Pharm D Program

(2023/2024)

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 Pharm
PharmDDProgram
Program
(2024/2025)
(2023/2024)

(PM 704)

Lecture No. (7)

Introduction to Virology

By
Professor
Yasser El Mohammadi
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 Pharm
PharmDDProgram
Program
(2024/2025)
(2023/2024)

Lecture’s Aim

To let the student discover the main features of viruses and why viral
infections are the most prevalent all over the world.

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 Pharm
PharmDDProgram
Program
(2024/2025)
(2023/2024)

Lecture’s Competencies

To enable the student to

1- Describe the general biological and physical properties of viruses and how
they differ from other infectious agents.
2- Describe the virus structures, function, and replication.
3- Mention the importance of cultivation of virus in diagnosis.

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 Pharm
PharmDDProgram
Program
(2024/2025)
(2023/2024)

Lecture’s Contents
Introduction to Virology
General properties of viruses
A) Definition
B) Structure
C) Morphology (symmetry)
D) Virus replication
Cultivation of viruses
Antiviral Treatment Strategies
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Virology
Course Outline
Virology

- Introduction

- DNA viruses

- RNA viruses
Introduction to Virology
• General properties
A) Definition:
- Viruses are obligate intracellular parasites infecting man, animal, insects,
plants and even bacteria.
- Viruses are the smallest known infectious agents.
- Viruses cause many of the diseases that are very common around the world:
common cold, influenza, hepatitis, AIDS, Ebola
And now …. Corona (Covid19).
- The virus must first recognize and bind to host cell that permits its
replication; this is due to certain legends on viral surface and receptors on
the host cell.

- Viruses are not a living cells due to:

1- No cell wall or cell membrane.
2- Metabolically inactive (no metabolic enzymes).
3- No energy production.
4- No ribosome for protein synthesis.
5- They can neither grow nor respond to the environment.
B) Structure:
• The virus particle (virion) consists of:
1- Core (genome):
- Composed of either DNA or RNA, single or double stranded, linear or
circular.
- The RNA may be of positive sense (acts as mRNA) or negative sense (act as
anti mRNA).
- The RNA may exist as segmented or non-segmented strand(s).

2- Coat
Coat (capsid):
(capsid):

Shell of protein made of subunits called capsomeres (composed of one or

different protein types), which are bounded by non covalent bonds to
facilitate release of the genome during replication.
3- Envelop
- Found in only some viruses.
Composed of phospholipids and proteins (typically derived from portions of
the host cell membranes), but include some viral glycoproteins.
• The outer layer (proteins and glycoproteins) may exist as spikes which may
act as legends for the virus or have certain other activities, i.e. often play a
role in the recognition of host cells.

4- Enzymes:
Found only in very few numbers of viruses.
• The virus if composed of core and coat only may be termed nucleocapsid
nucleocapsid or
naked virus.
 Structure

• Core
• Coat (Capsid)

 Envelop
C) Morphology (symmetry)

1- Icosahedral: resembling crystal, with several surfaces, several angles and

more than one axis of symmetry, e.g. herpes virus (enveloped), adenovirus
(non-enveloped).

2- Helical: the genome is arranged in a spiral with capsomeres arranged

around it in a ribbon like. Helical viruses are usually enveloped e.g. Influenza
virus.

3- Complex: complicated structure, e.g. poxvirus, which is brick shaped with

ridges or tubules on its surface.
 Morphology (symmetry)

Icosahedral Helical Complex

Icosahedral
 Virion Morphologies

• Genetic material is DNA or RNA

• Coat is protein

Complex virus
Helical virus Polyhedral virus (bacteriophage)
Virions (Virion Particle)
D) Virus replication:
• The host cell acts as a factory, providing substrates, energy and machinery
for synthesis of coat proteins, and nucleic acid genomes. Viruses have
evolved many ways to use and manipulate the host cell for their purposes.
Viruses can regulate cellular enzymes, modify cellular structure and perturb
metabolic pathways.
• Virus replication consists of the following steps:

1) Recognition and attachment to the target cell (Adsorption):

• Depends on legends of the virus and receptors in the host cell e.g. the
hemagglutinin spikes of the enveloped influenza virus.
• Some viruses use multiple receptors, which may allow them to invade a
variety of cell types as infection in the host progresses.
• Viruses may prefer certain target tissue (Tropism), accordingly several
viruses may cause the same disease if they have the same target tissue e.g.
hepatitis viruses and common cold viruses.
• Specific antibodies could prevent the process of attachment.

2) Penetration (viropexis):
viropexis
• Naked viruses are taken by host cell by endocytosis.
• Enveloped viruses penetrate the host cell either by fusion of the envelope
with the cell membrane and delivery of the nucleocapsid into the cytoplasm
or by endocytosis.
. Syncytia: some viruses at neutral pH promote cell-to-cell fusion e.g.
measles, paramyxovirus, retroviruses (HIV), & herpes simplex virus (all are
enveloped).
Syncitium Formation
uninfected
cells

activated
fusion protein

budding
virus

syncytium
3) Uncoating:
• Enveloped viruses are usually uncoated upon fusion to the cell membrane.
The virus is then delivered to the replication site.
• DNA viruses replicates in the nucleus except poxvirus.
poxvirus
• RNA viruses replicates in the cytoplasm except retroviruses (HIV).

4) Synthesis of macromolecules:
• The most important step in virus replication.
• DNA viruses that replicate in the nucleus utilize the cell's DNA dependent
RNA polymerase to synthesize their own mRNA (just as the host cell does),
while poxvirus which replicates in the cytoplasm must encode for such
enzyme.
• RNA viruses must encode for enzymes to make their mRNA from RNA, which
involves a different mechanism.

• Protein synthesis takes place in 2 stages:

• Early stage: synthesis of proteins that inhibit the host cell metabolism and
enzymes (polymerases) necessary for nucleic acid replication.
• Late stage: synthesis of protein capsids.
5) Assembly (Maturation):
• Association of cores and coats. Usually starts as soon as the necessary pieces
are synthesized.

6) Release:
• Enveloped viruses are released usually by budding.
budding Each virion acquires a
portion of cell membrane, which becomes the viral envelope (during
synthesis, some viral glycoproteins are inserted into cellular membranes, and
these proteins become the glycoprotein spikes on the surface of the viral
envelope).
• Naked viruses are released in one of two ways: Either they may be extruded
from the cell by exocytosis, in a manner similar to budding but without the
acquisition of an envelope, or after inducing lysis and death of the host cell.
• The time interval after penetration and before assembly is called eclipse cycle.
 adsorption
DNA Enveloped Virus Replication 1) Attachment

penetration 2) Penetration
(viropexis)
uncoating
Transcription Translation
synthesis of viral genes 3) Uncoating
DNA replication
Proteins

4) Synthesis of
macromolecules
Assembly (nucleic acids
maturation & proteins)

5) Assembly
(Maturation)

budding 6) Release
Virus Envelopes (Spikes)
Enveloped Virus Budding
Reproduction of
bacteriophage
(Replication or
life cycle)

1- Attachment

2- Penetration

3- Biosynthesis

4- Maturation

5- Release
 Cultivation of viruses

Viruses grow only in living cells, which may be:

I) Chick or duck embryo
Advantages:
i- inexpensive
ii- among the largest of cells
Iii- free of contaminating microbes
Chick embryo
II) Tissue culture
• Animal or human tissue culture pieces treated with trypsin to separate the
cell.
• They are grown in presence of growth medium containing serum.
• A monolayer or sheet of cells is formed on the flat surface of the container
(glass or plastic bottle or tube).
Tissue culture
III) Intact animal
Rats, mice, guinea pigs, rabbits & pigs have been used to culture and study
animal viruses,
e.g. the white suckling mouse is widely used for encephalitis viruses, calves
are used for pox virus.

Disadvantages
Maintaining laboratory animals can be
1) Difficult
2) Expensive
3) This practice raises ethical issues for some.
4) Cultivation in animals has the disadvantage of easy transmission of infection.
Cultivation of animal viruses
Antiviral Treatment Strategies
• Treatment of viral infections
• Since viruses are metabolically inactive, it is difficult to find antiviral
chemotherapeutic agents.
• However, few antiviral drugs are in clinical use for example:
1) Agents preventing attachment:
attachment
e.g. neutralizing antibodies.

2) Agents preventing uncoating:

e.g. Amantadine and Rimantadine used for prophylaxis against influenza type A.
3) Agents inhibiting the replication:
a- Azidothymidine (AZT): thymidine analogue that inhibits the HIV by
inhibiting its reverse transcriptase. AZT reduces the morbidity and mortality
in AIDS patients, however it is very toxic to lymphocytes and very expensive.

b- Purine and pyrimidine analogues

- Acyclovir: inhibits herpes simplex virus by inhibiting virus specific DNA
polymerase.
Used locally for herpatic ulcers and parentrally to treat serious systemic
infections e.g. herpes encephalitis.
- Ribaverine: used as aerosol for treatment of influenza virus infections. It acts
by interfering with mRNA synthesis.
c- Interferons: They are 3 types (α- , β – and gamma)
- Natural proteins produced by viral infected cells.
- Non specific i.e. acting against several viruses (DNA or RNA) except gamma-
interferon which is specific.
- They are species specific i.e. human interferon protects humans only.
- Act by inhibiting the translation of viral mRNA indirectly, by attaching to
certain cell surface receptors triggering the formation (activation) of
intracellular kinase, without affecting the translation of human cellular
mRNA.

- Used mainly for:

- 1- Prophylaxis in hepatitis B to delay the appearance of liver cancer.
2- Treatment of hepatitis C.
 Pharm
PharmDDProgram
Program
(2024/2025)
(2023/2024)

Lecture’s References

Review of Medical Microbiology and Immunology.

By Warren Levinson - 10th Edition (2008).
Publisher: McGraw Hill - Lange.

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