, including low or highly pathogenic forms.

RESULTS

Analysis of 13,046 cloacal samples collected from 225 bird species in 41 US states between 2005 and 2008 indicates that the average prevalence of influenza in passerines is greater than the prevalence in eight other avian orders. Our regression model identifies the Great Plains and the Pacific Northwest as high-risk areas for AIV. Highly significant predictors of AIV include the amount of harvested cropland and the first day of the year when a county is snow free.

CONCLUSIONS

Although the prevalence of influenza in waterfowl has long been appreciated, we show that 22 species of song birds and perching birds (order Passeriformes) are influenza reservoirs in the contiguous US.

Pneumonia in novel swine-origin influenza A (H1N1) virus infection: high-resolution CT findings

Objective

The purpose of our study was to review the initial high-resolution CT (HRCT) findings in pneumonia patients with presumed/laboratory-confirmed novel swine-origin influenza A (H1N1) virus (S-OIV) infection and detect pneumonia earlier.

Materials and methods

High-resolution CT (HRCT) findings of 106 patients with presumed/laboratory-confirmed novel S-OIV (H1N1) infection were reviewed. The 106 patients were divided into two groups according to the serious condition of the diseases. The pattern (consolidation, ground-glass, nodules, and reticulation), distribution, and extent of abnormality on the HRCT were evaluated in both groups. The dates of the onset of symptoms of the patients were recorded.

Results

The predominant CT findings in the patients at presentation were unilateral or bilateral multifocal asymmetric ground-glass opacities alone (n = 29, 27.4%), with unilateral or bilateral consolidation (n = 50, 47.2%). The consolidation had peribronchovascular and subpleural predominance. The areas of consolidation were found mainly in the posterior, middle and lower regions of the lungs. Reticular opacities were found in 6 cases of the initial MDCT scan. The extent of disease was greater in group 1 patients requiring advanced mechanical ventilation, with diffuse involvement in 19 patients (63.3%) of group 1 patients, and only 15/76 (19.7%) of group 2 patients (p < 0.01, χ² test). 20 cases (19%) of the 106 patients had small bilateral or unilateral pleural effusions. None had evidence of hilar or mediastinal lymph node enlargement on CT performed at admission or later.

Conclusions

The most common radiographic and CT findings in patients with S-OIV infection are unilateral or bilateral ground-glass opacities with or without associated focal or multifocal areas of consolidation. On HRCT, the ground-glass opacities had a predominant peribronchovascular and subpleural distribution. CT plays an important role in the early recognition of severe S-OIV (H1N1).

Pharmacokinetics and disposition of CS-8958, a long-acting prodrug of the novel neuraminidase inhibitor laninamivir in rats

CS-8958, a prodrug of laninamivir (R-125489), is currently under development as an inhaled anti-influenza drug. In this study, the pharmacokinetics and disposition of CS-8958 were characterized in rats. After intratracheal administration of 14C-CS-8958, radioactivity was retained over long periods in the target tissues (trachea and lung) as its active metabolite R-125489 - 19.12% of the dose was retained in the lung at 24 h. After intratracheal administration of CS-8958, plasma R-125489 concentration was slowly eliminated, and its half-life (14.1 h) was considerably longer than that after intravenous administration of R-125489. The radioactivity of intratracheally administered 14C-CS-8958 was mainly excreted into the urine (67.5% of dose), and this excretion lasted over long periods. R-125489 accounted for most of the urinary radioactivity recovered after 24 h. These results demonstrated that CS-8958 administered intratracheally to rats was converted/hydrolysed to R-125489 in the target tissues, and that the R-125489 was slowly excreted into the urine via an absorption rate-limiting process. Such distinctive pharmacokinetics attributed to the slow release of R-125489 suggests the potential for a long-acting anti-influenza drug.

Modifications to the hemagglutinin cleavage site control the virulence of a neurotropic H1N1 influenza virus

A key determinant of influenza virus pathogenesis is mutation in the proteolytic cleavage site of the hemagglutinin (HA). Typically, low-pathogenicity forms of influenza virus are cleaved by trypsin-like proteases, whereas highly pathogenic forms are cleaved by different proteases (e.g., furin). Influenza virus A/WSN/33 (WSN) is a well-studied H1N1 strain that is trypsin independent in vitro and has the ability to replicate in mouse brain. Previous studies have indicated that mutations in the neuraminidase (NA) gene allow the recruitment of an alternate protease (plasminogen/plasmin) for HA activation. In this study we have identified an additional mutation in the P2 position of the WSN HA cleavage site (S328Y) that appears to control virus spread in a plasmin-dependent manner. We reconstructed recombinant WSN viruses containing tyrosine (Y), phenylalanine (F), or serine (S) in the P2 position of the cleavage site. The Y328 and F328 viruses allowed plaque formation in the absence of trypsin, whereas the S328 virus was unable to form plaques under these conditions. In mice, Y328 and F328 viruses were able to efficiently spread following intracranial inoculation; in contrast, the S328 virus showed only limited infection of mouse brain. Following intranasal inoculation, all viruses could replicate efficiently, but with Y328 and F328 viruses showing a limited growth defect. We also show that wild-type HA (Y328) was more efficiently cleaved by plasmin than S328 HA. Our studies form the foundation for a more complete understanding of the molecular determinants of influenza virus pathogenesis and the role of the plasminogen/plasmin system in activating HA.

Evolutionary analyses on the HA gene ofpandemic H1N1/09: early findings

The HA protein is responsible for influenza virus attachment and the subsequent fusion of viral and cellular membranes. Antigenic drift is driven by an accumulation of point mutations in the HA. And, the receptor-binding specificity of HA is responsible for the host range restriction of the virus. In April 2009, large outbreaks of novel H1N1 influenza in human population were reported from North America. The pandemic H1N1 virus originated from swine influenza virus. Evolutionary process of the pandemic virus after its introduction to human population remains to be clarified. We conducted phylogenetic analyses constructing a phylogenetic tree for and calculating site-by-site selective pressures in the HA gene. Phylogenetic tree showed that pandemic viruses were not clustered clearly by their geographical location or isolation time in the phylogenetic tree. The virus has been circulating the globe extensively with multiple introductions into most geographical areas. We found 3 sites positively selected in the HA gene for pandemic H1N1 virus. Among them, position 206 is located in an antigenic site. We did not find significant negative selection on any of the receptor binding sites. The virus has been evolving under unique selective pressure.

Influenza A virus polymerase: structural insights into replication and host adaptation mechanisms

The heterotrimeric RNA-dependent RNA polymerase of influenza viruses catalyzes RNA replication and transcription activities in infected cell nuclei. The nucleotide polymerization activity is common to both replication and transcription processes, with an additional cap-snatching function being employed during transcription to steal short 5'-capped RNA primers from host mRNAs. Cap-binding, endonuclease, and polymerase activities have long been studied biochemically, but structural studies on the polymerase and its subunits have been hindered by difficulties in producing sufficient quantities of material. Recently, because of heightened effort and advances in expression and crystallization technologies, a series of high resolution structures of individual domains have been determined. These shed light on intrinsic activities of the polymerase, including cap snatching, subunit association, and nucleocytoplasmic transport, and open up the possibility of structure-guided development of new polymerase inhibitors. Furthermore, the activity of influenza polymerase is highly host- and cell type-specific, being dependent on the identity of a few key amino acid positions in the different subunits, especially in the C-terminal region of PB2. New structures demonstrate the surface exposure of these residues, consistent with ideas that they might modulate interactions with host-specific factors that enhance or restrict activity. Recent proteomic and genome-wide interactome and RNA interference screens have suggested the identities of some of these potential regulators of polymerase function.

Crystal structure of the swine-origin A (H1N1)-2009 influenza A virus hemagglutinin (HA) reveals similar antigenicity to that of the 1918 pandemic virus

Influenza virus is the causative agent of the seasonal and occasional pandemic flu. The current H1N1 influenza pandemic, announced by the WHO in June 2009, is highly contagious and responsible for global economic losses and fatalities. Although the H1N1 gene segments have three origins in terms of host species, the virus has been named swine-origin influenza virus (S-OIV) due to a predominant swine origin. 2009 S-OIV has been shown to highly resemble the 1918 pandemic virus in many aspects. Hemagglutinin is responsible for the host range and receptor binding of the virus and is therefore a primary indicator for the potential of infection. Primary sequence analysis of the 2009 S-OIV hemagglutinin (HA) reveals its closest relationship to that of the 1918 pandemic influenza virus, however, analysis at the structural level is necessary to critically assess the functional significance. In this report, we report the crystal structure of soluble hemagglutinin H1 (09H1) at 2.9 Å, illustrating that the 09H1 is very similar to the 1918 pandemic HA (18H1) in overall structure and the structural modules, including the five defined antiboby (Ab)-binding epitopes. Our results provide an explanation as to why sera from the survivors of the 1918 pandemics can neutralize the 2009 S-OIV, and people born around the 1918 are resistant to the current pandemic, yet younger generations are more susceptible to the 2009 pandemic.

[Virological characteristics of pandemic (H1N1) 2009 influenza virus]

In the spring of 2009, a novel swine-origin H1N1 virus, whose antigenicity is quite different from those of seasonal human H1N1 strains, emerged in Mexico and readily transmitted and spread among humans, resulting in the first influenza pandemic in the 21st century. This novel H1N1 virus was shown to be a triple reassortant comprising genes derived from avian, human, and swine viruses. Here, we review our current knowledge of this pandemic influenza virus and discuss future aspects of the pandemic.

The 2009 A (H1N1) influenza virus pandemic: A review

In March and early April 2009 a new swine-origin influenza virus (S-OIV), A (H1N1), emerged in Mexico and the USA. The virus quickly spread worldwide through human-to-human transmission. In view of the number of countries and communities which were reporting human cases, the World Health Organization raised the influenza pandemic alert to the highest level (level 6) on June 11, 2009. The propensity of the virus to primarily affect children, young adults and pregnant women, especially those with an underlying lung or cardiac disease condition, and the substantial increase in rate of hospitalizations, prompted the efforts of the pharmaceutical industry, including new manufacturers from China, Thailand, India and South America, to develop pandemic H1N1 influenza vaccines. All currently registered vaccines were tested for safety and immunogenicity in clinical trials on human volunteers. All were found to be safe and to elicit potentially protective antibody responses after the administration of a single dose of vaccine, including split inactivated vaccines with or without adjuvant, whole-virion vaccines and live-attenuated vaccines. The need for an increased surveillance of influenza virus circulation in swine is outlined.

Lethal dissemination of H5N1 influenza virus is associated with dysregulation of inflammation and lipoxin signaling in a mouse model of infection

Periodic outbreaks of highly pathogenic avian H5N1 influenza viruses and the current H1N1 pandemic highlight the need for a more detailed understanding of influenza virus pathogenesis. To investigate the host transcriptional response induced by pathogenic influenza viruses, we used a functional-genomics approach to compare gene expression profiles in lungs from 129S6/SvEv mice infected with either the fully reconstructed H1N1 1918 pandemic virus (1918) or the highly pathogenic avian H5N1 virus Vietnam/1203/04 (VN/1203). Although the viruses reached similar titers in the lung and caused lethal infections, the mean time of death was 6 days for VN/1203-infected animals and 9 days for mice infected with the 1918 virus. VN/1203-infected animals also exhibited an earlier and more potent inflammatory response. This response included induction of genes encoding components of the inflammasome. VN/1203 was also able to disseminate to multiple organs, including the brain, which correlated with changes in the expression of genes associated with hematological functions and lipoxin biogenesis and signaling. Both viruses elicited expression of type I interferon (IFN)-regulated genes in wild-type mice and to a lesser extent in mice lacking the type I IFN receptor, suggesting alternative or redundant pathways for IFN signaling. Our findings suggest that VN/1203 is more pathogenic in mice as a consequence of several factors, including the early and sustained induction of the inflammatory response, the additive or synergistic effects of upregulated components of the immune response, and inhibition of lipoxin-mediated anti-inflammatory responses, which correlated with the ability of VN/1203 to disseminate to extrapulmonary organs.

Swine-origin influenza-virus-induced acute lung injury: Novel or classical pathogenesis?

Influenza viruses are common respiratory pathogens in humans and can cause serious infection that leads to the development of pneumonia. Due to their host-range diversity, genetic and antigenic diversity, and potential to reassort genetically in vivo, influenza A viruses are continual sources of novel influenza strains that lead to the emergence of periodic epidemics and outbreaks in humans. Thus, newly emerging viral diseases are always major threats to public health. In March 2009, a novel influenza virus suddenly emerged and caused a worldwide pandemic. The novel pandemic influenza virus was genetically and antigenically distinct from previous seasonal human influenza A/H1N1 viruses; it was identified to have originated from pigs, and further genetic analysis revealed it as a subtype of A/H1N1, thus later called a swine-origin influenza virus A/H1N1. Since the novel virus emerged, epidemiological surveys and research on experimental animal models have been conducted, and characteristics of the novel influenza virus have been determined but the exact mechanisms of pulmonary pathogenesis remain to be elucidated. In this editorial, we summarize and discuss the recent pandemic caused by the novel swine-origin influenza virus A/H1N1 with a focus on the mechanism of pathogenesis to obtain an insight into potential therapeutic strategies.

Substitution of lysine at 627 position in PB2 protein does not change virulence of the 2009 pandemic H1N1 virus in mice

A lysine at the 627 position (627K) of PB2 protein of influenza virus has been recognized as a determinant for host adaptation and a virulent element for some influenza viruses. While seasonal influenza viruses exclusively contained 627K, the pandemic (H1N1) 2009 possessed a glutamic acid (627E), even after circulation in humans for more than 6months. To explore the potential role of E627K substitution in PB2 in the pandemic (H1N1) 2009 virus, we compared pathogenicity and growth properties between a recombinant virus containing 627K PB2 gene and the parental A/California/4/2009 strain containing 627E. Our results showed that substitution of 627K in PB2 gene does not confer higher virulence and growth rate for the pandemic (H1N1) 2009 virus in mice and cell culture respectively, suggesting 627K is not required for human adaptation of the pandemic (H1N1) 2009 virus.

Anti-influenza activity of phenethylphenylphthalimide analogs derived from thalidomide

Swine-origin influenza A virus has caused pandemics throughout the world and influenza A is regarded as a serious global health issue. Hence, novel drugs that will target these viruses are very desirable. Influenza A expresses an RNA polymerase essential for its transcription and replication which comprises PA, PB1, and PB2 subunits. We identified potential novel anti-influenza agents from a screen of 34 synthesized phenethylphenylphthalimide analogs derived from thalidomide (PPT analogs). For this screen we used a PA endonuclease inhibition assay, a PB2 pathogenicity-determinant domain-binding assay, and an anti-influenza A virus assay. Three PPT analogs, PPT-65, PPT-66, and PPT-67, were found to both inhibit PA endonuclease activity and retard the growth of influenza A, suggesting a correlation between their activities. PPT-28 was also found to inhibit the growth of influenza A. These four analogs have a 3,4-dihydroxyphenethyl group in common. We also discuss the possibility that 3,4-dihydroxyphenethyl group flexibility may play an important functional role in PA endonuclease inhibition. Another analog harboring a dimethoxyphenethyl group, PPT-62, showed PB2 pathogenicity-determinant domain-binding activity, but did not inhibit the growth of the virus. Our present results indicate the utility of the PA endonuclease assay in the screening of anti-influenza drugs and are therefore useful for future strategies to develop novel anti-influenza A drugs and for mapping the function of the influenza A RNA polymerase subunits.

Recombinant H1N1 virus-like particle vaccine elicits protective immunity in ferrets against the 2009 pandemic H1N1 influenza virus

The pandemic virus of 2009 (2009 H1N1) continues to cause illness worldwide, especially in younger age groups. The widespread H1N1 virus infection further emphasizes the need for vaccine strategies that are effective against emerging pandemic viruses and are not dependent on the limitations of traditional egg-based technology. This report describes a recombinant influenza virus-like particle (VLP) vaccine consisting of hemagglutinin (HA), neuraminidase (NA), and matrix (M1) proteins of influenza A/California/04/2009 (H1N1) virus. Influenza H1N1 VLPs with a diameter of approximately 120nm were released into the culture medium from Sf9 insect cells infected with recombinant baculovirus coexpressing HA, NA, and M1 proteins. Purified recombinant H1N1 VLPs morphologically resembled influenza virions and exhibited biological characteristics of influenza virus, including HA and NA activities. In the ferret challenge model, 2009 influenza H1N1 VLPs elicited high-titer serum hemagglutination inhibition (HI) antibodies specific for the 2009 H1N1 virus and inhibited replication of the influenza virus in the upper and lower respiratory tract tissues following A/Mexico/4482/09 (H1N1) virus challenge. Moreover, a single 15mug dose of H1N1 VLPs resulted in complete virus clearance in the ferret lung. These results provide support for the use of recombinant influenza VLP vaccine as an effective strategy against pandemic H1N1 virus.

HLA class I binding 9mer peptides from influenza A virus induce CD4 T cell responses

Background

Identification of human leukocyte antigen class I (HLA-I) restricted cytotoxic T cell (CTL) epitopes from influenza virus is of importance for the development of new effective peptide-based vaccines.

Methodology/Principal Findings

In the present work, bioinformatics was used to predict 9mer peptides derived from available influenza A viral proteins with binding affinity for at least one of the 12 HLA-I supertypes. The predicted peptides were then selected in a way that ensured maximal coverage of the available influenza A strains. One hundred and thirty one peptides were synthesized and their binding affinities for the HLA-I supertypes were measured in a biochemical assay. Influenza-specific T cell responses towards the peptides were quantified using IFNγ ELISPOT assays with peripheral blood mononuclear cells (PBMC) from adult healthy HLA-I typed donors as responder cells. Of the 131 peptides, 21 were found to induce T cell responses in 19 donors. In the ELISPOT assay, five peptides induced responses that could be totally blocked by the pan-specific anti-HLA-I antibody W6/32, whereas 15 peptides induced responses that could be completely blocked in the presence of the pan-specific anti-HLA class II (HLA-II) antibody IVA12. Blocking of HLA-II subtype reactivity revealed that 8 and 6 peptide responses were blocked by anti-HLA-DR and -DP antibodies, respectively. Peptide reactivity of PBMC depleted of CD4⁺ or CD8⁺ T cells prior to the ELISPOT culture revealed that effectors are either CD4⁺ (the majority of reactivities) or CD8⁺ T cells, never a mixture of these subsets. Three of the peptides, recognized by CD4⁺ T cells showed binding to recombinant DRA1*0101/DRB1*0401 or DRA1*0101/DRB5*0101 molecules in a recently developed biochemical assay.

Conclusions/Significance

HLA-I binding 9mer influenza virus-derived peptides induce in many cases CD4⁺ T cell responses restricted by HLA-II molecules.

First case in Italy of acquired resistance to oseltamivir in an immunocompromised patient with influenza A/H1N1v infection

A pandemic influenza A/H1N1v strain with the neuraminidase H274Y mutation was detected in nasal secretions of a 2-year-old leukemic patient with influenza-like illness after 18 days of treatment with oseltamivir. At baseline, no drug-resistant virus was found, while 4 days after treatment initiation a mixture of wild-type and mutated virus was detected. After treatment interruption, the wild type influenza virus re-emerged and became prevalent in nasal secretions after a few days, suggesting the lower fitness of the mutated virus strain. The patient slowly improved concurrently with a decrease in virus load, which resulted negative 42 days after diagnosis. No other drug-resistant influenza A/H1N1v virus strains have been detected in Italy (up to the end of November 2009) since the first case of the novel A/H1N1v virus was identified in the country (May 2009).

A candidate H1N1 pandemic influenza vaccine elicits protective immunity in mice

BACKGROUND

In 2009 a new pandemic disease appeared and spread globally. The recent emergence of the pandemic influenza virus H1N1 first isolated in Mexico and USA raised concerns about vaccine availability. We here report our development of an adenovirus-based influenza H1N1 vaccine tested for immunogenicity and efficacy to confer protection in animal model.

METHODS

We generated two adenovirus(Ad5)-based influenza vaccine candidates encoding the wildtype or a codon-optimized hemagglutinin antigen (HA) from the recently emerged swine influenza isolate A/California/04/2009 (H1N1)pdm. After verification of antigen expression, immunogenicity of the vaccine candidates were tested in a mouse model using dose escalations for subcutaneous immunization. Sera of immunized animals were tested in microneutalization and hemagglutination inhibition assays for the presence of HA-specific antibodies. HA-specific T-cells were measured in IFNgamma Elispot assays. The efficiency of the influenza vaccine candidates were evaluated in a challenge model by measuring viral titer in lung and nasal turbinate 3 days after inoculation of a homologous H1N1 virus.

CONCLUSIONS/SIGNIFICANCE

A single immunization resulted in robust cellular and humoral immune response. Remarkably, the intensity of the immune response was substantially enhanced with codon-optimized antigen, indicating the benefit of manipulating the genetic code of HA antigens in the context of recombinant influenza vaccine design. These results highlight the value of advanced technologies in vaccine development and deployment in response to infections with pandemic potential. Our study emphasizes the potential of an adenoviral-based influenza vaccine platform with the benefits of speed of manufacture and efficacy of a single dose immunization.

Pathogenesis of pandemic H1N1 2009 influenza virus infection and the implication on management

The pandemic H1N1 2009 influenza virus has caused the first influenza pandemic of the 21st century, leading to disproportionate fatalities in the low-risk population despite the generally mild nature of the illness. Advances in science and technology have allowed very detailed study on the pathogenesis of this novel virus, and many have already been published in less than a year after the start of the pandemic. Information generated from cell lines, animal models, and clinical data analysis has provided us with greater understanding of the behavior of this virus and the associated host response. The new knowledge will allow us to formulate scientifically sound and evidence-based management plans.

Glycosylation at 158N of the hemagglutinin protein and receptor binding specificity synergistically affect the antigenicity and immunogenicity of a live attenuated H5N1 A/Vietnam/1203/2004 vaccine virus in ferrets

A live attenuated influenza A/Vietnam/1203/2004 (H5N1) vaccine virus (VN04 ca) has receptor binding specificity to alpha2,3-linked sialosides (alpha2,3SAL), and a single dose induces a minimal serum antibody response in mice and ferrets. In contrast, A/Hong Kong/213/2003 (H5N1) vaccine virus (HK03 ca) binds to both alpha2,6SAL and alpha2,3SAL and generates a stronger serum antibody response in animals. Among the 9 amino acids that differed between the two H5 HA1 proteins, several HK03-specific residues enabled the VN04 ca virus to bind to both alpha2,3SAL and alpha2,6SAL receptors, but only the removal of the 158N glycosylation, together with an S227N change, resulted in more-efficient viral replication in the upper respiratory tract of ferrets and an increased serum antibody response. However, the antibody response was HK03 strain specific and did not significantly cross-neutralize VN04 virus. A second approach was taken to adapt the H5N1 VN04 ca virus in MDCK cells to select HA variants with larger plaque morphology. Although a number of large-plaque-size HA variants with amino acid changes in the HA receptor binding region were identified, none of these mutations affected virus receptor binding preference and immunogenicity. In addition, the known receptor binding site changes, Q226L and G228S, were introduced into the HA protein of the VN04 ca virus. Only in conjunction with the removal of the 158N glycosylation did the virus replicate efficiently in the upper respiratory tract of ferrets and became more immunogenic, yet the response was also HK03 specific. Thus, the mask of the antigenic epitopes by 158N glycosylation at the HA globular head and its alpha2,3SAL binding preference of VN04 ca virus affect virus antigenicity and replication in the host, resulting in a lower antibody response.

Dynamics of clinical symptoms in patients with pandemic influenza A (H1N1)

We evaluated the dynamics of clinical symptoms of 2009 pandemic influenza A (H1N1) using a four-point scale sheet. The most frequent symptoms were fever and cough. The sum of symptom score was high during the first 4 days. Systemic symptoms peaked earlier, by day 2, and resolved faster than upper respiratory symptoms and lower respiratory symptoms after oseltamivir treatment. The lower respiratory symptoms resolved slowly over 2 weeks. The 2009 pandemic influenza A (H1N1) virus might involve primarily lower respiratory tract and could be the main cause of pneumonia.

Potent immunity to low doses of influenza vaccine by probabilistic guided micro-targeted skin delivery in a mouse model

BACKGROUND

Over 14 million people die each year from infectious diseases despite extensive vaccine use [1]. The needle and syringe--first invented in 1853--is still the primary delivery device, injecting liquid vaccine into muscle. Vaccines could be far more effective if they were precisely delivered into the narrow layer just beneath the skin surface that contains a much higher density of potent antigen-presenting cells (APCs) essential to generate a protective immune response. We hypothesized that successful vaccination could be achieved this way with far lower antigen doses than required by the needle and syringe.

METHODOLOGY/PRINCIPAL FINDINGS

To meet this objective, using a probability-based theoretical analysis for targeting skin APCs, we designed the Nanopatch, which contains an array of densely packed projections (21025/cm(2)) invisible to the human eye (110 microm in length, tapering to tips with a sharpness of <1000 nm), that are dry-coated with vaccine and applied to the skin for two minutes. Here we show that the Nanopatches deliver a seasonal influenza vaccine (Fluvax 2008) to directly contact thousands of APCs, in excellent agreement with theoretical prediction. By physically targeting vaccine directly to these cells we induced protective levels of functional antibody responses in mice and also protection against an influenza virus challenge that are comparable to the vaccine delivered intramuscularly with the needle and syringe--but with less than 1/100(th) of the delivered antigen.

CONCLUSIONS/SIGNIFICANCE

Our results represent a marked improvement--an order of magnitude greater than reported by others--for injected doses administered by other delivery methods, without reliance on an added adjuvant, and with only a single vaccination. This study provides a proven mathematical/engineering delivery device template for extension into human studies--and we speculate that successful translation of these findings into humans could uniquely assist with problems of vaccine shortages and distribution--together with alleviating fear of the needle and the need for trained practitioners to administer vaccine, e.g., during an influenza pandemic.

Species-specific contribution of the four C-terminal amino acids of influenza A virus NS1 protein to virulence

Large-scale sequence analyses of influenza viruses revealed that nonstructural 1 (NS1) proteins from avian influenza viruses have a conserved C-terminal ESEV amino acid motif, while NS1 proteins from typical human influenza viruses have a C-terminal RSKV motif. To test the influence of the C-terminal domains of NS1 on the virulence of an avian influenza virus, we generated a wild-type H7N1 virus with an ESEV motif and a mutant virus with an NS1 protein containing a C-terminal RSKV motif by reverse genetics. We compared the phenotypes of these viruses in vitro in human, mouse, and duck cells as well as in vivo in mice and ducks. In human cells, the human C-terminal RSKV domain increased virus replication. In contrast, the avian C-terminal ESEV motif of NS1 increased virulence in mice. We linked this increase in pathogenicity in mice to an increase in virus replication and to a more severe lung inflammation associated with a higher level of production of type I interferons. Interestingly, the human C-terminal RSKV motif of NS1 increased viral replication in ducks. H7N1 virus with a C-terminal RSKV motif replicated to higher levels in ducks and induced higher levels of Mx, a type I interferon-stimulated gene. Thus, we identify the C-terminal domain of NS1 as a species-specific virulence domain.

Influenza pathogenesis: lessons learned from animal studies with H5N1, H1N1 Spanish, and pandemic H1N1 2009 influenza

Because cases of highly pathogenic influenza are rare, no systematic clinical studies have evaluated different therapeutic approaches. Instead, treatment recommendations are aimed at the alleviation of clinical signs and symptoms, especially the restoration of respiratory function, and at the inhibition of virus replication, assuming viral load is responsible for disease phenotype. Studies of highly pathogenic influenza in different animal models, especially nonhuman primates and ferrets, reproduce many of the key observations from clinical cases. Host-response kinetics reveal a delayed but broad activation of genes involved in the innate and acquired immune responses (innate responses produce inflammatory responses), which continue after the virus has been cleared and may contribute importantly to the clinical signs observed. Experimental animal models point to an important role for immune dysregulation in the pathogenesis of highly pathogenic influenza. The use of these models to develop and validate therapeutic approaches is just beginning, but published studies reveal the importance of early treatment with antivirals and show the potential and limitations of approaches aimed at the host response.

Influenza A viral loads in respiratory samples collected from patients infected with pandemic H1N1, seasonal H1N1 and H3N2 viruses

BACKGROUND

Nasopharyngeal aspirate (NPA), nasal swab (NS), and throat swab (TS) are common specimens used for diagnosis of respiratory virus infections based on the detection of viral genomes, viral antigens and viral isolation. However, there is no documented data regarding the type of specimen that yields the best result of viral detection. In this study, quantitative real time RT-PCR specific for M gene was used to determine influenza A viral loads present in NS, NPA and TS samples collected from patients infected with the 2009 pandemic H1N1, seasonal H1N1 and H3N2 viruses. Various copy numbers of RNA transcripts derived from recombinant plasmids containing complete M gene insert of each virus strain were assayed by RT-PCR. A standard curve for viral RNA quantification was constructed by plotting each Ct value against the log quantity of each standard RNA copy number.

RESULTS

Copy numbers of M gene were obtained through the extrapolation of Ct values of the test samples against the corresponding standard curve. Among a total of 29 patients with severe influenza enrolled in this study (12 cases of the 2009 pandemic influenza, 5 cases of seasonal H1N1 and 12 cases of seasonal H3N2 virus), NPA was found to contain significantly highest amount of viral loads and followed in order by NS and TS specimen. Viral loads among patients infected with those viruses were comparable regarding type of specimen analyzed.

CONCLUSION

Based on M gene copy numbers, we conclude that NPA is the best specimen for detection of influenza A viruses, and followed in order by NS and TS.

Assessment of the efficacy of commercially available and candidate vaccines against a pandemic H1N1 2009 virus

Background. The emergence and global spread of the pandemic H1N1 2009 influenza virus have raised questions regarding the protective effect of available seasonal vaccines and the efficacy of a newly produced matched vaccine.

Methods. Ferrets were immunized with the 2008–2009 formulations of commercially available live attenuated (FluMist; MedImmune) or split-inactivated (Fluviral; GlaxoSmithKline) vaccines, a commercial swine vaccine (FluSure; Pfizer), or a laboratory-produced matched inactivated whole-virus vaccine (A/Mexico/InDRE4487/2009). Adaptive immune responses were monitored, and the animals were challenged with A/Mexico/InDRE4487/2009 after 5 weeks.

Results. Only animals that received the swine or matched vaccines developed detectable hemagglutination- inhibiting antibodies against the challenge virus, whereas a T cell response was exclusively detected in animals vaccinated with FluMist. After challenge, all animals had high levels of virus replication in the upper respiratory tract. However, preexisting anti—pandemic H1N1 2009 antibodies resulted in reduced clinical signs and improved survival. Surprisingly, FluMist was associated with a slight increase in mortality and greater lung damage, which correlated with early up-regulation of interleukin-10.

Conclusions. The present study demonstrates that a single dose of matched inactivated vaccine confers partial protection against a pandemic H1N1 2009 virus, and it suggests that a higher dose or prime-boost regimen may be required. The consequences of mismatched immunity to influenza merit further investigation.

Bench-to-bedside review: vaccine protection strategies during pandemic flu outbreaks

Vaccination is the most effective means for the prevention of influenza, including pandemic strains. An ideal pandemic influenza vaccine should provide effective protection with the fewest number of doses in the shortest amount of time, and among the greatest proportion of the population. The current manufacturing processes required for embryonated chicken-egg-based influenza vaccines are limited in their ability to respond to pandemic situations - these limitations include problems with surge capacity, the need for egg-adapted strains, the possibility of contamination, and the presence of trace egg protein. Several vaccine strategies to circumvent the deficiencies intrinsic to an egg-based influenza vaccine are in various phases of development. These include the use of cell-culture-based growth systems, concomitant use of adjuvants, whole virus vaccines, recombinant protein vaccines, plasmid DNA vaccines, virus-like particle vaccines, and universal flu vaccines.

Evolution of highly pathogenic avian H5N1 influenza viruses and the emergence of dominant variants

Highly pathogenic avian H5N1 viruses have circulated in South-east Asia for more than a decade and have now spread to more than 60 countries. The evolution of these viruses is characterized by frequent reassortment of the so-called 'internal' genes, creating novel genotypes. Additionally, over time, the surface glycoprotein, haemagglutinin (HA), which is the primary target of the adaptive immune response, has evolved by point mutation into 20 genetically and potentially antigenically distinct clades. To investigate the evolution of avian H5N1 influenza viruses, we undertook a high-resolution analysis of the reassortment of internal genes and evolution of HA of 651 avian H5N1 viruses from 2000 to 2008. Our analysis suggested: (i) all current H5N1 genotypes were derived from a single, clearly defined sequence of initial reassortment events; (ii) reassortment of just three of the internal genes had the most importance in avian H5N1 virus evolution; (iii) HA and the constellation of internal genes may be jointly important in the emergence of dominant variants. Further, our analysis led to the identification of evolutionarily significant molecular changes in the internal genes that may be significant for the emergence of these dominant variants.

BioTorrents: a file sharing service for scientific data

The transfer of scientific data has emerged as a significant challenge, as datasets continue to grow in size and demand for open access sharing increases. Current methods for file transfer do not scale well for large files and can cause long transfer times. In this study we present BioTorrents, a website that allows open access sharing of scientific data and uses the popular BitTorrent peer-to-peer file sharing technology. BioTorrents allows files to be transferred rapidly due to the sharing of bandwidth across multiple institutions and provides more reliable file transfers due to the built-in error checking of the file sharing technology. BioTorrents contains multiple features, including keyword searching, category browsing, RSS feeds, torrent comments, and a discussion forum. BioTorrents is available at http://www.biotorrents.net.

Diagnostic approach for the differentiation of the pandemic influenza A(H1N1)v virus from recent human influenza viruses by real-time PCR

Background

The current spread of pandemic influenza A(H1N1)v virus necessitates an intensified surveillance of influenza virus infections worldwide. So far, in many laboratories routine diagnostics were limited to generic influenza virus detection only. To provide interested laboratories with real-time PCR assays for type and subtype identification, we present a bundle of PCR assays with which any human influenza A and B virus can be easily identified, including assays for the detection of the pandemic A(H1N1)v virus.

Principal Findings

The assays show optimal performance characteristics in their validation on plasmids containing the respective assay target sequences. All assays have furthermore been applied to several thousand clinical samples since 2007 (assays for seasonal influenza) and April 2009 (pandemic influenza assays), respectively, and showed excellent results also on clinical material.

Conclusions

We consider the presented assays to be well suited for the detection and subtyping of circulating influenza viruses.

Total synthesis of (+)-stachyflin: a potential anti-influenza A virus agent

The first enantioselective total synthesis of (+)-stachyflin, a potential anti-influenza A virus agent, was achieved; the method features a BF(3).Et(2)O-induced domino epoxide-opening/rearrangement/cyclization reaction to stereoselectively form the requisite pentacyclic ring system in one step.

Cross-clade protection against HPAI H5N1 influenza virus challenge in BALB/c mice intranasally administered adjuvant-combined influenza vaccine

The avian H5N1 influenza virus has the potential to cause a new pandemic. The increasing number of recent outbreaks of highly pathogenic avian influenza H5N1 in birds and humans emphasizes the urgent need to develop a potent H5N1 vaccine. Here, we studied the immunogenicity and protective effect of a vaccine prepared from H5N1 inactivated whole virus. This vaccine was intranasally co-administered in mice with phosphate buffered saline, recombinant cholera toxin B subunit (rCTB), cholera toxin (CT), rCTB containing a trace amount of holotoxin (rCTB/CT), polyinosinic:polycytidylic acid double-stranded RNA (polyI:C), or MF59 as an adjuvant. Intranasal administration of H5N1 inactivated whole virus vaccine with rCTB, CT, rCTB/CT, polyI:C, and MF59 elicited an immunological response with both secretory IgA (sIgA) in nasal, lung, and vaginal lavage, and IgG antibody in serum, showing protective immunity against lethal H5N1 infection. Cross-clade protection was also observed in animals immunized with a vaccine derived from Anhui/01/2005(H5N1) with rCTB, CT, rCTB/CT, polyI:C, or MF59 as adjuvants that were subsequently challenged with the A/OT/SZ/097/03 influenza strain.

Swine-origin H1N1 influenza A virus and dental practice: a critical review

Since the spring of 2009, there have been a considerable number of infected as well as fatal cases by virologically confirmed swine-origin H1N1 influenza A virus (S-OIV). The virus continues to spread globally. The World Health Organization (WHO) has now raised the level of S-OIV influenza pandemic alert to phase 6 ('the pandemic phase') because of the human-to-human transmission of the virus and the community-level outbreaks worldwide. The WHO also issues its concerns about the global surveillance, the diagnostic capacity for the infection and the pandemic preparedness plan in every country. However, no critical review on S-OIV influenza and dental practice published in the literature exists hitherto. Based on information up to November 2009, the aim of this article was to summarise significant data on this novel virus and a clinical practice guideline for dental professionals.

Contribution of company affiliation and social contacts to risk estimates of between-farm transmission of avian influenza

Background

Models of between-farm transmission of pathogens have identified service vehicles and social groups as risk factors mediating the spread of infection. Because of high levels of economic organization in much of the poultry industry, we examined the importance of company affiliation, as distinct from social contacts, in a model of the potential spread of avian influenza among broiler poultry farms in a poultry-dense region in the United States. The contribution of company affiliation to risk of between-farm disease transmission has not been previously studied.

Methodology/Principal Findings

We obtained data on the nature and frequency of business and social contacts through a national survey of broiler poultry growers in the United States. Daily rates of contact were estimated using Monte Carlo analysis. Stochastic modeling techniques were used to estimate the exposure risk posed by a single infectious farm to other farms in the region and relative risk of exposure for farms under different scenarios. The mean daily rate of vehicular contact was 0.82 vehicles/day. The magnitude of exposure risk ranged from <1% to 25% under varying parameters. Risk of between-farm transmission was largely driven by company affiliation, with farms in the same company group as the index farm facing as much as a 5-fold increase in risk compared to farms contracted with different companies. Employment of part-time workers contributed to significant increases in risk in most scenarios, notably for farms who hired day-laborers. Social visits were significantly less important in determining risk.

Conclusions/Significance

Biosecurity interventions should be based on information on industry structure and company affiliation, and include part-time workers as potentially unrecognized sources of viral transmission. Modeling efforts to understand pathogen transmission in the context of industrial food animal production should consider company affiliation in addition to geospatial factors and pathogen characteristics. Restriction of social contacts among farmers may be less useful in reducing between-farm transmission.

Cross-reactive antibody responses to the 2009 A/H1N1v influenza virus in the Italian population in the pre-pandemic period

To assess in Italy the pre-pandemic susceptibility of the general population to the 2009 A/H1N1v influenza virus, 587 serum samples collected in 2004 were analyzed using haemagglutination-inhibition (HI), single-radial-haemolysis (SRH) and microneutralisation (MN) assays. Serum samples were stratified by age group, gender, and geographic area. Overall, using HI assay, the proportion of subjects showing antibodies cross-reacting with 2009 A/H1N1v virus at seroprotection level (>or=1:40) was estimated to be 6.7%, 12.4%, and 22.4% in individuals born between 2004 and 1949, 1948 and 1939, 1938 and 1909, respectively. With a HI antibody titre of >or=1:10, in the same birth cohort, the seroprotection levels were 13.5%, 19.2%, and 58.2%, respectively. The results suggest that the Italian population was not fully naïf to the current pandemic virus and that the possible previous exposure and immune response increases with age.

[Interspecies transmission, adaptation to humans and pathogenicity of animal influenza viruses]

The emergence in 2009 of a novel A(H1N1)v influenza virus of swine origin and the regular occurrence since 2003 of human cases of infection with A(H5N1) avian influenza viruses underline the zoonotic and pandemic potential of type A influenza viruses. Influenza viruses from the wild aquatic birds reservoir usually do not replicate efficiently in humans. Domestic poultry and swine can act as intermediate hosts for the acquisition of determinants that increase the potential of transmission and adaptation to humans, through the accumulation of mutations or by genetic reassortment. The rapid evolution of influenza viruses following interspecies transmission probably results from the selection of genetic variations that favor optimal interactions between viral proteins and cellular factors, leading to an increased multiplication potential and a better escape to the host antiviral response. Whereas influenza viruses usually cause asymptomatic infections in wild aquatic birds, they may be highly pathogenic in other species. Molecular determinants of host-specificity and pathogenesis have been identified in most viral genes, notably in genes that encode viral surface glycoproteins, proteins involved in the viral genome replication, and proteins that counteract the host immune response. However, our knowledge of these numerous and interdependant determinants remains incomplete, and the molecular mechanisms involved are still to be understood.

Nanotechnology diagnostics for infectious diseases prevalent in developing countries

Infectious diseases are prevalent in the developing world and are one of the developing world's major sources of morbidity and mortality. While infectious diseases can initiate in a localized region, they can spread rapidly at any moment due to the ease of traveling from one part of the world to the next. This could lead to a global pandemic. One key to preventing this spread is the development of diagnostics that can quickly identify the infectious agent so that one can properly treat or in some severe cases, quarantine a patient. There have been major advances in diagnostic technologies but infectious disease diagnostics are still based on 50-year technologies that are limited by speed of analysis, need for skilled workers, poor detection threshold and inability to detect multiple strains of infectious agents. Here, we describe advances in nanotechnology and microtechnology diagnostics for infectious diseases. In these diagnostic schemes, the nanomaterials are used as labels or barcodes while microfluidic systems are used to automate the sample preparation and the assays. We describe the current state of the field and the challenges.

Unseasonal transmission of H3N2 influenza A virus during the swine-origin H1N1 pandemic

The initial wave of swine-origin influenza A virus (pandemic H1N1/09) in the United States during the spring and summer of 2009 also resulted in an increased vigilance and sampling of seasonal influenza viruses (H1N1 and H3N2), even though they are normally characterized by very low incidence outside of the winter months. To explore the nature of virus evolution during this influenza "off-season," we conducted a phylogenetic analysis of H1N1 and H3N2 sequences sampled during April to June 2009 in New York State. Our analysis revealed that multiple lineages of both viruses were introduced and cocirculated during this time, as is typical of influenza virus during the winter. Strikingly, however, we also found strong evidence for the presence of a large transmission chain of H3N2 viruses centered on the south-east of New York State and which continued until at least 1 June 2009. These results suggest that the unseasonal transmission of influenza A viruses may be more widespread than is usually supposed.

Genetic characterization of the influenza A pandemic (H1N1) 2009 virus isolates from India

Background

The Influenza A pandemic H1N1 2009 (H1N1pdm) virus appeared in India in May 2009 and thereafter outbreaks with considerable morbidity and mortality have been reported from many parts of the country. Continuous monitoring of the genetic makeup of the virus is essential to understand its evolution within the country in relation to global diversification and to track the mutations that may affect the behavior of the virus.

Methods

H1N1pdm viruses were isolated from both recovered and fatal cases representing major cities and sequenced. Phylogenetic analyses of six concatenated whole genomes and the hemagglutinin (HA) gene of seven more isolates from May-September 2009 was performed with reference to 685 whole genomes of global isolates available as of November 24, 2009. Molecular characterization of all the 8 segments was carried out for known pathogenic markers.

Results

The first isolate of May 2009 belonged to clade 5. Although clade 7 was the dominant H1N1pdm lineage in India, both clades 6 and 7 were found to be co-circulating. The neuraminidase of all the Indian isolates possessed H275, the marker for sensitivity to the neuraminidase inhibitor Oseltamivir. Some of the mutations in HA are at or in the vicinity of antigenic sites and may therefore be of possible antigenic significance. Among these a D222G mutation in the HA receptor binding domain was found in two of the eight Indian isolates obtained from fatal cases.

Conclusions

The majority of the 13 Indian isolates grouped in the globally most widely circulating H1N1pdm clade 7. Further, correlations of the mutations specific to clade 7 Indian isolates to viral fitness and adaptability in the country remains to be understood. The D222G mutation in HA from isolates of fatal cases needs to be studied for pathogenicity.

Influenza virus m2 ion channel protein is necessary for filamentous virion formation

Influenza A virus buds from cells as spherical (approximately 100-nm diameter) and filamentous (approximately 100 nm x 2 to 20 microm) virions. Previous work has determined that the matrix protein (M1) confers the ability of the virus to form filaments; however, additional work has suggested that the influenza virus M2 integral membrane protein also plays a role in viral filament formation. In examining the role of the M2 protein in filament formation, we observed that the cytoplasmic tail of M2 contains several sites that are essential for filament formation. Additionally, whereas M2 is a nonraft protein, expression of other viral proteins in the context of influenza virus infection leads to the colocalization of M2 with sites of virus budding and lipid raft domains. We found that an amphipathic helix located within the M2 cytoplasmic tail is able to bind cholesterol, and we speculate that M2 cholesterol binding is essential for both filament formation and the stability of existing viral filaments.

Efficacy of the new neuraminidase inhibitor CS-8958 against H5N1 influenza viruses

Currently, two neuraminidase (NA) inhibitors, oseltamivir and zanamivir, which must be administrated twice daily for 5 days for maximum therapeutic effect, are licensed for the treatment of influenza. However, oseltamivir-resistant mutants of seasonal H1N1 and highly pathogenic H5N1 avian influenza A viruses have emerged. Therefore, alternative antiviral agents are needed. Recently, a new neuraminidase inhibitor, R-125489, and its prodrug, CS-8958, have been developed. CS-8958 functions as a long-acting NA inhibitor in vivo (mice) and is efficacious against seasonal influenza strains following a single intranasal dose. Here, we tested the efficacy of this compound against H5N1 influenza viruses, which have spread across several continents and caused epidemics with high morbidity and mortality. We demonstrated that R-125489 interferes with the NA activity of H5N1 viruses, including oseltamivir-resistant and different clade strains. A single dose of CS-8958 (1,500 microg/kg) given to mice 2 h post-infection with H5N1 influenza viruses produced a higher survival rate than did continuous five-day administration of oseltamivir (50 mg/kg twice daily). Virus titers in lungs and brain were substantially lower in infected mice treated with a single dose of CS-8958 than in those treated with the five-day course of oseltamivir. CS-8958 was also highly efficacious against highly pathogenic H5N1 influenza virus and oseltamivir-resistant variants. A single dose of CS-8958 given seven days prior to virus infection also protected mice against H5N1 virus lethal infection. To evaluate the improved efficacy of CS-8958 over oseltamivir, the binding stability of R-125489 to various subtypes of influenza virus was assessed and compared with that of other NA inhibitors. We found that R-125489 bound to NA more tightly than did any other NA inhibitor tested. Our results indicate that CS-8958 is highly effective for the treatment and prophylaxis of infection with H5N1 influenza viruses, including oseltamivir-resistant mutants.

A novel H1N1 virus causes the first pandemic of the 21st century

A novel H1N1 virus of swine origin (H1N1v ) is currently spreading in humans, giving rise to the first pandemic in 40 years. The disease is of moderate severity but has notable differences from seasonal influenza. In contrast to seasonal influenza, those over 60 years are relatively spared, a likely consequence of the presence of H1N1v cross-neutralizing antibody in this age group. Most patients appear to have mild influenza-like illness and many of the complications leading to hospitalization and mortality occur in those with underlying disease conditions or pregnancy. Studies in animal models suggest that the novel H1N1v pandemic virus causes a more severe illness and appears to have a greater predilection for the alveolar epithelium than seasonal influenza viruses. As there are as yet little data on the pathogenesis and immunology of H1N1v infection in humans, we have reviewed relevant data from past pandemics, from seasonal influenza and avian influenza H5N1 to highlight key issues pertaining to pathogenesis and immunology.

Alternative live-attenuated influenza vaccines based on modifications in the polymerase genes protect against epidemic and pandemic flu

Human influenza is a seasonal disease associated with significant morbidity and mortality. Influenza vaccination is the most effective means for disease prevention. We have previously shown that mutations in the PB1 and PB2 genes of the live-attenuated influenza vaccine (LAIV) from the cold-adapted (ca) influenza virus A/Ann Arbor/6/60 (H2N2) could be transferred to avian influenza viruses and produce partially attenuated viruses. We also demonstrated that avian influenza viruses carrying the PB1 and PB2 mutations could be further attenuated by stably introducing a hemagglutinin (HA) epitope tag in the PB1 gene. In this work, we wanted to determine whether these modifications would also result in attenuation of a so-called triple reassortant (TR) swine influenza virus (SIV). Thus, the TR influenza A/swine/Wisconsin/14094/99 (H3N2) virus was generated by reverse genetics and subsequently mutated in the PB1 and PB2 genes. Here we show that a combination of mutations in this TR backbone results in an attenuated virus in vitro and in vivo. Furthermore, we show the potential of our TR backbone as a vaccine that provides protection against the 2009 swine-origin pandemic influenza H1N1 virus (S-OIV) when carrying the surface of a classical swine strain. We propose that the availability of alternative backbones to the conventional ca A/Ann Arbor/6/60 LAIV strain could also be useful in epidemic and pandemic influenza and should be considered for influenza vaccine development. In addition, our data provide evidence that the use of these alternative backbones could potentially circumvent the effects of original antigenic sin (OAS) in certain circumstances.