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33 Cards in this Set
- Front
- Back
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Properties of viruses
Size |
20 nm in diameter
10nm smallest Foot + Mouth HB 15 nm < ribosome 250 lrgst in Pox grp |
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Properties of viruses
Structure |
All have 2 basic parts
1. Central core of nucleic acid (DNA or RNA) 2. Coat (protein + lipid) envelope (optioanal, host cellular material) |
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Properties of viruses
Reproduction |
Only in living cells
aninmal, plant, bacteria, fungal Not known to cross species Viruses may invade more than one host |
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Properties of viruses
Infection |
Infection of a host by a virus does not necessarily = disease
Infection may be asymptomatic Disease may be mild or severe |
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Properties of virus
Viral replication |
Viral replication does not necessarily destroy the host
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Properties of viruses
Cytopathic Effect |
The Cytopathic Effect is visible cell changes and/or destruction in laboratory cell cultures
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Properties of viruses
specificity |
Viruses exhibit a high degree of specificity for host cell type.
eg.: Influenza virus found on respiratory cells Polio virus found on nerve nad gut cells Hence, there is mostly a relationship between cell preference and disease locality Campbell p. 321 |
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Properties of viruses
Reproduction |
Depending on the type and arrangement of nucleic acid, viruses reproduce in quite different ways to the binary fission of bacteria
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Properties of viruses
Metabolism |
Viruses have no metabolism per se
no replicative process limits treatment viruses are obligate intracellular parasites, they can reproduce only within a host cell. An isolated virus is unable to reproduce, except infect a host cell. Viruses lack the enzymes for metabolism, have no ribosomes. Isolated viruses are merely packaged sets of genes in transit from one host to another (Campbell p 321) |
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Properties of viruses
Treatment |
Unaffected by bacterial treatments
Anti-viral therapy requires interference w/ sp. viral replicative processes non-essential to the host |
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Structure of Viruses
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3 types
Icosohedral (eg Human papilloma, adenovirus) Helical (eg Influenza A, measles) Complex (eg Pox) Phages infect bacteria, polyhedral head (DNA) and tail apparatus (injection) All viruses have a protein + coat and a nucleic acid core, some have an envelope |
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Viruses
Physical and chemical effects General |
At room temperature and outside the body, many viruses are very labile, and only survive a few hours. (eg. Influenza, HIV, throat washings must be stored and transported cool)
Some viruses are much more resistant days, weeks months: eg. Enteroviruses |
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Viruses - Physical and chemical Effects
Heat Cold |
Heat: Pathogenic viruses generally inactivated by moderate heat 56 - 60 C)
Cold: Like bacteria, all viruses are resistent to extremes of cold- preserved at -70 and -199 C Liquid nitrogen Freeze drying is used for preserving viruses and vaccines |
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Viruses - Physical and chemical effects
pH |
Viable between pH 5-9
Viruses are destroyed by extremes of acidity and alkalinity eg. do not pass thr the stomach well |
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Viruses - Physical and Chemical effects
Disinfectants |
Oxidizing agents:
Hypochlorites Organic iodine derivatives H2O2 hydrogen peroxide Potassium permanganate Soap/ detergent Proprietary mixed disinfectants |
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Viruses - Physical + chemical effects
Antibiotics and other therapeutic agents |
Interferon 1st line of defense
AB, (penicillin, streptomycin, tetracyclin, sulphonimides) have no effect, virus lacks metabolism some agents are anti-viral and used for tx. AB can prevent superinfection, immuno suppressed, used prin. in severe respiratory infection |
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Viral Replication
6 Stages |
1. Electrostatic adsorption followed by chemical attachment at specific receptors
Us. best at 37 C and Mg + Ca ions help Viruses must bind to cell surface to get into it. interfere w/ e.ads. metal ions help |
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Viral replication
6 stages |
2. Penetration
Penetration of virus (sometimes just viral nucleic acid)occurs by: Pinocytosis (engulfment) commonest Membrane fusion envelop virus from pinocytosed lysosome Enzymes possibly assist |
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Viral replication
6 stages |
3. Uncoating (Eclipse phase)
No visible activity - no cell changes Metabolic re-organization Microscope will not see anything. virus switch off host cell genes to allow it to take over, make dau. virus particles. |
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Viral replication
6 stages |
4. Formation of viral proteins and NA's
Occurs characteristically in the nucleus or cytoplasm depending on the virus type Often visible as inclusion bodies May cause alteration in cell morphology (cytopathic effect or CPE) see changes, visible areas of material |
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Viral Replication
Assembly |
Newly formed nucleic acid and protein coats assemble to form daughter virions.
Envelope where present added last at cell membrane |
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Viral Replication
Capsid Capsomere |
Capsid: Protein coat that encloses the viral genome
maybe rod shaped, (helical), polyhedral, or complex capsids are built from a large no. of protein units called capsomeres capsomere # of units are genetically detemined. Eg adenovirus has 252 id protein mol. arranged into a polyhedral capsule w/ 20 triangular facets |
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Viral replication
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Tx strategy
Continuous proteins -> capsomeres enzymes arrange assembly Stop proteases, cont. protein capsomeres, favored for attack w/ HIV virus |
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Viral Replication
Release of virions Note: A virion is the whole infective virus particle w/ enzymes |
Daughter virions may leave cell singly or in a single burst. (the latter normally destroying the cell)
Normally ONE virus invades and several hundred daughter virions are produced |
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DNA virus replication
How does it work? |
Entry of viral DNA into host
Transcription of viral DNA into mRNA by host cell RNA polymerase Translation of mRNA -> virus specific proteins |
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RNA virus replication
+ ve stranded input strand ? |
input strand = mRNA
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RNA Virus Replication
-ve standed input strand? |
input strand not mRNA
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Retrovirus replication
How does it work? |
Reverse transcriptase makes a DNA copy of viral RNA
DNA copy is integrated into the host genome = provirus DNA provirus DNA is trnascribed into both new genomic RNA and mRNA for translation into viral proteins |
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DNA Virus families
of medical significance |
ds DNA
Poxviruses smallpox, cowpox, vaccinia Herpes viruses hepadnaviruses Adenoviruses respiratory papovavirus papilloma ssDNA parvovirus |
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RNA Viruses of medical importance
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Retroviruses
Bunyaviruses Coronaviruses SARS Rhabdoviruses rabies Arena virus Filovirus Toga virus rubella flavivirus yellow fever Calicivirus human diarrhea Picornavirus polio Reovirus Orthomyxo virus measles Paramyxovirus influenza |
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Other Replcative Entities
Viroids Prions Virinos |
Viroids: Small virus like ssRNA; some times protein free; mainly plant disease; eg. Hep D Delta hepatitis
Prions: Infectious proteins with no nucleic acids (eg. CJD, BSE, Kuru) Virinos: Small nucleic fragments, complexed with protein, derived from host cell |
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Diagnostic Virology Summary
Ddemonstrate relevant virus by: |
Isolation in animals No
fertile hen eggs cell culture Immunofluorescence Electron microscopy Molecular techniques (PCR) |
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Diagnostic virology summary
Demonstration of significant AB to a relevant virus by: |
Enzyme-immunoassay (ELISA)
Heme agglutination - inhinition Complement fixation Chemiluminescence |
