This document provides information about virus structure and classification. It begins with the history of virology and defines viruses. It describes the differences between bacteria and viruses, and between DNA and RNA viruses. It outlines the characteristics, structure, replication process, and reaction to physical and chemical agents of viruses. It discusses viral morphology, classification based on shape and presence of an envelope. It also covers bacteriophage structure and important human viruses classified by genome type and associated disease.

1. VIRUS
STRUCTURE
• ASHISH RANGHANI
• PG PART 2
• GDCH, AHMEDABAD
UNDER GUIDANCE OF
DR. J.S SHAH
PROFESSOR AND HEAD
ORAL MEDICINE AND
RADIOLOGY
GDCH
DATE- 27/07/2016

2. CONTENTS
1. History of virology
2. Definition
3. Difference Between Bacteria & Virus
4. Difference Between DNA & RNA Virus
5. Characteristics Of Virus
6. Viral Structure
7. General Morphology
8. Virus Replication
9. Reaction To Physical And Chemical
Agents
10. Virus Classification
11. Viruses In Dental Diseases
12. Oncogenic viruses
13. Transmission Of Viruses
14. Methods of Inactivating Viruses

3. History of virology
• In 1898 Martinus Beijerinck is
considered one of the
founders of virology
• Bacteriophages were
discovered in the early 20th
century, by the English
bacteriologist Frederick Twort MARTINUS BEIJERINCK
Essential Microbiology, Stuart Hogg

4. Definition of a Virus
• Obligate
• Intracellular
• Parasite
• The latin word virus means venom or poison.
• Defined as sub microscopic entity consisting of a single nucleic
acid surrounded by a protein coat and capable of replication only
within the living cells of bacteria, animals or plants.
Essential Microbiology, Stuart Hogg, The University of Glamorgan, UK
Shafer’s textbook of oral pathology, 6th edition

5. Difference Between Bacteria And Virus
BACTERIA
• Living organism,
unicellular, one cell
• Larger (1000nm)
• In latin means little
sticks
• Usually treated with
antibiotics
VIRUSES
• Not living, no cells
• Smaller (20-300nm)
• In latin means
poison
• Antibiotics will not
effect the disease
1. Ananthanarayan & paniker’s textbook of microbiology, seventh edition

6. DNA VIRUS
• Double
stranded
• Nitrogenous
bases
(Adenine,
Cytosine,
Guanine, &
Thymine
• Type of sugar-
Deoxyribose
• Location in
Nucleus
RNA VIRUS
• Single
Stranded
• Nitrogenous
bases
(Adenine,
Cytosine,
Guanine, &
Uracil
• Type of sugar-
Ribose
• Location in
Nucleus &
cytoplasm
Difference Between DNA & RNA Virus
Ananthanarayan & paniker’s textbook of microbiology, seventh edition

7. • They cannot be observed using a light microscope
• They have no internal cellular structure
• They contain either DNA or RNA, but not both
• They are incapable of metabolism
• Viruses are smaller than bacteria
• They replicate only inside living cells.
• Viruses lack cellular organelles, such as mitochondria and
ribosomes.
Essential Microbiology, Stuart Hogg, The University of Glamorgan, UK
Characteristics Of Viruses

8. Viral Structure - Overview
Nucleic acid
Capsid
Nucleocapsid
Envelope protein
Membrane protein
Viral envelope
Virion: The complete virus particle
nucleic acid + protein coat, which may be surrounded by an
envelope
The nucleic acid plus the capsid shell of a virus particle is often
called nucleocapsid

9. • Size
• Between 20-300 nm
diameter.
• Basic shape
• Rod-like
• “Spherical”
• Genomic material
• DNA or RNA never both
• Single- or double-stranded
Structure of Viruses
Jawetz, Melnick, & Adelberg’s, Medical Microbiology, Twenty-Sixth Edition

10. • Protective Shell – Capsid
• Made of many identical protein
subunits
• Protect the genetic material
• May be involved in cell entry
• Symmetrically organized
• 50% of weight
• Enveloped or non-enveloped
• Envelope: A lipid-containing
membrane that surrounds some
virus particles.
located outside the capsid)
It is acquired during viral
maturation
Structure of Viruses

11. Viral Structure: Capsid
Capsid = protein coat that
encloses and protects the
nucleic acid of a virus
• Accounts for most of the
viral mass
• Composed of single or
multiple proteins
• Each subunit =
capsomeres

12. Virus Classification 2
Based on Shape
• Polyhedral viruses
• Helical Viruses
• Complex viruses
Based on Envelope
• Naked viruses
• Enveloped viruses

13. General Morphology
Capsid Structure determines shape:
• Helical Viruses = nucleic acid is inside a hollow cylindrical
capsid with a helical structure
• Rabies, Ebola viruses, Tobacco Mosaic Virus
• Polyhedral viruses = many sided; icosahedron is common with
20 equilateral triangles as sides and 12 vertices
• Poliovirus, Adenovirus, herpes,
• Complex structures
• Pox virus & bacteriophage

14. Viral Structure: Envelope
a) Non-enveloped viruses/ Naked Viruses = viruses whose capsids
are not covered by an envelope
b) Sometimes, Capsid covered with envelope
• SPIKES = carbohydrate-protein complexes (glycoproteins) that
project from the envelope
• Can be used to attach to host cell

15. Viral Structure: General Morphology
Enveloped Viruses = can be helical or polyhedral, but the
capsid is surrounded by an envelope
• Helical: influenza virus
• Polyhedral (icosahedral): Herpes simplex virus

16. Complex viruses
•Complex structures; additional
structures attached to capsids,
combos of helical and polyhedral,
may have several coats around
nucleic acid
•Bacteriophage, poxviruses

17. BACTERIOPHAGE4
•Viruses that infect bacterial cells are called
bacteriophages (phages for short), which means
‘bacteria eaters’
•These are large, complex viruses, with a
characteristic head and tail structure
•The double-stranded, linear DNA genome contains
over 100 genes, and is contained within the
icosahedral head
Essential Microbiology, Stuart Hogg, The University of Glamorgan, UK

18. • Capsid (head): polyhedral and the
tail sheath is helical.
• Head - the nucleic acid.
• Tail : hollow tube through which the
nucleic acid passes during infection
• T4 -largest phage.
• T4 tail - surrounded by a contractile
sheath, which contracts during
infection of the bacterium.
• End of the tail: base plate and one
or more tail fibers attached to it.
• The base plate and tail fibers -
involved in the binding of the
phage to the bacterial cell.
• Not all phages have base plates and
tail fibers.
18

19. How Viruses Multiply4
- Viruses

20. Virus Replication2
1 Virus attachment
1 2 Penetration
2
3 Uncoating
3
4 Transcription
5 Genome replication4
5
6 Translation of virus
mRNAs
6
7 Virion assembly
7
8 Release of new
virus particles
8
20Jawetz, Melnick, & Adelberg’s, Medical Microbiology, Twenty-Sixth Edition

21. • The first step in viral infection is attachment, interaction of a
virion with a specific receptor site on the surface of a cell.
• Receptor molecules differ for different viruses but are generally
glycoproteins.
• human immunodeficiency virus binds to the CD4 receptor on
cells of the immune system,
• Rhinoviruses bind intercellular adhesion molecule 1 (ICAM-1),
• Epstein-Barr virus recognizes the CD21 receptor on B cells.
• The presence or absence of receptors plays an important
determining role in viral pathogenesis.
• The attachment step may initiate irreversible structural changes
in the virion.
ATTACHMENT

22. Penetration
• After binding, the virus particle is taken up inside the cell.
This step is referred to as penetration

23. UNCOATING
• Uncoating occurs shortly after penetration.
• Uncoating is the physical separation of the viral nucleic acid from the outer
structural components of the virion so that it can function.
• The genome may be released as free nucleic acid (picornaviruses) or as a
nucleocapsid (reoviruses).
• The nucleocapsids usually contain polymerases.
• Uncoating may require acidic pH in the endosome.
TRANSCRIPTION:
• Virus mRNA is produced using either cellular enzymes or
virus-coded enzymes.

24. GENOME REPLICATION
• This stage can take place in either the cytoplasm or nucleus
of the infected cell.
• Depending on the size of the virus genome the enzymes
involved in genome replication may be encoded by either
the virus itself or the host cell
• This stage uses the host cell machinery - ribosomes and
enzymes etc.
• Various proteins are synthesised - structural - only in virion
- and non-structural - detected only in the virus-infected
cell.
TRANSLATION

25. VIRION ASSEMBLY
• The newly formed virus proteins and genomic nucleic acid assemble
to produce the new virus particles.
VIRION RELEASE
• Various strategies are available for the release of the
progeny virus from the infected cell depending on the
particular virus group.
• The virus may bud through the cell membrane OR
• The virus may simply cause lysis of the cell resulting in cell
death and the release of progeny virus particles.

26. REACTION TO PHYSICAL AND
CHEMICAL
AGENTS2
Jawetz, Melnick, & Adelberg’s, Medical Microbiology, Twenty-Sixth Edition

27. Heat and Cold
• Viral infectivity is generally destroyed by heating at 50–60°C
for 30 minutes
• Viruses can be preserved by storage at subfreezing
temperatures and can thus be preserved in the dry state at
4°C.
pH
• Viruses are usually stable between pH values of 5.0 and 9.0.
• Some viruses (eg, enteroviruses) are resistant to acidic
conditions.
• All viruses are destroyed by alkaline conditions.

28. • Ultraviolet, x-ray, and high-energy particles inactivate
viruses.
Radiation
• Ether susceptibility can be used to distinguish viruses that
possess an envelope from those that do not
Ether Susceptibility
Formaldehyde
• Formaldehyde destroys viral infectivity by reacting with
nucleic acid.
• Viruses with single-stranded genomes are inactivated much
more readily than those with double-stranded genomes.

29. Classification of major virus groups
1. Herpesvirus
2. Poxvirus
3. Adenovirus
4. Parvovirus
5. Papovavirus
1. Orthomyxovirus
2. Paramyxovirus
3. Rhabdovirus
4. Tagovirus
5. Retrovirus
6. Reovirus
7. Picornavirus
8. Coronavirus
Shafer’s textbook of oral pathology, 6th edition
DNA VIRUSES RNA VIRUS

30. Virus Classification 2
• Based on genome structure
•BALTIMORE CLASSIFICATION
• DNA or RNA (never both)
• ssDNA viruses
• dsDNA viruses
• ssRNA viruses
• Plus Strand (+RNA viruses)
• Same
• Negative strand (- RNA viruses)
• Complementary
• Retroviruses
• Converted into complementary DNA, then into the cell for
replication
• dsRNA viruses

31. Important viruses of humans
VIRUS DISEASE Genome Type
Adenovirus Respiratory infections dsDNA
Epstein barr virus Infectious mononucleosis
Nasopharyngeal carcinoma
Burkitt's lymphoma
dsDNA
Herpes simplex Type 1 Cold sores dsDNA
Herpes simplex Type 2 Genital warts dsDNA
HIV AIDS (+)ssRNA
HPV Warts dsDNA
Influenza virus Influenza (-)ssRNA
Essential Microbiology, Stuart Hogg, The University of Glamorgan, UK

32. VIRUS DISEASE Genome Type
Ebola virus Haemorrhagic
fever
(-)ssRNA
Paramyxo virus Mumps (-)ssRNA
Polio virus Poliomyelitis (+)ssRNA
Rabies Virus Rabies (-)ssRNA
Rubella virus German measles (+)ssRNA
Small pox Small pox dsDNA
Vericella Zoster Chicken pox,
shingles
dsDNA
Essential Microbiology, Stuart Hogg, The University of Glamorgan, UK

33. 1. Medical Microbiology and Infection at a Glance, Stephen H. Gillespie, 4th edition

34. 1- Double stranded DNA families
• 1- POX VIRUS
• 2- HERPES VIRUS
• 3- HEPADNA VIRUS
• 4- ADENO VIRUS
• 5- PAPOVA VIRUS

35. 2- Single stranded DNA families.
3- Double stranded RNA families.
• Single stranded DNA family:
1- Parvoviridae.
• Double stranded RNA family:
1- Reoviridae .

36. 4- Single stranded RNA families with positive strands
• 1-Picornaviridae.
• 2- Caliciviridae.
• 3- Astroviridae.
• 4- Coronaviridae.
• 5- Flaviviradae.
• 6- Togaviridae.
• The viral genome acts directly as m-RNA.

37. 5- Single stranded RNA families with negative strands
• 1- Orthomyxoviridae.
• 2- Paramyxoviridae.
• 3- Rhabdoviridae.
• 4- Filoviridae.
• The viral genome does not act as m-RNA.
• It must be transcribed by the viral enzyme transcriptase into
m-RNA.
• Virions contain the enzyme transcriptase.

38. 6-Single stranded RNA viruses associated with the
enzyme reverse transcriptase
• Retroviruses.
• The viral genome is reverse transcribed into a
complementary DNA strand using the enzyme reverse
transcriptase.

39. X-RAY CRYSTALLOGRAPHY
In visualizing the structure of a virus
•It is a means of
determining the physical
structure, dimensions of
the individual proteins
and components of the
virus.
•It is used to generate
information about the
overall shape of the
virus; it is also used
with diagnostic
purposes through
detection of virus
Electron microscopy

40. Viruses In Dental Diseases
•HSV Virus
•Varicella Zoster Virus
•Small Pox Virus
•Paramyxovirus
•HPV Virus
•Measles Virus
•Coxsackie Virus
•HIV Virus
•HHV-8 Virus

41. HSV STRUCTURE
• Virions are spherical, 150-
200nm in diameter
• HSV-1 and HSV-2 contains
i. Genome (linear, a large
double-stranded viral DNA;
encoding 70-200 proteins)
ii. An icosahedral capsid
iii. A tegument—an amorphous
layer of proteins that surround
the capsid
iv. An envelope- derived from the
nuclear membrane of the
infected cell; contains viral
glycoproteins
v. Incubation period is 1- 26
days
Ananthanarayan & paniker’s textbook of microbiology, seventh edition

42. Herpes viruses1
Herpesviruses are divided into three groups:
• α-herpesviruses are fast-growing cytolytic viruses that
establish latent infections in neurones (e.g. herpes simplex
and varicella zoster);
• β-herpesviruses are slow-growing viruses that become
latent in secretory glands and kidneys (e.g. cytomegalovirus
[CMV], HHV6 and 7);
• γ-herpesviruses are latent in lymphoid tissues (e.g. Epstein–
Barr virus [EBV], HHV-8).
Classification
Medical Microbiology and Infection at a Glance, Stephen H. Gillespie, 4th edition

43. VARICELLA ZOSTER VIRUS
• VZV is similar to the
herpes simplex virus
in morphology
• Incubation period 7-
23 days
• Disease –
1. Herpes zoster
2. Chicken pox
Ananthanarayan & paniker’s textbook of microbiology, seventh edition

44. SMALLPOX VIRUS
• The virion is brick shaped
• In vertical section it consists of a
double layered membrane which
surrounds a biconcave nucleoid
containing the DNA core
• On either side of the nucleoid is a
lens shaped structure called the
lateral body
• Incubation period of 7-10 days
Ananthanarayan & paniker’s textbook of microbiology, seventh edition

45. PARAMYXO VIRUS
• Paramyxoviruses resemble
orthomyxoviruses in morphology but
larger and more pleomorphic
• They are spherical in shape & size from
100 to 300nm
• The genome is a linear single stranded
RNA
• The Nucleocapsid is surrounded by a lipid
envelop which has matrix M protein at its
base & two types of glycoprotein spike at
the surface
• The longer spike is hemagglutinin(H) or
HN protein. Its responsible for absorption
of the virus to the host cell surface
• The second spike is F (fusion) protein
• Responsible for MUMPS (Epidemic
Ananthanarayan & paniker’s
textbook of microbiology, seventh
edition

46. MEASLES VIRUS
• The virus has the general
morphology of paramyxoviruses
• It is a roughly spherical but often
pleomorphic particle
• 120-250 nm in diameter
• The tightly coiled helical
nucleocapsid is surrounded by
the lipoprotein envelope carrying
on its surface hemagglutinin (H)
spikes
• Incubation periods 9 to 11 days
Ananthanarayan & paniker’s textbook of microbiology, seventh edition

47. HPV VIRUS
• These are small, enveloped, double-
stranded DNA viruses with more than 100
types
• Icosahedral particles (52-55nm)
• 72 capsomers (60 hexameric + 12
pentameric)
• There are 2 capsid proteins, 1 major
(encoded by the L1 gene) and 1 minor
• Infects only humans
• High risk (oncogenic) types
• 16, 18, 31, 33, 35
• Low risk (non-oncogenic) types
• 6, 11, 40, 42, 43
Ananthanarayan & paniker’s textbook of microbiology, seventh edition

48. • HPV 16, 18 are responsible for
1. LEUKOPLAKIA
2. SQUAMOUS CELL CARCINOMA
3. VERRUCOUS CARCINOMA
• HPV 6 & 11 for SQUAMOUS
PAPILLOMA
• HPV 9,11,13,16,18,24,25,26 for
KERATOCANTHOMA
• HPV 13,32 for Hecks disease
• VERRUCA VALGARIS mosly cause
by type 1,2,3,4.
• Some are responsible for
common warts and genital warts.
• Types 16 and 18 predominate in
cervical neoplasia
HPV VIRUS
Shafer’s textbook of oral pathology, 6th edition

49. STRUCTURE OF ADENOVIRUS
• Adenoviruses are medium
sized (70-90nm)
unenveloped, icosahedral,
double-stranded DNA
viruses
• There are more than 50
serotypes of human
adenoviruses, which are
divided into six groups (A–F)
on the basis of their
genomic homology
Ananthanarayan & paniker’s textbook of microbiology, seventh edition

50. COXSACKIEVIRUS
• 24-30nm
• Spherical
• Naked, icosahedral
• +ssRNA
• Multiply in the cytoplasmAt least 23 serotypes
(1-22, 24) of group A and 6 serotypes (1-6) of
group B are recognized
• Diseases Caused by Coxsackievirus
• Herpangina
• coxsackie A virus
• Hand-foot-and-mouth disease
• Coxsackievirus A16
• Myocardial and pericardial infections
• coxsackie B virus. (B3)
Ananthanarayan & paniker’s textbook of microbiology, seventh edition

51. PARVOVIRUS1
• Parvoviruses are small, unenveloped , icosahedral, single-stranded
DNA viruses with one serotype, B19, known to cause human
• disease and given the genus name Erythrovirus.
Ananthanarayan & paniker’s textbook of microbiology, seventh edition

52. HIV VIRUS
• Family : Retroviridae
• HIV is Spherical enveloped RNA virus
about 90-120nm in diameter
• Envelope gp160; gp120 & gp41
• Icosahedral symmetry
• Nucelocapsid
• Outer matrix protein (p17)
• Major capsid protein (p24)
• Nuclear protein (p7)
• Diploid RNA with several copies of
reverse transcriptase
52Ananthanarayan & paniker’s textbook of microbiology, seventh edition

53. HIV VIRUS
53
Each receptor is composed of 3 subunits of gp41 and 3
subunits of gp120.

54. HEPATITIS B VIRUS
• It is a DNA virus
• It belongs to the
• Family: Hepadnaviridae
• GENOTYPE A-H
• A1 & D in INDIA
Ananthanarayan & paniker’s textbook of microbiology, seventh edition

55. .
• Surface of virions consists of possibly 240 subunits comprising
of 3 different polypeptides termed Large, middle, small
surface(HBs) proteins
• The lipid in the outer protein shell or the HBs particles is
derived from an intracellular compartment & not the plasma
membrane

56. Viruses and cancer
• 10% of cancer is caused by viruses
• An oncovirus is a virus that can cause cancer
• An oncogene is a cancer causing gene
• Oncogenic viruses
• DNA viruses
• Human papillomavirus – cervical cancer
• Hepatitis B causes liver cancer

57. 57
Major human Oncogenic Viruses
DNA VIRUSES
Small DNA tumor viruses
- Human Papilloma virus (HPV)
-Adenovirus
Herpesviruses (large)
- Epstein Barr virus (EBV)
- Kaposi’s Sarcoma Herpesvirus (KSHV)
Other
- Hepatitis virus B
RNA viruses
Human T-cell Leukemia Virus 1 (HTLV1)
Hepatitis virus C
Ananthanarayan & paniker’s textbook of microbiology, seventh edition

58. VIRUSES NEOPLASMS
DNA VIRUSES
Human papilloma virus Cervical Ca, warts, ano
genital carcinoma
Herpes simplex virus II Cervical carcinoma
Epstein-Barr virus NPCa, African Burkitt’s
Human Herpes virus 8 Kaposi’s sarcoma
Hepatitis B virus Hepatocellular Ca
Herpes simplex virus 6 Certain B cell
(HBLV) lymphomas
58
Viruses Associated With The Development
Of Human Neoplasia

59. VIRUSES NEOPLASMS
RNA VIRUSES
Human T-cell leukemia virus I Some T-cell leukemia,
Lymphoma
Human T-cell leukemia virus II Some cases of hairy
cell leukemia
Human immunodeficiency virus Lymphoma; Kaposi’s
sarcoma
Viruses Associated With The Development
Of Human Neoplasia
59

60. Transmission of Viruses5
• Respiratory transmission
• Influenza A virus
• Faecal-oral transmission
• Enterovirus
• Blood-borne transmission
• Hepatitis B virus
• Sexual Transmission
• HIV
• Animal or insect vectors
• Rabies virus

61. Common Methods of Inactivating Viruses
for Various Purposes5
• Sterilize laboratory supplies and equipment,
• Disinfect surfaces or skin,
• Sterilization may be accomplished by
1. steam under pressure,
2. dry heat,
3. ethylene oxide,
4. γ-irradiation.
• Surface disinfectants include
1. sodium hypochlorite,
2. glutaraldehyde,
3. formaldehyde.
• Skin disinfectants include
• chlorhexidine, 70% ethanol, and iodophores.

62. REFERENCES
1. Medical Microbiology and Infection at a Glance, Stephen H.
Gillespie, 4th edition
2. Jawetz, Melnick, & Adelberg’s, Medical Microbiology, Twenty-Sixth
Edition
3. General Characteristics, Structure and Taxonomy of Viruses, G.R.
Carter, D. J. Wise and E. Furtado Flores, 6-Dec-2004
4. Essential Microbiology, Stuart Hogg, The University of Glamorgan,
UK
5. Ananthanarayan & paniker’s textbook of microbiology, seventh
edition
6. Shafer’s textbook of oral pathology, 6th edition