Filamentous influenza A virus infection predisposes mice to fatal septicemia following superinfection with Streptococcus pneumoniae serotype 3

How Influenza Virus Uses Host Cell Pathways during Uncoating

Influenza is a zoonotic respiratory disease of major public health interest due to its pandemic potential, and a threat to animals and the human population. The influenza A virus genome consists of eight single-stranded RNA segments sequestered within a protein capsid and a lipid bilayer envelope. During host cell entry, cellular cues contribute to viral conformational changes that promote critical events such as fusion with late endosomes, capsid uncoating and viral genome release into the cytosol. In this focused review, we concisely describe the virus infection cycle and highlight the recent findings of host cell pathways and cytosolic proteins that assist influenza uncoating during host cell entry.

Increased Pulmonary Pneumococcal Clearance after Resolution of H9N2 Avian Influenza Virus Infection in Mice

H9N2 avian influenza virus has been continuously circulating among poultry and can infect mammals, indicating that this virus is a potential pandemic strain. During influenza pandemics, secondary bacterial (particularly pneumococcal) pneumonia usually contributes to excessive mortality. In the present study, we observed the dynamic effect of H9N2 virus infection on host defense against secondary pneumococcal infection in mice. BALB/c mice were intranasally inoculated with 1.2 × 10⁵ PFU of H9N2 virus followed by 1 × 10⁶ CFU of Streptococcus pneumoniae at 7, 14, or 28 days post-H9N2 infection (dpi). The bacterial load, histopathology, body weight, and survival were assessed after pneumococcal infection. Our results showed that H9N2 virus infection had no significant impact on host resistance to secondary pneumococcal infection at 7 dpi. However, H9N2 virus infection increased pulmonary pneumococcal clearance and reduced pneumococcal pneumonia-induced morbidity after secondary pneumococcal infection at 14 or 28 dpi, as reflected by significantly decreased bacterial loads, markedly alleviated pulmonary histopathological changes, and significantly reduced weight loss in mice infected with H9N2 virus followed by S. pneumoniae compared with mice infected only with S. pneumoniae. Further, the significantly decreased bacterial loads were observed when mice were previously infected with a high dose (1.2 × 10⁶ PFU) of H9N2 virus. Also, similar to the results obtained in BALB/c mice, improvement in pulmonary pneumococcal clearance was observed in C57BL/6 mice. Overall, our results showed that pulmonary pneumococcal clearance is improved after resolution of H9N2 virus infection in mice.

Synergistic PA and HA mutations confer mouse adaptation of a contemporary A/H3N2 influenza virus

The mouse is the most widely used animal model for influenza virus research. However, the susceptibility of mice to seasonal influenza virus depends on the strain of mouse and on the strain of the influenza virus. Seasonal A/H3N2 influenza viruses do not replicate well in mice and therefore they need to be adapted to this animal model. In this study, we generated a mouse-adapted A/H3N2 virus (A/Switzerland/9715293/2013 [MA-H3N2]) by serial passaging in mouse lungs that exhibited greater virulence compared to the wild-type virus (P0-H3N2). Seven mutations were found in the genome of MA-H3N2: PA(K615E), NP(G384R), NA(G320E) and HA(N122D, N144E, N246K, and A304T). Using reverse genetics, two synergistically acting genes were found as determinants of the pathogenicity in mice. First, the HA substitutions were shown to enhanced viral replication in vitro and, second, the PA-K615E substitution increased polymerase activity, although did not alter virus replication in vitro or in mice. Notably, single mutations had only limited effects on virulence in vitro. In conclusion, a co-contribution of HA and PA mutations resulted in a lethal mouse model of seasonal A/H3N2 virus. Such adapted virus is an excellent tool for evaluation of novel drugs or vaccines and for study of influenza pathogenesis.

Direct interactions with influenza promote bacterial adherence during respiratory infections

Epidemiological observations and animal models have long shown synergy between influenza virus infections and bacterial infections. Influenza virus infection leads to an increase in both the susceptibility to secondary bacterial infections and the severity of the bacterial infections, primarily pneumonias caused by Streptococcus pneumoniae or Staphylococcus aureus. We show that, in addition to the widely described immune modulation and tissue-remodelling mechanisms of bacterial-viral synergy, the virus interacts directly with the bacterial surface. Similar to the recent observation of direct interactions between enteric bacteria and enteric viruses, we observed a direct interaction between influenza virus on the surface of Gram-positive, S. pneumoniae and S. aureus, and Gram-negative, Moraxella catarrhalis and non-typeable Haemophilus influenzae, bacterial colonizers and pathogens in the respiratory tract. Pre-incubation of influenza virus with bacteria, followed by the removal of unbound virus, increased bacterial adherence to respiratory epithelial cells in culture. This result was recapitulated in vivo, with higher bacterial burdens in murine tissues when infected with pneumococci pre-incubated with influenza virus versus control bacteria without virus. These observations support an additional mechanism of bacteria-influenza virus synergy at the earliest steps of pathogenesis.

Pneumonia severity index in viral community acquired pneumonia in adults

Pneumonia severity index (PSI) is an important scoring system that can assess the severity of community acquired pneumonia and determine admission status. However, there is a lack of research on whether this scoring system can be applied to viral community acquired pneumonia. The purpose of this study was to evaluate the usefulness of PSI in viral community acquired pneumonia. This retrospective cohort study included 1,434 adult patients (aged ≥18 years) who were admitted to the emergency department of a university hospital during 2013–2015 because of community-acquired pneumonia. Viral infections were diagnosed by multiplex PCR. Patients diagnosed with non-viral community-acquired pneumonia were included in the control group (N = 1,173). The main outcome was 30-day all-cause mortality. multivariate Cox regression analyses were performed to calculate the risk of death. Respiratory viruses were detected in 261 (18.2%) patients with community-acquired pneumonia. Two types of respiratory viruses were detected in 7 cases. Of the 254 cases detected with only one virus, 62 were influenza A, 18 were influenza B, 65 were rhinovirus, 35 were respiratory syncytial virus, 25 were metapneumovirus, 20 were parainfluenza, 17 were coronavirus, 7 were bocavirus, and 5 were adenovirus. Mortality was not significantly different between patients with respiratory virus and those without respiratory virus; the 30-day all-cause mortality rates were 20.3% and 22.4%, respectively (P = 0.45). Mortality rate increased with an increasing PSI score with or without respiratory viral infection. Pulmonary severity index was significantly associated with mortality adjusted for respiratory virus detection (hazard ratio = 1.024, 95% confidence interval = 1.020–1.028). Pneumonia severity index score is an important factor for assessing the prognosis of patients with community-acquired pneumonia, regardless of respiratory virus detection.

New Approaches to Treat Sepsis: Animal Models «Do Not Work» (Review)

Like many other pathological infectious processes, sepsis is mainly studied in vivo using mice models. Over the past 30 years, such studies have led to significant achievements in understanding of the sepsis pathophysiology. However, unfortunately, none of them led to any «discoveries» in the treatment of patients. In this review, we question the relevance of the experimental models applied, list some aspects rarely taken into account and discuss ways to resolve the deadlock.

The text is a translation of the article: Cavail-lon J. M. New methods of treating sepsis: failure of animal models, Bull. Assoc. Anc. El. Inst. Pastor, 2017, 59,230, 58—60. Translation from French by «Akademperevod», Moscow, Russia.

The inflammatory response triggered by Influenza virus: a two edged sword

Influenza A virus (IAV) is a relevant respiratory tract pathogen leading to a great number of deaths and hospitalizations worldwide. Secondary bacterial infections are a very common cause of IAV associated morbidity and mortality. The robust inflammatory response that follows infection is important for the control of virus proliferation but is also associated with lung damage, morbidity and death. The role of the different components of immune response underlying protection or disease during IAV infection is not completely elucidated. Overall, in the context of IAV infection, inflammation is a 'double edge sword' necessary to control infection but causing disease. Therefore, a growing number of studies suggest that immunomodulatory strategies may improve disease outcome without affecting the ability of the host to deal with infection. This review summarizes recent aspects of the inflammatory responses triggered by IAV that are preferentially involved in causing severe pulmonary disease and the anti-inflammatory strategies that have been suggested to treat influenza induced immunopathology.

Influenza-Induced Priming and Leak of Human Lung Microvascular Endothelium upon Exposure to Staphylococcus aureus

A major cause of death after influenza virus infection is lung injury due to a bacterial superinfection, yet the mechanism is unknown. Death has been attributed to virus-induced immunosuppression and bacterial overgrowth, but this hypothesis is based on data from the preantibiotic era and animal models that omit antimicrobial therapy. Because of diagnostic uncertainty, most patients with influenza receive antibiotics, making bacterial overgrowth unlikely. Respiratory failure after superinfection presents as acute respiratory distress syndrome, a disorder characterized by lung microvascular leak and edema. The objective of this study was to determine whether the influenza virus sensitizes the lung endothelium to leak upon exposure to circulating bacterial-derived molecular patterns from Staphylococcus aureus. In vitro as well as in vivo models of influenza followed by S. aureus superinfection were used. Molecular mechanisms were explored using molecular biology, knockout mice, and human autopsy specimens. Influenza virus infection sensitized human lung endothelium to leak when challenged with S. aureus, even at low doses of influenza and even when the pathogens were given days apart. Influenza virus increased endothelial expression of TNFR1 both in vitro and in intact lungs, a finding corroborated by human autopsy specimens of patients with influenza. Leak was recapitulated with protein A, a TNFR1 ligand, and sequential infection caused protein A-dependent loss of IκB, cleavage of caspases 8 and 3, and lung endothelial apoptosis. Mice infected sequentially with influenza virus and S. aureus developed significantly increased lung edema that was protein A and TNFR1 dependent. Influenza virus primes the lung endothelium to leak, predisposing patients to acute respiratory distress syndrome upon exposure to S. aureus.

Galectins regulate the inflammatory response in airway epithelial cells exposed to microbial neuraminidase by modulating the expression of SOCS1 and RIG1

Influenza patients frequently display increased susceptibility to Streptococcus pneumoniae co-infection and sepsis, the prevalent cause of mortality during influenza pandemics. However, the detailed mechanisms by which an influenza infection predisposes patients to suffer pneumococcal pneumonia are not fully understood. A murine model for influenza infection closely reflects the observations in human patients, since if the animals that have recovered from influenza A virus (IAV) sublethal infection are challenged with S. pneumoniae, they undergo a usually fatal uncontrolled cytokine response. We have previously demonstrated both in vitro and in vivo that the expression and secretion of galectin-1 (Gal1) and galectin-3 (Gal3) are modulated during IAV infection, and that the viral neuraminidase unmasks galactosyl moieties in the airway epithelia. In this study we demonstrate in vitro that the binding of secreted Gal1 and Gal3 to the epithelial cell surface modulates the expression of SOCS1 and RIG1, and activation of ERK, AKT or JAK/STAT1 signaling pathways, leading to a disregulated expression and release of pro-inflammatory cytokines. Our results suggest that the activity of the viral and pneumococcal neuraminidases on the surface of the airway epithelial cells function as a "danger signal" that leads to rapid upregulation of SOCS1 expression to prevent an uncontrolled inflammatory response. The binding of extracellular Gal1 or Gal3 to the galactosyl moieties unmasked on the surface of airway epithelial cells can either "fine-tune" or severely disregulate this process, respectively, the latter potentially leading to hypercytokinemia.

Influenza virus infection is associated with increased risk of death amongst patients hospitalized with confirmed pulmonary tuberculosis in South Africa, 2010-2011

BACKGROUND

Data on the association between influenza and tuberculosis are limited. We describe the characteristics of patients with laboratory-confirmed tuberculosis, laboratory-confirmed influenza and tuberculosis-influenza co-infection.

METHODS

Patients hospitalized with severe respiratory illness (acute and chronic) were enrolled prospectively in four provinces in South Africa. Naso/oropharyngeal specimens were tested for influenza virus by real time reverse transcriptase polymerase chain reaction. Tuberculosis testing was conducted as part of clinical management.

RESULTS

From June 2010 through December 2011, 8032 patients were enrolled and influenza testing was conducted on 7863 (98%). Influenza virus was detected in 765 (10%) patients. Among 2959 patients with tuberculosis and influenza results, 2227 (75%) were negative for both pathogens, 423 (14%) were positive for tuberculosis alone, 275 (9%) were positive for influenza alone and 34 (1%) had influenza and tuberculosis co-infection. On multivariable analysis amongst individuals with symptoms for ≥7 days, tuberculosis influenza co-infection was associated with increased risk of death, (adjusted relative risk ratio (aRRR) (6.1, 95% confidence interval (CI) 1.6-23.4), as compared to tuberculosis only infection. This association was not observed in individuals with symptoms for <7 days (aRRR.0.8, 95% CI 0.1-7.0).

CONCLUSION

Tuberculosis and influenza co-infection compared to tuberculosis single infection was associated with increased risk of death in individuals with symptoms ≥7 days. The potential public health impact of influenza vaccination among persons with laboratory-confirmed tuberculosis should be explored.

Innate immunity to influenza virus: implications for future therapy

Innate immunity is critical in the early containment of influenza virus infection. The innate response is surprisingly complex. A variety of soluble innate inhibitors in respiratory secretions provide an initial barrier to infection. Dendritic cells, phagocytes and natural killer cells mediate viral clearance and promote further innate and adaptive responses. Toll-like receptors 3 and 7 and cytoplasmic RNA sensors are critical for activating these responses. In general, the innate response restricts viral replication without injuring the lung; however, the 1918 pandemic and H5N1 strains cause more profound, possibly harmful, innate responses. In this review, we discuss the implications of burgeoning knowledge of innate immunity for therapy of influenza.

Type I interferon protects against pneumococcal invasive disease by inhibiting bacterial transmigration across the lung

Streptococcus pneumoniae infection is a leading cause of bacterial pneumonia, sepsis and meningitis and is associated with high morbidity and mortality. Type I interferon (IFN-I), whose contribution to antiviral and intracellular bacterial immunity is well established, is also elicited during pneumococcal infection, yet its functional significance is not well defined. Here, we show that IFN-I plays an important role in the host defense against pneumococci by counteracting the transmigration of bacteria from the lung to the blood. Mice that lack the type I interferon receptor (Ifnar1^−/−) or mice that were treated with a neutralizing antibody against the type I interferon receptor, exhibited enhanced development of bacteremia following intranasal pneumococcal infection, while maintaining comparable bacterial numbers in the lung. In turn, treatment of mice with IFNβ or IFN-I-inducing synthetic double stranded RNA (poly(I:C)), dramatically reduced the development of bacteremia following intranasal infection with S. pneumoniae. IFNβ treatment led to upregulation of tight junction proteins and downregulation of the pneumococcal uptake receptor, platelet activating factor receptor (PAF receptor). In accordance with these findings, IFN-I reduced pneumococcal cell invasion and transmigration across epithelial and endothelial layers, and Ifnar1^−/− mice showed overall enhanced lung permeability. As such, our data identify IFN-I as an important component of the host immune defense that regulates two possible mechanisms involved in pneumococcal invasion, i.e. PAF receptor-mediated transcytosis and tight junction-dependent pericellular migration, ultimately limiting progression from a site-restricted lung infection to invasive, lethal disease.

Streptococcus pneumoniae infection is a leading cause of bacterial pneumonia and invasive diseases such as sepsis and meningitis, which are associated with high morbidity and mortality. Here we identified type I Interferons (IFN-I) as critical mediators that prevent the progression of a local lung infection with S. pneumoniae to invasive disease. We found that mice lacking the receptor for IFN-I, or which received antibodies that interfere with receptor activation, showed increased development of bacteremia upon lung infection with S. pneumoniae. Treating mice, or cell lines, with IFN-I protected against bacterial migration across epithelial and endothelial cell barriers, correlating with increased expression of tight junction proteins, which enhance the lung's barrier function, and reduced surface expression levels of platelet activating factor receptor, a host receptor known to be hijacked by bacteria for migration across the lung/blood and blood/brain barriers. Together, our results identify IFN-I as an important component of the host immune defense against invasion from a gram-positive, extracellular bacterium, possibly reflecting a general mechanism for the regulation of epithelial and endothelial barrier function that is critical for protection from pathogen invasion.

Kinetics of coinfection with influenza A virus and Streptococcus pneumoniae

Secondary bacterial infections are a leading cause of illness and death during epidemic and pandemic influenza. Experimental studies suggest a lethal synergism between influenza and certain bacteria, particularly Streptococcus pneumoniae, but the precise processes involved are unclear. To address the mechanisms and determine the influences of pathogen dose and strain on disease, we infected groups of mice with either the H1N1 subtype influenza A virus A/Puerto Rico/8/34 (PR8) or a version expressing the 1918 PB1-F2 protein (PR8-PB1-F2(1918)), followed seven days later with one of two S. pneumoniae strains, type 2 D39 or type 3 A66.1. We determined that, following bacterial infection, viral titers initially rebound and then decline slowly. Bacterial titers rapidly rise to high levels and remain elevated. We used a kinetic model to explore the coupled interactions and study the dominant controlling mechanisms. We hypothesize that viral titers rebound in the presence of bacteria due to enhanced viral release from infected cells, and that bacterial titers increase due to alveolar macrophage impairment. Dynamics are affected by initial bacterial dose but not by the expression of the influenza 1918 PB1-F2 protein. Our model provides a framework to investigate pathogen interaction during coinfections and to uncover dynamical differences based on inoculum size and strain.

Influenza virus infected individuals often become coinfected with a bacterial pathogen and, consequently, morbidity and mortality are significantly increased. A better understanding of how these pathogens interact with each other and the host is of key importance. Here, we use data from infected mice together with mathematical modeling and quantitative analyses to understand how each pathogen influences the other, and how the 1918 influenza PB1-F2 protein and the bacterial strain and dose contribute to coinfection kinetics. We find that influenza viral titers increase when Streptococcus pneumoniae is present and that the bacteria establish and grow rapidly when influenza is present. Our model and analyses suggest that the influenza infection reduces the bacterial clearance ability of alveolar macrophages and that the subsequent S. pneumoniae infection enhances viral release from infected cells. These results provide new insights into the mechanisms of influenza coinfection and the differences in pathogenesis of influenza and S. pneumoniae strains.

Otitis media among high-risk populations: can probiotics inhibit Streptococcus pneumoniae colonisation and the risk of disease?

Otitis media is the second most common infection in children and the leading cause for seeking medical advice. Indigenous populations such as the Inuits, indigenous Australians and American Indians have a very high prevalence of otitis media and are considered to be high-risk populations. Streptococcus pneumoniae, one of the three main bacterial causes of otitis media, colonises the nasopharynx prior to disease development. In high-risk populations, early acquisition of high bacterial loads increases the prevalence of otitis media. In these settings, current treatment strategies are insufficient. Vaccination is effective against invasive pneumococcal infection but has a limited impact on otitis media. Decreasing the bacterial loads of otitis media pathogens and/or colonising the nasopharynx with beneficial bacteria may reduce the prevalence of otitis media. Probiotics are live microorganisms that offer health benefits by modulating the microbial community and enhancing host immunity. The available data suggest that probiotics may be beneficial in otitis media. This review discusses the potential use of probiotics to reduce pathogen colonisation and decrease the prevalence of otitis media, providing justification for further investigation.

Potential use of Atlantic cod trypsin in biomedicine

Surface proteins of viruses and bacteria used for cell attachment and invasion are candidates for degradation by proteases. Trypsin from Atlantic cod (Gadus morhua) was previously demonstrated to have efficacy against influenza viruses in vitro and on skin. In this paper, cod trypsin is shown to be 3–12 times more effective in degrading large native proteins than its mesophilic analogue, bovine trypsin. This is in agreement with previous findings where cod trypsin was found to be the most active among twelve different proteases in cleaving various cytokines and pathological proteins. Furthermore, our results show that cod trypsin has high efficacy against herpes simplex virus type 1 (HSV-1) and the respiratory syncytial virus (RSV) in vitro. The results on the antipathogenic properties of cod trypsin are important because rhinovirus, RSV, and influenza are the most predominant pathogenic viruses in upper respiratory tract infections. Results from a clinical study presented in this paper show that a specific formulation containing cod trypsin was preferred for wound healing over other methods used in the study. Apparently, the high digestive ability of the cold-adapted cod trypsin towards large native proteins plays a role in its efficacy against pathogens and its positive effects on wounds.

Increased nasopharyngeal bacterial titers and local inflammation facilitate transmission of Streptococcus pneumoniae

The transmission of the bacterium Streptococcus pneumoniae (the pneumococcus) marks the first step toward disease development. To date, our ability to prevent pneumococcal transmission has been limited by our lack of understanding regarding the factors which influence the spread of this pathogen. We have previously developed an infant mouse model of pneumococcal transmission which was strictly dependent on influenza A virus (IAV) coinfection of both the experimentally colonized “index mice” and the naive cohoused “contact mice.” Here, we sought to use this model to further elucidate the factors which facilitate S. pneumoniae transmission. In the present report, we demonstrate that increasing the nasopharyngeal load of S. pneumoniae in the colonized index mice (via the depletion of neutrophils) and inducing a proinflammatory response in the naive cohoused contact mice (as demonstrated by cytokine production) facilitates S. pneumoniae transmission. Thus, these data provide the first insights into the factors that help mediate the spread of S. pneumoniae throughout the community.

Streptococcus pneumoniae (the pneumococcus) is a major cause of worldwide morbidity and mortality and is a leading cause of death among children under the age of five years. Transmission of S. pneumoniae marks the first step toward disease development. Therefore, understanding the factors that influence the spread of pneumococci throughout the community plays an essential role in preventing pneumococcal disease. We previously developed the first reproducible infant mouse model for pneumococcal transmission and showed that coinfection with influenza virus facilitates the spread of S. pneumoniae. Here, we show that increasing the bacterial load in the nasal cavity of colonized individuals as well as inducing an inflammatory response in naive “contact cases” facilitates the spread of pneumococci. Therefore, this study helps to identify the factors which must be inhibited in order to successfully prevent pneumococcal disease.

A Time Course for Susceptibility to Staphylococcus aureus Respiratory Infection during Influenza in a Swine Model

Bacterial superinfections following influenza A virus (IAV) are predominant causes of morbidity in humans. The recent emergence of methicillin-resistant Staphylococcus aureus (MRSA) and highly virulent IAV strains has reduced treatment options. Development of an appropriate animal model to study secondary S. aureus infections may provide important information regarding disease pathogenesis. Pigs are natural hosts to both IAV and S. aureus and have respiratory physiology and immune response comparable to humans. To establish a time course of susceptibility to S. aureus after IAV infection, nursery pigs infected intranasally with IAV were challenged with MRSA at different time points. Lung pathology scores and MRSA CFU were evaluated in dual-infected animals after IAV infection. Flow cytometric analysis of bronchoalveolar lavage fluid indicated differences between treatments. These results demonstrate the appropriateness of an intranasal challenge model in nursery pigs for studying the pathogenesis of IAV and S. aureus coinfection and provide insights into the timeframe for susceptibility of IAV-infected pigs to secondary S. aureus infection.

Adaption of seasonal H1N1 influenza virus in mice

The experimental infection of a mouse lung with influenza A virus has proven to be an invaluable model for studying the mechanisms of viral adaptation and virulence. The mouse adaption of human influenza A virus can result in mutations in the HA and other proteins, which is associated with increased virulence in mouse lungs. In this study, a mouse-adapted seasonal H1N1 virus was obtained through serial lung-to-lung passages and had significantly increased virulence and pathogenicity in mice. Genetic analysis indicated that the increased virulence of the mouse-adapted virus was attributed to incremental acquisition of three mutations in the HA protein (T89I, N125T, and D221G). However, the mouse adaption of influenza A virus did not change the specificity and affinity of receptor binding and the pH-dependent membrane fusion of HA, as well as the in vitro replication in MDCK cells. Notably, infection with the mouse adapted virus induced severe lymphopenia and modulated cytokine and chemokine responses in mice. Apparently, mouse adaption of human influenza A virus may change the ability to replicate in mouse lungs, which induces strong immune responses and inflammation in mice. Therefore, our findings may provide new insights into understanding the mechanisms underlying the mouse adaption and pathogenicity of highly virulent influenza viruses.

Seasonal influenza epidemiology in sub-Saharan Africa: a systematic review

Acute respiratory infection (ARI) is a leading cause of mortality worldwide, of which influenza is an important cause that can be prevented with vaccination. We did a systematic review of research published from 1980 to 2009 on seasonal influenza epidemiology in sub-Saharan Africa to identify data strengths and weaknesses that might affect policy decisions, to assess the state of knowledge on influenza disease burden, and to ascertain unique features of influenza epidemiology in the region. We assessed 1203 papers, reviewed 104, and included 49 articles. 1-25% of outpatient ARI visits were caused by influenza (11 studies; mean 9·5%; median 10%), whereas 0·6-15·6% of children admitted to hospital for ARI had influenza identified (15 studies; mean 6·6%; median 6·3%). Influenza was highly seasonal in southern Africa. Other data were often absent, particularly direct measurement of influenza incidence rates for all ages, within different patient settings (outpatient, inpatient, community), and for all countries. Data from sub-Saharan Africa are insufficient to allow most countries to prioritise strategies for influenza prevention and control. Key data gaps include incidence and case-fatality ratios for all ages, the contribution of influenza towards admission of adults to hospital for ARI, representative seasonality data, economic burden, and the interaction of influenza with prevalent disorders in Africa, such as malaria, HIV, and malnutrition.

Postinfluenza bacterial pneumonia: host defenses gone awry

Influenza is a common respiratory pathogen causing both seasonal and pandemic disease. Influenza infection predisposes the host to secondary bacterial infection of the respiratory tract, which is a major cause of both morbidity and mortality in flu-related disease. In this review, we will discuss innate and adaptive antiviral responses during influenza infection, and review how these responses modulate protective immunity against secondary bacterial pathogens of the lung. Specific emphasis will be placed on implications of bacterial superinfection and mechanisms involved.

Inactivated and live, attenuated influenza vaccines protect mice against influenza: Streptococcus pyogenes super-infections

Mortality associated with influenza virus super-infections is frequently due to secondary bacterial complications. To date, super-infections with Streptococcus pyogenes have been studied less extensively than those associated with Streptococcus pneumoniae. This is significant because a vaccine for S. pyogenes is not clinically available, leaving vaccination against influenza virus as our only means for preventing these super-infections. In this study, we directly compared immunity induced by two types of influenza vaccine, either inactivated influenza virus (IIV) or live, attenuated influenza virus (LAIV), for the ability to prevent super-infections. Our data demonstrate that both IIV and LAIV vaccines induce similar levels of serum antibodies, and that LAIV alone induces IgA expression at mucosal surfaces. Upon super-infection, both vaccines have the ability to limit the induction of pro-inflammatory cytokines within the lung, including IFN-γ which has been shown to contribute to mortality in previous models of super-infection. Limiting expression of these pro-inflammatory cytokines within the lungs subsequently limits recruitment of macrophages and neutrophils to pulmonary surfaces, and ultimately protects both IIV- and LAIV-vaccinated mice from mortality. Despite their overall survival, both IIV- and LAIV-vaccinated mice demonstrated levels of bacteria within the lung tissue that are similar to those seen in unvaccinated mice. Thus, influenza virus:bacteria super-infections can be limited by vaccine-induced immunity against influenza virus, but the ability to prevent morbidity is not complete.

Long-term impairment of Streptococcus pneumoniae lung clearance is observed after initial infection with influenza A virus but not human metapneumovirus in mice

Human metapneumovirus (hMPV) is a paramyxovirus responsible for respiratory tract infections in humans. Our objective was to investigate whether hMPV could predispose to long-term bacterial susceptibility, such as previously observed with influenza viruses. BALB/c mice were infected with hMPV or influenza A and, 14 days following viral infection, challenged with Streptococcus pneumoniae. Only mice previously infected with influenza A demonstrated an 8% weight loss of their body weight 72 h following S. pneumoniae infection, which correlated with an enhanced lung bacterial replication of >7 log(10) compared with pneumococcus infection alone. This enhanced bacterial replication was not related to altered macrophage or neutrophil recruitment or deficient production of critical cytokines. However, bacterial challenge induced the production of gamma interferon in bronchoalveolar lavages of influenza-infected mice, but not in those of hMPV-infected animals. In conclusion, hMPV does not cause long-term impairment of pneumococcus lung clearance, in contrast to influenza A virus.

Viral and bacterial interactions in pneumonia

Respiratory tract infections are the most common infectious illnesses that afflict humans. In general, viral infections of the upper respiratory tract result in mild self-limiting symptoms. However, more serious lower respiratory tract infections can lead to the development of pneumonia. While viral infections alone may cause pneumonia, it is increasingly clear that they also play an important role in increasing the risk of bacterial infection and have been shown to substantially worsen clinical outcomes from bacterial pneumonia. Advances in our understanding of the immune response to these infections are beginning to demonstrate how these microorganisms can interact, subvert the normally effective immune response and facilitate the development of more severe and even life-threatening disease.

A mouse model of lethal synergism between influenza virus and Haemophilus influenzae

Secondary bacterial infections that follow infection with influenza virus result in considerable morbidity and mortality in young children, the elderly, and immunocompromised individuals and may also significantly increase mortality in normal healthy adults during influenza pandemics. We herein describe a mouse model for investigating the interaction between influenza virus and the bacterium Haemophilus influenzae. Sequential infection with sublethal doses of influenza and H. influenzae resulted in synergy between the two pathogens and caused mortality in immunocompetent adult wild-type mice. Lethality was dependent on the interval between administration of the bacteria and virus, and bacterial growth was prolonged in the lungs of dual-infected mice, although influenza virus titers were unaffected. Dual infection induced severe damage to the airway epithelium and confluent pneumonia, similar to that observed in victims of the 1918 global influenza pandemic. Increased bronchial epithelial cell death was observed as early as 1 day after bacterial inoculation in the dual-infected mice. Studies using knockout mice indicated that lethality occurs via a mechanism that is not dependent on Fas, CCR2, CXCR3, interleukin-6, tumor necrosis factor, or Toll-like receptor-4 and does not require T or B cells. This model suggests that infection with virulent strains of influenza may predispose even immunocompetent individuals to severe illness on secondary infection with H. influenzae by a mechanism that involves innate immunity, but does not require tumor necrosis factor, interleukin-6, or signaling via Toll-like receptor-4.

Microbial interactions in the respiratory tract

Upper respiratory tract infections are caused by the synergistic and antagonistic interactions between upper respiratory tract viruses and 3 predominant bacterial pathogens: Streptococcus pneumoniae, nontypeable Haemophilus influenzae (NTHi), and Moraxella catarrhalis, which are members of the commensal flora of the nasopharynx. For many bacterial pathogens, colonization of host mucosal surfaces is a first and necessary step in the infectious process. S. pneumoniae and H. influenzae have intricate interactions in the nasopharynx. The host innate immune response may influence these interactions and therefore influence the composition of the colonizing flora and the invading bacteria. S. pneumoniae, nontypeable H. influenzae, and M. catarrhalis can behave as opportunistic pathogens of the middle ear when conditions are optimal. Chronic otitis media (OM) and recurrent OM include a biofilm component. Each of the 3 predominant pathogens of OM can form a biofilm and have been shown to comprise biofilms present on middle ear mucosa specimens recovered from children with recurrent or chronic OM. Some of these characterized biofilms are of mixed bacterial etiology, suggesting that progress made on single-microbe directed strategies for treatment and/or prevention of OM, although highly encouraging, are likely to be inadequate. A significantly greater understanding about microbial physiology is required as it relates to the involvement of biofilms in OM, to identify points in the natural course of the disease that are perhaps more amenable to treatment strategies, as well as to identify biofilm-relevant antigenic targets that would be helpful in the rational design of vaccines to prevent OM.

Incorporation of membrane-bound, mammalian-derived immunomodulatory proteins into influenza whole virus vaccines boosts immunogenicity and protection against lethal challenge

Background

Influenza epidemics continue to cause morbidity and mortality within the human population despite widespread vaccination efforts. This, along with the ominous threat of an avian influenza pandemic (H5N1), demonstrates the need for a much improved, more sophisticated influenza vaccine. We have developed an in vitro model system for producing a membrane-bound Cytokine-bearing Influenza Vaccine (CYT-IVAC). Numerous cytokines are involved in directing both innate and adaptive immunity and it is our goal to utilize the properties of individual cytokines and other immunomodulatory proteins to create a more immunogenic vaccine.

Results

We have evaluated the immunogenicity of inactivated cytokine-bearing influenza vaccines using a mouse model of lethal influenza virus challenge. CYT-IVACs were produced by stably transfecting MDCK cell lines with mouse-derived cytokines (GM-CSF, IL-2 and IL-4) fused to the membrane-anchoring domain of the viral hemagglutinin. Influenza virus replication in these cell lines resulted in the uptake of the bioactive membrane-bound cytokines during virus budding and release. In vivo efficacy studies revealed that a single low dose of IL-2 or IL-4-bearing CYT-IVAC is superior at providing protection against lethal influenza challenge in a mouse model and provides a more balanced Th₁/Th₂ humoral immune response, similar to live virus infections.

Conclusion

We have validated the protective efficacy of CYT-IVACs in a mammalian model of influenza virus infection. This technology has broad applications in current influenza virus vaccine development and may prove particularly useful in boosting immune responses in the elderly, where current vaccines are minimally effective.

Parapneumonic empyema deaths during past century, Utah

Vaccine strategies and antimicrobial drug stockpiling to control empyema will increase preparedness as we prepare for the next influenza pandemic.

Bacterial pneumonia with empyema is a serious complication of influenza and commonly resulted in death during the 1918 influenza pandemic. We hypothesize that deaths caused by parapneumonic empyema are increasing in Utah once again despite advances in critical care and the availability of antimicrobial drugs and new vaccines. In this study, we analyzed the historical relationship between deaths caused by empyema and influenza pandemics by using 100 years of data from Utah. Deaths caused by empyema have indeed increased from 2000–2004 when compared with the historic low death rates of 1950–1975. Vaccine strategies and antimicrobial drug stockpiling to control empyema will be important as we prepare for the next influenza pandemic.

Increased susceptibility for superinfection with Streptococcus pneumoniae during influenza virus infection is not caused by TLR7-mediated lymphopenia

Influenza A virus (IAV) causes respiratory tract infections leading to recurring epidemics with high rates of morbidity and mortality. In the past century IAV induced several world-wide pandemics, the most aggressive occurring in 1918 with a death toll of 20-50 million cases. However, infection with IAV alone is rarely fatal. Instead, death associated with IAV is usually mediated by superinfection with bacteria, mainly Streptococcus pneumoniae. The reasons for this increased susceptibility to bacterial superinfection have not been fully elucidated. We previously demonstrated that triggering of TLR7 causes immune incompetence in mice by induction of lymphopenia. IAV is recognized by TLR7 and infections can lead to lymphopenia. Since lymphocytes are critical to protect from S. pneumoniae it has long been speculated that IAV-induced lymphopenia might mediate increased susceptibility to superinfection. Here we show that sub-lethal pre-infections of mice with IAV-PR8/A/34 strongly increased their mortality in non-lethal SP infections, surprisingly despite the absence of detectable lymphopenia. In contrast to SP-infection alone co-infected animals were unable to control the exponential growth of SP. However, lymphopenia forced by TLR7-triggering or antibody-mediated neutropenia did not increase SP-susceptibility or compromise the ability to control SP growth. Thus, the immune-incompetence caused by transient lympho- or leukopenia is not sufficient to inhibit potent antibacterial responses of the host and mechanisms distinct from leukodepletion must account for increased bacterial superinfection during viral defence.

Animal models for the study of influenza pathogenesis and therapy

Influenza A viruses causes a variety of illnesses in humans. The most common infection, seasonal influenza, is usually a mild, self-limited febrile syndrome, but it can be more severe in infants, the elderly, and immunodeficient persons, in whom it can progress to severe viral pneumonitis or be complicated by bacterial superinfection, leading to pneumonia and sepsis. Seasonal influenza also occasionally results in neurologic complications. Rarely, viruses that have spread from wild birds to domestic poultry can infect humans; such “avian influenza” can range in severity from mild conjunctivitis through the rapidly lethal disease seen in persons infected with the H5N1 virus that first emerged in Hong Kong in 1997. To develop effective therapies for this wide range of diseases, it is essential to have laboratory animal models that replicate the major features of illness in humans. This review describes models currently in use for elucidating influenza pathogenesis and evaluating new therapeutic agents.

Infection with human metapneumovirus predisposes mice to severe pneumococcal pneumonia

Human metapneumovirus (hMPV) is a recently described paramyxovirus that causes respiratory tract infections. Prior clinical studies have highlighted the importance of respiratory viruses, such as influenza virus, in facilitating secondary bacterial infections and increasing host immunopathology. The objective of the present work was to evaluate the effects of initial viral infection with hMPV or influenza A virus followed by Streptococcus pneumoniae superinfection 5 days later in a murine model. Both groups of superinfected mice demonstrated significant weight loss (mean of 15%) and higher levels of airway obstruction (mean enhanced pause value of 2.7) compared to those of mice infected with hMPV, influenza virus, or pneumococcus alone. Bacterial counts increased from 5 x 10(2) CFU/lung in mice infected with pneumococcus only to 10(7) and 10(9) CFU/lung in mice with prior infections with hMPV and influenza A virus, respectively. A more pronounced interstitial and alveolar inflammation correlated with higher levels of inflammatory cytokines and chemokines such as interleukin-1alpha (IL-1alpha), IL-1beta, IL-6, IL-12, monocyte chemotactic protein 1, macrophage inflammatory protein 1alpha, KC, and granulocyte colony-stimulating factor, as well as greater expression of Toll-like receptor 2 (TLR2), TLR6, TLR7, and TLR13 in the lungs of superinfected animals compared to results for single infections, with similar immunological effects seen in both coinfection models. Prior infection with either hMPV or influenza A virus predisposes mice to severe pneumococcus infection.

The role of phagocytic cells in enhanced susceptibility of broilers to colibacillosis after Infectious Bronchitis Virus infection

Colibacillosis results from infection with avian pathogenic Escherichia coli bacteria. Healthy broilers are resistant to inhaled E. coli, but previous infection with vaccine or virulent strains of Infectious Bronchitis Virus (IBV) predisposes birds for severe colibacillosis. We investigated whether IBV affects recruitment and function of phagocytic cells and examined NO production, phagocytic and bactericidal activity, and kinetics of peripheral blood mononuclear cells (PBMC) and splenocytes. Moreover, we measured cytokine mRNA expression in lung and spleen samples. Broilers were inoculated with IBV H120 vaccine or virulent M41 and challenged 5 days later with E. coli 506. A PBS control and E. coli group without previous virus inoculation were also included. Birds were sacrificed at various time points after inoculation (h/dpi). Inoculation with IBV induced extended and more severe colibacillosis than with E. coli alone. At 4 dpi, the number of KUL-01⁺ PBMC in all E. coli-inoculated groups was significantly higher than in PBS-inoculated birds, which correlated with lesion scores. From 1 to 4 dpi, NO production by PBMC from all E. coli-inoculated animals was elevated compared to PBS birds. Bactericidal activity of PBMC in IBV-inoculated animals at 7 dpi was lower than in PBS- and E. coli-inoculated birds, but phagocytic capacity and recruitment were not severely impaired. In spleen samples of IBV-infected animals reduced expression of IL-1β, IL-6, IL-8, IL-10, IL-18 and IFN-γ mRNA was found 1 dpi. Our results suggest that enhanced colibacillosis after IBV infection or vaccination is caused at least by altered innate immunity and less by impairment of phagocytic cell function.