Research on Viruses

9 Key excerpts on "Research on Viruses"

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  Viral and Rickettsial Infections of Animals

  • A. O. Betts, C. J. York, A. O. Betts, C. J. York(Authors)
  • 2013(Publication Date)
  • Academic Press

    (Publisher)

  CHAPTER 1 General Nature of Viruses SIR CHRISTOPHER ANDREWES I. Introduction 1 II. History of Virology 2 III. Definition of a Virus 4 IV. Origin of Viruses 5 V. Replication of Viruses 6 VI. Pathogenesis 7 VII. Basis of Virus Classification 9 VIII. Chemical Composition 10 IX. Morphology 11 X. RNA Viruses 13 A. Picornaviruses 13 B. Reoviruses 14 C. Arboviruses 14 D. Myxoviruses 15 XI. DNA Viruses 16 A. Adenoviruses 16 B. Papovaviruses 16 C. Herpesviruses 16 D. Poxviruses 17 E. Parvoviruses 17 XII. Other Agents 17 XIII. Immunity 18 XIV. Virus Ecology , 19 XV. Control of Virus Infections 23 References 24 I. I N T R O D U C T I O N Within recent years virology, the study of viruses, has attained the dignity of a branch of biology in its own right. No longer are viruses considered to be merely small parasitic agents, discussion of which can be tacked on as an addendum to an extended account of bacteria. Viruses, it is now realized, constitute a separate category of living things—for they have almost all the attributes of life—having a mode of replication that sets them apart from larger beings. The growth of virology has been greatly helped by the techniques of experimental pathology, histopathology, electron microscopy, genetics, and biochemistry. Lately virology has begun to repay this debt: study of the details of virus replication has been throwing light 1 2 Sir Christopher Andrewes on intimate biological processes of enormous interest to other branches of biology. Virology, in its more academic aspects, is thus in the forefront of exciting new advances in knowledge. In practical ways, too, it is contributing greatly. The discovery of new methods of cultivating viruses and of modifying their properties is opening up new possibilities of specific protection against virus infections of man and domestic animals. Perhaps even more important for this purpose is the increased knowledge of the virus ecology.

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  Studies in Viral Ecology, Volume 2

  Animal Host Systems

  • Christon J. Hurst(Author)
  • 2011(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  The purpose of this book is to define the ecology of viruses and, in so doing, try to approach the question of what life is like from a “virocentric” (as opposed to our normal anthropocentric) point of view. Ecology is defined as the branch of science which addresses the relationships between an organism of interest and the other organisms with which it interacts, the interactions between the organism of interest and its environment, and the geographic distribution of the organism of interest. The objective of this chapter is to introduce the main concepts of viral ecology. The remaining chapters of this book set, Studies in Viral Ecology volumes 1 and 2, will then address those concepts in greater detail and illustrate the way in which those concepts apply to various host systems.

  1.1.1 What is a Virus?

  Viruses are biological entities which possess a genome composed of either ribonucleic acid (RNA) or deoxyribonucleic acid (DNA). Viruses are infectious agents which do not possess a cellular structure of their own, and hence are “acellular infectious agents”. Furthermore, the viruses are obligate intracellular parasites, meaning that they live (if that can be said of viruses) and replicate within living host cells at the expense of those host cells. Viruses accomplish their replication by usurping control of the host cell's biomolecular machinery. Those which are termed “classical viruses” will form a physical structure termed a “virion” that consists of their RNA or DNA genome surrounded by a layer of proteins (termed “capsid proteins”) which form a shell or “capsid” that protects the genomic material. Together, this capsid structure and its enclosed genomic material are often referred to as being a “nucleocapsid”. The genetic coding for the capsid proteins generally is carried by the viral genome. Most of the presently known virus types code for their own capsid proteins. However, there are some viruses which are termed as being “satellite viruses”. The satellite viruses encapsidate with proteins that are coded for by the genome of another virus which coinfects (simultaneously infects) that same host cell. That virus which loans its help by giving its capsid proteins to the satellite virus is termed as being a “helper virus”. The capsid or nucleocapsid is, in the case of some groups of viruses, surrounded in turn by one or more concentric lipid bilayer membranes which are obtained from the host cell. There exist many other types of acellular infectious agents which have commonalities with the classical viruses in terms of their ecology. Two of these other types of acellular infectious agents, the viroids and prions, are included in this book set and are addressed within their own respective chapters (Volume 1, chapters 10 and 12). Viroids are biological entities akin to the classical viruses and likewise can replicate only within host cells. The viroids possess RNA genomes but lack capsid proteins. The agents which we refer to as prions were once considered to be nonclassical viruses. However, we now know that the prions appear to be aberrant cellular protein products which, at least in the case of those afflicting mammals, have acquired the potential to be environmentally transmitted. The natural environmental acquisition of a prion infection occurs when a susceptible host mammal ingests the bodily material of an infected host mammal. The reproduction of prions is not a replication, but rather seems to result from a conversion of a normal host protein into an abnormal form (Volume 1, chapter 10). The Acidianus two-tailed virus, currently the sole member of the viral family Bicaudaviridae, undergoes a morphological maturation following its release from host cells and this is unique among all of the biological entities now considered to be viruses suggesting that this species may represent the initial discovery of an entirely new category of biological entities.

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  Viruses

  Molecular Biology, Host Interactions, and Applications to Biotechnology

  • Paula Tennant, Gustavo Fermin, Jerome E. Foster(Authors)
  • 2018(Publication Date)
  • Academic Press

    (Publisher)

  Chapter 1

  Introduction

  A Short History of Virology

  Gustavo Fermin1 and Paula Tennant2 ,    

  1 Universidad de Los Andes, Mérida, Venezuela

  ,    

  2 The University of the West Indies, Mona, Jamaica

  Summary

  Viruses have played a major role in 20th-century Biology and continue to serve as ideal tools for the dissection of the most intricate life processes. Initially, much of the early studies were focused on deciphering the nature of these unique entities, their interactions with hosts and pathogenesis. Much of what has been learnt proved applicable to understanding of the nature and structure of genes, how genes and genomes operate and how genetic information is replicated over generations. Scientists have since rapidly harnessed the biology of the viruses for the development of new tools and applications in molecular biology, medicine, and agriculture. It is interesting that the very traits employed by viruses to establish infection and induce disease in their hosts are now being manipulated for the production of vectors and biologics that are safe and efficacious. Indeed the convergence of biology, genetics, biochemistry, and physics has propelled the development of molecular biology and advanced the field of Virology, culminating with the realization that viruses are ancient, the most diverse and uncharacterized components of the major ecosystems on Earth, that might also have played a major part in the emergence and consequent structure of modern cellular life.

  Keywords

  Virus definition; history of virology; filterable agents; viral symbionts; viruses and biotechnology

  [Physicists] feel that the field of bacterial viruses is a fine playground for serious children who ask ambitious questions. Max Delbrück

  As masterly expressed by the French microbiologist André Lwoff in his Nobel Lecture of 1965, “

  For the philosopher, order is the entirety of repetitions manifested, in the form of types or of laws, by perceived objects. Order is an intelligible relation. For the biologist, order is a sequence in space and time. However, according to Plato, all things arise out of their opposites. Order was born of the original disorder, and the long evolution responsible for the present biological order necessarily had to engender disorder. An organism is a molecular society, and biological order is a kind of social order. Social order is opposed to revolution, which is an abrupt change of order, and to anarchy, which is the absence of order. I am presenting here today both revolution and anarchy, for which I am fortunately not the only one responsible. However, anarchy cannot survive and prosper except in an ordered society, and revolution becomes sooner or later the new order. Viruses have not failed to follow the general law. They are strict parasites which, born of disorder, have created a very remarkable new order to ensure their own perpetuation.

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  Molecular Detection of Human Viral Pathogens

  • Dongyou Liu(Author)
  • 2016(Publication Date)
  • CRC Press

    (Publisher)

  1 1.1 PREAMBLE Viruses (singular, virus, meaning toxin or poison in Latin) are noncellular, submicroscopic infectious agents that can only replicate inside the cells of another organism. Measuring from 20 to 400 nm (or 10 –8 –10 –6 mm) in diameter, viruses are 10–100 times smaller than prokaryotes (10 –7 –10 –4 mm), 1000 times smaller than eukaryotes (10 –5 –10 –3 mm). Since the majority of the viruses (including those described in the early reports) are small enough to pass through conventional sterilizing filters (0.2 μ m), viruses were initially described as filterable agents. Morphologically, viral particles (or viri-ons) vary from simple helical and icosahedral forms, to more complex structures with tails or an envelope. The envelope is composed of lipids and proteins, which may display as spikes in some viruses giving distinct appearance. A major role of the envelope is to protect a virus from adverse external con-ditions. Underneath lies at least one protein surrounded by a protein shell (known as capsid). The protein capsid guards the nucleic acid within [either a single- or double-stranded nucleic acid made up of ribonucleic acid (RNA) or deoxyri-bonucleic acid (DNA)] while other proteins (enzymes) enable the virus to enter its appropriate host cells, to reproduce by taking advantage of host cellular machinery, and to evolve within infected cells by natural selection [1]. Virology is a branch of biological sciences that is devoted to the studies of viruses including their identification, biology, ecology, epidemiology, pathogenesis, genetics, immunology, control, and prevention, and so on. Correct identification of the viruses to species and/or subspecies level is a prerequisite for the study of virology. Without knowledge of virus iden-tity, attempts to investigate other aspects of a particular virus may be flawed.

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  Microbial Forensics

  • Bruce Budowle, Steven E. Schutzer, Roger G. Breeze(Authors)
  • 2005(Publication Date)
  • Academic Press

    (Publisher)

  Viruses are ubiquitous in nature. They prey on all forms of life from archaea and eubacteria to fungi, plants, and animals. It has been estimated that viruses that target sea-dwelling organisms, such as algae, turn over half of the world’s biomass each day. As such, viruses are an important part of the ecological balance on earth. Of the vast collection of ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) viruses, research has focused on the tiny fraction that cause disease in humans, domestic animals, and crops. Modern virology, coupled with public health initiatives, has seen many triumphs including the development of effective vaccines against yellow fever, poliomyelitis, smallpox, mumps, measles, rubella, hepatitis A and B, and papillomavirus-associated cervical cancer. The global eradication of smallpox and poliovirus as well as the prediction and successful prophylactic vaccination against influenza represent tremendous gains for public health. Antiviral therapy against human immunodeficiency virus (HIV) and some herpesviruses, as well as rapid detection and containment of emerging viruses such as the severe acute respiratory syndrome coronavirus (SARS-CoV) illustrate the successful application of viral research programs as well as the need for ongoing efforts focused on rapid identification and elucidation of viral distribution, kinetics, and pathogenesis. With the growth of knowledge about replication, transmission, and disease, viruses have also taken the stage as possible biowarfare, bioterrorist, and criminal agents.

  In our unpredictable world, viral diagnostics and forensics are becoming increasingly important and sophisticated. The purpose of this chapter is to introduce basic concepts in virology and to provide several examples of how current technology has been used to identify and track viral pathogens. The first part of the chapter discusses virus structure, replication strategies, classification, and evolution. The second part highlights the varied modes of transmission, infection, and disease manifestations as they relate to the different diagnostic methods for virus identification. We follow this with examples of how emerging viruses were identified and tracked (Sin Nombre, Nipah, West Nile, SARS coronavirus, and monkeypox). With regard to viral forensics, the Schmidt case is a fascinating example illustrating how the study of RNA virus evolution and relatedness was used in a criminal investigation. Finally, we provide a few snapshot views into new technologies that allow the creation of manmade or “engineered” viruses, some exciting new frontiers in viral diagnostics, and a few thoughts on the future of virology.

  WHAT IS A VIRUS? BASIC VIROLOGY

  VIRUS ANATOMY

  Viruses are extremely simple “life” forms without metabolic capacity, organelles, translational machinery, or autonomous replicative potential; the essential elements of a virus are consequently minimal. Virus particles are either enveloped or nonenveloped. Enveloped viruses contain one or more envelope glycoproteins embedded in a lipid bilayer that is acquired by budding through host cell membranes. Nonenveloped viruses are made up of a tight protein shell. In both kinds of viral particles, the envelope or protein shell serves to protect the viral genome from the hazardous extracellular environment, since without such protection, the fragile nucleic acid genome would be vulnerable to physical, chemical, and/or enzymatic destruction. Surface proteins also harbor functions required for virus entry into host cells. Inside the virus particle, the viral genome is associated with one or more proteins to form a complex usually referred to as the nucleocapsid. In addition to nucleic acid binding proteins, some viruses also carry enzymes required to initiate replication (like polymerases). Although not all virus particles are highly structured, two kinds of symmetry are common. Helical symmetry is reflected by the arrangement of the protein subunits in a “spring-like” or stacked lock-washer fashion, whereas icosahedral symmetry comprises 20 triangular faces that form the surface of a sphere. In the simplest icosahedral capsid, one protein subunit is at each triangular point of the 20 faces, requiring 60 total subunits.

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  Epidemiology

  Current Perspectives on Research and Practice

  • Nuno Lunet(Author)
  • 2012(Publication Date)
  • IntechOpen

    (Publisher)

  7 Viral Evolutionary Ecology: Conceptual Basis of a New Scientific Approach for Understanding Viral Emergence J. Usme-Ciro 1,2* , R. Hoyos-López 1,2,3* and J.C. Gallego-Gómez 1,2† 1 Viral Vector Core and Gene Therapy (Neurosciences Group of Antioquia), Faculty of Medicine, University of Antioquia, Medellin, 2 Translational and Molecular Medicine Group, Faculty of Medicine, University of Antioquia, Medellin, 3 Molecular Systematics Group, National University of Colombia, Medellin, Colombia 1. Introduction Kilbourne first applied the term of Molecular Epidemiology in 1973 in a paper on influenza [1], since then the term has been extensively used for other diseases caused by viruses [2-4], bacteria [5-7], parasites [8-10] and even non-infectious diseases [11, 12]. Molecular epidemiology was subsequently accompanied by a more integrative definition of eco-epidemiology [13, 14] with little impact in scientific literature. Although molecular epidemiology and eco-epidemiology are important in the understanding of disease and disease emergence [15, 16], we postulate here that the medical science community needs to consider a new conceptual approach to epidemiological studies of emerging infectious diseases (e.g. viral diseases). Emerging viral diseases are mainly caused by RNA viruses whose transmission cycles involve the ecological interaction with several actors and the evolutionary responses through time. The new approach called Viral Evolutionary Ecology (VEE) [17, 18] combined with epidemiology will help us to better explain many emerging viral diseases by encompassing the complex interface between such factors as genetic structure, evolutionary biology and ecology of pathogens [19], and environmental aspects such as biodiversity, society, and human impact on natural ecosystems, all of them closely interplaying in ways often as yet unknown [20, 21].

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  Studies in Viral Ecology, Volume 1

  Microbial and Botanical Host Systems

  • Christon J. Hurst(Author)
  • 2011(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  There is much debate on the precise status of viruses: Can they be considered alive? Do they have a place on the tree of life? How long have they existed? Do they predate the first living cells? Should the different types of viruses really be considered under the same “virus” banner? Regardless of the answer to these questions, it is undeniable that, whatever their status, viruses have had and continue to have a profound influence on the composition and function of the planet's living biota (Villarreal and Witzany, 2010). By their very definition, viruses, as obligate intracellular parasites, manipulate and selfishly hijack their host organisms purely for their own survival. This in itself leads to an interesting paradox: any virus that is too successful will ultimately go extinct since it will have no host left to infect. This paradox has effectively led to the field of viral ecology whereby viruses and their hosts are in a continuous, yet hugely dynamic and intricate relationship. These complex relationships between hosts and their viruses are at least as old as life on Earth itself. Clearly, the roots run deep in viral family trees and their interaction with their host(s) will run just as deep. The diverse nature of viral genomic material betrays their multiple and ancient ancestral origins (i.e., single- versus double-stranded, RNA versus DNA genomes). This polyphyletic group consists of many distinct lineages with independent origins that are all grouped under the “virus” banner by virtue of their lifestyle. Thus, a comprehensive tome on the topic of virus–host coevolution would need to encompass such a wide range of systems of such varying nature that it would justify at least a book all to itself, not merely a chapter! For this reason, I will attempt to provide an overview of the issues and processes associated with virus–host coevolution, using specific examples wherever necessary to illustrate points, but retaining a more generalist approach to the topic. Working with viruses has taught us many things in the life sciences, chiefly expect the unexpected and that there are exceptions to every rule. With this in mind, I invite the reader to read on with an open mind, never take anything at face value, question all ideas and hypotheses herein, but most importantly retain your wonder and amazement at the sheer audacity and beauty of this truly wonderful group of selfish and uncompromising biological replicators!

  4.2 The Obsession with Death: Mortality from a Viral Perspective

  From our human-centric perspective, viruses are associated with illness, disease, and often death. Yet, from a viral perspective every infection ultimately ends in death: either of the host cell or of the virus itself. A key difference between multicellular (the so-called “complex”) organisms and their unicellular counterparts is that a successful infection in a multicellular organism does not usually lead to the death of the entire organism. This applies to hosts at all levels of complexity from fungi to mammals and trees. A successful infection in a single-cell organism will always lead to an untimely death of that cell. A successful infection in a multicellular organism will lead to the death of some cells, but usually leave the remainder of the host intact. Indeed, despite some incredibly virulent viruses ultimately causing the total death of their multicellular hosts (and not just the subpopulation of cells they actually infect), rarely does the physical loss of the infected cells cause death: the mortality is usually a product of “particularly” nasty viral dispersal mechanisms such as hemorrhage and diarrhea that are induced to aid the transfer of the virus to new hosts. A multicellular host offers a unique environment to a virus: a homogeneous population of cells within a contained system. Although a classic viral infection (e.g., by the influenza viruses, members of the family Orthomyxoviridae) is usually regarded by the patient as a single infection, the symptoms observed are actually a product of thousands of cells being infected. If a virus can successfully infect one type of cell within an organism, there is usually no reason for viral progeny to subsequently infect every other identical cell type within the organism. Clearly, this would have disastrous consequences, and this is why multicellular organisms have evolved defensive strategies (such as immune systems) against such an occurrence. These systems can actively seek out and destroy both virus and infected cells to stop the infection from spreading out of control. When viruses attack the cells involved in these processes, such as in the case of HIV infection (human immunodeficiency virus 1 and 2, both of the family Retroviridae, genus Lentivirus ), the results are catastrophic to the host concerned. Crucially though, it is not HIV infection per se

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  A New History of Vaccines for Infectious Diseases

  Immunization - Chance and Necessity

  • Anthony R. Rees, Anthony Robert Rees(Authors)
  • 2022(Publication Date)
  • Academic Press

    (Publisher)

  Chapter 8: Viruses: epic challenges for vaccinology

  Abstract

  This chapter discussed theories on the origin of viruses as primitive pseudo-organisms, requiring living cells for their existence and propagation; classes of DNA and RNA viruses, their properties, and their potential for increased infection of the human population during global warming; the relationship between animal hosts and humans and the mechanisms by which humans become susceptible to animal viruses. The discovery and characterization of viruses, initially in plants, and the long road to understanding that they are nonliving entities requiring host cells for their survival. Also, the contribution of bacterial virus discovery, the bacteriophages, and their short but innovative foray into the treatment arena for bacterial infections; the eventual understanding of how viruses work from biochemical and three-dimensional structural studies, the latter made possible by the development of electron microscopy in the 1940s are described. Controversy on what exactly the virus genome consisted of, resolved with the eventual realization that it was DNA or RNA. An introduction to how viruses are transmitted, and the relationship between a virus and its host from basic epidemiology has been discussed. The impact of anti-viral vaccines on virus “fitness” and how a virus counters vaccine effects leading in many but not all cases to its eventual decline.

  Keywords

  Bacteriophages; DNA and RNA viruses; Electron microscopy and viruses; Origin of viruses; Virus hosts; Virus vaccines, epidemiology and viral diseases; Viruses

  The origin of viruses

  There are two hypotheses, broadly speaking, on the emergence of viruses. The first suggests that viruses existed before the emergence of cellular life (first came protocells as primitive cellular entities) which then evolved into prokaryotes (lacking a nucleus) and eukaryotes (with a nucleus). The second hypothesis has two possible paths. The first path has viruses as pieces of cellular genomes that essentially escaped from primitive cells, robbing them of genes en route , and emerged with some of the functions necessary for replication but still requiring host cells to provide the missing pieces for their complete reproduction. In the second path, viruses emerged as a result of the breakdown and loss of key functions in cellular organisms until the resulting partially decimated cellular entity had lost the ability to self-replicate but continued to survive as a virus. The recent discovery of giant viruses able to infect the single-cell ameba organism and which appear to be genetically dissimilar to all known cellular or viral genomes, including the amoebal genome itself, is thought by some authors to be evidence of this second mechanism.

  1

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  Quantitative Viral Ecology

  Dynamics of Viruses and Their Microbial Hosts

  • Joshua S. Weitz(Author)
  • 2016(Publication Date)
  • Princeton University Press

    (Publisher)

  PART I VIROLOGY: AN ECOLOGICAL PERSPECTIVE Passage contains an image CHAPTER ONE What Is a Virus? 1.1  WHAT IS A VIRUS? Efforts to define a virus inevitably raise the question of exceptions. Nonetheless, a definition or two can help guide us in identifying what is common to all viruses. Merriam-Webster’s Online Dictionary: an extremely small living thing that causes a disease and that spreads from one person or animal to another. Introduction to Modern Virology: submicroscopic, parasitic particles of genetic material contained in a protein coat (Dimmock et al. 2007).

  These two definitions are useful, as they reflect the difference in perception as well as current understanding of what a virus is. In that respect, the roots of the term virus are also revealing:

  Oxford English Dictionary: late Middle English (denoting the venom of a snake): from Latin, literally “slimy liquid, poison.”

  Irrespective of source, it would seem that viruses have a bad reputation. Informal surveys tend to yield similar results. For example, when I ask undergraduates to name a virus, some of the most common answers are HIV, influenza, Ebola, chickenpox, herpes, rabies—not a friendly one in the bunch. The answers represent a typical conflation of the disease with the virus. Nonetheless, this conflation is not entirely inappropriate, as viruses do often negatively affect their hosts, whether by causing disease in humans, plants, or animals or killing their microbial hosts.

  In fact, one version of the history of viruses begins more or less as follows (Dimmock et al. 2007)—with smallpox. Smallpox is one of the most vicious of diseases, with historical estimates of mortality rates on the order of 30%. Smallpox is caused by a virus, so-called variola, from the Latin varius or varus

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