Biological Sciences
Pathogenic Viruses
Pathogenic viruses are infectious agents that cause disease in their host organisms. They can infect a wide range of organisms, including humans, animals, and plants. Pathogenic viruses are responsible for a variety of illnesses, from the common cold to more severe diseases such as influenza, HIV/AIDS, and COVID-19.
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10 Key excerpts on "Pathogenic Viruses"
eBook - PDF- Edward K. Wagner, Martinez J. Hewlett, David C. Bloom, David Camerini(Authors)
- 2009(Publication Date)
- Wiley-Blackwell(Publisher)
This is, of course, in addition to its importance to the scientific and medical communities. The study of effects of viral infection on the host is broadly defined as the study of viral pathogenesis. The sum total of the virus-encoded functions that contribute to virus propaga- CHAPTER 1 INTRODUCTION – THE IMPACT OF VIRUSES ON OUR VIEW OF LIFE 5 tion in the infected cell, in the host organism, and in the population is defined as pathogenicity of that virus. This term essentially describes the genetic ability of members of a given specific virus population (which can be considered to be genetically more or less equivalent) to cause a disease and spread through (propagate in) a population. Thus, a major factor in the patho- genicity of a given virus is its genetic makeup or genotype. The basis for severity of the symptoms of a viral disease in an organism or a population is complex. It results from an intricate combination of expression of the viral genes controlling pathogenicity, physiological response of the infected individual to these pathogenic determi- nants, and response of the population to the presence of the virus propagating in it. Taken together, these factors determine or define the virulence of the virus and the disease it causes. A basic factor contributing to virulence is the interaction among specific viral genes and the genetically encoded defenses of the infected individual. It is important to understand, however, that virulence is also affected by the general health and genetic makeup of the infected popula- tion, and in humans, by the societal and economic factors that affect the nature and extent of the response to the infection. The distinction and gradation of meanings between the terms pathogenesis and virulence can be understood by considering the manifold factors involved in disease severity and spread exhibited in a human population subjected to infection with a disease-causing virus.
eBook - PDFRespiratory Disease and Infection
A New Insight
- Bassam H. Mahboub(Author)
- 2013(Publication Date)
- IntechOpen(Publisher)
Thus, the immunopathology vi‐ ral respiratory infection is a frequent consequence of the immune response against many of respiratory pathogens. Furthermore, if the infection is established, the factors or viral viru‐ lence determinants and physiological conditions of the host cell will determine which direc‐ tion the infection will take. A virus is pathogenic when it is able to infect and cause disease in a host, while it is virulent when it causes more severe disease than another virus of a dif‐ ferent strain, although both remain pathogens. Each virus can cause different cytopathic ef‐ fects in the host cell, which may lead to several symptoms and disease. In addition, developing a disease reflects the existence of an abnormality of the host, either structural or functional, induced by the invading virus. © 2013 Manjarrez-Zavala et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 2. Viral pathogenesis The term “pathogenesis” refers to the processes or mechanisms to generate an injury or ill‐ ness, in this case induced by a viral infection. The results of a viral infection depend on fac‐ tors related to the nature of the virus, the host and the environment. They include: number of infectious particles, the way to reach the target tissue, the rate of multiplication, the effect of virus on cell functions and the host’s immune response.
eBook - PDF- Dave Wessner, Christine Dupont, Trevor Charles, Josh Neufeld(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
A few selected viruses and their associated diseases will be examined in depth to illustrate our main points. Although we will focus primarily on viruses that infect mammals, we also will note the pathogenesis of viruses that infect plants and viruses that infect bacteria. We will conclude by investigating the evolution of viral pathogenesis. As we explore these topics, we will address the following questions: • How do viruses cause disease? (22.1) • How do viruses interact with host cells? (22.2) • How do some viruses cause cancer? (22.3) • How do some viruses become highly virulent? (22.4) 22.1 Recurring Themes in Viral Pathogenesis • How do viruses cause disease? As we mentioned previously, all viruses must replicate within host cells. This viral replication leads to some damage of the host. The type and extent of damage, however, can differ dra- matically. So, what exactly do we mean by viral pathogenesis a. Productive infection: Permissive cell Host cell Infection Replication of viral genome, transcription, and translation Assembly Release of new infectious viral particles b. Abortive infection: Non-permissive cell Host cell Infection No viral replication FIGURE 22.1 Productive versus abortive infections Infection refers to the entry of a viral genome into a cell. a. If new viral particles are produced, then the infection is productive and the infected cell is referred to as permissive. b. If no new viral particles are produced, then the infection is abortive and the infected cell is referred to as non-permissive. 22.1 Recurring Themes in Viral Pathogenesis 785 stops. Some event then may cause the production of new viral particles to resume, a process referred to as reactivation. Probably the best‐studied mammalian viruses that exhibit latency are the herpesviruses. Members of the Herpesviridae family (Table 22.1) cause a variety of diseases in humans (Figure 22.3).
eBook - PDF- Nina Parker, Mark Schneegurt, Anh-Hue Thi Tu, Brian M. Forster, Philip Lister(Authors)
- 2016(Publication Date)
- Openstax(Publisher)
The viruses that infect bacteria are called bacteriophages, or simply phages. The word phage comes from the Greek word for devour. Other viruses are just identified by their host group, such as animal or plant viruses. Once a cell is infected, the effects of the virus can vary depending on the type of virus. Chapter 6 | Acellular Pathogens 243 Viruses may cause abnormal growth of the cell or cell death, alter the cell’s genome, or cause little noticeable effect in the cell. Viruses can be transmitted through direct contact, indirect contact with fomites, or through a vector: an animal that transmits a pathogen from one host to another. Arthropods such as mosquitoes, ticks, and flies, are typical vectors for viral diseases, and they may act as mechanical vectors or biological vectors. Mechanical transmission occurs when the arthropod carries a viral pathogen on the outside of its body and transmits it to a new host by physical contact. Biological transmission occurs when the arthropod carries the viral pathogen inside its body and transmits it to the new host through biting. In humans, a wide variety of viruses are capable of causing various infections and diseases. Some of the deadliest emerging pathogens in humans are viruses, yet we have few treatments or drugs to deal with viral infections, making them difficult to eradicate. Viruses that can be transmitted from an animal host to a human host can cause zoonoses. For example, the avian influenza virus originates in birds, but can cause disease in humans. Reverse zoonoses are caused by infection of an animal by a virus that originated in a human. Fighting Bacteria with Viruses The emergence of superbugs, or multidrug resistant bacteria, has become a major challenge for pharmaceutical companies and a serious health-care problem.
eBook - PDF- Carlos Tello Lacal(Author)
- 2019(Publication Date)
- Delve Publishing(Publisher)
7.1.1 Cellular Pathogenesis Following infection, a virulent virus may cause direct cell death and disease. Usually, viruses are devoid of mechanisms to manufacture their viral structural constituents and the genome. They therefore hijack the host machinery and use it for replication of the viral genome and the manufacture of its structural components. This dependence results in the impaired functioning of the cells. They are deprived of energy, and thus, they cannot manufacture their structural components thus leading to damage, disease, and even death. Cellular pathogenesis proceeds in stages that at long last results to cellular diseases. The parasitic replication of the viral genome and the host-dependent manufacture of the viral components are implicated for disease development in the cell. The virus has developed genetic elements responsible for virulence which the virus uses to engineer competition for Principles of Molecular Virology 174 the cellular resources, for example, the ribosomes, hence corrupting the cellular functions. 7.1.2 Tissue Tropism This refers to the expression of specific attraction and adaptation of viruses to specific tissues in the body. This is due to the presence of the favorable characteristics in the cells of the tissue that support the survival of that particular virus such as weak host defenses, favorable local temperature and pH, less physical barriers, and selective susceptibility of the cells. Because of this phenomenon, particular viruses are likely to be found affecting certain specific tissues, for example, rhinoviruses are known to infect the upper respiratory tract that has the right conditions for their replication, that is, high oxygen supply, low temperature, and pH. Enteroviruses commonly affect the small intestines. They are adapted to this environment due to their ability to resist insult from bile acids and digestive enzymes.
eBook - PDF- N A Khan(Author)
- 2008(Publication Date)
- CRC Press(Publisher)
These, transformed cells, have reduced requirement for growth factors and become cancerous, i.e., grow forever. 5.3.4 Progressive Infections These infections take years to show any clinical symptoms. They normally begin with influenza-like symptoms and become latent. During the latent period, they propagate infectious particles. Once reactivated, they overwhelm the immune system, e.g., HIV. 6. VIRAL PATHOGENESIS The process of viral infection leading to disease is called viral pathogenesis. Our ability to understand the basic pathogenic mechanisms associated with viral diseases both at the cellular and molecular level are crucial for identifying therapeutic targets. As indicated above, there are hundreds of human viruses causing diverse diseases. The description of each virus with their mode of action is beyond the scope of this book. Here, HIV has 94 been used as a model virus to describe various features associated with its clinical and non-clinical aspects. 7. CONTROL OF VIRAL INFECTIONS Infections due to viruses vary from acute fatal infections that last for a few days to chronic infections that last for years with varied severity. There is no single parameter that could be used to control all viral infections and each virus requires a different set of measures to help control its infection. Below, the most widely, known measures are indicated for the control of viral infections. It is important to note that since viruses depend on the host cells for their survival, it is unlikely that host killing is the objective, and host death is most likely a result of the side effects. Thus, viruses usually produce mild infections with the obvious exceptions of HIV, ebola virus, rabies virus, hanta virus, etc. However, the extremely close association of the virus and its host means that any consideration of treatment of therapeutic interventions must be viewed with this in mind.
eBook - PDF- Frank J. Fenner, B. R. McAuslan, C. A. Mims(Authors)
- 2013(Publication Date)
- Academic Press(Publisher)
I INTRODUCTION At the molecular and cellular CHAPTER 9 levels with which we have been I concerned so far, viruses behave m quite differently from other in-PathOgeneSIS: The Spread Of fectious agents. This clear dis-VirUSeS through the Body tinction disappears when we consider their effects on whole I organisms and on populations; both the pathogenesis and the epidemiology of viral infections have much in common with these aspects of many bacterial and protozoal infections. In this and the following two chapters we will consider the interactions of viruses with vertebrate organisms from three points of view: (a) the way in which different viruses spread through the body, (b) the immune response and its influence in viral infections, and (c) genetic resistance and some nonimmuno-logical factors that affect virus-host interactions. A great variety of diseases results from such interactions, which involve several hundred viruses and many animal species. Descriptions of viral diseases in a single animal, man, can be found in Horsfall and Tamm (1965), and in abbreviated form in Fermer and White (1970). Much less work has been done on viral infections of other animals and no comprehensive modern textbook exists, hence in this chapter many of the examples will come from human viral infections. Except in immunology, which is discussed in Chapter 10, our understanding of the interactions between animal viruses and whole animals has increased more slowly than has our knowledge of the molecular events that occur when viruses infect cells in culture. This slow rate of growth is reflected in the fact that this chapter has required a less drastic revision than most of the other chapters in this book. MECHANISMS OF CELL DAMAGE Before exploring viral pathogenesis at the level of organism we shall sum-marize briefly what is known of the cytopathic effects of viruses at the cellular level.
eBook - PDF- Marc H.V. van Regenmortel, Brian W.J. Mahy(Authors)
- 2010(Publication Date)
- Academic Press(Publisher)
Nature 439: 682–687. Martin MP and Carrington M (2005) Immunogenetics of viral infections. Current Opinion in Immunology 17: 510–516. Nathanson N, Ahmed R, Brinton MA, et al. (eds.) (2007) Viral Pathogenesis and Immunity, 2nd edn. London: Academic Press. Nathanson N and Tyler K (2005) The pathogenesis of viral infections. In: Mahy BWJ and ter Meulen V (eds.) Topley and Wilson’s Microbiology , pp. 236–269. London: Hodder Arnold. Racaniello VR (2006) One hundred years of poliovirus pathogenesis. Virology 344: 9–16. Tumpey TM, Basler CF, Aguilar PV, et al. (2005) Characterization of the reconstructed 1918 Spanish influenza pandemic virus. Science 310: 77–80. Antiviral Agents H J Field, University of Cambridge, Cambridge, UK R A Vere Hodge, Vere Hodge Antivirals Ltd., Reigate, UK ã 2008 Published by Elsevier Ltd. Introduction There have been two previous articles in Encyclopedia of Virology, the latter being in 1999. That review, by A. K. Field and C. A. Laughlin, gave a good update, especially in the treatment of HIV. In order to avoid repetition, we have focused on antiviral targets. We have not attempted to cover vaccines nor immunomodulating agents, such as interferons, except when these are men-tioned briefly in those cases in which they are the therapy of choice. These approaches which utilize a cellular target are outside the scope of this article but the reader is referred to a recent review by L. Schang. The term ‘virucidal’ has long been used to describe an agent that destroys virions while outside the host cell. A few compounds inactivate viruses by highly specific mechanisms but many, such as alcohol wipes, have a broad spectrum of activity against many infectious entities. Virucidal agents have an important role, especially in hospitals, in preventing the transmission of viruses and may be useful in reducing the risk of virus transmission between individuals, for example, during sexual contact.
eBook - PDF- Frederick A. Murphy, E. Paul J. Gibbs, Marian C. Horzinek, Michael J. Studdert(Authors)
- 1999(Publication Date)
- Academic Press(Publisher)
PART I Principles of Virology This Page Intentionally Left Blank CHAPTER 1 The Nature of Viruses as Etiologic Agents of Veterinary and 9 Q Zoonot c D seases Veterinary and Zoonotic Virology as Infectious Disease Sciences ................. 3 Viruses, At the Edge of Life ...................................................................... 6 Viral Morphology .......................................................................................... 7 Chemical Composition of Virions ................................................................. 15 Stability of Viral Infectivity ........................................................................... 19 Further Reading ............................................................................................. 20 Veterinary and Zoonotic Virology as Infectious Disease Sciences Infectious disease is one of the few genuine adven- tures left in the world. The dragons are all dead and the lance grows rusty in the chimney corner.. 9 . About the only sporting proposition that remains unimpaired by the relentless domestication of a once free-living human speciesis the war against those ferocious little fellow creatures, which lurk in the dark corners and stalk us in the bodies of rats, mice, and all kinds of domestic animals; which fly and crawl with the insects, and waylay us in our food and drink and even in our love. This quote is taken from the book Rats, Lice and His- tory, written in 1935 by the great microbiologist Hans Zinsser as he reflected on his life in infectious disease science. Zinsser's thought has challenged generations of students and professionals ever since, and now it chal- lenges those who use this book, those who, by their own clinical and scholarly experiences, understand that the infectious diseases of today are as demanding as those that faced Zinsser.
Humans often have a symbiotic, or shared, relationship with fungi, although some fungi are unfortunately pathogenic and cause human illness, such as ringworm. Parasites, conversely, are simple organisms (either plant or animal) that exist either in or on another living entity, often at some cost to the host. Parasites can cause a variety of diseases, including hookworm and scabies in humans. Perhaps the most striking difference between bacteria, fungi, or parasites and viruses is, of course, that viruses are not considered by most scientists to be alive. They do not eat, drink, have sex, or produce waste. They are simply genetic material surrounded by an enveloping substance that allows the virus to enter a host. Usually, the surrounding substance has to be removed for the virus to cause disease. Examples of human diseases caused by viruses include acquired immunodeficiency syndrome (AIDS), chicken pox, hepatitis, and polio. Viruses are also able to infect other biological organisms, including animals and even bacteria themselves. The viruses that infect bacteria are called bacteriophages (or simply phages), and they are currently a topic of much study and discussion because it is hoped that phages might be able to be used as treatments to target specific bacterial strains that act as human pathogens. The exact origin of viruses on earth is not known. There are several theories that might explain their existence, however. One hypothesis suggests that viruses may be the result of ‘‘escaped’’ pieces of genetic material that originally came from a living organism. A second hypothesis is that viruses were derived from living cells that ‘‘devolved’’ through a streamlining process known as reverse evolution. Another view suggests that viruses originated as a primitive molecule capable of replication, implying that more advanced life forms could have evolved from them.
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