Based on viruses

1. VIRUS MORPHOLOGY &
VIRUS MORPHOLOGY &
CLASSIFICATION
CLASSIFICATION
ELIZABETH P. QUILES, M.D., FPASMAP
ELIZABETH P. QUILES, M.D., FPASMAP
OUR LADY OF FATIMA UNIVERSITY
OUR LADY OF FATIMA UNIVERSITY
COLLEGE OF MEDICINE
COLLEGE OF MEDICINE

2. • Not cells
Not cells
• Smallest infectious agent (20nm to 300
Smallest infectious agent (20nm to 300
nm)
nm)
– smallest RNA virus
smallest RNA virus 
 Picornavirus
Picornavirus
– smallest DNA virus
smallest DNA virus 
 Parvovirus
Parvovirus
– largest virus
largest virus 
 Poxvirus
Poxvirus

3. • Most have spherical shapes EXCEPT
Most have spherical shapes EXCEPT
– Rhabdovirus
Rhabdovirus 
 bullet-shaped
bullet-shaped
– Poxvirus
Poxvirus 
 brick-shaped
brick-shaped
– Bacteriophage
Bacteriophage 
 tadpole-shaped
tadpole-shaped
– Tobacco Mosaic virus
Tobacco Mosaic virus 
 rod-shaped
rod-shaped

4. • Composed of only one type of nucleic acid
Composed of only one type of nucleic acid
• Obligate intracellular parasites
Obligate intracellular parasites 
 inert in
inert in
the extracellular environment
the extracellular environment 
 multiply
multiply
only in living cells
only in living cells 
 parasites at the
parasites at the
genetic levels
genetic levels

5. • Do not undergo mitosis or binary fission
Do not undergo mitosis or binary fission
• Do not have cell wall & ribosome
Do not have cell wall & ribosome
• Sensitive to interferon
Sensitive to interferon

6. STRUCTURE
STRUCTURE
• VIRAL NUCLEIC ACID (GENOME)
VIRAL NUCLEIC ACID (GENOME)
– contain the genetic material necessary for
contain the genetic material necessary for
replication
replication
– either a DNA or RNA
either a DNA or RNA
– maybe single-stranded or double-stranded
maybe single-stranded or double-stranded

7. – can be linear or circular
can be linear or circular
– Segmented or nonsegmented
Segmented or nonsegmented
– haploid
haploid 
 contain only one copy of their
contain only one copy of their
genes EXCEPT Retroviruses
genes EXCEPT Retroviruses
– used as major criterion in the classification of
used as major criterion in the classification of
viruses
viruses

8. • CAPSID
CAPSID
– protein coat made up of repeating subunits
protein coat made up of repeating subunits 

CAPSOMERES (gives the virus its geometric
CAPSOMERES (gives the virus its geometric
symmetry)
symmetry)
– 2 forms of symmetry:
2 forms of symmetry:
1. icosahedral – capsomeres arranged in 20
1. icosahedral – capsomeres arranged in 20
triangles
triangles
2. helical – arranged in a hollow coil that
2. helical – arranged in a hollow coil that
appears rod-shaped
appears rod-shaped

9. HELICAL SYMMETRY
HELICAL SYMMETRY

10. ICOSAHEDRAL SYMMETRY
ICOSAHEDRAL SYMMETRY

11. Functions of the viral capsid:
Functions of the viral capsid:
1. protect the genetic material
1. protect the genetic material
2. site of receptors
2. site of receptors 
 mediate
mediate
attachment
attachment
3. serve as antigenic determinants
3. serve as antigenic determinants
4. induce antibody production
4. induce antibody production
5. determinants of type specificity
5. determinants of type specificity
6. Provide the structural symmetry of the
6. Provide the structural symmetry of the
virus
virus

12. • ENVELOPE
ENVELOPE
– a lipoprotein derived from the host cell
a lipoprotein derived from the host cell
membrane & virus specific protein
membrane & virus specific protein
– composed of glycoproteins (peplomers)
composed of glycoproteins (peplomers)
that appear as spikes
that appear as spikes
– Acquired through budding from the
Acquired through budding from the
host’s cell membrane in the course of
host’s cell membrane in the course of
maturation
maturation

13. – Confers instability to the virus because
Confers instability to the virus because
of the loss of infectivity due to
of the loss of infectivity due to
disruption or loss of lipid
disruption or loss of lipid 
 more
more
sensitive to heat, detergents & lipid
sensitive to heat, detergents & lipid
solvents
solvents

14. –Functions:
Functions:
1. site of receptors
1. site of receptors 
 attach to
attach to
host cell receptors &
host cell receptors &
membrane fusion
membrane fusion
2. antigenic determinants
2. antigenic determinants
3. stimulate antibody production
3. stimulate antibody production
4. determinants of type specificity
4. determinants of type specificity

15. TERMINOLOGIES
TERMINOLOGIES
• VIRION – a complete viral particle
VIRION – a complete viral particle
- in naked viruses
- in naked viruses
 virion is identical to
virion is identical to
the nucleocapsid
the nucleocapsid
- in enveloped viruses
- in enveloped viruses 
 must acquire
must acquire
envelop before it is considered a virion
envelop before it is considered a virion
• NUCLEOPCAPSID – a protein-nucleic acid
NUCLEOPCAPSID – a protein-nucleic acid
complex
complex

16. ATYPICAL VIRUS-LIKE AGENTS
ATYPICAL VIRUS-LIKE AGENTS
• DEFECTIVE VIRUSES – composed of
DEFECTIVE VIRUSES – composed of
nucleic acid & proteins but cannot
nucleic acid & proteins but cannot
replicate without a helper virus
replicate without a helper virus
• PSEUDOVIRION – contain host cell DNA
PSEUDOVIRION – contain host cell DNA
instead of viral DNA within the capsid
instead of viral DNA within the capsid

17. • VIROIDS – consist solely of a single
VIROIDS – consist solely of a single
molecule of circular RNA without a protein
molecule of circular RNA without a protein
coat or envelope
coat or envelope
• PRIONS – infectious protein particles
PRIONS – infectious protein particles
composed solely of proteins
composed solely of proteins

18. Yes
No
Inflammatory
Response
Yes
No
Antibody
Response
Icosahedral or helical
Amyloid-like
Appearance
Yes
No
Heat
Inactivation
Yes, encoded by viral
genes
Yes, encoded by
cellular genes
Protein
Yes
No
Nucleic acid
CONVENTIONAL
VIRUSES
PRIONS
FEATURE

19. VIRUS CLASSIFICATION
VIRUS CLASSIFICATION
1.
1. Virion morphology - size, shape,
Virion morphology - size, shape,
symmetry, +/- of peplomers, +/- of
symmetry, +/- of peplomers, +/- of
membrane
membrane
2.
2. Virus genome – DNA or RNA, size,
Virus genome – DNA or RNA, size,
strandedness, segments
strandedness, segments
3.
3. Physicochemical properties of the virion
Physicochemical properties of the virion
– molecular mass, bouyant density,
– molecular mass, bouyant density,
stability & susceptability
stability & susceptability

20. 1.
1. Antigenic properties
Antigenic properties
2.
2. Virus protein properties – number, size,
Virus protein properties – number, size,
activities
activities
3.
3. Biological properties – host range, MOT,
Biological properties – host range, MOT,
vector relationships, pathogenicity, tissue
vector relationships, pathogenicity, tissue
tropism & pathology
tropism & pathology

21. Vaccinia,
Variola,
Molluscum
contangiosum
DS, linear
Complex
+
Poxviruses
HSV, VZV,
CMV, EBV,
HHV6
DS, linear
Icosahedral
+
Herpesviruses
Hepatitis B
virus
DS, incomplete
circular
Icosahedral
+
Hepadnavirus
Adenoviruses
DS, linear
Icosahedral
-
Adenovirus
HPV, Polyoma
DS, circular
Icosahedral
-
Papovavirus
B19 virus
SS, linear
Icosahedral
-
Parvovirus
IMPORTANT
VIRUSES
DNA
STRUCTURE
SYMMETRY
ENVELOPE
FAMILY

22. Orthoviridae,
Bunyaviridae
Rhabdoviridae,
Paramyxoviridae,
Filoviridae
SS segmented
SS
Enveloped
Helical
Flaviviridae
Arenaviridae
Coronaviridae
Retroviridae
SS
SS segmented
SS
SS diploid
Enveloped
Unknown or
complex
Togaviridae
SS
Enveloped
Picornaviridae
Astroviridae
Caliciviridae
Reoviridae
SS
SS
SS
DS segmented
Naked
Icosahedral

23. GENERAL PRINCIPLES
GENERAL PRINCIPLES
DNA VIRUSES:
DNA VIRUSES:
• Double stranded DNA except Parvovirus
Double stranded DNA except Parvovirus
• Naked except Herpes, Hepadna &
Naked except Herpes, Hepadna &
Poxviruses
Poxviruses
• Icosahedral symmetry except Poxviruses
Icosahedral symmetry except Poxviruses
• Replicate in the nucleus except Poxviruses
Replicate in the nucleus except Poxviruses

24. RNA VIRUSES
RNA VIRUSES:
:
• Single stranded RNA except Reovirus
Single stranded RNA except Reovirus
• Enveloped except Reovirus & Picornavirus
Enveloped except Reovirus & Picornavirus
• Helical symmetry except Reovirus,
Helical symmetry except Reovirus,
Picornavirus & Togavirus
Picornavirus & Togavirus
• Replicate in the cytoplasm except
Replicate in the cytoplasm except
Orthomyxovirus & retroviruses
Orthomyxovirus & retroviruses