Term
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Definition
Definitions:
Virus – genetic element that cannot replicate independently of a living (host) cell
Virus particle – extracellular form of a virus; allows virus to exist outside host and facilitates transmission from one host cell to another
Virion – infectious virus particle; the nucleic acid genome surrounded by a protein coat and, in some cases, other layers of material
Found in almost every environment on Earth
•5000 described
•Estimated that viruses are the most abundant form of ‘life’
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Term
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Definition
Viruses must have a host cell in which to replicate
All viruses have genes (DNA or RNA)
All have associated proteins to protect the genetic material
Some have lipid bilayers derived from their host cells (envelopes)
Transmission
Vector, fecal-oral, droplet, direct
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Definition
genetic element that cannot replicate independently of a living (host) cell
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Definition
extracellular form of a virus; allows virus to exist outside host and facilitates transmission from one host cell to another |
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Definition
infectious virus particle; the nucleic acid genome surrounded by a protein coat and, in some cases, other layers of material |
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Definition
Found in almost every environment on Earth
•5000 described
•Estimated that viruses are the most abundant form of ‘life’
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Definition
1.Acute – rapid onset with viral clearance •Influenza, smallpox
2.Chronic – long term infections which are rarely (if ever) cleared completely
•EBV, CMV, HIV
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Definition
1.Vaccines – prevention
2.Anti-viral drugs – slow growth
3.No virus has ever been ‘cured’
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| Virus Evolutionary Theory |
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Definition
•Viruses potentially evolved from 3 routes
1.Small parasitic bacteria
2.Mobile genetic elements (jumping genes)
3.Co-evolution with cellular life as simple pieces of genetic information
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| History of Virology and Cell Culture |
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Definition
•Chamberland – worked with Pasteur to create filters
•Filtered out bacteria to isolate infectious particles
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| Research in the 1920-40’s developed cell culture techniques |
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Definition
•Minced/ground animal tissue (heart, lymph, kidney)
•Fertilized eggs (nashville)
•Culminating with human cell culture techniques
•Many viruses are difficult to grow in culture – HepC
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History of virology and cell cultures
cont'd |
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Definition
1940-50’s provided EM pictures of viruses
•1950-80’s launched Virology into the mainstream
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Definition
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| Viral Structure and Function |
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Definition
Wide variation in viral structures
General structures found in many viruses
•Genetic material protected by protein coats (capsids)
•Helical capsids
•Icosahedral Symmetry
•Lipid bilayer envelopes
•Enzymes for viral specific function
•Genes for manipulating host cell machinery
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Definition
Icosahedral Symmetry in Viruses
•Multiple polygon faces interacting together to enclose a particle
•A stable protein enclosure for all viral components
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Term
| Common Viral Genome Organization |
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Definition
Wide variation
Everything has nucleotides…after that…
•DNA (ss, ds)
•RNA (ss +/-, ds +/-)
•Circular, linear, segmented
•Small <10 genes
•Large >200 genes
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Term
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Definition
Baltimore Classification System
•Based on nucleic acid type (genetic material) Classes I-VII
ICTV (Int’l Committee on Taxonomy of Viruses) System
•Based on morphology, genetic material, replication, host range, pathogenesis
Both types of classifications are used in contemporary taxonomy
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Baltimore’s Classifications 1
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Definition
1.Type I – dsDNA
•Herpesviruses, poxviruses, adenoviruses
•VZV, HSVI&II
2.Type II – ssDNA
•Parvoviruses – no known human varieties
3.Type III – dsRNA
•Reoviruses
•Rotavirus
4.Type IV – ssRNA (+ sense)
•Picornoviruses
•Rhinoviruses, Hep A
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| Baltimore's Classification - 2 |
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Definition
5.Type V – ssRNA (- sense)
•Orthomyxoviruses, rhabdoviruses
•Influenza, rabies
6.Type VI – ssRNA (DNA intermediate)
•Retroviruses
•HIV, HTLV
7.Type VII – dsDNA (RNA intermediate)
•Hepadnaviruses
•HepB
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| Viral Effects on Host Cells |
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Definition
1.Cytopathic effects
2.Cell death
1.Lysis from bursting
2.Cell surface molecule rearragement and loss of signal control
3.Apoptosis – programmed cell death (suicide/kamikaze)
3.Latent infections
1.Few cytopathic effects
2.Herpesviruses infect long-lived cells and persist in these compartments without immune activation or cell death
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| Virus Restriction by the Host |
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Definition
Why don’t all viruses infect all animals (cells)?
•Not all cells have a receptor - tropism
•Innate proteins which interfere with viral reproduction or assembly
•Degradation of viral genetic material RNA or DNA
•Infection signals from cells
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| Viral Evasion of Host Defenses |
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Definition
Co-evolution – many viruses have evolved to avoid host defenses
•Mimic cytokines to confuse responding immune cells
•Latency
•Infection of leukocytes and interruption of normal immune response
•Interference with adaptive response and antigen presentation/recognition
•Reduce secretion of cytokine danger signals
•Stop internal cell death mechanisms (apoptosis)
•Rapid reproduction and evolution
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| Basic Viral Reproduction Process |
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Definition
1.Attachment – viral attachment protein binds to cell surface receptor
2.Penetration – virion is internalized
3.Uncoating – capsid proteins and genetic material are unloaded in cytoplasm
4.Replication – genetic material is copied
5.Protein production – viral proteins are made by cellular machinery
6.Assembly – new viral particles are assembled in the cell or at the surface
7.Release – cell lysis
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Definition
•These viruses ‘creep’ – they all have a latent phase
•HSV-I (oral) and HSV-II (genital) – neural cells
•VZV – chickenpox and shingles – neural cells
•EBV (Epstein Barr Virus) – B-cells
•CMV (cytomegalo virus) – monocytes and lymphocytes
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| •These viruses ‘creep’ – they all have a latent phase |
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Definition
•Large dsDNA genomes, icosahedral capsid, envelope
•Symptomatic infection is caused by acute lytic infection
•Latency associated gene products (LAT) accumulate in a ‘latent’ cells
•Reactivation causes production of lytic gene products and re-emergence of symptoms
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Term
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Definition
Variola, Vaccinia, Cowpox, Monkeypox viruses
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•Only human infection to have been eradicated – 1979
300-500 million deaths in the 20th centurySmallpox – Variola major (35% mortality) and Variola minor (1%) VERY large, enveloped virions, 250 genes, dsDNA |
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Definition
Enteroviruses and Rhinoviruses
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•Replicate optimally at 37 (entero) and 33 degrees (rhino)
Infecting the enteric tract and the nosePico-RNA viruses – small RNA genomes with capsid shells |
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| Orthomyxoviruses - Influenza |
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Definition
Influenza A, B, C (A and C are multi-species, B is exclusively human)
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•Classified further by surface proteins
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•H1N2 – endemic in humans and pigs
H5N1 pandemic flu threat in 2006-7 (and today) H1N1 (Spanish Flu of 1918 and today) 16 HA and 9 NA subtypes have been identified Hemagglutinin (H/HA) and Neuraminidase (N/NA) Pleomorphic virion (many shapes) with a segmented genome of ssRNA (- sense) comprised of 8 segments |
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| Orthomyxoviruses - Influenza |
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Definition
The Influenza Cycle
•Seasonal epidemics originate in Southeast and Eastern Asia
•Antigenic drift – minor changes in the virus which accumulate over time
•Antigenic shift – major changes in genome when 1 or more gene segments are exchanged by 2 viruses infecting the same host
•Often associated with pandemics
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Definition
•Seasonal epidemics originate in Southeast and Eastern Asia
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Definition
•minor changes in the virus which accumulate over time
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Definition
major changes in genome when 1 or more gene segments are exchanged by 2 viruses infecting the same host
•Often associated with pandemics
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Definition
Human Immunodeficiency Virus infection leads to AIDS (Acquired Immunodeficiency Syndrome) |
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Definition
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•Transmitted via direct transfer in bodily fluids
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•35+ million are infected around the world
Currently one of the most important global pathogens
HIV infects CD4 T-cells and interrupts the normal immune functionRelatively small, ssRNA (- sense) genome |
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