Discussion Viruses Discuss why viruses are more difficult to treat than bacteria and how they affect our body.  Identify properties  of viruses, character

Discussion Viruses Discuss why viruses are more difficult to treat than bacteria and how they affect our body. 

Identify properties  of viruses, characteristics, viral nucleic acids and life cycle of animal viruses.   (You can help yourself to answer this question reading the PowerPoint in the Modules here in Canvas Chapter 5  Viral structures and multiplication, pages 8-10, 14, 18, 20, 21, 26, 27, 41-44.)
Pick one virus ( HIV, COVID-19, Influenza, Herpes, Smallpox, Rotavirus or any other you may have heard) and research about that virus: characteristics, how does it enter human body, and how does it affect the human body and if it is any prevention and treatment for it.

When doing research online, make sure you search more than one source and write the reference of your sources in your work.

 Discussion Expectations: 

 This should be a substantive response (between 75 -150 words minimum) to the topic(s) in your own words, referencing (using APA format) what you have discovered in your required reading and other learning activities. Microbiology FUNDAMENTALS A Clinical Approach Third Edition

Marjorie Kelly Cowan

&

Heidi Smith

with

Jennifer Lusk

BSN RN CCRN

©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom.  No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.

Chapter 5

Viral Structure and Multiplication

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Learning Outcomes Section 5.1

Explain what it means when viruses are described as filterable.

Identify better terms for viruses than alive or dead.

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The Position of Viruses in the Biological Spectrum

Viruses infect every type of cell, including bacteria, algae, fungi, protozoa, plants, and animals

Seawater can contain 10 million viruses per milliliter

For many years, the cause of viral infections was unknown:

Louis Pasteur hypothesized that rabies was caused by a “living thing” smaller than bacteria

He also proposed the term virus, which is Latin for “poison”

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Discovery of Viruses

Ivanovski and Beijerinck showed that a disease in tobacco was caused by a virus.

Loeffler and Frosch discovered an animal virus that causes foot-and-mouth disease in cattle.

Filterable virus:

These early researchers found that when fluids from host organisms passed through porcelain filters designed to trap bacteria, the filtrate remained infectious.

This proved that an infection could be caused by a fluid containing agents smaller than bacteria.

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Questions About Viruses Remain

Are they organisms; that is, are they alive?

What role did viruses play in the evolution of life?

What are their distinctive biological characteristics?

How can particles so small, simple, and seemingly insignificant be causing disease and death?

What is the connection between viruses and cancer?

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The Viral Debate

Two sides of the debate:

Since viruses are unable to multiply independently from the host cell, they are not living things and should be called infectious molecules

Even though viruses do not exhibit most of the life processes of cells, they can direct them, and thus are certainly more than inert and lifeless molecules

Viruses are better described as active or inactive rather than alive or dead

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The Vital Role of Viruses in Evolution

Infect cells and influence their genetic makeup

Shape the way cells, tissues, bacteria, plants, and animals have evolved

8% of the human genome consists of sequences that come from viruses

10 to 20% of bacterial DNA contains viral sequences

Obligate intracellular parasites:

Cannot multiply unless they invade a specific host cell and instruct its genetic and metabolic machinery to make and release new viruses

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Properties of Viruses(1)

Are obligate intracellular parasites of bacteria, protozoa, fungi, algae, plants, and animals

Estimated 10 31 virus particles on earth, approximately 10 times the number of bacteria and archaea combined

Are ubiquitous in nature and have had major impact on development of biological life

Are ultramicroscopic in size, ranging from 20 nm up to 1,000 nm (diameter)

Are not cells; structure is very compact and economical

Do not independently fulfill the characteristics of life

Basic structure consists of protein shell (capsid) surrounding nucleic acid core

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Properties of Viruses(2)

Nucleic acid can be either DNA or RNA, but not both

Nucleic acids can be double-stranded DNA, single-stranded DNA, single-stranded RNA, or double-stranded RNA

Molecules on virus surfaces give them high specificity for attachment to host cell

Multiply by taking control of host cell’s genetic material and regulating the synthesis and assembly of new viruses

Lack enzymes for most metabolic processes

Lack machinery for synthesizing proteins

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How Viruses Are Classified and Named

For many years, animal viruses were classified on the basis of their hosts and the diseases they caused

Newer classification systems emphasize the following:

Hosts and diseases they cause

Structure

Chemical composition

Similarities in genetic makeup

International Committee on the Taxonomy of Viruses:

8 orders and 38 families (another 84 families not yet assigned to any order)

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Concept Check (1)

Which of the following best describes viruses?

Heterotrophic

Saprobic

Obligate intracellular parasites

Chemoautotrophic

Photosynthetic

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Learning Outcomes Section 5.2

Discuss the size of viruses relative to other microorganisms.

Describe the function and structure(s) of viral capsids.

Distinguish between enveloped and naked viruses.

Explain the importance of viral surface proteins, or spikes.

Diagram the possible nucleic acid configurations that viruses may possess.

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Virus Size Range

Smallest infectious agents

Smallest viruses: parvoviruses around 20 nm in diameter

Largest viruses: herpes simplex virus around 150 nm in length

Some cylindrical viruses can be relatively long (800 nm) but are so narrow in diameter (15 nm) that their visibility is limited without an electron microscope

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Size Comparison of Viruses with a Eukaryotic Cell (Yeast) and Bacteria

Jump to long description

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Viral Architecture Is Best Observed with Special Stains and Electron Microscopy

Source: CDCl/Dr. F. A. Murphy (a); ©Phototake (b); ©A.B. Dowsette/SPL/Science Source (c)

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Viral Components(1)

Viruses bear no resemblance to cells and lack any of the protein-synthesizing machinery found in cells

Viral structure is composed of regular, repeating subunits that give rise to their crystalline appearance

The structure contains only those parts needed to invade and control a host cell:

External coating

Core containing one or more nucleic acid strains of DNA or RNA

Sometimes one or two enzymes

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Viral Components(2)

Capsid: protein shell that surrounds the nucleic acid:

Nucleocapsid: the capsid together with the nucleic acid

Naked viruses consist only of a nucleocapsid.

Envelope: external covering of a capsid, usually a modified piece of the host’s cell membrane

Spikes can be found on naked or enveloped viruses:

Project from the nucleocapsid or the envelope

Allow viruses to dock with host cells

Virion: a fully formed virus that is able to establish an infection in a host cell

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Structure of Viruses

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Viral Capsid

Capsid:

Most prominent feature of viruses

Constructed from identical protein subunits called capsomeres

Capsomeres spontaneously self-assemble into the finished capsid

Two different types:

Helical

Icosahedral

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Viral Envelope

Enveloped viruses:

Take a bit of the cell membrane when they are released from a host cell

Enveloped viruses can bud from:

Cell membrane

Nuclear envelope

Endoplasmic reticulum

More flexible than the capsid so enveloped viruses are pleomorphic

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Helical Capsid Structure

Helical Capsids The simpler helical capsids have rod-shaped capsomeres that bond together to form a series of hollow discs resembling a bracelet. During the formation of the nucleocapsid, these discs link with other discs to form a continuous helix into which the nucleic acid strand is coiled.
Naked The nucleocapsids of naked helical viruses are very rigid and tightly wound into a cylinder-shaped package. An example is the tobacco mosaic virus, which attacks tobacco leaves.
Enveloped Enveloped helical nucleocapsids are more flexible and tend to be arranged as a looser helix within the envelope. This type of morphology is found in several enveloped human viruses, including influenza, measles, and rabies.

Naked Capsids

Enveloped Capsids

©Science Source, Source: CDC/Dr. Fred Murphy

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Icosahedral Capsid Structure

Icosahedral Capsids These capsids form an icosahedron (eye″-koh-suh-hee′-drun)—a three-dimensional, 20-sided figure with 12 evenly spaced corners. The arrangements of the capsomeres vary from one virus to another. Some viruses construct the capsid from a single type of capsomere, while others may contain several types of capsomeres. There are major variations in the number of capsomeres; for example, a poliovirus has 32, and an adenovirus has 252 capsomeres.
Naked Adenovirus is an example of a naked icosahedral virus. In the photo you can clearly see the spikes, some of which have broken off.
Enveloped Two very common viruses, hepatitis B virus and the herpes simplex virus, possess enveloped icosahedrons.

Naked Capsids

Enveloped Capsids

©Dr. Linda M. Stannard, University of Cape Town/Science Source, ©Dr. Linda M. Stannard, University of Cape Town/Science Source (hep B virus); ©Eye of Science/Science Source

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Complex Capsid Structure

Complex Capsids Complex capsids, only found in the viruses that infect bacteria, may have multiple types of proteins and take shapes that are not symmetrical. They are never enveloped. The one pictured on the right is a T4 bacteriophage.

©AmiImages/Science Source

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Nucleic Acids: At the Core of a Virus

Genome: the sum total of the genetic information carried by an organism

Viruses contain DNA or RNA, but not both

The number of viral genes is quite small compared with that of a cell:

Four genes in hepatitis B virus

Hundreds of genes in some herpesviruses

Possess only the genes needed to invade host cells and redirect their activity

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Variety in Viral Nucleic Acid

DNA viruses: Single-stranded (ss) or double-stranded (ds; linear or circular)

RNA viruses: can be double-stranded, but more often single-stranded:

Positive-sense RNA: ready for immediate translation

Negative-sense RNA: must be converted before translation can occur

Segmented: individual genes exist on separate pieces of RNA

Retroviruses: carry their own enzymes to create DNA out of their RNA

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Viral Nucleic Acid

Virus Name Disease It Causes
DNA Viruses Examples
Double-stranded DNA Variola virus Smallpox
Herpes simplex II Genital herpes
Single-stranded DNA Parvovirus Erythema infectiosum (skin condition)
RNA Viruses–Examples
Single-stranded (+) sense Poliovirus Poliomyelitis
Single-stranded (−) sense Influenza virus Influenza
Double-stranded RNA Rotavirus Gastroenteritis
Single-stranded RNA + reverse transcriptase HIV AIDS

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Other Substances in the Virus Particle

Enzymes for specific operations within their host cell:

Polymerases that synthesize DNA and RNA

Replicases that copy RNA

Reverse transcriptase synthesizes DNA from RNA

Completely lack the genes for synthesis of metabolic enzymes

Some viruses carry away substances from their host cell:

Arenaviruses pack along host ribosomes

Retroviruses borrow the host’s tRNA molecules

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Concept Check (2)

Which of the following is not a type of viral nucleic acid?

Single-stranded DNA

Double-stranded RNA

Double-stranded DNA

Segmented RNA

All of the types listed are found in viruses.

©McGraw-Hill Education

Learning Outcomes Section 5.3

Diagram the five-step life cycle of animal viruses.

Define the term cytopathic effect and provide one example.

Discuss both persistent and transforming infections.

Provide thorough descriptions of both lysogenic and lytic bacteriophage infections.

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Modes of Viral Multiplication

Viruses are minute parasites that seize control of the synthetic and genetic machinery of cells

The nature of the viral replication cycle dictates:

The way the virus is transmitted

What it does to the host

Responses of immune defenses

Human measures to control viral infection

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Multiplication Cycles in Animal Viruses

General phases of the animal viral replication cycle:

Adsorption

Penetration

Uncoating

Synthesis

Assembly

Release

The length of the replication cycle varies from 8 hours in polioviruses to 36 hours in herpesviruses

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Adsorption

A virus can invade its host cell only through making an exact fit with a specific host molecule

Host range: the limited range of cells that a virus can infect:

Hepatitis B: liver cells of humans

Poliovirus: intestinal and nerve cells of primates

Rabies: various cells of all mammals

Cells that lack compatible virus receptors are resistant to adsorption and invasion by that virus

Tropisms: specificities of viruses for certain tissues

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Viral Attachment Process

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Penetration and Uncoating

The flexible cell membrane of the host is penetrated by the whole virus or its nucleic acid

Penetration through endocytosis happens when an entire virus is engulfed by the cell and enclosed in a vacuole or vesicle

Direct fusion of the viral envelope with the host cell membrane:

Envelope merges directly with the cell membrane, liberating the nucleocapsid into the cell’s interior

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Penetration by Animal Viruses

Jump to long description

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Synthesis: Replication and Protein Production

DNA viruses:

Enter the host cell’s nucleus and are replicated and assembled there

RNA viruses:

Replicated and assembled in the cytoplasm

Retroviruses turn their RNA genomes into DNA

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Life Cycle of dsDNA Viruses

Early phase:

Viral DNA enters the nucleus, where genes are transcribed into a messenger RNA

RNA transcript moves into the cytoplasm to be translated into viral proteins (enzymes) needed to replicate the viral DNA

The host cell’s DNA polymerase is involved in this phase

Late phase:

Parts of the viral genome are transcribed and translated into proteins required to form the capsid and other structures

New viral genomes and capsids are assembled

Mature viruses are released by budding or cell disintegration

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Assembly and Release

Assembly: virus is put together using “parts” manufactured during the synthesis process

Release: the number of viruses released by infected cells is variable, controlled by:

Size of the virus

Health of the host cell

Poxvirus-infected cell: 3,000 to 4,000 virions

Poliovirus-infected cell: 100,000 virions

Immense potential for rapid viral proliferation

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Maturation and Release of Enveloped Viruses

©Chris Bjornberg/Science Source (b)

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Life Cycle of Animal Viruses(1)

Adsorption

The virus encounters a susceptible host cell and adsorbs specifically to receptor sites on the cell membrane

The membrane receptors that viruses attach to are usually proteins that the cell requires for its normal function

Glycoprotein spikes on the envelope (or on the capsid of naked viruses) bind to the cell membrane receptors

Penetration and Uncoating

In this example, the entire virus is engulfed (endocytosed) by the cell and enclosed in a vacuole or vesicle

When enzymes in the vacuole dissolve the envelope and capsid, the virus is said to be uncoated, a process that releases the viral nucleic acid into the cytoplasm

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Life Cycle of Animal Viruses(2)

Synthesis: Replication and Protein Production

Viral nucleic acid begins to synthesize the building blocks for new viruses

First, the + ssRNA, which is ready to serve as mRNA, starts being translated into viral proteins, especially those useful for further viral replication

The + strand is then replicated into ssRNA becoming the template for the creation of many new + ssRNAs, used as the viral genomes for new viruses

Additional + ssRNAs are synthesized and used for late-stage mRNAs

Some viruses come equipped with the necessary enzymes for synthesis of viral components; others utilize those of the host

Proteins for the capsid, spikes, and viral enzymes are synthesized on the host’s ribosomes using its amino acids

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Life Cycle of Animal Viruses(3)

Assembly

Mature virus particles are constructed from the growing pool of parts

Capsid is first laid down as an empty shell that will serve as a receptacle for the nucleic acid strand

Viral spikes are inserted into the host’s cell membrane so they can be picked up as the virus buds off with its envelope

Release

Assembled viruses leave their host in one of two ways:

Nonenveloped and complex viruses that reach maturation in the cell nucleus or cytoplasm are released when the cell lyses or rupture

Enveloped viruses are liberated by budding from the membranes of the cytoplasm, nucleus, endoplasmic reticulum, or vesicles

During this process, the nucleocapsid binds to the membrane, which curves completely around it and forms a small pouch

Pinching off the pouch releases the virus with its envelope

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Damage to the Host Cell

Cytopathic effects (CPEs): virus-induced damage to the cell that alters its microscopic appearance

Types of CPEs include:

Gross changes in shape and size

Development of intracellular changes

Inclusion bodies: compacted masses of viruses or damaged cell organelles in the nucleus and cytoplasm

Syncytia: fusion of multiple damaged host cells into single large cells containing multiple nuclei (giant cells)

Accumulated damage from a virus infection kills most host cells

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Cytopathic Changes

Source: CDC (a); Courtesy Massimo Battaglia, INeMM CNR, Rome Italy (b)

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Persistent Infections

Some cells maintain a carrier relationship: cell harbors the virus and is not immediately lysed:

Can last from a few weeks to the remainder of the host’s life

Can remain latent in the cytoplasm

Provirus:

Viral DNA incorporated into the DNA of the host

Measles virus

Chronic latent state:

Periodically become activated under the influence of various stimuli

Herpes simplex and herpes zoster viruses

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Viruses and Cancer(1)

Experts estimate that 13% of cancers are caused by viruses

Transformation: the effect of oncogenic, or cancer-causing viruses:

Some viruses carry genes that directly cause cancer

Other viruses produce proteins that induce a loss of growth regulation, leading to cancer

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Viruses and Cancer(2)

Transformed cells:

Increased rate of growth

Changes in their chromosomes

Changes in cell’s surface molecules

Capacity to divide indefinitely

Oncoviruses: mammalian viruses capable of initiating tumors:

Papillomaviruses

Herpesviruses

Hepatitis B virus

HTLV-I

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Viral Induction of Cancer

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Viruses That Infect Bacteria

Bacteriophage: “bacteria eating”:

Most contain double-stranded DNA, but some RNA types exist as well

Every bacterial species is parasitized by various specific bacteriophages

The bacteria they infect are often more pathogenic for humans

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T-Even Bacteriophage

Infect E. coli

Structure:

Icosahedral capsid containing DNA

Central tube surrounded by a sheath

Collar

Base plate

Tail pins

Fibers

Jump to long description

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Events in the Lytic Cycle of T-even Bacteriophages(1)

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Events in the Lytic Cycle of T-even Bacteriophages(2)

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Lysogeny: The Silent Virus Infection

Temperate phages:

Undergo adsorption and penetration

Do not undergo replication or release immediately

Viral DNA enters an inactive prophage state:

Inserted into bacterial chromosome

Copied during normal bacterial cell division

Lysogeny: a condition in which the host chromosome carries bacteriophage DNA

Induction: prophage in a lysogenic cell becomes activated and progresses directly into viral replication and the lytic cycle

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The Role of Lysogeny in Human Disease

Occasionally, phage genes in the bacterial chromosome cause the production of toxins or enzymes that the bacterium would not otherwise have

Lysogenic conversion: when a bacterium acquires a new trait from its temperate phage:

Corynebacterium diphtheriae – diphtheria toxin

Vibrio cholerae – cholera toxin

Clostridium botulinum – botulinum toxin

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Concept Check (3)

Put the phases of the life cycle of animal viruses in the correct order.

Assembly

Penetration

Release

Adsorption

Synthesis

Uncoating

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Learning Outcomes Section 5.4

List the three principal purposes of cultivating viruses.

Describe three ways in which viruses are cultivated.

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Techniques in Cultivating and Identifying Animal Viruses

Viruses require living cells as their “medium”:

In vivo: laboratory-bred animals and embryonic bird tissues

In vitro: cell or tissue culture methods

Primary purposes of viral cultivation:

Isolate and identify viruses in clinical specimens

Prepare viruses for vaccines

Do detailed research on viral structure, multiplication cycles, genetics, and effects on host cells

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Using Live Animal Inoculation

Specially bred strains of white mice, rats, hamsters, guinea pigs, and rabbits are the usual choices for viral cultivation

Occasionally, invertebrates such as insects or nonhuman primates are used

Because viruses exhibit host specificity, certain animals can propagate viruses more readily than others

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Using Bird Embryos

Bird eggs containing embryos:

Intact and self-supporting unit

Sterile environment

Contain their own nourishment

Chicken, duck, and turkey eggs are the most common choices for inoculation

Viruses are injected through the eggshell by drilling a small hole or making a small window

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Using Cell (Tissue) Culture Techniques

Isolated animal cells are grown in vitro in cell or tissue culture rather than in an animal or egg

Cell culture, or tissue culture:

Grown in sterile chambers with special media that contain the correct nutrients for cells to survive

Cells form a monolayer, or single, confluent sheet of cells that supports viral multiplication

Allows for the close inspection of culture for signs of infection

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Detection of Viral Growth in Culture

Observation of degeneration and lysis of infected cells

Plaques: areas where virus-infected cells have been destroyed show up as clear, well-defined patches in the cell sheet:

Visible manifestation of cytopathic effects (CPEs)

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Normal and Infected Cell Culture

Source: Bakonyi T, Lussy H, Weissenböck H, Hornyák A, Nowotny N. Emerging Infectious Diseases, Vol. 11, No. 2, Feb. 2005.

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Detection of Bacteriophages

This same technique is used to detect and count bacteriophages:

Plaques develop when the viruses released by an infected host cell radiate out to adjacent host cells

New cells become infected, die and release more viruses, and the process continues

Plaque manifests as a macroscopic, round, clear space that corresponds to areas of dead cells

©McGraw-Hill Education

Concept Check (4)

Which of the following is not an in vivo method of culturing animal viruses?

Embryonated chicken eggs

Guinea pigs

Dog kidney cell culture

White mice

All of the choices are in vivo methods.

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Learning Outcomes Section 5.5

Name three noncellular infectious agents besides viruses.

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Prions

Composed primarily of protein (no nucleic acid)

Exact mode of infection is still being investigated

Deposited as long protein fibrils in the brain tissue of humans and animals:

Creutzfeldt-Jakob disease: afflicts the central nervous system and causes degeneration and death

Bovine spongiform encephalopathy (“mad cow disease”)

Shy-Drager syndrome or multiple system atrophy resembles Parkinson’s disease

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Satellite Viruses

Dependent on other viruses for replication

Adeno-associated virus (AAV):

Originally thought that it could only replicate in cells infected with the adenovirus

Can also infect cells that are infected with other viruses

Delta agent:

Naked circle of RNA

Expressed only in the presence of the hepatitis B virus

Worsens the severity of liver damage

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Viroids

Virus-like agents that parasitize plants

About one-tenth the size of an average virus

Composed of naked strands of RNA, lacking a capsid or any other type of coating

Significant pathogens in economically important plants: tomatoes, potatoes, cucumbers, citrus trees, chrysanthemums

©McGraw-Hill Education

Concept Check (5)

Creutzfeldt-Jakob disease and Bovine spongiform encephalopathy are caused by prions. Which of the following best describes a prion?

Viral particle

Naked DNA

Infectious protein

Small bacterium

Naked RNA

©McGraw-Hill Education

Learning Outcomes Section 5.6

Analyze the relative importance of viruses in human infection and disease.

Discuss the primary reason that antiviral drugs are more difficult to design than antibacterial drugs.

©McGraw-Hill Education

Viruses and Human Health

Common causes of acute infections:

Colds, hepatitis, chickenpox, influenza, herpes, warts

Prominent viral infections worldwide:

Dengue fever, Rift Valley fever, yellow fever

Infections with high mortality rates:

Rabies, AIDS, Ebola

Infections that cause long-term disability:

Polio, neonatal rubella

Connection to chronic infections:

Type 1 diabetes, MS, various cancers, Alzheimer’s, obesity

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Treatment of Animal Viral Infections

Antibiotics designed to treat bacterial infections have no effect on viruses

Difficult to find drugs that will affect viruses without damaging host cells

Almost all antiviral drugs licensed so far have been designed to target one of the steps in the viral life cycle:

Integrase inhibitor class of HIV drugs interrupts the ability of HIV genetic information to incorporate into the host cell DNA

Easier to develop vaccines to prevent viral diseases

©McGraw-Hill Education

Concept Check (6)

Antibiotics are an effective method for treating viral infections.

True

False

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Appendix of Image Long Descriptions

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Size Comparison of Viruses With a Eukaryotic Cell (Yeast) and Bacteria – Appendix

The yeast cell is approximately 7 micrometers, E. coli is about 2 micrometers long, Streptococcus is about 1 micrometer, and Rickettsia is about 0.3 micrometers long. Most viruses are smaller than eukaryotic and bacterial cells. The largest in this image is Pandovirus, the same size as Streptococcus bacteria, about 1 micrometer. Mimivirus is 450 nanometers, Herpes simplex virus is 150 nanometers, Rabies virus is 125 nanometers, HIV is 110 nanometers, Influenza virus is 100 nanometers, Adenovirus is 75 nanometers, T2 bacteriophage is 65 nanometers, Polio virus is 30 nanometers, and Yellow fever virus is 22 nanometers. For comparison, a hemoglobin molecule (protein molecule) is 15 nanometers.

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Viral Architecture is Best Observed With Special Stains and Electron Microscopy – Appendix

(a) Negative staining ofinfluenza virus revealing details of its outer coat. (b) Positive stain of the Ebola virus, a type of filovirus, so named because of its tendency to form long strands. (c) Shadowcasting image of a vaccinia virus.

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Structure of Viruses – Appendix

Shown on the left of this figure, the simplest virus is a naked virus (nucelocapsid), consisting of a geometric capsid assembled around a nucleic acid strand or strands. On the right of the figure, an enveloped virus is composed of a nucleocapsid (as shown on the left) surrounded by a flexible membrane called an envelope. In the figure it is represented as a sphere with special receptor spikes inserted into its surface.

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Viral Attachment Process – Appendix

An enveloped coronavirus with prominent spikes. The configuration of the spike has a complementary fit for cell receptors. The process in which the virus lands on the cell and plugs into receptors is termed docking.

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Penetration by Animal Viruses – Appendix

Endocytosis (engulfment) and uncoating of a herpesvirus: 1. specific attachment, 2. engulfment, 3. virus in vesicle, and 4 vesicle,, envelope, and capsid break down; uncoating of nucleic acid. Fusion of the cell membrane with the viral envelope: 1. specific attachment, 2. membrane fusion, 3. entry of nucleocapsid, and 4. uncoating of nucleic acid.

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Cytopathic Changes – Appendix

(a) Human epithelial cells infected by herpes simplex virus demonstrate giant cells with multiple nuclei. (b) Fluorescent-stained human cells infected with cytomegalovirus showing the inclusion bodies. Both viruses disrupt the cohesive junctions between cells, which would ordinarily be arranged side by side in neat patterns.

Jump to the image

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Viral Induction of Cancer – Appendix

Some retroviruses: Viral oncogenes …

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