Rapid response research to emerging infectious diseases: lessons from SARS

New insights from nanotechnology in SARS-CoV-2 detection, treatment strategy, and prevention

The recent outbreak of SARS-CoV-2 resulted into the deadly COVID-19 pandemic, which has made a profound impact on mankind and the world health care system. SARS-CoV-2 is mainly transmitted within the population via symptomatic carriers, enters the host cell via ACE2 and TMPSSR2 receptors and damages the organs. The standard diagnostic tests and treatment methods implemented lack required efficiency to beat SARS-CoV-2 in the race of its spreading. The most prominently used diagnostic test,reverse transcription-polymerase chain reaction (a nucleic acid-based method), has limitations including a prolonged time taken to reveal results, limited sensitivity, a high rate of false negative results, and lacking specificity due to a homology with other viruses. Furthermore, as part of the treatment, antiviral drugs such as remdesivir, favipiravir, lopinavir/ritonavir, chloroquine, daclatasvir, atazanavir, and many more have been tested clinically to check their potency for the treatment of SARS-CoV-2 but none of these antiviral drugs are the definitive cure or suitable prophylaxis. Thus, it is always required to combat SARS-CoV-2 spread and infection for a better and precise prognosis. This review answers the above mentioned challenges by employing nanomedicine for the development of improved detection, treatment, and prevention strategies for SARS-CoV-2. In this review, nanotechnology-based detection methods such as colorimetric assays, photothermal biosensors, molecularly imprinted nanoparticles sensors, electrochemical nanoimmunosensors, aptamer-based biosensors have been discussed. Furthermore, nanotechnology-based treatment strategies involving polymeric nanoparticles, metallic nanoparticles, lipid nanoparticles, and nanocarrier-based antiviral siRNA delivery have been depicted. Moreover, SARS-CoV-2 prevention strategies, which include the nanotechnology for upgrading personal protective equipment, facemasks, ocular protection gears, and nanopolymer-based disinfectants, have been also reviewed. This review will provide a one-site informative platform for researchers to explore the crucial role of nanomedicine in managing the COVID-19 curse more effectively.

The use of E-health during the COVID-19 pandemic: a case study in China's Hubei province

Globally, the use of e-health has accelerated dramatically during the coronavirus pandemic. Based on both quantitative and qualitative data collected in China's Hubei province (i.e. the first epicentre of COVID-19), this research explores how the pandemic influences the practices of e-health from the perspective of users. Through analysis of 1,033 surveys and 14 in-depth interviews, we find that e-health has played a crucial role in residents' healthcare during the COVID-19 pandemic. Certain external factors influence the choice of digital health, including the high risk of infection outdoors, the shutting down of transport systems, and dysfunctional healthcare facilities that neglect non-COVID-19 patients' clinical demands. Against this backdrop, we argue digital health acts as a functional equivalent to traditional medical treatment and has largely satisfied patients and users in the crisis period. Additionally, the COVID-19 pandemic has unintentionally sped up the diffusion of digital medicine over the long term as respondents expressed their willingness to continue use of e-health in the post-COVID-19 phase. However, we assert that despite the increasing use of e-health, it cannot fully substitute traditional offline treatment. Thus, we suggest a combination of online and offline healthcare will be more commonly practiced in the future.

Vaccine efficacy in mutant SARS-CoV-2 variants

Many aspects of the SARS-CoV-2 virus remain poorly understood, including its rapid mutation and its effects on populations of different ages. The present literature of review is focused on the effectiveness of current available vaccines in view of immerging several SARS-CoV-2 variants. The most dangerous and infectious SARS-CoV-2 strain, B117, was recently discovered in the United Kingdom, and another new variant, 501.V2, was discovered in South Africa. In countries such as the United States, Japan, India, and Brazil, the variant B117 spread far more quickly than the original strain. The new SARS-CoV-2 mutations have made producing a universal and effective vaccine more difficult. SARS-CoV-2's S protein, which aids in receptor identification and membrane fusion, is a primary target for vaccine development using its mRNA or inactivated virus. Currently, in the interval of few days new more infectious SARS-CoV-2 mutant is detected, started from SARS-CoV-2 Alpha (B.1.1.7), beta (B.1.351), delta (B.1.617.2), delta plus, gamma (P.1) and now variant lamda. The variant detected first in Peru and spread almost 27 countries including UK that accounts for 82% of new infections. These mutant variants are posing new challenge even to the fully vaccinated individuals and a challenge for the public health. Thus, a need to review current treatment vaccination guideline and strategy as early as possible. Reporting all new SARS-CoV-2 variants and their effectiveness in response to several available vaccines, we would like to draw the attention of health care provider, and all developed countries health care agencies including WHO to frame new guidelines for vaccination and immediate intervention to control the development of new SARS-CoV-2 variants from the third world countries by providing vaccines to the poor countries as early as possible.

Postulated Adjuvant Therapeutic Strategies for COVID-19

The number of COVID-19 patients is still growing exponentially worldwide due to the high transmissibility of the SARS-CoV-2 virus. Therapeutic agents currently under investigation are antiviral drugs, vaccines, and other adjuvants that could relieve symptoms or improve the healing process. In this review, twelve therapeutic agents that could play a role in prophylaxis or improvement of the COVID-19-associated symptoms (as add-on substances) are discussed. Agents were identified based on their known pharmacologic mechanism of action in viral and/or nonviral fields and are postulated to interact with one or more of the seven known mechanisms associated with the SARS-CoV-2 virus: (i) regulation of the immune system; (ii) virus entrance in the cell; (iii) virus replication; (iv) hyperinflammation; (v) oxidative stress; (vi) thrombosis; and (vii) endotheliitis. Selected agents were immune transfer factor (oligo- and polypeptides from porcine spleen, ultrafiltered at <10 kDa; Imuno TF®), anti-inflammatory natural blend (Uncaria tomentosa, Endopleura uchi and Haematoccocus pluvialis; Miodesin®), zinc, selenium, ascorbic acid, cholecalciferol, ferulic acid, spirulina, N-acetylcysteine, glucosamine sulfate potassium hydrochloride, trans-resveratrol, and maltodextrin-stabilized orthosilicic acid (SiliciuMax®). This review gives the scientific background on the hypothesis that these therapeutic agents can act in synergy in the prevention and improvement of COVID-19-associated symptoms.

PATHOLOGICAL ANATOMY OF INFECTION CAUSED BY SARS-COV-2

Autopsy data from 80 patients who died of the COVID-19 infection were analysed. Using macro- and microscopic studies, specific features of pathological processes in various organs were identified. The obtained experimental data, along with information from literature sources, allowed conclusions to be drawn about the mechanisms of damaging internal organs and body systems, as well as assumptions to be made about individual links in the pathogenesis of COVID-19. The thanatogenesis of the disease and the main causes of death are discussed, including acute cardiopulmonary failure, acute renal failure, pulmonary thromboembolism, shock involving multiple organ failure and sepsis. The critical importance of autopsy is emphasized, which provides valuable information on the morphological substrate for this infection closely associated with possible clinical manifestations.

Morphology, Genome Organization, Replication, and Pathogenesis of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2)

SARS-CoV-2 is a single-stranded RNA virus of ~30 kb genome size which belongs to genus Coronavirus and family Coronaviridae. SARS-CoV-2 has recently emerged and has been declared as a pandemic by the World Health Organization. Genomic characterization of SARS-CoV-2 has shown that it is of zoonotic origin. The structure of SARS-CoV-2 is found to be similar to SARS-CoV with virion size ranging from 70 to 90 nm. Spike, membrane, and envelope surface viral proteins of coronavirus are embedded in host membrane-derived lipid bilayer encapsulating the helical nucleocapsid comprising viral RNA. The genome comprises of 6–11 open reading frames (ORFs) with 5′ and 3′ flanking untranslated regions (UTRs). Sequence variation among SARS-CoV-2 and SARS-CoV revealed no significant difference in ORFs and nsps. The nsps includes two viral cysteine proteases including papain-like protease (nsp3), chymotrypsin-like, 3C-like, or main protease (nsp5), RNA-dependent RNA polymerase (nsp12), helicase (nsp13), and others likely to be involved in the transcription and replication of SARS-CoV-2. The structure of spike glycoprotein structure of SARS-CoV-2 resembles that of the spike protein of SARS-CoV with an root-mean-square deviation (RMSD) of 3.8 Å. Like SARS-CoV, SARS-CoV-2 uses the ACE2 receptor for internalization and TMPRSS2 serine proteases for S protein priming. Histopathological investigation of tissues from SARS-CoV-2 infected patients showed virus-induced cytopathic effect with signs of acute respiratory distress syndrome in lung cells. This chapter discusses about the morphology, genome organization, replication, and pathogenesis of SARS-CoV-2 that may help us understand the disease that may leads to identification of effective antiviral drugs and vaccines.

[Conducting clinical studies during the epidemics of communicable diseases: perspectives of methodology and health economics]

In the setting of epidemics of communicable diseases, early initiation of epidemiological and clinical data collection and analysis and conducting relevant researches are essential to the success of epidemic containment. The coronavirus disease 2019 (COVID-19), starting initially as an epidemic in China in late 2019 and now becoming a pandemic globally, poses grave challenges to the global health care systems while also provides an opportunity for studying infectious diseases in the perspective of methodology. The authors propose the evaluation methods for case reports, randomized controlled trials (RCTs), real-world evidence studies and health economics researches during an epidemic. Case reports, which are of important value for health care workers during outbreaks of infectious diseases, should be written in standard format and style and published following a strict peer review process. RCTs provides the gold standard for evaluating the effectiveness of a given treatment for the patients from the outbreaks. We review the potential challenges faced in conducting RCTs during the outbreaks. The real-world data collected from the cases in designated hospitals allow the verification of the safety and effectiveness of the intervention measures. The data from health economics research also provide important support for optimizing communicable disease prevention and control strategies. Herein we summarize the health economics research methods, study design, and technical points during the outbreaks. We recommend that clinical research and health economics research be incorporated into the prevention and control plan and measures be taken to ensure both the standards and feasibility of these studies to improve the response capacity against outbreaks of communicable diseases.

Structural Insight Into the Viral 3C-Like Protease Inhibitors: Comparative SAR/QSAR Approaches

Severe acute respiratory syndrome (SARS), caused by SARS-coronavirus (SARS-CoV), is a dreadful infection worldwide having economic and medical importance and a global threat for health. It was turned into an epidemic in South China followed by a chain of infections across three generations. A number of pathogeneses in human may occur due to the virus. This infection has not been taken into account before the SARS outbreak, and still it is a neglected one. Therefore, there is an urgent need to develop small molecule antivirals to combat the SARS-CoV. No vaccines are available till date though a number of SARS-CoV 3C-like and 3C protease inhibitors were reported. In this chapter, quantitative structure–activity relationship technique is used for development of anti-SARS and anti-HRV drugs and outcome discussed in details. This approach may be a useful strategy to design novel and potential anti-SARS drugs to combat these dreadful viral diseases.

Developing model-based public health policy through knowledge translation: the need for a 'Communities of Practice'

OBJECTIVES

The 2009 influenza A (H1N1) pandemic prompted public health agencies worldwide to respond in a context of substantial uncertainty. While many lessons around successful management strategies were learned during the influenza A (H1N1) pandemic, the usefulness and impact of mathematical models to optimize policy decisions in protecting public health were poorly realized. The authors explored the experiences of modellers and public health practitioners in trying to develop model-based public health policies in the management of the 2009 influenza A (H1N1) pandemic in Canada.

STUDY DESIGN

A qualitative case study design based on interviews and other textual data was used.

METHODS

Individual interviews were conducted with mathematical modellers and public health professionals from academia and government health departments during the second wave of the 2009 influenza A (H1N1) pandemic (both prior to and following the vaccine roll-out), using a convergent interviewing process. Interviews were supplemented with discussions held during three separate workshops involving representatives from these groups on the role of modelling in pandemic preparedness and responses. NVivo9™ was used to analyse interview data and associated notes.

RESULTS

Mathematical models were underutilized during the response phase of the 2009 influenza A (H1N1) pandemic, largely because many public health professionals were unaware of modelling infrastructure in Canada. Challenges were reflected in three ways: 1) the relevance of models to public health priorities; 2) the need for clear communication and plain language around modelling and its contributions and limitations; and 3) the need for increased trust and collaboration to develop strong working relationships.

CONCLUSIONS

Developing a 'Communities of Practice' between public health professionals and mathematical modellers during inter-pandemic periods based on common targeted goals, using plain language, and where relationships between individuals and organizations are developed early, could be an effective strategy to assist the process of public health policy decision-making, particularly when characterized by high levels of uncertainty.

Animal models in virus research: their utility and limitations

Viral diseases are important threats to public health worldwide. With the number of emerging viral diseases increasing the last decades, there is a growing need for appropriate animal models for virus studies. The relevance of animal models can be limited in terms of mimicking human pathophysiology. In this review, we discuss the utility of animal models for studies of influenza A viruses, HIV and SARS-CoV in light of viral emergence, assessment of infection and transmission risks, and regulatory decision making. We address their relevance and limitations. The susceptibility, immune responses, pathogenesis, and pharmacokinetics may differ between the various animal models. These complexities may thwart translating results from animal experiments to the humans. Within these constraints, animal models are very informative for studying virus immunopathology and transmission modes and for translation of virus research into clinical benefit. Insight in the limitations of the various models may facilitate further improvements of the models.

Global health justice and governance

While there is a growing body of work on moral issues and global governance in the fields of global justice and international relations, little work has connected principles of global health justice with those of global health governance for a theory of global health. Such a theory would enable analysis and evaluation of the current global health system and would ethically and empirically ground proposals for reforming it to more closely align with moral values. Global health governance has been framed as an issue of national security, human security, human rights, and global public goods. The global health governance literature is essentially untethered to a theorized framework to illuminate or evaluate governance. This article ties global health justice and ethics to principles for governing the global health realm, developing a theoretical framework for global and domestic institutions and actors.

Research preparedness paves the way to respond to pandemic H1N1 2009 influenza virus

The international community has been preparing for an influenza pandemic because of the threat posed by H5N1 avian influenza. Over the past several years, Canada has dedicated funding to boost capacity for research, and public health and health care system readiness and response in the event of a pandemic. The current H1N1/09 influenza pandemic is now testing our readiness. From a research perspective, the present commentary discusses how have we prepared, along with the research gaps. We conclude that: sources of pandemics are not always predictable; investment in the past few years has paid off in a rapid response to pandemic H1N1/09 virus in Canada; and research to meet the challenges of infectious diseases has to be done on an ongoing long-term basis, and its funding has to be flexible, available and predictable to maintain capacity and expertise. In addition, new vaccine technologies are needed to develop and produce vaccines for public health emergencies in a timely fashion.

Human genomics and preparedness for infectious threats

Public health preparedness requires effective surveillance of and rapid response to infectious disease outbreaks. Inclusion of research activities within the outbreak setting provides important opportunities to maximize limited resources, to enhance gains in scientific knowledge, and ultimately to increase levels of preparedness. With rapid advances in laboratory technologies, banking and analysis of human genomic specimens can be conducted as part of public health investigations, enabling valuable research well into the future.

Severe acute respiratory syndrome vaccine efficacy in ferrets: whole killed virus and adenovirus-vectored vaccines

Although the 2003 severe acute respiratory syndrome (SARS) outbreak was controlled, repeated transmission of SARS coronavirus (CoV) over several years makes the development of a SARS vaccine desirable. We performed a comparative evaluation of two SARS vaccines for their ability to protect against live SARS-CoV intranasal challenge in ferrets. Both the whole killed SARS-CoV vaccine (with and without alum) and adenovirus-based vectors encoding the nucleocapsid (N) and spike (S) protein induced neutralizing antibody responses and reduced viral replication and shedding in the upper respiratory tract and progression of virus to the lower respiratory tract. The vaccines also diminished haemorrhage in the thymus and reduced the severity and extent of pneumonia and damage to lung epithelium. However, despite high neutralizing antibody titres, protection was incomplete for all vaccine preparations and administration routes. Our data suggest that a combination of vaccine strategies may be required for effective protection from this pathogen. The ferret may be a good model for SARS-CoV infection because it is the only model that replicates the fever seen in human patients, as well as replicating other SARS disease features including infection by the respiratory route, clinical signs, viral replication in upper and lower respiratory tract and lung damage.

Protective immunity and susceptibility to infectious diseases: lessons from the 1918 influenza pandemic

The influenza pandemic of 1918 killed nearly 50 million people worldwide and was characterized by an atypical W-shaped mortality curve, where adults between the ages of 30–60 years fared better than younger adults aged 18–30 years. In this review, we will discuss why this influenza virus strain was so virulent and how immunological memory to the 1918 virus may have shaped the W mortality curve. We will end on the topic of the 'honeymoon' period of infectious diseases—the clinically documented period between the ages of 4–13 years during which children demonstrate less morbidity and/or mortality to infectious diseases, in general, compared with young adults.

Les enseignements du SRAS

Les virus peuvent ne pas être adaptés à la transmission interhumaine, et donc être plus faciles à maîtriser, lors de leur première émergence chez l'homme ; d'où l'importance d'une détection précoce par la surveillance des foyers épidémiques inhabituels.

Nos systèmes de santé sont très vulnérables face à des virus ayant un tropisme particulier pour le personnel hospitalier.

La collaboration internationale, tant pour les équipes d'épidémiologistes que de virologues, a été la clef du succès de la lutte contre le SRAS (Syndrome respiratoire aigu sévère).

Nous avons eu beaucoup de chance avec le SRAS : le virus était finalement peu transmissible, et seulement après le début des symptômes, permettant d'identifier et d'isoler les cas avant la période contagieuse.

L'épidémie de SRAS a servi de “répétition générale”, permettant la prise de conscience par les pouvoirs publics des enjeux posés par les pandémies d'origine infectieuse. De nouvelles épidémies, quelles qu'elles soient, sont inéluctables.

Screening and identification of severe acute respiratory syndrome-associated coronavirus-specific CTL epitopes

Severe acute respiratory syndrome (SARS) is a highly contagious and life-threatening disease that emerged in China in November 2002. A novel SARS-associated coronavirus was identified as its principal etiologic agent; however, the immunopathogenesis of SARS and the role of special CTLs in virus clearance are still largely uncharacterized. In this study, potential HLA-A*0201-restricted spike (S) and nucleocapsid protein-derived peptides were selected from an online database and screened for potential CTL epitopes by in vitro refolding and T2 cell-stabilization assays. The antigenicity of nine peptides which could refold with HLA-A*0201 molecules was assessed with an IFN-gamma ELISPOT assay to determine the capacity to stimulate CTLs from PBMCs of HLA-A2(+) SARS-recovered donors. A novel HLA-A*0201-restricted decameric epitope P15 (S411-420, KLPDDFMGCV) derived from the S protein was identified and found to localize within the angiotensin-converting enzyme 2 receptor-binding region of the S1 domain. P15 could significantly enhance the expression of HLA-A*0201 molecules on the T2 cell surface, stimulate IFN-gamma-producing CTLs from the PBMCs of former SARS patients, and induce specific CTLs from P15-immunized HLA-A2.1 transgenic mice in vivo. Furthermore, significant P15-specific CTLs were induced from HLA-A2.1-transgenic mice immunized by a DNA vaccine encoding the S protein; suggesting that P15 was a naturally processed epitope. Thus, P15 may be a novel SARS-associated coronavirus-specific CTL epitope and a potential target for characterization of virus control mechanisms and evaluation of candidate SARS vaccines.

La recherche sur les maladies infectieuses en Colombie-Britannique: Besoins, lacunes et occasions dans l’optique de la santé publique et de la santé des populations

Background

A review of infectious disease research activity and capacity was performed in British Columbia and linked to a process for identifying needs, gaps and opportunities from a public health perspective.

Methods

The study was organized in three phases: an environmental scan to describe current research activity in BC; a consultation to identify needs, gaps and opportunities with those conducting research (key informants) and the end users of research results (stakeholders); and a prioritization of the research needs emerging from the consultation.

Results

Analysis and synthesis of the consultation data resulted in the identification of nine research themes, which were prioritized in the following order: efficacy and cost-benefit, disease patterns, emerging infectious disease, immunology and vaccines, disease-specific research, health promotion and communications, safe food and water, knowledge translation research and genomics. Six capacity-building themes were also identified: attraction and retention, education and training, collaboration and networks, funding, dissemination of findings, and public health input, surveillance, informatics and databases.

Interpretation

The findings were helpful in developing a multi-disciplinary, multi-level infectious disease research agenda linking researchers in universities, hospitals and public health institutions with practitioners and policy-makers in British Columbia’s public health system. The approach is both feasible and important to undertake at the national level.

Electronic Supplementary Material

Supplementary material is available for this article at 10.1007/BF03405394 and is accessible for authorized users.

Pandemic influenza threat and preparedness

New vaccine technologies and antiviral drugs are needed to prepare for the next influenza pandemic.

The threat of a human influenza pandemic has greatly increased over the past several years with the emergence of highly virulent avian influenza viruses, notably H5N1 viruses, which have infected humans in several Asian and European countries. Previous influenza pandemics have arrived with little or no warning, but the current widespread circulation of H5N1 viruses among avian populations and their potential for increased transmission to humans and other mammalian species may afford us an unprecedented opportunity to prepare for the next pandemic threat. The US Department of Health and Human Services is coordinating a national strategy to respond to an influenza pandemic that involves multiple agencies, including the Centers for Disease Control and Prevention, the Food and Drug Administration, and the National Institutes of Health (NIH). Within NIH, the National Institute of Allergy and Infectious Diseases (NIAID) conducts basic and clinical research to develop new vaccine technologies and antiviral drugs against influenza viruses. We describe recent research progress in preparing for pandemic influenza.

Comparative evaluation of two severe acute respiratory syndrome (SARS) vaccine candidates in mice challenged with SARS coronavirus

Two different severe acute respiratory syndrome (SARS) vaccine strategies were evaluated for their ability to protect against live SARS coronavirus (CoV) challenge in a murine model of infection. A whole killed (inactivated by beta-propiolactone) SARS-CoV vaccine and a combination of two adenovirus-based vectors, one expressing the nucleocapsid (N) and the other expressing the spike (S) protein (collectively designated Ad S/N), were evaluated for the induction of serum neutralizing antibodies and cellular immune responses and their ability to protect against pulmonary SARS-CoV replication. The whole killed virus (WKV) vaccine given subcutaneously to 129S6/SvEv mice was more effective than the Ad S/N vaccine administered either intranasally or intramuscularly in inhibiting SARS-CoV replication in the murine respiratory tract. This protective ability of the WKV vaccine correlated with the induction of high serum neutralizing-antibody titres, but not with cellular immune responses as measured by gamma interferon secretion by mouse splenocytes. Titres of serum neutralizing antibodies induced by the Ad S/N vaccine administered intranasally or intramuscularly were significantly lower than those induced by the WKV vaccine. However, Ad S/N administered intranasally, but not intramuscularly, significantly limited SARS-CoV replication in the lungs. Among the vaccine groups, SARS-CoV-specific IgA was found only in the sera of mice immunized intranasally with Ad S/N, suggesting that mucosal immunity may play a role in protection for the intranasal Ad S/N delivery system. Finally, the sera of vaccinated mice contained antibodies to S, further suggesting a role for this protein in conferring protective immunity against SARS-CoV infection.

Deciphering the biosynthetic codes for the potent anti-SARS-CoV cyclodepsipeptide valinomycin in Streptomyces tsusimaensis ATCC 15141

Valinomycin was recently reported to be the most potent agent against severe acute respiratory-syndrome coronavirus (SARS-CoV) in infected Vero E6 cells. Aimed at generating analogues by metabolic engineering, the valinomycin biosynthetic gene cluster has been cloned from Streptomyces tsusimaensis ATCC 15141. Targeted disruption of a nonribosomal peptide synthetase (NRPS) gene abolishes valinomycin production, which confirms its predicted nonribosomal-peptide origin. Sequence analysis of the NRPS system reveals four distinctive modules, two of which contain unusual domain organizations that are presumably involved in the generation of biosynthetic precursors D-alpha-hydroxyisovaleric acid and L-lactic acid. The respective adenylation domains in these two modules contain novel substrate-specificity-conferring codes that might specify for a class of hydroxyl acids for the biosynthesis of the depsipeptide natural products.

Severe acute respiratory syndrome: responses of the healthcare system to a global epidemic

PURPOSE OF REVIEW

To evaluate recent developments in the response of the healthcare system to the threat of severe acute respiratory syndrome in the context of the Toronto experience.

RECENT FINDINGS

The severe acute respiratory syndrome outbreak affected over 8000 people killing 774 by July 2003. It particularly affected those providing health care. The initial response of the healthcare system was to use infection control techniques to prevent transmission to staff and patients. This had a dramatic impact on healthcare provision for non-severe acute respiratory syndrome patients during this period.

SUMMARY

The ongoing response to severe acute respiratory syndrome is continued effective infection control education, development of local and global policies for reacting to a severe acute respiratory syndrome-like outbreak in the future, and continued work on a vaccine for severe acute respiratory syndrome.

Poxvirus tropism

Despite the success of the WHO-led smallpox eradication programme a quarter of a century ago, there remains considerable fear that variola virus, or other related pathogenic poxviruses such as monkeypox, could re-emerge and spread disease in the human population. Even today, we are still mostly ignorant about why most poxvirus infections of vertebrate hosts show strict species specificity, or how zoonotic poxvirus infections occur when poxviruses occasionally leap into novel host species. Poxvirus tropism at the cellular level seems to be regulated by intracellular events downstream of virus binding and entry, rather than at the level of specific host receptors as is the case for many other viruses. This review summarizes our current understanding of poxvirus tropism and host range, and discusses the prospects of exploiting host-restricted poxvirus vectors for vaccines, gene therapy or tissue-targeted oncolytic viral therapies for the treatment of human cancers.

Poxvirus host range varies markedly ? some viruses, such as variola and molluscum contagiosum virus (both of which are human-specific), exhibit strict species tropism, whereas others such as cowpox virus are able to infect multiple host species.

Members of four of the eight genera of chordopoxviruses can zoonotically infect man. For example, monkeypox virus can cause severe smallpox-like disease in humans that clinically resembles variola virus.

The species tropism that is exhibited by many poxviruses in terms of causing disease is frequently quite different from the range of cultured cells that can be infected by these viruses.

Specific host-cell receptors do not mediate the distinction between cells that are permissive as opposed to non-permissive for poxvirus infection. Rather, restrictive host cells fail to support the full replication cycle of the infecting poxvirus at a point downstream of binding and entry.

A variety of poxviral host-range genes have been identified that contribute to the control of permissive versus non-permissive infection of cultured mammalian cells. The gene products of these host-range genes regulate the ability of the virus to complete its cytoplasmic replication cycle.

The development of host-restricted vaccines, like modified vaccinia Ankara (MVA), that do not replicate in humans but that retain potent immunogenicity, will provide safer platforms for recombinant vaccines.

Another advance has been the development of poxvirus-based oncolytic vectors that replicate preferentially in human tumour cells.