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 History
 General properties of viruses.
 Structure of viruses.
 General Morphology of virus.
Dr. Dalia M. Mohsen
Prof. In microbiology
 One hundred years ago, researchers could not
imagine submicroscopic particles.
 By the I930s,scientists had begun using the word
virus, the Latin word for poison, to describe these
filterable agents.
Dr. Dalia M. Mohsen
Prof. In microbiology
 The nature of viruses, however, remained elusive until 1935,
when Wendell Stanley, an American chemist, isolated
tobacco mosaic virus, making it possible for the first time to
carry out chemical and structural studies on a purified virus.
 At about the same time, the invention of the electron
microscope made it possible to see viruses.
Dr. Dalia M. Mohsen
Prof. In microbiology
Dr. Dalia M. Mohsen
Prof. In microbiology
 The host range of a virus is the: spectrum of host cells the
virus can infect.
 They can infect :
 Man
 Animals
 Insects
 Plants
 Bacteria
Dr. Dalia M. Mohsen
Prof. In microbiology
 Viruses
that
infect
bacteria
are
called
bacteriophages, or phages.
 most viruses are able to infect specific types of
cells of only one host species.
Dr. Dalia M. Mohsen
Prof. In microbiology
1. They are very small in size.
2. They contain one kind of nucleic acid (RNA or DNA ) as
their genome.
3. They are obligate intracellular parasites i.e. can only
replicate inside living cells.
4. They cannot be grown on artificial culture media and are
grown in tissue culture, embryonated eggs or living
animals.
Dr. Dalia M. Mohsen
Prof. In microbiology
1. They vary in size from 20-1000 nm.
2. They can pass through bacterial filters.
3. They are only seen by electron microscope.
• Each virus particle or virion is composed of :
A
• Protein coat
(Capsid)
B
• Nucleic acid core
 Viruses contain either DNA or RNA but not both.
 The nucleic acid may be linear or circular.
Dr. Dalia M. Mohsen
Prof. In microbiology
• They employ all four possible nucleic acid
types:
single-stranded DNA,
double-stranded DNA,
single-stranded RNA,
double-stranded RNA.
Dr. Dalia M. Mohsen
Prof. In microbiology
• Functions of the
nucleic acid :
a) It is the infectious part of
the virus
b) It
carries
information
the
genetic
for
virus
replication .
Dr. Dalia M. Mohsen
Prof. In microbiology
 The nucleic acid of a virus is protected by a
protein coat called the capsid.
 It is composed of small protein subunits called
capsomers.
Dr. Dalia M. Mohsen
Prof. In microbiology
1) It protects the viral genome (DNA or RNA )against
inactivation by nucleases.
2) It is responsible for the structural symmetry of virions i.e.
icosahedral or helical
3) It participates in attachment of virion to susceptible cells.
Dr. Dalia M. Mohsen
Prof. In microbiology
4) Capsid proteins are important antigen that induce
antibodies that neutralize virus infectivity.
5) Variation in capsid proteins is responsible for the
different viral serotypes in non- enveloped viruses.
Dr. Dalia M. Mohsen
Prof. In microbiology
• Many viruses are
surrounded by lipid or
lipoprotein envelope,
which may be covered
by glycoprotein spike
which attach to host cell
receptor during the
entry of the virus into
the cell
Dr. Dalia M. Mohsen
Prof. In microbiology
• virion :
• Is a complete, fully developed,
infectious
viral
particle
Composed of nucleic acid and
surrounded by a protein coat
that protects it from the
environment.
Dr. Dalia M. Mohsen
Prof. In microbiology
• Viruses may be classified into several different
morphological types on the basis of their capsid
archi- tecture:
1.Helical Viruses
2.Polyhedral Viruses
3.Enveloped Viruses
4.Complex Viruses
Dr. Dalia M. Mohsen
Prof. In microbiology
• 1.Helical viruses:
 Helical viruses resemble long
rods that may be rigid or
flexible.
 The viral nucleic acid is found
within a hollow, cylindrical
capsid that has a helical
structure
Dr. Dalia M. Mohsen
Prof. In microbiology
• 2. Polyhedral Viruses:
 The capsid of most polyhedral
viruses is in the shape of an
icosahedron.
 A regular polyhedron with 20
triangular faces and 12 corners.
 The capsomeres of each face form
an equilateral triangle.
Dr. Dalia M. Mohsen
Prof. In microbiology
• 3. Enveloped Viruses:
 As noted earlier, the capsid of
some viruses is covered by an
envelope.
 Enveloped viruses are roughly
spherical.
 When helical or polyhedral viruses
are enclosed by envelopes, they
are called enveloped helical or
enveloped polyhedral viruses.
Dr. Dalia M. Mohsen
Prof. In microbiology
• 4. Complex Viruses :
• Some
viruses,
particularly
bacterial
viruses,
have
complicated structures and are called complex viruses.
One example of a complex virus is a bacteriophage. Some
bacteriophages
have
capsids
to
which
structures are attached.
Dr. Dalia M. Mohsen
Prof. In microbiology
additional
• 4. Complex Viruses :
• in this figure, notice that the
capsid (head) is polyhedral and
that the tail sheath is helical.
The head contains the nucleic
acid.
Dr. Dalia M. Mohsen
Prof. In microbiology
:
• Are composed of viral nucleic acid and proteins but
cannot replicate without a helper virus, which
provides the missing function. These usually have a
mutation or a deletion of part of their genetic
material.
Dr. Dalia M. Mohsen
Prof. In microbiology
• Contain host cell DNA instead of viral DNA within the capsid.
They are formed during infection with certain viruses when
the host cell DNA is fragmented and pieces are incorporated
within the capsid. Pseudovirions can infect cell, but they don’t
replicate.
Dr. Dalia M. Mohsen
Prof. In microbiology
1) Are infectious particles that are composed solely of
protein.
2) They contain no detectable nucleic acid.
Dr. Dalia M. Mohsen
Prof. In microbiology
• is the process of naming viruses and placing them into a
taxonomic system.
 Morphologys
 Nucleic acid type
 Host organisms
 Type of disease they cause
• Most clinically important viruses can be classified into groups
according to their structural characters into:
A
•RNA Viruses
B
•DNA Viruses
Dr. Dalia M. Mohsen
Prof. In microbiology
• DNAviruses are viruses that have DNA but no RNA
1. Hepadnaviruses.
2. Herpesviridae,
3. Papovaviridae
4. Poxviridae
5. Adenoviridae.
Dr. Dalia M. Mohsen
Prof. In microbiology
• Hepadnaviruses cause serum hepatitis.
The hepatitis B virus (HBV):
• The hepatitis B virus (HBV) is a common form of this
virus that enters the body via hypodermic needles,
blood transfusion, or sexual relations
Dr. Dalia M. Mohsen
Prof. In microbiology
DNA Non-Enveloped viruses
DNA Enveloped viruses
Herpes viruses
- HSV 1&2
- Varicella
- CMV
Adenoviruses
Hepadna virus (HBV)
Pox viruses (Smallpox,
Cowpox)
Papiloma virus
Parvoviruses
Polyomaviruses
Dr. Dalia M. Mohsen
Prof. In microbiology
RNA Non-Enveloped viruses
RNA Enveloped viruses
Picorna viruses
Orthomyxoviruses (Influenza virus)
Reoviruses
Paramyxoviruses (Measles, Mumps,
- Enteroviruses (Polio virus &Coxackievirus)
- Hepato virus
- Rhinoviruses
Parainfluenza)
Caiciviruses
Rhabdoviruses (Rabies virus)
Astro viruses
Retroviruses (HIV )
Togaviruses (Encephalitis viruses)
Flaviviruses (Yellow fever ,Dengue, HCV)
Bunyaviruses
Filoviruses
Arenaviruses
Corona viruses
Delta virus
• Viral the level of order and follows as thus, with the taxon
suffixes classification starts at given in italics:
Order
• Virales
• e.g.
Herpesvirales
Family
• Viridae
• e.g.
Herpesviridae
Dr. Dalia M. Mohsen
Genus
• Virus
• e.g. Herpes
simplex virus
Prof. In microbiology