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8/2/2019 Virology Far

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VIROLOGY

Ridha Wahyutomo, MD

Dept. Clinical Microbiology andInfectious Disease


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Viruses are the smallest infectiousagents (20-300 nanometers)

Possess only one kind of nucleic acid,either DNA or RNA as their genome

Capable of replication only within

living cells (genetic parasites)


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Viral Structure

VirusParticle

Covering

Capsid

Envelope

CentralCore

Nucleic

Acid

Others


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General Structure of

Viruses Size range

most


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Prions - misfolded proteins, contain no nucleic acid cause transmissible spongiform encephalopathies fatal

neurodegenerative diseases

common in animals: scrapie in sheep & goats

bovine spongiform encephalopathies (BSE), aka mad cowdisease

wasting disease

humans Creutzfeldt-Jakob Syndrome (CJS)

Extremely resistant to usual sterilization techniques


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Other noncellular infectiousagents

Satellite viruses dependent on otherviruses for replication

adeno-associated virus replicate only incells infected with adenovirus

delta agent naked strand of RNA expressedonly in the presence of hepatitis B virus

Viroids - short pieces of RNA, no proteincoat; only been identified in plants, so far


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Viral Structure: Covering

FUNCTIONS: Protects the nuclear material

Responsible for introduction of viral nucleicacid into a suitable host cell

Stimulates the immune system


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Viral Structure: Covering

- CAPSID CAPSID: The outer protective shell

The most prominent geometric feature

Composed of identical protein subunitsCAPSOMERS

Formed by spontaneous self-assembly ofcapsomers


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Viral Structure: Naked

Viruses


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Viral Structure: Covering -

ENVELOPE Formed when the viral particle carries

off a part of the host cells membrane

(any part of the endomembranesystem may be used)

SPIKES or PEPLOMERS

Protein spikes protruding through theenvelope from the capsid

Essential for attachment to the next host


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Viral Structure:

Enveloped Viruses


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Viral Structure: Central Core

Nucleic Acids Genetic materialof the particle

Viruses maycontain eitherDNA or RNABUTNOT BOTH

DNA or RNA mayexist as single ordouble-stranded


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Viral Morphology

Helical Icosahedral


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Viral Morphology

Enveloped Complex


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Modes of Viral Multiplication

Adsorption - binding of virus to specificmolecule on host cell

Penetration - genome enters host cell

Uncoating the viral nucleic acid is releasedfrom the capsid

Synthesis viral components are produced

Assembly new viral particles are constructed

Release assembled viruses are released bybudding (exocytosis) or cell lysis


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Release

budding exocytosis; nucleocapsid bindsto membrane which pinches off and shedsthe viruses gradually; cell is notimmediately destroyed

lysis nonenveloped and complex virusesreleased when cell dies and ruptures

Number of viruses released is variable

3,000-4,000 released by poxvirus >100,000 released by poliovirus


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Cytopathic effects - virus-induceddamage to cells

Changes in size & shape

Cytoplasmic inclusion bodies

Nuclear inclusion bodies Cells fuse to form multinucleated cells.

Cell lysis

Alter DNA Transform cells into cancerous cells


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Persistent Infections Persistent infections - cell harbors the

virus and is not immediately lysed

Can last weeks or hosts lifetime; several

can periodically reactivatechronic latentstate

measles virus may remain hidden in brain cellsfor many years

herpes simplex virus cold sores and genitalherpes

herpes zoster virus chickenpox and shingles


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20 Some animal viruses enter host cell and permanently alter

its genetic material resulting in cancertransformationof the cell.

Transformed cells have increased rate of growth,alterations in chromosomes, and capacity to divide for

indefinite time periods resulting in tumors. Mammalian viruses capable of initiating tumors are called

oncoviruses.

Papillomavirus cervical cancer

Epstein-Barr virusBurkitts lymphoma


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Lysogeny Lysogeny results in the spread of the virus

without killing the host cell.

Phage genes in the bacterial chromosome

can cause the production of toxins orenzymes that cause pathologylysogenic conversion. Corynebacterium diphtheriae

Vibrio cholerae Clostridium botulinum


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Lysogeny


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Modes of entry

Respiratory tract though inhalation

Gastrointestinal tract

Skin

Sexual

Direct contact

Transfusion of blood


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Effects of virus on the

host cell CPE or cellular effect

Transformation of normal cell to

malignant cell

Latent infection

Clumping of RBC


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Some of the MedicallyImportant Viruses

Family Genus Common Nameof GenusMembers

Disease

DNA VirusesHerpesviridae Simplexvirus Herpes simplex

1&2 virusCold sores, genitalherpes

Varicella zostervirus

Chicken pox

Adenoviridae Mastadenovirus Human adenovirus Colds, URIPapovaviridae Papillomavirus Human

papillomavirus(HPV)

Warts

Hepadnaviridae Hepadnavirus Hepatits B virus Serum hepatitis


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Some of the Medically Important Viruses

Family Genus Common Name

of GenusMembers

Disease

RNA Viruses

Picornaviridae Enterovirus Poliovirus Poliomyelitis

Hepatovirus Hepatitis A virus Short-term

hepatitisRhinovirus Human rhinovirus Common colds

Togaviridae Alphavirus Rubella virus German measles

Flaviviridae Flavivirus Dengue fever virus Dengue fever

Filoviridae Filovirus Ebola virus Ebola feverOrthomyxoviridae Influenza virus Influenza virus Influenza

Paramyxoviridae Paramyxovirus Measles virus Measles

Rhabdoviridae Lyssavirus Rabies virus Rabies

Retroviridae Lentivirus HIV AIDS

Coronaviridae Coronavirus SARS virus SARS


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