Molecular character of influenza A/H1N1 2009: Implications for spread and control

The world is experiencing a pandemic of influenza that emerged in March 2009, due to a novel strain designated influenza A/H1N1 2009. This strain is closest in molecular sequence to swine influenza viruses, but differs from all previously known influenza by a minimum of 6.1%, and from prior "seasonal" H1N1 by 27.2%, giving it great potential for widespread human infection. While spread into India was delayed for two months by an aggressive interdiction program, since 1 August 2009 most cases in India have been indigenous. H1N1 2009 has differentially struck younger patients who are naïve susceptibles to its antigenic subtype, while sparing those >60 who have crossreactive antibody from prior experience with influenza decades ago and the 1977 "swine flu" vaccine distributed in the United States. It also appears to more severely affect pregnant women. It emanated from a single source in central Mexico, but its precise geographical and circumstantial origins, from either Eurasia or the Americas, remain uncertain. While currently a mild pandemic by the standard of past pandemics, the seriousness of H1N1 2009 especially among children should not be underestimated. There is potential for the virus, which continues to adapt to humans, to change over time into a more severe etiologic agent by any of several foreseeable mutations. Mass acceptance of the novel H1N1 2009 vaccine worldwide will be essential to its control. Having spread globally in a few months, affecting millions of people, it is likely to remain circulating in the human population for a decade or more.

Symbiont genomics, our new tangled bank

Microbial symbionts inhabit the soma and surfaces of most multicellular species and instigate both beneficial and harmful infections. Despite their ubiquity, we are only beginning to resolve major patterns of symbiont ecology and evolution. Here, we summarize the history, current progress, and projected future of the study of microbial symbiont evolution throughout the tree of life. We focus on the recent surge of data that whole-genome sequencing has introduced into the field, in particular the links that are now being made between symbiotic lifestyle and molecular evolution. Post-genomic and systems biology approaches are also emerging as powerful techniques to investigate host-microbe interactions, both at the molecular level of the species interface and at the global scale. In parallel, next-generation sequencing technologies are allowing new questions to be addressed by providing access to population genomic data, as well as the much larger genomes of microbial eukaryotic symbionts and hosts. Throughout we describe the questions that these techniques are tackling and we conclude by listing a series of unanswered questions in microbial symbiosis that can potentially be addressed with the new technologies.

The emergence of pandemic influenza viruses

Pandemic influenza has posed an increasing threat to public health worldwide in the last decade. In the 20th century, three human pandemic influenza outbreaks occurred in 1918, 1957 and 1968, causing significant mortality. A number of hypotheses have been proposed for the emergence and development of pandemic viruses, including direct introduction into humans from an avian origin and reassortment between avian and previously circulating human viruses, either directly in humans or via an intermediate mammalian host. However, the evolutionary history of the pandemic viruses has been controversial, largely due to the lack of background genetic information and rigorous phylogenetic analyses. The pandemic that emerged in early April 2009 in North America provides a unique opportunity to investigate its emergence and development both in human and animal aspects. Recent genetic analyses of data accumulated through long-term influenza surveillance provided insights into the emergence of this novel pandemic virus. In this review, we summarise the recent literature that describes the evolutionary pathway of the pandemic viruses. We also discuss the implications of these findings on the early detection and control of future pandemics.

2009 H1N1 influenza

Within 2 months of its discovery last spring, a novel influenza A (H1N1) virus, currently referred to as 2009 H1N1, caused the first influenza pandemic in decades. The virus has caused disproportionate disease among young people with early reports of virulence similar to that of seasonal influenza. This clinical review provides an update encompassing the virology, epidemiology, clinical manifestations, diagnosis, treatment, and prevention of the 2009 H1N1 virus. Because information about this virus, its prevention, and treatment are rapidly evolving, readers are advised to seek additional information. We performed a literature search of PubMed using the following keywords: H1N1, influenza, vaccine, pregnancy, children, treatment, epidemiology, and review. Studies were selected for inclusion in this review on the basis of their relevance. Recent studies and articles were preferred.

Innate immune evasion strategies of influenza viruses

Influenza viruses are globally important human respiratory pathogens. These viruses cause seasonal epidemics and occasional worldwide pandemics, both of which can vary significantly in disease severity. The virulence of a particular influenza virus strain is partly determined by its success in circumventing the host immune response. This article briefly reviews the innate mechanisms that host cells have evolved to resist virus infection, and outlines the plethora of strategies that influenza viruses have developed in order to counteract such powerful defences. The molecular details of this virus-host interplay are summarized, and the ways in which research in this area is being applied to the rational design of protective vaccines and novel antivirals are discussed.

Avian influenza--a review for doctors in travel medicine

First identified in humans in Hong Kong, influenza A/H5N1, known commonly as avian influenza, has caused human disease in 15 countries around the world. Although the current number of confirmed patients is tiny compared to seasonal and the recently emerged H1N1 'swine' influenza, H5N1 remains a candidate for the next highly pathogenic influenza pandemic. Currently, H5N1 has very limited ability to spread from person-to-person but this may change because of mutation or reassortment with other influenza viruses leading to an influenza pandemic with high mortality. If this occurs travellers are likely to be affected and travel medicine doctors will need to consider avian influenza in returning febrile travellers. The early clinical features may be dismissed easily as 'the flu' resulting in delayed treatment. Treatment options are limited. Oral oseltamivir alone has been the most commonly used drug but mortality remains substantial, up to 80% in Indonesia. Intravenous peramivir has been filed for registration and IV zanamivir is being developed. This review will focus on the epidemiological and clinical features of influenza A/H5N1 avian influenza and will highlight aspects relevant to travel medicine doctors.

Prophylaxis of Healthcare Workers in an Influenza Pandemic

The threat of an imminent influenza pandemic has galvanized global efforts to identify effective preparedness strategies and consider securing health resources. As the nations prepare to meet this threat, public health interventions are being carefully gauged within the context of influenza epidemiology, populations, and healthcare systems. A pandemic will place enormous demands on healthcare systems that include at the center of planning efforts the protection of healthcare workers. During an influenza pandemic, healthcare workers will be on the front lines delivering care to patients and preventing further spread of the disease. Protecting these workers from acquiring or transmitting infection in the hospital ward and outside the workplace is critical to containing a pandemic and limiting morbidity and mortality of the population. Several approaches to protecting healthcare workers include vaccination, antiviral 10.1007/978-0-387-78665-0_6443, use of personal protective equipment, and adherence to other infection control practices. In the absence of vaccination, application of antiviral drugs has been rationalized as the first-line defense against the 10.1007/978-0-387-78665-0_6288. While the treatment of ill individuals is top priority in most national contingency plans, the use of drugs as prophylaxis has been debatable. This chapter attempts to highlight the importance of a competent healthcare system in response to an influenza pandemic, and presents the conflicting issues that are surrounding an antiviral prophylaxis strategy. An overview of potential benefits and limitations, logistical constraints, and clinical and epidemiological consequences of healthcare worker prophylaxis is also provided.

Influenza A (H1N1) 2009: a pandemic alarm

At this critical juncture when the world has not yet recovered from the threat of avian influenza, the virus has returned in the disguise of swine influenza, a lesser known illness common in pigs. It has reached pandemic proportions in a short time span with health personnel still devising ways to identify the novel H1N1 virus and develop vaccines against it. The H1N1 virus has caused a considerable number of deaths within the short duration since its emergence. Presently, there are no effective methods to contain this newly emerged virus. Therefore, a proper and clear insight is urgently required to prevent an outbreak in the future and make preparations that may be planned well in advance. This review is an attempt to discuss the historical perspective of the swine flu virus, its epidemiology and route of transmission to better understand the various control measures that may be taken to fight the danger of a global pandemic.

Controlling infectious disease outbreaks: Lessons from mathematical modelling

Epidemiological analysis and mathematical models are now essential tools in understanding the dynamics of infectious diseases and in designing public health strategies to contain them. They have provided fundamental concepts, such as the basic and effective reproduction number, generation times, epidemic growth rates, and the role of pre-symptomatic infectiousness, which are crucial in characterising infectious diseases. These concepts are outlined and their relevance in designing control policies for outbreaks is discussed. They are illustrated using examples from the 2003 severe acute respiratory syndrome outbreak, which was brought under control within a year, and from pandemic influenza planning, where mathematical models have been used extensively.

Pandemic influenza vaccines - the challenges

Recent years' enzootic spread of highly pathogenic H5N1 virus among poultry and the many lethal zoonoses in its wake has stimulated basic and applied pandemic vaccine research. The quest for an efficacious, affordable and timely accessible pandemic vaccine has been high on the agenda. When a variant H1N1 strain of swine origin emerged as a pandemic virus, it surprised many, as this subtype is well-known to man as a seasonal virus. This review will cover some difficult vaccine questions, such as the immunological challenges, the new production platforms, and the limited supply and global equity issues.

Synthetic viruses: a new opportunity to understand and prevent viral disease

Rapid progress in DNA synthesis and sequencing is spearheading the deliberate, large-scale genetic alteration of organisms. These new advances in DNA manipulation have been extended to the level of whole-genome synthesis, as evident from the synthesis of poliovirus, from the resurrection of the extinct 1918 strain of influenza virus and of human endogenous retroviruses and from the restructuring of the phage T7 genome. The largest DNA synthesized so far is the 582,970 base pair genome of Mycoplasma genitalium, although, as yet, this synthetic DNA has not been 'booted' to life. As genome synthesis is independent of a natural template, it allows modification of the structure and function of a virus's genetic information to an extent that was hitherto impossible. The common goal of this new strategy is to further our understanding of an organism's properties, particularly its pathogenic armory if it causes disease in humans, and to make use of this new information to protect from, or treat, human viral disease. Although only a few applications of virus synthesis have been described as yet, key recent findings have been the resurrection of the 1918 influenza virus and the generation of codon- and codon pair-deoptimized polioviruses.

The emergence of the novel H1N1 virus: implications for global mental health

The emergence of the novel swine-origin influenza A (H1N1) virus in humans has aroused great concern among medical professionals about the possible evolution of a full-blown influenza pandemic, one on the scale of the “Spanish” influenza pandemic of 1918–19 (Belshe, 2009). It has been speculated that the return of a pandemic virus equivalent in pathogenicity to the virus of 1918 would likely kill more than 100 million people worldwide, including a large number of economically active young people (Taubenberger and Morens, 2006). Health administrations worldwide have stepped up reporting and surveillance of the deaths and illnesses associated with H1N1, and most countries have national strategies to fight the outbreak, though skeptics doubt how such plans could be operationalized, especially in developing countries (Coker, 2009). As of 6 July 2009, the cumulative total of H1N1 cases exceeds 90,000 in over 100 countries, with over 400 deaths directly related to the infection (World Health Organization, 2009a). Optimists might believe this pandemic is not going to match the scale of the historical 1918 pandemic given the relatively low fatality rate observed thus far. However, the World Health Organization has cautioned that we have just entered Phase 6 of the pandemic – i.e. we are in the early days of the 2009 flu pandemic (Chan, 2009). The course of the pandemic is thus unpredictable at this stage but it is evident that international multilateral plans and agreements have enabled much greater coordination of communication and action than ever before. The guidance behind these multilateral international actions, rooted in the World Health Organization's International Health Regulations (IHR) 2005, only came into being five years ago in response to the threat of emerging infectious diseases and particularly by the events related to the emergence of Severe Acute Respiratory Syndrome (SARS) (Katz, 2009). The morbidity and mortality directly resulting from this novel influenza A H1N1 outbreak are in the center of the world media's spotlight, but the potential impact of the pandemic on global mental health has not yet received the attention it deserves.

Assessment of intervention strategies against a novel influenza epidemic using an individual-based model

OBJECTIVES

The objective of this study was to assess intervention strategies against a novel influenza epidemic through simulations of various scenarios in Sapporo city, Hokkaido, Japan. A series of interventions were examined: administration of antiviral drugs by two approaches [targeted antiviral prophylaxis (TAP) and school-age targeted antiviral prophylaxis (STAP)], school closure, restraint, and combinations of these four interventions.

METHODS

In order to generate a more realistic situation, we constructed an individual-based model (IBM) for the transmission of influenza in which each individual was assigned personal information on the basis of the National Census and Employment Status Survey of Sapporo city. In addition, data on high-risk casual contact groups commuting in crowded trains and buses were obtained from a census on transportation modes and introduced into the model. Observational data from previous pandemics were used for the epidemiological parameters.

RESULTS

Both TAP and STAP interventions were highly effective in suppressing the spread of infection during the early period of an outbreak, but STAP was inferior to TAP in terms of the ripple effect of the administration of antiviral drugs. School closure and restraint were able to bring about a delay in the peak of infection. The combination of TAP, school closure, and restraint interventions were highly effective in decreasing the total number of patients and shortening the epidemic period.

CONCLUSIONS

Based on the simulation results, we recommend implementing TAP together with both school closure and restraint as strategies against a future novel influenza outbreak.

Vaccines for military use

Vaccines have long been used by military forces in order to prevent communicable diseases and thereby preserve the fighting force. A tradition that began with the mass vaccination of the Continental Army against smallpox during the War of the American Revolution in the late 18th century continues today with routine and deployment-based vaccination of military forces against potential pathogens of nature and biological weapon threats. As their role has expanded in recent years to include humanitarian and peacekeeping missions, the military's use of vaccines against infectious diseases has concomitantly broadened to include civilian populations worldwide. The emergence of new threats and the recognition of additional global challenges will continue to compel the development and promotion of vaccines to combat infectious diseases of military significance.

Novel pandemic influenza A(H1N1) viruses are potently inhibited by DAS181, a sialidase fusion protein

BACKGROUND

The recent emergence of a novel pandemic influenza A(H1N1) strain in humans exemplifies the rapid and unpredictable nature of influenza virus evolution and the need for effective therapeutics and vaccines to control such outbreaks. However, resistance to antivirals can be a formidable problem as evidenced by the currently widespread oseltamivir- and adamantane-resistant seasonal influenza A viruses (IFV). Additional antiviral approaches with novel mechanisms of action are needed to combat novel and resistant influenza strains. DAS181 (Fludase) is a sialidase fusion protein in early clinical development with in vitro and in vivo preclinical activity against a variety of seasonal influenza strains and highly pathogenic avian influenza strains (A/H5N1). Here, we use in vitro, ex vivo, and in vivo models to evaluate the activity of DAS181 against several pandemic influenza A(H1N1) viruses.

METHODS AND FINDINGS

The activity of DAS181 against several pandemic influenza A(H1N1) virus isolates was examined in MDCK cells, differentiated primary human respiratory tract culture, ex-vivo human bronchi tissue and mice. DAS181 efficiently inhibited viral replication in each of these models and against all tested pandemic influenza A(H1N1) strains. DAS181 treatment also protected mice from pandemic influenza A(H1N1)-induced pathogenesis. Furthermore, DAS181 antiviral activity against pandemic influenza A(H1N1) strains was comparable to that observed against seasonal influenza virus including the H274Y oseltamivir-resistant influenza virus.

CONCLUSIONS

The sialidase fusion protein DAS181 exhibits potent inhibitory activity against pandemic influenza A(H1N1) viruses. As inhibition was also observed with oseltamivir-resistant IFV (H274Y), DAS181 may be active against the antigenically novel pandemic influenza A(H1N1) virus should it acquire the H274Y mutation. Based on these and previous results demonstrating DAS181 broad-spectrum anti-IFV activity, DAS181 represents a potential therapeutic agent for prevention and treatment of infections by both emerging and seasonal strains of IFV.

Detection of novel swine origin influenza A virus (H1N1) by real-time nucleic acid sequence-based amplification

Rapid detection of novel swine origin influenza A virus (S-OIV) (H1N1) is crucial for timely implementation of infection control measures. In this study, a haemagglutinin (HA) gene-based real-time nucleic acid sequence-based amplification (NASBA) assay was developed for the specific detection of S-OIV (H1N1). The assay was evaluated and validated by comparing it with existing detection methods for S-OIV (H1N1). Results obtained in a 10-fold dilution series assay demonstrated the analytic sensitivity of the present assay was comparable to that of a commercial S-OIV (H1N1) real-time RT-PCR kit and higher than that of the Centers for Disease Control and Prevention (CDC) TaqMan assay. The actual detection limit of the real-time NASBA assay was approximately 50 copies per reaction. Compared with reference methods (viral culture, conventional RT-PCR, and real-time RT-PCR), the sensitivity, specificity, positive predictive value, and negative predictive value of the present assay were all 100%. Overall, the results showed that the real-time NASBA assay could be used for sensitive and specific detection of S-OIV (H1N1).

Library of prefabricated locked nucleic acid hydrolysis probes facilitates rapid development of reverse-transcription quantitative real-time PCR assays for detection of novel influenza A/H1N1/09 virus

BACKGROUND

The emergence of a novel pandemic human strain of influenza A (H1N1/09) has clearly demonstrated the need for flexible tools enabling the rapid development of new diagnostic methods.

METHODS

We designed a set of reverse-transcription quantitative real-time PCR (RT-qPCR) assays based on the Universal ProbeLibrary (UPL)--a collection of 165 presynthesized, fluorescence-labeled locked nucleic acid (LNA) hydrolysis probes--specifically to detect the novel influenza A virus. We evaluated candidate primer/UPL-probe pairs with 28 novel influenza A/H1N1/09 patient samples of European and Mexican origin.

RESULTS

Of 14 assays in the hemagglutinin (HA) and neuraminidase (NA) genes, 12 detected viral nucleic acids from diluted patient samples without need for further optimization. We characterized the diagnostic specificity of the 2 best-performing assays with a set of samples comprising various influenza virus strains of human and animal origin that showed no cross-reactivity. The diagnostic sensitivity of these 2 primer/probe combinations was in the range of 100-1000 genomic copies/mL. In comparison to a reference assay recommended by the German health authorities, the analytical sensitivities and specificities of the assays were equivalent.

CONCLUSIONS

Facing the emergence of novel influenza A/H1N1/09, we were able to develop, within 2 days, a set of sensitive and specific RT-qPCR assays for the laboratory diagnosis of suspected cases. H1N1/09 served as a model to show the feasibility of the UPL approach for the expedited development of new diagnostic assays to detect emerging pathogens.

The influenza A(H1N1) epidemic in Mexico. Lessons learned

Several influenza pandemics have taken place throughout history and it was assumed that the pandemic would emerge from a new human virus resulting from the adaptation of an avian virus strain. Mexico, since 2003 had developed a National Preparedness and Response Plan for an Influenza Pandemic focused in risk communication, health promotion, healthcare, epidemiological surveillance, strategic stockpile, research and development. This plan was challenged on April 2009, when a new influenza A(H1N1) strain of swine origen was detected in Mexico. The situation faced, the decisions and actions taken, allowed to control the first epidemic wave in the country. This document describes the critical moments faced and explicitly point out the lessons learned focused on the decided support by the government, the National Pandemic Influenza Plan, the coordination among all the government levels, the presence and solidarity of international organizations with timely and daily information, diagnosis and the positive effect on the population following the preventive hygienic measures recommended by the health authorities. The international community will be able to use the Mexican experience in the interest of global health.

Surveillance and oseltamivir resistance of human influenza a virus in Turkey during the 2007-2008 season

Monitoring the activity of influenza viruses is important for establishing the circulating types and for detection of the emergence of novel sub-types and antiviral resistant strains. This is the first report from Turkey on the surveillance and oseltamivir resistance of influenza viruses in 2007-2008. Five hundred twenty-four nasal swabs were tested from different geographical regions in Turkey during November 2007-April 2008. One hundred sixty-three (31%) samples were positive for influenza viruses of which 111 (68%) were influenza A, 52 (31%) influenza B using an immuno-capture ELISA. Forty isolates were selected at random from influenza A positive samples and grown in MDCK cell cultures. The supernatant of the cell cultures was used for RNA extraction followed by RT-PCR to detect the sub-types. Sub-typing revealed all samples as A/H1N1. The N1 gene segment of 30 A/H1N1 samples was sequenced in part, from the 201st to 365th residue, which included the critical region for oseltamivir resistance. Then resulting sequences were analyzed with oseltamivir sensitive and resistant strains obtained from National Center for Biotechnology Information (NCBI) GenBank by CLC Main Workbench Software. H275Y (H274Y according to N2 numbering) mutation, which is known to confer resistance to oseltamivir, was detected in 6 out of 30 (20%) H1N1 isolates from four cities (Istanbul, Bursa, Ankara, and Izmir). The D354G mutation was observed in all oseltamivir resistant H1N1 isolates but not in the oseltamivir sensitive isolates. Assay of neuraminidase activity revealed that these isolates were resistant to oseltamivir, but sensitive to zanamivir.

Understanding influenza transmission, immunity and pandemic threats

Abstract  The current pandemic threat can be best understood within an ecological framework that takes account of the history of past pandemics caused by influenza A, the relationships between pandemic and seasonal spread of influenza viruses, and the importance of immunity and behavioural responses in human populations. Isolated populations without recent exposure to seasonal influenza seem more susceptible to new pandemic viruses, and much collateral evidence suggests that this is due to immunity directed against epitopes shared between pandemic and previously circulating strains of inter‐pandemic influenza A virus. In the highly connected modern world, most populations are regularly exposed to non‐pandemic viruses, which can even boost immunity without causing influenza symptoms. Such naturally‐induced immunity helps to explain the low attack‐rates of seasonal influenza, as well as the moderate attack‐rates in many urbanized populations affected by 1918–1919 and later pandemics. The effectiveness of immunity, even against seasonal influenza, diminishes over time because of antigenic drift in circulating viruses and waning of post‐exposure immune responses. Epidemiological evidence suggests that cross‐protection against a new pandemic strain could fade even faster. Nevertheless, partial protection, even of short duration, induced by prior seasonal influenza or vaccination against it, could provide important protection in the early stages of a new pandemic.

An early 'classical' swine H1N1 influenza virus shows similar pathogenicity to the 1918 pandemic virus in ferrets and mice

The 1918 pandemic influenza virus has demonstrated significant pathogenicity in animal models and is the progenitor of 'classical' swine and modern seasonal human H1N1 lineages. Here we characterize the pathogenicity of an early 'classical' swine H1N1 influenza A virus isolated in 1931 compared to the pathogenicity of the 1918 pandemic virus and a seasonal H1N1 virus in mice and ferrets. A/Swine/Iowa/31 (Sw31) and the 1918 influenza viruses were uniformly lethal in mice at low doses and produced severe lung pathology. In ferrets, Sw31 and 1918 influenza viruses caused severe clinical disease and lung pathology with necrotizing bronchiolitis and alveolitis. The modern H1N1 virus caused little disease in either animal model. These findings revealed that in these models the virulence factors of the 1918 influenza virus are likely preserved in the Sw31 virus and suggest that early swine viruses may be a good surrogate model to study 1918 virulence and pathogenesis.

Investment decisions in influenza pandemic contingency planning: cost-effectiveness of stockpiling antiviral drugs

BACKGROUND

The threat of an influenza pandemic has led to stockpiling of antiviral drugs in order to mitigate a plausible outbreak. If the stockpile would be used in relation to the recent pandemic alert, an investment decision about renewing the stock for a possible subsequent pandemic is essential. The decision should include cost-effectiveness considerations.

METHODS

We constructed a cost-effectiveness analysis in the Dutch context, explicitly including risk of an outbreak. Outcomes from a dynamic transmission model, comparing an intervention with a non-intervention scenario, were input in our health economic calculations.

RESULTS

Stockpiling was cost-effective from the health-care perspective if the actual risk is 37% for 30 years. If less than 60% of the population would take the antiviral drugs or the attack rate is about 50%, the investment would not be cost-effective from this perspective.

CONCLUSION

Risk perception, realistic coverage among population and size of a pandemic are crucial parameters and highly decisive for the investment decision.

The hemagglutinin structure of an avian H1N1 influenza A virus

The interaction between hemagglutinin (HA) and receptors is a kernel in the study of evolution and host adaptation of H1N1 influenza A viruses. The notion that the avian HA is associated with preferential specificity for receptors with Siaalpha2,3Gal glycosidic linkage over those with Siaalpha2,6Gal linkage is not all consistent with the available data on H1N1 viruses. By x-ray crystallography, the HA structure of an avian H1N1 influenza A virus, as well as its complexes with the receptor analogs, was determined. The structures revealed no preferential binding of avian receptor analogs over that of the human analog, suggesting that the HA/receptor binding might not be as stringent as is commonly believed in determining the host receptor preference for some subtypes of influenza viruses, such as the H1N1 viruses. The structure also showed difference in glycosylation despite the preservation of related sequences, which may partly contribute to the difference between structures of human and avian origin.

Dating the emergence of pandemic influenza viruses

Pandemic influenza viruses cause significant mortality in humans. In the 20th century, 3 influenza viruses caused major pandemics: the 1918 H1N1 virus, the 1957 H2N2 virus, and the 1968 H3N2 virus. These pandemics were initiated by the introduction and successful adaptation of a novel hemagglutinin subtype to humans from an animal source, resulting in antigenic shift. Despite global concern regarding a new pandemic influenza, the emergence pathway of pandemic strains remains unknown. Here we estimated the evolutionary history and inferred date of introduction to humans of each of the genes for all 20th century pandemic influenza strains. Our results indicate that genetic components of the 1918 H1N1 pandemic virus circulated in mammalian hosts, i.e., swine and humans, as early as 1911 and was not likely to be a recently introduced avian virus. Phylogenetic relationships suggest that the A/Brevig Mission/1/1918 virus (BM/1918) was generated by reassortment between mammalian viruses and a previously circulating human strain, either in swine or, possibly, in humans. Furthermore, seasonal and classic swine H1N1 viruses were not derived directly from BM/1918, but their precursors co-circulated during the pandemic. Mean estimates of the time of most recent common ancestor also suggest that the H2N2 and H3N2 pandemic strains may have been generated through reassortment events in unknown mammalian hosts and involved multiple avian viruses preceding pandemic recognition. The possible generation of pandemic strains through a series of reassortment events in mammals over a period of years before pandemic recognition suggests that appropriate surveillance strategies for detection of precursor viruses may abort future pandemics.

Managing public health crises: the role of models in pandemic preparedness

Background  Given the enormity of challenges involved in pandemic preparedness, design and implementation of effective and cost‐effective public health policies is a major task that requires an integrated approach through engagement of scientific, administrative, and political communities across disciplines. There is ample evidence to suggest that modeling may be a viable approach to accomplish this task.

Methods  To demonstrate the importance of synergism between modelers, public health experts, and policymakers, the University of Winnipeg organized an interdisciplinary workshop on the role of models in pandemic preparedness in September 2008. The workshop provided an excellent opportunity to present outcomes of recent scientific investigations that thoroughly evaluate the merits of preventive, therapeutic, and social distancing mechanisms, where community structures, priority groups, healthcare providers, and responders to emergency situations are given specific consideration.

Results  This interactive workshop was clearly successful in strengthening ties between various disciplines and creating venues for modelers to effectively communicate with policymakers. The importance of modeling in pandemic planning was highlighted, and key parameters that affect policy decision‐making were identified. Core assumptions and important activities in Canadian pandemic plans at the provincial and national levels were also discussed.

Conclusions  There will be little time for thoughtful and rapid reflection once an influenza pandemic strikes, and therefore preparedness is an unavoidable priority. Modeling and simulations are key resources in pandemic planning to map out interdependencies and support complex decision‐making. Models are most effective in formulating strategies for managing public health crises when there are synergies between modelers, planners, and policymakers.

Novel swine-origin influenza A virus in humans: another pandemic knocking at the door

Influenza A viruses represent a continuous pandemic threat. In April 2009, a novel influenza A virus, the so-called swine-origin influenza A (H1N1) virus (S-OIV), was identified in Mexico. Although S-OIV originates from triple-reassortant swine influenza A (H1) that has been circulating in North American pig herds since the end of the 1990s, S-OIV is readily transmitted between humans but is not epidemic in pigs. After its discovery, S-OIV rapidly spread throughout the world within few weeks. In this review, we sum up the current situation and put it into the context of the current state of knowledge of influenza and influenza pandemics. Some indications suggest that a pandemic may be mild but even "mild" pandemics can result in millions of deaths. However, no reasonable forecasts how this pandemic may develop can be made at this time. Despite stockpiling by many countries and WHO, antiviral drugs will be limited in case of pandemic and resistances may emerge. Effective vaccines are regarded to be crucial for the control of influenza pandemics. However, production capacities are restricted and development/production of a S-OIV vaccine will interfere with manufacturing of seasonal influenza vaccines. The authors are convinced that S-OIV should be taken seriously as pandemic threat and underestimation of the menace by S-OIV to be by far more dangerous than its overestimation.

The 1918 "Spanish flu" in Spain

The 1918-1919 influenza pandemic was the most devastating epidemic in modern history. Here, we review epidemiological and historical data about the 1918-1919 influenza epidemic in Spain. On 22 May 1918, the epidemic was a headline in Madrid's ABC newspaper. The infectious disease most likely reached Spain from France, perhaps as the result of the heavy railroad traffic of Spanish and Portuguese migrant workers to and from France. The total numbers of persons who died of influenza in Spain were officially estimated to be 147,114 in 1918, 21,235 in 1919, and 17,825 in 1920. However, it is likely that >260,000 Spaniards died of influenza; 75% of these persons died during the second period of the epidemic, and 45% died during October 1918 alone. The Spanish population growth index was negative for 1918 (net loss, 83,121 persons). Although a great deal of evidence indicates that the 1918 A(H1N1) influenza virus unlikely originated in and spread from Spain, the 1918-1919 influenza pandemic will always be known as the Spanish flu.

Mortality burden of the 1918-1919 influenza pandemic in Europe

Background  The origin and estimated death toll of the 1918–1919 epidemic are still debated. Europe, one of the candidate sites for pandemic emergence, has detailed pandemic mortality information.

Objective  To determine the mortality impact of the 1918 pandemic in 14 European countries, accounting for approximately three‐quarters of the European population (250 million in 1918).

Methods  We analyzed monthly all‐cause civilian mortality rates in the 14 countries, accounting for approximately three‐quarters of the European population (250 million in 1918). A periodic regression model was applied to estimate excess mortality from 1906 to 1922. Using the 1906–1917 data as a training set, the method provided a non‐epidemic baseline for 1918–1922. Excess mortality was the mortality observed above this baseline. It represents the upper bound of the mortality attributable to the flu pandemic.

Results  Our analysis suggests that 2·64 million excess deaths occurred in Europe during the period when Spanish flu was circulating. The method provided space variation of the excess mortality: the highest and lowest cumulative excess/predicted mortality ratios were observed in Italy (+172%) and Finland (+33%). Excess‐death curves showed high synchrony in 1918–1919 with peak mortality occurring in all countries during a 2‐month window (Oct–Nov 1918).

Conclusions  During the Spanish flu, the excess mortality was 1·1% of the European population. Our study highlights the synchrony of the mortality waves in the different countries, which pleads against a European origin of the pandemic, as was sometimes hypothesized.

Pandemic Influenza: Impact on Perianesthesia Nursing Areas

As our readers are aware, these pages are typically used by the editors. However, in light of the recent events and concerns surrounding the swine flu, the editors have elected to quickly substitute an informative piece regarding influenza for the usual editorial. We thank Dr. Daphne Stannard for her willingness to disseminate her knowledge on the topic. The Editors

Stockpiling drugs for an avian influenza outbreak: examining the surge in oseltamivir prescriptions during heightened media coverage of the potential for a worldwide pandemic

OBJECTIVE

During fall 2005, personal stockpiling of oseltamivir for use during an outbreak of H5N1 influenza virus infection was widely reported. The present study aimed to identify indications for oseltamivir prescriptions to determine whether oseltamivir that was not intended for seasonal influenza was inappropriately consumed and to compare persons who were likely to have stockpiled oseltamivir and those who did not with respect to their knowledge, understanding, concerns, and expectations regarding avian influenza.

DESIGN

Survey to evaluate usage patterns for oseltamivir and assess views about avian influenza.

SUBJECTS

A total of 109 outpatients who received a prescription for oseltamivir between September 1, 2005, and December 31, 2005, and 825 matched control subjects.

RESULTS

Of 109 prescriptions, 36 (33.0%) were prescribed for patients with appropriate indications. Sixty-eight (62.4%) of 109 patients identified as having received oseltamivir and 440 (53.3%) of 825 individuals identified as not having received it responded to the questionnaire. Only 2 prescription recipients whose oseltamivir was not intended for immediate consumption reported that they had consumed the oseltamivir. Persons who probably intended to stockpile oseltamivir were older and more often white than those unlikely to stockpile it. They also reported greater worry about avian influenza and more often expected avian influenza to spread to the United States than those unlikely to stockpile, but there were no significant differences in responses to other questionnaire items.

CONCLUSIONS

A large proportion of the oseltamivir prescriptions written in fall 2005 were probably intended for personal stockpiling. Similarities in participants' responses to questionnaire items suggest that educational campaigns may not be an effective method to curtail stockpiling of antimicrobial medications during an infectious threat. Promoting appropriate prescribing practices among providers may be a better means by which to minimize personal stockpiling.

Current status and progress of prepandemic and pandemic influenza vaccine development

H5N1 viruses are widely considered to be a probable cause of the next influenza pandemic. Influenza vaccines are considered to form the main prophylactic measure against pandemic influenza. The world's population is expected to have no pre-existing immunity against the pandemic virus strain and will need two vaccine doses to acquire protective immunity. A pandemic outbreak will spread much faster than it will take for pandemic vaccines to be produced and distributed. Therefore, increasing efforts are being made to develop prepandemic vaccines that can induce broad cross-protective responses and that can be administered as soon as a pandemic is declared or even before, in order to successfully prime the immune system and allow for a rapid and protective antibody response with one dose of the pandemic vaccine. Several vaccine manufacturers have developed candidate pandemic and prepandemic vaccines, predominantly based on reverse-genetics reference strains and have improved the immunogenicity by formulating these vaccines with different adjuvants. Clinical studies with inactivated split-virion or whole-virion vaccines based on H5N1 indicate that two immunizations appear necessary to elicit the level of immunity required to meet licensure criteria. A detailed overview is given of the most successful candidate vaccines developed by seven vaccine manufacturers.

School closure may be effective in reducing transmission of respiratory viruses in the community

Proposed measures to contain pandemic influenza include school closure, although the effectiveness of this has not been investigated. We examined the effect of a nationwide elementary school strike in Israel in 2000 on the incidence of influenza-like illness. In this historical observational study of 1.7 million members of a preferred provider organization, we analysed diagnoses from primary-care visits during the winter months in 1998-2002. We calculated the weekly ratio of influenza-like diagnoses to non-respiratory diagnoses, and fitted regression models for school-aged children, children's household members, and all other individuals aged >12 years. For each population the steepest drop in the ratio of influenza-like diagnoses to non-respiratory diagnoses occurred in the strike year 2 weeks after the start of the strike. The changes in the weekly ratio of influenza-like diagnoses to non-respiratory diagnoses were statistically significant (P=0.0074) for school children for the strike year compared to other years. A smaller decrease was also seen for the adults with no school-aged children in 1999 (P=0.037). The Chanukah holiday had a negative impact on the ratio for school-aged children in 1998, 1999 and 2001 (P=0.008, 0.006 and 0.045, respectively) and was statistically significant for both adult groups in 1999 and for adults with no school-aged children in 2001. School closure should be considered part of the containment strategy in an influenza pandemic.

Different evolutionary trajectories of European avian-like and classical swine H1N1 influenza A viruses

In 1979, a lineage of avian-like H1N1 influenza A viruses emerged in European swine populations independently from the classical swine H1N1 virus lineage that had circulated in pigs since the Spanish influenza pandemic of 1918. To determine whether these two distinct lineages of swine-adapted A/H1N1 viruses evolved from avian-like A/H1N1 ancestors in similar ways, as might be expected given their common host species and origin, we compared patterns of nucleotide and amino acid change in whole genome sequences of both groups. An analysis of nucleotide compositional bias across all eight genomic segments for the two swine lineages showed a clear lineage-specific bias, although a segment-specific effect was also apparent. As such, there appears to be only a relatively weak host-specific selection pressure. Strikingly, despite each lineage evolving in the same species of host for decades, amino acid analysis revealed little evidence of either parallel or convergent changes. These findings suggest that although adaptation due to evolutionary lineages can be distinguished, there are functional and structural constraints on all gene segments and that the evolutionary trajectory of each lineage of swine A/H1N1 virus has a strong historical contingency. Thus, in the context of emergence of an influenza A virus strain via a host switch event, it is difficult to predict what specific polygenic changes are needed for mammalian adaptation.

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.

Influenza in dogs and cats

Influenza has been long absent from the list of infectious diseases considered as possibilities in dogs and cats. With the discovery that avian influenza H5N1 can infect cats and dogs, and the appearance of canine influenza H3N8, small animal veterinarians have an important role to play in detection of influenza virus strains that may become zoonotic. Small animal veterinarians must educate staff and clients about influenza to improve understanding as to when and where influenza infection is possible, and to avert unreasonable fears.

Experimental infection of pigs with the human 1918 pandemic influenza virus

Swine influenza was first recognized as a disease entity during the 1918 "Spanish flu" pandemic. The aim of this work was to determine the virulence of a plasmid-derived human 1918 pandemic H1N1 influenza virus (reconstructed 1918, or 1918/rec, virus) in swine using a plasmid-derived A/swine/Iowa/15/1930 H1N1 virus (1930/rec virus), representing the first isolated influenza virus, as a reference. Four-week-old piglets were inoculated intratracheally with either the 1930/rec or the 1918/rec virus or intranasally with the 1918/rec virus. A transient increase in temperature and mild respiratory signs developed postinoculation in all virus-inoculated groups. In contrast to other mammalian hosts (mice, ferrets, and macaques) where infection with the 1918/rec virus was lethal, the pigs did not develop severe respiratory distress or become moribund. Virus titers in the lower respiratory tract as well as macro- and microscopic lesions at 3 and 5 days postinfection (dpi) were comparable between the 1930/rec and 1918/rec virus-inoculated animals. In contrast to the 1930/rec virus-infected animals, at 7 dpi prominent lung lesions were present in only the 1918/rec virus-infected animals, and all the piglets developed antibodies at 7 dpi. Presented data support the hypothesis that the 1918 pandemic influenza virus was able to infect and replicate in swine, causing a respiratory disease, and that the virus was likely introduced into the pig population during the 1918 pandemic, resulting in the current lineage of the classical H1N1 swine influenza viruses.

Role of sialic acid binding specificity of the 1918 influenza virus hemagglutinin protein in virulence and pathogenesis for mice

The 1918 influenza pandemic caused more than 40 million deaths and likely resulted from the introduction and adaptation of a novel avian-like virus. Influenza A virus hemagglutinins are important in host switching and virulence. Avian-adapted influenza virus hemagglutinins bind sialic acid receptors linked via alpha2-3 glycosidic bonds, while human-adapted hemagglutinins bind alpha2-6 receptors. Sequence analysis of 1918 isolates showed hemagglutinin genes with alpha2-6 or mixed alpha2-6/alpha2-3 binding. To characterize the role of the sialic acid binding specificity of the 1918 hemagglutinin, we evaluated in mice chimeric influenza viruses expressing wild-type and mutant hemagglutinin genes from avian and 1918 strains with differing receptor specificities. Viruses expressing 1918 hemagglutinin possessing either alpha2-6, alpha2-3, or alpha2-3/alpha2-6 sialic acid specificity were fatal to mice, with similar pathology and cellular tropism. Changing alpha2-3 to alpha2-6 binding specificity did not increase the lethality of an avian-adapted hemagglutinin. Thus, the 1918 hemagglutinin contains murine virulence determinants independent of receptor binding specificity.

Readiness exercise to combat avian influenza

AIM

To examine the readiness of our hospital for the potential pandemic threat of avian influenza, we developed and implemented simulation case scenarios in our hospital.

METHODS

Two volunteers, who assumed the identity of 'actual' patients, were trained to simulate acute respiratory symptoms following a visit to an avian influenza-affected area, and their identities and locations were kept confidential prior to the readiness exercise. A team of auditors was stationed at high-risk areas to assess adherence to the use of personal protective equipment (PPE) and infection control procedures.

RESULTS

A total of 324 healthcare workers and 84 administrators participated in this hospital-wide exercise. Following disclosure of their symptoms, the 'patients' were masked and isolated in negative-pressure rooms. A quarantine order was enforced on 38 inpatients and 45 healthcare workers who were present in the affected wards at the time of the exercise, which mandated the use of PPE. Although all affected healthcare workers were competent in the use of PPE, we observed breaches in PPE and isolation procedures in eight medical and nursing students, and 10 healthcare attendants. The exercise concluded after H5N1 tests returned negative.

CONCLUSION

We recommend the use of case simulation as an effective means of assessing potential breaches in infection control procedures.

Proteolytic activation of the 1918 influenza virus hemagglutinin

Proteolytic activation of the hemagglutinin (HA) protein is indispensable for influenza virus infectivity, and the tissue expression of the responsible cellular proteases impacts viral tropism and pathogenicity. The HA protein critically contributes to the exceptionally high pathogenicity of the 1918 influenza virus, but the mechanisms underlying cleavage activation of the 1918 HA have not been characterized. The neuraminidase (NA) protein of the 1918 influenza virus allows trypsin-independent growth in canine kidney cells (MDCK). However, it is at present unknown if the 1918 NA, like the NA of the closely related strain A/WSN/33, facilitates HA cleavage activation by recruiting the proprotease plasminogen. Moreover, it is not known which pulmonary proteases activate the 1918 HA. We provide evidence that NA-dependent, trypsin-independent cleavage activation of the 1918 HA is cell line dependent and most likely plasminogen independent since the 1918 NA failed to recruit plasminogen and neither exogenous plasminogen nor the presence of the A/WSN/33 NA promoted efficient cleavage of the 1918 HA. The transmembrane serine protease TMPRSS4 was found to be expressed in lung tissue and was shown to cleave the 1918 HA. Accordingly, coexpression of the 1918 HA with TMPRSS4 or the previously identified HA-processing protease TMPRSS2 allowed trypsin-independent infection by pseudotypes bearing the 1918 HA, indicating that these proteases might support 1918 influenza virus spread in the lung. In summary, we show that the previously reported 1918 NA-dependent spread of the 1918 influenza virus is a cell line-dependent phenomenon and is not due to plasminogen recruitment by the 1918 NA. Moreover, we provide evidence that TMPRSS2 and TMPRSS4 activate the 1918 HA by cleavage and therefore may promote viral spread in lung tissue.

A spatiotemporal statistical model of the risk factors of human cases of H5N1 avian influenza in South-east Asian countries and China

OBJECTIVES

This article aims to quantify the risk factors associated with the human cases of H5N1 avian influenza in South-east Asian countries and China; a dangerous region for this disease that has the potential for a pandemic outbreak.

STUDY DESIGN

A statistical model with time and spatial dimensions was built to capture the international spread patterns of this disease.

METHODS

The grid search method was used to fit the model with 2004-2006 data. The grid search approach is a simple procedure that allows the fit of any function to data.

RESULTS

This study found that: (1) when the number of domestic H5N1 human cases increases by one person in a certain time period, the chance that the country will have a human case in the next period increases by 22.10%; (2) when the number of human cases in a neighbouring country increases by one person in a certain time period, the chance that the country will have a human case in the next period increases by 1.62%; (3) when the number of avian cases in a neighbouring country increases by one, the chance that the country will have a human case increases by 0.02%; (4) as the human population increases by one unit, the chance that the country will have a human case increases by 0.10%; (5) when the quantity of imported poultry increases by 1000 metric tons, the chance that the country will have a human case increases by 0.03%; (6) when the outbreak of the disease among domestic birds increases by one, the chance that the country will have a human case increases by 0.19%; and finally (7) when the number of birds destroyed increases by 1000, the chance that the country will have a human case decreases by 0.30%.

CONCLUSIONS

These findings shed new light on the spatiotemporal characteristics of the epidemic, and thus need to be taken into consideration in interdisciplinary and scientific discussion of the disease.