Download #23 Viruses made by: marah marahleh corrected by: Amer Al

#23
Viruses
made by: marah marahleh
corrected by: Amer Al-salamat
date: 4/12/2016
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Viruses
Viruses are very different from bacteria because they are an acellular entity unlike
fungi which are similar to bacteria because both can be grown on media.
Non-living agents that infect all life forms (plants, phages, and animal
viruses)
Viral cultivation differs from bacterial cultivation
Viruses can't be grown on synthetic media it needs tissue media because viruses
need cells to use their metabolic machinery for its own replication and therefore
propagation unlike fungi which can be grown on dextrose media ( ex: candida can be
grown on CHROM agar ).
Only EM allowed for visualization of viruses
Can't be seen by light microscope it needs at least 600,000X.
Viruses have one major characteristic in common:
(They are obligate intracellular parasites). It can't live separately from cells.
No virus is able to produce its own energy (ATP) to drive
macromolecularsynthesis.
Phage: viruse that infect bacteria
Bacteriophage: mostly infect
E.coli.
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Slide 4
General Characteristics of Viruses
•Contain DNA or RNA (viruses contain NA which can be DNA or RNA but
never both. viruses can be classified according to the presence of DNA or RNA which
can also be considered as virulence factors.
•Contain a protein coat = Capsid that made up of Capsomeres
(NA + capsid neucleocapsid).
•Some are enclosed by an Envelope (Naked, Enveloped) Naked: without
envelope.
•Some viruses have Spikes (COH/protein) Spikes either from the envelope or
the capsid.
•Most viruses are tissue specific.
Most but not all for example AB viruse can bind to more than one type of cell
(epithelial cells , lymphocyte and mesencymel cells ) .For every tissue there is a
specific viruse : viruse –receptor interaction .
•Host range is determined by specific host attachment sites and cellular
factors:
Depends on receptor found on the surface of the cell.
Slide 5
Was read.
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Slide 6
Receptor
Viruse
Polio: cause polio mellitus.
ICAM-1(intracellular adhesion
molecule 1 present on WBC,
endothelium
CD4
HIV: suppress immune system and cause
T-helper cell lysis.
Acetylcholine (neural impulse
transduction)
Rabies
EGF (epidermal growth
factor)
Vaccinia (small pox )
Epstein-barr
CR2/CD21(complement
receptors
HVEM (herpesvirus entry
mediator
Herpes
Influenza , corona
Sialic acid(common component
of extracellular glycosylated
proteins, surface cells)
Slide 7
90% of viruses are tissue specific.
Host Range and Specificity
Virus and host cell interaction usually very specific (narrow host range)
Specific Tissue tropism is the cells and tissues of a host which support
growth of a particular virus.
-Some bacteria and viruses have a Broad tissue tropism and can infect
many types of cells and tissues like EB viruse.
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For example rabies virus affects primarily neuronal tissue (specific
tropism).
Slide 8
First studied viruse: infect tobacco plant
bullet shaped
cause RT infection
Biggest viruse: Ebola viruse which cause:
Fever, diarrhea, headache, decrease in kidney and liver function, bleeding,
hypotension and sore throat.
Mortality rate: 50%.
Transmitted by direct contact: - body fluid (semen fluid and milk).
-bats: fruit bats specially (carry the viruse but not infected with the disease)
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Every bacteria has a different phage: phage typing is important in epidemiological
studies
Ex : S.aureus cause food poisoning if I have a case of food poisoning in salt and
another Case in aqaba , in epidemiological studies I need to know if the same strain
of the bacteria caused the food poisoningin both cases . so we take the bacteria
samples that have collected and infect it with a viruse if it become lysised then that
means that the bacteria is the same strain if not then it's mere coincidence .
Slide 9
Structural Classes
1) Icosahedral symmetryhave 20 similar faces
2) Helical symmetry
3) Non enveloped naked
4) Enveloped.
Slide 10, 11, 12 was read
Slide 13—23:27m
1)Satillite virus
Contain nucleic acid
Depend on co-infection (simultaneously) with a helper virus or
superinfection (carrier, chronic)
Satellite viruse mean viruse that follow the infection with another so the
viruse can't exist without the existence of another viruse (helper viruse) ex:
a person can't get hepatitis D without being infected with hepatitis C first.
Superinfection: a person infected previously then became a carrier.
Mostly in plants, can be human e.g. Hepatitis delta virus (HDV),
cannot propagate without HBV
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2) Viroids
Without capsid
Unencapsidated, small circular ssRNA molecules that replicate
autonomously
ss: single strand
Only in plants, e.g. potato spindle tuber viroid.
3) Prions
No nucleic acid
Infectious protein e.g. BSE (bovine spongiform encephalopathy
or mad cow disease)
4) Virons (viruse)
A complete viral particle, consisting of RNA or DNA surrounded
by a protein shell and constituting the infective form of a virus.
Slide 14 was read.
Slide 15
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Attachment is receptor specific
Assembly: DNA/RNA with capsule.
DNA goes under transcription and translation but RNA goes under
translation only.
Slide 16, 17, 18, 19, 20, 21 was read
Slide 22
Viral Replication
Obligate intracellular parasites using host cell machinery.
Very limited number of genes encodes proteins for:
1) Capsid formation
2) Viral nucleic acid replication
3) Movement of virus into and out of cell.
>>Kill or live in harmony within the host cell if the cell dies then the
viruse is killed as well
>>Outside the cell, viruses are inert: because it's a cellular.
Slide 23
How are viruses named?
Based on: •
1- The disease they cause: poliovirus, rabies virus
2- The type of disease:
murine leukemia virus‫يصيب الفئران‬
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3- Geographic locations: Sendai virus, Coxsackie virus
4- Their discovers: Epstein-Barr virus
5- How they were originally thought to be contracted
From mosquito:
Dengue virus evil spirit of Ba ylonia ) cramp-like seizure.
Influenza virus the influen e of ad air.
6- Combinations of the above: Rous Sarcoma virus.
Whenever you feel like giving up,
Think of all the people that would love to see you fail.
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