an introduction to the viruses
DESCRIPTION
An Introduction to the Viruses. Chapter 6. The Search for the Elusive Virus. ______________ postulated that rabies was caused by a virus (1884) Ivanovski and Beijerinck showed a disease in tobacco was caused by a virus (1890s) 1950s virology was a multifaceted discipline - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/1.jpg)
An Introduction to the An Introduction to the VirusesViruses
Chapter 6
![Page 2: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/2.jpg)
22
The Search for the Elusive The Search for the Elusive VirusVirus
• ______________ postulated that rabies was ______________ postulated that rabies was caused by a virus (1884)caused by a virus (1884)
• Ivanovski and Beijerinck showed a Ivanovski and Beijerinck showed a disease in tobacco was caused by a virus disease in tobacco was caused by a virus (1890s)(1890s)
• 1950s virology was a multifaceted 1950s virology was a multifaceted disciplinediscipline– Viruses: noncellular particles with a definite Viruses: noncellular particles with a definite
size, shape, and chemical composition size, shape, and chemical composition
![Page 3: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/3.jpg)
33
The Position of Viruses in the The Position of Viruses in the Biological SpectrumBiological Spectrum
• There is no universal agreement on There is no universal agreement on how and when viruses originatedhow and when viruses originated
• Viruses are considered the most Viruses are considered the most abundant microbes on earthabundant microbes on earth
• Viruses played a role in evolution of Viruses played a role in evolution of Bacteria, Archaea, and EukaryaBacteria, Archaea, and Eukarya
• Viruses are obligate intracellular Viruses are obligate intracellular parasitesparasites
3
![Page 4: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/4.jpg)
![Page 5: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/5.jpg)
Size of virusesSize of viruses
![Page 6: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/6.jpg)
Naming virusesNaming virusesClassified based on structures, size, nucleic acids, Classified based on structures, size, nucleic acids,
host species, target cells.host species, target cells.• 3 orders, 63 families, and 263 genera of viruses3 orders, 63 families, and 263 genera of viruses• Family name ends in -viridae Family name ends in -viridae • Genus name ends in -virus, SimplexGenus name ends in -virus, Simplexvirus, virus,
HantaHantavirusvirus, Entero, Enterovirusvirus• Name of genus or family Name of genus or family beginsbegins with with
description of virus description of virus – appearance: appearance: togatogavirus, virus, coronacoronavirusvirus– place collected: place collected: adenoadenovirus, virus, hantahantavirusvirus– effect on host: effect on host: lentilentivirusvirus– acronymns: acronymns: picornapicornavirus; (virus; (arboarbovirus)virus)
![Page 7: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/7.jpg)
777
![Page 8: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/8.jpg)
ExamplesExamples
• Family – HerpesviridaeFamily – Herpesviridae
• Genus – VaricellovirusGenus – Varicellovirus
• Common name – chickenpox virusCommon name – chickenpox virus
• Disease - chickenpoxDisease - chickenpox
• Family – HerpesviridaeFamily – Herpesviridae
• Genus – SimplexvirusGenus – Simplexvirus
• Common name – herpes virus Common name – herpes virus (Herpes simplex virus I (HSV-I)(Herpes simplex virus I (HSV-I)
• Disease – fever blisters, cold soresDisease – fever blisters, cold sores
![Page 9: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/9.jpg)
99
terminologyterminology
• Virus = virus particleVirus = virus particle•___________– fully formed, virulent, fully formed, virulent,
extracellularextracellular•___________– host cell is lysed – host cell is lysed
(broken) to release virions(broken) to release virions•___________– viruses are inactive – viruses are inactive
(latent stage) and host cell isn’t lysed (latent stage) and host cell isn’t lysed (virus may be integrated within host (virus may be integrated within host genome)genome)
![Page 10: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/10.jpg)
1010
Viral structureViral structure
•___________ (with spikes/receptors; (with spikes/receptors; 13/20 – derived from host cell) – 13/20 – derived from host cell) – may may not be presentnot be present
•___________ (morphologies: helical, (morphologies: helical, icosohedral, complex)icosohedral, complex)
• Nucleic acidNucleic acid (DNA/RNA; ds or ss) (DNA/RNA; ds or ss)
• Matrix proteinsMatrix proteins (some enzymes) (some enzymes)
![Page 11: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/11.jpg)
1111
![Page 12: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/12.jpg)
capsidscapsids• Nearly all viruses have Nearly all viruses have capsids-capsids- protein protein
coats that enclose & protect their nucleic coats that enclose & protect their nucleic acidacid
• Each Each capsidcapsid is constructed from identical is constructed from identical subunits called subunits called capsomerscapsomers made of protein – made of protein – can self-assemblecan self-assemble
•___________= capsid & nucleic acid= capsid & nucleic acid
• 2 types (based on shape): 2 types (based on shape): – helical helical – icosahedralicosahedral
![Page 13: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/13.jpg)
1313
EnvelopeEnvelope
• If present, made primarily of lipidsIf present, made primarily of lipids
•______________________ ; ; (ER, nuclear (ER, nuclear envelope, cell membrane-budding)envelope, cell membrane-budding)
• May be embedded with spikes for May be embedded with spikes for host recognition/bindinghost recognition/binding
![Page 14: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/14.jpg)
1414
4 morphological types4 morphological types
• Due to capsule shape and/or Due to capsule shape and/or whether it’s envelopedwhether it’s enveloped
1.1. HelicalHelical
2.2. IcosahedralIcosahedral
3.3. Enveloped (with Hel. or Icos. Enveloped (with Hel. or Icos. capsid)capsid)
4.4. complexcomplex
![Page 15: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/15.jpg)
1515
1. Helical capsid1. Helical capsid• Rod-shaped Rod-shaped
capsomerscapsomers
• Coil around hollow Coil around hollow centercenter
• Nucleic acid is Nucleic acid is kept inside – kept inside – wound-up within wound-up within tube tube (nucleocapsid)(nucleocapsid)
Morphological types
![Page 16: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/16.jpg)
Helical – capsid surrounds DNA like hollow tubeEx: TMV, influenza, measles, rabies (last 3 are enveloped)
Morphological types
![Page 17: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/17.jpg)
1717
Tobacco Mosiac Virus
Influenza virus
Morphological types
![Page 18: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/18.jpg)
2. icosahedral2. icosahedral
• 20-sided with 12 20-sided with 12 cornerscorners
• Vary in the number Vary in the number of capsomersof capsomers
• Each capsomer may Each capsomer may be made of 1 or be made of 1 or several proteinsseveral proteins
• Some are envelopedSome are enveloped
Morphological types
![Page 19: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/19.jpg)
191919
Figure 6.7 Figure 6.8
![Page 20: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/20.jpg)
Icosahedral – 3D, 20 sided
Human papilloma virusAdenovirus Herpesvirus
Morphological types
![Page 21: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/21.jpg)
2121
3. envelope3. envelope• Naked virusesNaked viruses
– Capsid proteins exposed to environmentCapsid proteins exposed to environment– Released from cells as cells Released from cells as cells ____________________– Not a good pathogenic feature should keep host Not a good pathogenic feature should keep host
alivealive
• Enveloped virusesEnveloped viruses– Covered with a lipid bilayerCovered with a lipid bilayer– ______________________– Host cell keeps producing virus much longer Host cell keeps producing virus much longer
sometimes for extended periodssometimes for extended periods– Can bud off cellCan bud off cell – thereby not destroying (lysing) it – thereby not destroying (lysing) it
Morphological types
![Page 22: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/22.jpg)
2222
Enveloped vs. naked virusesEnveloped vs. naked viruses
Morphological types
![Page 23: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/23.jpg)
2323
4. Complex viruses4. Complex viruses
• Have additional or special structuresHave additional or special structures• Examples: Examples: •___________– lack normal capsid – – lack normal capsid –
instead, layers of lipoprotiens and instead, layers of lipoprotiens and fibrils on surfacefibrils on surface
•___________viruses have a polyhedral viruses have a polyhedral head, helical tail and fibers for head, helical tail and fibers for attachment. attachment.
Morphological types
![Page 24: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/24.jpg)
Fig 6.9a,c
Morphological types
![Page 25: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/25.jpg)
2525
![Page 26: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/26.jpg)
262626
Nucleic AcidsNucleic Acids• Viral genomeViral genome – either DNA or – either DNA or
RNA but never bothRNA but never both
• Carries genes necessary to invade Carries genes necessary to invade host cell and redirect cell’s activity host cell and redirect cell’s activity to make new virusesto make new viruses
• Number of genes varies for each Number of genes varies for each type of virus – few to hundredstype of virus – few to hundreds
![Page 27: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/27.jpg)
272727
Nucleic AcidsNucleic Acids• DNA viruses DNA viruses
– Usually double stranded (ds) but may be Usually double stranded (ds) but may be single stranded (ss)single stranded (ss)
– Circular or linearCircular or linear
• RNA viruses RNA viruses – Usually single stranded, may be double Usually single stranded, may be double
stranded, may be segmented into separate stranded, may be segmented into separate RNA piecesRNA pieces
– ssRNA genomes ready for immediate ssRNA genomes ready for immediate translation are translation are positive-sense RNApositive-sense RNA
– ssRNA genomes that must be converted into ssRNA genomes that must be converted into proper form are proper form are negative-sense RNAnegative-sense RNA
![Page 28: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/28.jpg)
282828
Enzymes important to Enzymes important to replicationreplication
•Pre-formed enzymes may be Pre-formed enzymes may be presentpresent– ___________– DNA or RNA– DNA or RNA– ___________– copy RNA– copy RNA– ______________________– synthesis of – synthesis of
DNA from RNA (AIDS virus)DNA from RNA (AIDS virus)
![Page 29: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/29.jpg)
2929
Viral life cyclesViral life cycles
![Page 30: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/30.jpg)
Host rangeHost range• Spectrum of Spectrum of cellscells a virus can infect a virus can infect
– cell has to have a specific structure (receptor) on cell has to have a specific structure (receptor) on its surface for viral attachmentits surface for viral attachment
– cell has to contain all of the enzymes and cell has to contain all of the enzymes and materials needed to produce new virionsmaterials needed to produce new virions
• May be one May be one speciesspecies or many or many– HIV (only humans) vs rabies (many animals)HIV (only humans) vs rabies (many animals)– Bacteriophages – tend to be very specificBacteriophages – tend to be very specific
• May be one May be one tissuetissue or many within a host or many within a host– Hepatitis (liver) vs polio (intestinal & nerve cells)Hepatitis (liver) vs polio (intestinal & nerve cells)
Life cycle
![Page 31: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/31.jpg)
3131
DNA DNA replication in replication in virusesviruses
* Uses host machinery!*
![Page 32: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/32.jpg)
animal virus replication (life animal virus replication (life cycle)cycle)
![Page 33: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/33.jpg)
3333
Viral Multiplication – animal Viral Multiplication – animal virusesviruses
1. ___________– binding of virus to specific – binding of virus to specific molecule on host cellmolecule on host cell
2. ___________– genome enters host cell– genome enters host cell
3. ___________– the viral nucleic acid is – the viral nucleic acid is released from the capsidreleased from the capsid
4. ___________– viral components are produced– viral components are produced
5. ___________– new viral particles are – new viral particles are constructedconstructed
6. ___________– assembled viruses are released – assembled viruses are released by budding (exocytosis) or cell lysisby budding (exocytosis) or cell lysis
![Page 34: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/34.jpg)
343434
![Page 35: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/35.jpg)
353535
1. Adsorption and Host 1. Adsorption and Host RangeRange
• Virus coincidentally collides with a Virus coincidentally collides with a susceptible host cell and adsorbs susceptible host cell and adsorbs specifically to receptor sites on the cell specifically to receptor sites on the cell membranemembrane
• Spectrum of cells a virus can infect – Spectrum of cells a virus can infect – host host rangerange– ___________– human liver cells– human liver cells– ___________– primate intestinal and nerve cells– primate intestinal and nerve cells– ___________– various cells of many mammals– various cells of many mammals
![Page 36: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/36.jpg)
363636
1. Adsorption to host cell membrane(a) Coronavirus with envelope spikes (b) adenovirus (naked capsid) with surface capsid
spikes
![Page 37: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/37.jpg)
3737
Entry: (2. penetration & 3. Entry: (2. penetration & 3. uncoating)uncoating)Entry (viruses with envelopes)• first must attach to cell membrane using
receptors -- usually specific for host AND cell type• After adsorption _________ of membranes – (like
two soap bubbles) • leaves the capsid free in the cytoplasm
Entry (viruses without envelopes)• first must attach using receptors (specific) • if a match, then engulfment -- ___________• capsid then in the cytoplasm but within a
vacuole • virus must uncoat without the genes being
degraded
![Page 38: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/38.jpg)
3838
Figure 6.13
Entry of viruses into cells (penetration and uncoating)• Endocytosis and engulfment of herpesvirus; • Fusion of cell membrane with viral envelope
(mumps)
![Page 39: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/39.jpg)
393939
Synthesis: Replication and Protein Synthesis: Replication and Protein ProductionProduction
• Varies depending on whether the Varies depending on whether the virus is a DNA or RNA virusvirus is a DNA or RNA virus
• DNA virusesDNA viruses generally are replicated generally are replicated and assembled in the and assembled in the ___________
• RNA virusesRNA viruses generally are replicated generally are replicated and assembled in the and assembled in the ___________– Positive-sense RNA contain the message Positive-sense RNA contain the message
for translationfor translation– Negative-sense RNA must be converted Negative-sense RNA must be converted
into positive-sense messageinto positive-sense message
![Page 40: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/40.jpg)
4040
Duplication and synthesis: viral Duplication and synthesis: viral replication (more details in Ch. replication (more details in Ch. 9)9)
Transport of DNA/RNA to nucleus• most viruses must get genes to nucleus to survive • some integrate into host DNA (leads to latency)
– may require conversion of RNA copy to DNA
• some remain independent chromosomes
Viral replication• some do direct copies of DNA->DNA or RNA->RNA • others use "reverse transcriptase" to do RNA-
>DNA conversion – then DNA->RNA using HOST enzymes – timing is important -- some replicate only late in the
cycle, after all proteins are made
![Page 41: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/41.jpg)
4141
5. Assembly: Filling the capsid
•Capsid proteins made in cytoplasm
•DNA or RNA gets fills empty capsids
•final modifications to capsid – to plug any holes from DNA/RNA entry – to mature the outer proteins
![Page 42: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/42.jpg)
424242
6. Release6. Release
• Two ways assembled viruses leave host Two ways assembled viruses leave host cell:cell:
1. ___________– exocytosis; nucleocapsid binds to – exocytosis; nucleocapsid binds to membrane which pinches off and sheds the membrane which pinches off and sheds the viruses gradually; cell is not immediately viruses gradually; cell is not immediately destroyeddestroyed
2. ___________– nonenveloped and complex – nonenveloped and complex viruses released when cell dies and rupturesviruses released when cell dies and ruptures
• Number of viruses released is variableNumber of viruses released is variable– 3,000-4,000 released by poxvirus3,000-4,000 released by poxvirus– >100,000 released by poliovirus>100,000 released by poliovirus
![Page 43: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/43.jpg)
4343
Budding of parainfluenza virus
Budding of HIV
Viral budding – picking up cell membrane upon exit
![Page 44: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/44.jpg)
444444
Damage to Host CellDamage to Host Cell
Cytopathic effectsCytopathic effects - virus-induced - virus-induced damage to cellsdamage to cells
1.1. Changes in size and shapeChanges in size and shape2.2. Cytoplasmic inclusion bodiesCytoplasmic inclusion bodies3.3. Inclusion bodiesInclusion bodies4.4. Cells fuse to form multinucleated cellsCells fuse to form multinucleated cells5.5. Cell lysisCell lysis6.6. Alter DNAAlter DNA7.7. Transform cells into cancerous cellsTransform cells into cancerous cells
![Page 45: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/45.jpg)
454545
Figure 6.16
![Page 46: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/46.jpg)
464646
![Page 47: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/47.jpg)
474747
Persistent infections with Persistent infections with virusesviruses
• Persistent infectionsPersistent infections - cell harbors the - cell harbors the virus and is not immediately lysedvirus and is not immediately lysed
• Can last weeks or host’s lifetime; several Can last weeks or host’s lifetime; several can periodically reactivate – can periodically reactivate – ______________________– Measles virusMeasles virus – may remain hidden in brain – may remain hidden in brain
cells for many yearscells for many years– Herpes simplex virusHerpes simplex virus – cold sores and genital – cold sores and genital
herpesherpes– Herpes zoster virusHerpes zoster virus – chickenpox and shingles – chickenpox and shingles
![Page 48: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/48.jpg)
4848
• Some animal viruses permanently alter genetic Some animal viruses permanently alter genetic material material ________________
• Transformed cells have increased rate of Transformed cells have increased rate of growth, altered chromosomes, and can growth, altered chromosomes, and can become “immortal” become “immortal” tumors (cancerous or tumors (cancerous or noncancerous growths)noncancerous growths)
• Mammalian viruses capable of initiating Mammalian viruses capable of initiating tumors are called tumors are called _________________– PapillomavirusPapillomavirus – genital warts/cervical cancer – genital warts/cervical cancer– Epstein-Barr virusEpstein-Barr virus – Burkitt’s lymphoma – Burkitt’s lymphoma– HBVHBV and liver cancer and liver cancer
Persistent infections with Persistent infections with virusesviruses
![Page 49: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/49.jpg)
4949
Multiplication Cycle in Multiplication Cycle in BacteriophagesBacteriophages
• ___________– bacterial viruses (phages)– bacterial viruses (phages)
• Most widely studied are those that infect Most widely studied are those that infect Escherichia coliEscherichia coli – complex structure, DNA – complex structure, DNA
• Multiplication goes through similar stages as Multiplication goes through similar stages as animal virusesanimal viruses
• Only the nucleic acid enters the cytoplasm - - uncoating is not necessaryuncoating is not necessary
• Release is a result of Release is a result of cell lysiscell lysis induced by induced by viral enzymes and accumulation of viruses - viral enzymes and accumulation of viruses - lytic cyclelytic cycle
![Page 50: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/50.jpg)
5050
6 Steps in Phage 6 Steps in Phage ReplicationReplication
1. Adsorption – binding of virus to specific molecule on host cell
2. Penetration – genome enters host cell3. Replication – viral components produced4. Assembly – viral components assembled5. Maturation – completion of viral
formation6. Release – viruses leave cell to infect
other cells
![Page 51: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/51.jpg)
515151
Figure 6.17
![Page 52: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/52.jpg)
525252
Figure 6.18
Figure 6.19
![Page 53: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/53.jpg)
535353
Lysogeny: The Silent Virus Lysogeny: The Silent Virus InfectionInfection• Not all phages complete the lytic cycleNot all phages complete the lytic cycle• Some DNA phages (Some DNA phages (temperate phagestemperate phages)), ,
undergo adsorption and penetration but don’t undergo adsorption and penetration but don’t replicatereplicate
• The viral genome The viral genome insertsinserts into bacterial genome into bacterial genome and becomes an and becomes an inactive inactive ___________– – the cell is the cell is not lysednot lysed
• Prophage is retained and copied during normal Prophage is retained and copied during normal cell division cell division transfer of temperate phage transfer of temperate phage genome to all host cell progeny – genome to all host cell progeny – ___________
• InductionInduction can occur resulting in can occur resulting in activationactivation of of lysogenic prophage followed by viral replication lysogenic prophage followed by viral replication and cell and cell lysislysis
![Page 54: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/54.jpg)
545454
Figure 6.17
![Page 55: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/55.jpg)
555555
Lysogeny Lysogeny
• Lysogeny results in the Lysogeny results in the spread of the spread of the virus without virus without ______________________
• Phage genes in the bacterial Phage genes in the bacterial chromosome can cause the production chromosome can cause the production of toxins or enzymes that cause of toxins or enzymes that cause pathology – pathology – lysogenic conversionlysogenic conversion– Corynebacterium diphtheriaeCorynebacterium diphtheriae – Vibrio choleraeVibrio cholerae– Clostridium botulinumClostridium botulinum
![Page 56: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/56.jpg)
565656
![Page 57: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/57.jpg)
Growing animal virusesGrowing animal virusesObligate intracellular parasites that require Obligate intracellular parasites that require appropriate cells to replicateappropriate cells to replicate
1.1. live animalslive animals (dependent on host (dependent on host specificity) specificity)
2.2. bird embryosbird embryos – chicken, duck; – chicken, duck; intact, self-supporting unit, sterile, intact, self-supporting unit, sterile, self-nourishedself-nourished
3.3. cell culturecell culture – can be used to – can be used to cultivate but also to test toxic (ex. cultivate but also to test toxic (ex. Hemolytic) effectsHemolytic) effects
Viral Culture
![Page 58: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/58.jpg)
5858
Figure 6.20
![Page 59: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/59.jpg)
5959
Figure 6.21
![Page 60: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/60.jpg)
6060
Medical Importance of Medical Importance of VirusesViruses
• Viruses are the most common cause of Viruses are the most common cause of acute infections acute infections
• Several billion viral infections per yearSeveral billion viral infections per year
• Some viruses have high mortality ratesSome viruses have high mortality rates
• Possible connection of viruses to chronic Possible connection of viruses to chronic afflictions of unknown causeafflictions of unknown cause
• Viruses are major participants in the Viruses are major participants in the earth’s ecosystemearth’s ecosystem
![Page 61: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/61.jpg)
6161
Detection of Animal Viral Detection of Animal Viral InfectionsInfections
• More difficult than other agentsMore difficult than other agents
• Consider overall clinical pictureConsider overall clinical picture
• Take appropriate sample Take appropriate sample – Infect cell culture – look for characteristic Infect cell culture – look for characteristic
cytopathic effectscytopathic effects– Screen for parts of the virusScreen for parts of the virus– Screen for immune response to virus Screen for immune response to virus
(antibodies)(antibodies)
![Page 62: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/62.jpg)
diagnosis
![Page 63: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/63.jpg)
6363
Treatment of viral infections
•Antiviral drugs
•Target viral replication – but usually lots of side effects (affects host cells too)
•Some drugs target virus-specific enzymes
Best bet…get ___________and avoid
infection
![Page 64: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/64.jpg)
6464
Clinically-important viruses (just a few examples!)
HepC
![Page 65: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/65.jpg)
6565
Important viruses you should Important viruses you should know…know…
• Smallpox (variola major, minor) – complex virus; inclusions
• Herpesviridae – (herpes; chicken pox – varicella zoster); chronic latent state reactivated; nuclear inclusions
• HPV – can transform cells; warts cervical cancer• Hepatovirus (A, B, C) – see table• Polio – enterovirus – enteric (oral vaccine)• Cold (Rhinovirus) – antibiotics ineffective! It’s a virus!!• West Nile – is a flavivirus; spread by moquitoes; bird is
reservoir• SARS – coronavirus (like the virus that causes
bronchitis); prominent spikes on envelope• influenza – Flu; Type A is the one you’ve had;• Rotavirus – viral food poisoning; vomiting and diarrhea
– sometimes concurrently!!• HIV – retrovirus; latency; (see slide)
![Page 66: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/66.jpg)
6666
HerpesviridaeHerpesviridae
• Examples:– _______________ (cold sores); 2 (genital herpes)– ______________________ (chicken pox)
• Have chronic latent phase in nerve cells
• Reactivated by various stimuli:– Foods– Sunlight– Stress
• Chicken pox reappears as “___________”
![Page 67: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/67.jpg)
6767
Hepatoviruses and HepatitisHepatoviruses and HepatitisOrganismOrganism Hep AHep A Hep BHep B Hep CHep C
VirusVirus Non-Non-enveloped; enveloped; ssRNAssRNA
Enveloped; ss and Enveloped; ss and dsDNAdsDNA
RNA (flaviviridae)RNA (flaviviridae)
DiseaseDisease Short-term Short-term hepatitishepatitis
Chronic infection Chronic infection (6%), liver cancer, (6%), liver cancer, deathdeath
Chronic infection Chronic infection (75-85%) liver (75-85%) liver disease very disease very common, cancer, common, cancer, deathdeath
TransmissioTransmissionn
Fecal/oralFecal/oral Blood/fluid contact Blood/fluid contact (IV, sex, tattoos); (IV, sex, tattoos); verticalvertical
Blood/fluid contact Blood/fluid contact (IV, sex, tattoos); (IV, sex, tattoos); verticalvertical
TreatmentTreatment Immune Immune globulinglobulin
Interferon, nucleoside Interferon, nucleoside analogsanalogs
Interferon or Interferon or ribavirinribavirin
PreventionPrevention VaccineVaccine VaccineVaccine No vaccine; avoid No vaccine; avoid exposureexposure
Special Special notesnotes
Resolves (self-Resolves (self-limiting); avoid limiting); avoid aspirin, alcoholaspirin, alcohol
Survives in infected Survives in infected blood for days, blood for days, freezingfreezing
““silent epidemic; silent epidemic; 4M people, 80% 4M people, 80% asymptomatic!asymptomatic!
![Page 68: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/68.jpg)
6868
InfluenzaInfluenza• Type A = Hong Kong, Asian, Swine flu; Type A = Hong Kong, Asian, Swine flu;
AvianAvian InfluenzaInfluenza (bird flu – emerging (bird flu – emerging disease)disease)
• Bird Bird human (right now) human (right now) Pandemic: Pandemic: human human human human; antigenic ; antigenic
shiftshift Influenza pandemic of Influenza pandemic of ________ killed 20+ killed 20+
million people! (more than plague?) million people! (more than plague?) The viruses of the last three global The viruses of the last three global
influenza pandemics were first found in influenza pandemics were first found in China. China.
![Page 69: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/69.jpg)
6969
HIVHIV• Retrovirus – ssRNA genome – depends on Reverse
Transcriptase to make DNA (will be covered later)• Latent phase – inserts in host genome – 2 wks. - 20
years? – can’t see virus particles in bloodstream• Infects cells – CD4+ T-cells (lymphocytes),
macrophages• Destroys immune system AIDS person frequently
dies from 2ndary infection and/or cancer• HIV also attacks organs directly (kidney, heart)
2007 data:• number of people living with HIV = ___________
• Number of people who died of AIDS = __________
![Page 70: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/70.jpg)
7070
HIV – enveloped virusHIV – enveloped virus
• HIV does not survive well outside the HIV does not survive well outside the human body or in the outside the human body or in the outside the environment. (environment. (Enveloped – fragile – does Enveloped – fragile – does not survive drying)not survive drying)
• The studies also shown that drying HIV The studies also shown that drying HIV reduces the amount of viral by nearly 95 reduces the amount of viral by nearly 95 percent within several hours. percent within several hours.
![Page 71: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/71.jpg)
7171
HIV/AIDS – stages HIV/AIDS – stages
• Stage I: asymptomatic, not categorized as AIDS
• Stage II: include minor mucocutaneous manifestations (ex. recurrent yeast infections) and recurrent upper respiratory tract infections
• Stage III: includes unexplained ______________ for longer than a month, severe bacterial infections and pulmonary tuberculosis. Wasting begins.
• Stage IV includes ___________of the brain, candidiasis of the esophagus or repiratory, Pnemocystis carinii pneumonia, and Kaposi's sarcoma (cancer); these diseases are used as indicators of AIDS.
![Page 72: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/72.jpg)
727272
___________- misfolded proteins, contain no nucleic acid
– Cause transmissible spongiform encephalopathies – fatal neurodegenerative diseases
– Common in animals:• Scrapie in sheep and goats
• Bovine spongiform encephalopathies (BSE), a.k.a. mad cow disease
• Wasting disease in elk
• Humans – Creutzfeldt-Jakob Syndrome (CJS)
– Extremely resistant to usual sterilization techniques
Other Other noncellularnoncellular infectious infectious particlesparticles
![Page 73: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/73.jpg)
737373
Figure 6.22
![Page 74: An Introduction to the Viruses](https://reader034.vdocument.in/reader034/viewer/2022051018/568145d8550346895db2da5b/html5/thumbnails/74.jpg)
747474
Other Noncellular Infectious Other Noncellular Infectious AgentsAgents
• Satellite virusesSatellite viruses – dependent on – dependent on other viruses for replicationother viruses for replication– Adeno-associated virus – replicates Adeno-associated virus – replicates
only in cells infected with adenovirusonly in cells infected with adenovirus– Delta agent – naked strand of RNA Delta agent – naked strand of RNA
expressed only in the presence of expressed only in the presence of hepatitis B virushepatitis B virus
• ___________ – short pieces of RNA, no – short pieces of RNA, no protein coat; only been identified in protein coat; only been identified in plantsplants