A brief lecture on medical virology for nurses

1. VIRUS
By Mr. Vincent Ejakait

2. Content
 Definition
 Characteristics
 Structure
 Classification
 Pathogenesis
 Medically relevant viruses
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3. Definitions
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4. Definition
 Virus is latin word which means poison.
 A virus is an entity whose genome is an element
of nucleic acid that replicate inside living cells,
using host’s machinery leading to transfer of
genome to other cells (Laura & Darnell, 1978).
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5. Cont..
 Virion: A complete virus particle
 Prion: Pathogen composed of proteins without
any detectable nucleic acid
 Bacteriophage: is a virus that infects and
replicates within Bacteria a
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6. Characteristics
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7. General characteristics
 Consist either of RNA or DNA but never both
 Obligate intracellular parasites
 Fails to grow on artificial media
 Smallest infectious agents
 Nucleic acid is encased in a protein shell
 Not inactivated by antibiotics
 Divide by replication
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8. General characteristic
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10. Structure (Morphology)
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11. MORPHOLOGY
 Viruses are composed of nucleic acids and
proteins.
 A single nucleic acid (RNA/DNA): stores all the
vital information required by the virus for
multiplication.
 Nucleic acid is surrounded by a coat of protein
called capsid.
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12. Morphology Cont..
• The nucleic acid and the capsid are collectively
called nucleocapsid
 The nucleocapsid in some viruses is surrounded
by an envelope (enveloped virus)
 While others have no envelope (naked virus)
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13. Morphology Cont..
 Enveloped viruses also have spikes composed of
glycoproteins on their surfaces.
 The envelope is typically a bilayer of lipid
membrane
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14. Morphology
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15. Morphology cont..
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16. Morphology cont..
 Viral nucleocapsid may have one of three
shapes:
i. Icosahedral (crystalline) shape
ii. Helical (elongated rod) shape
iii. Complex (unusual) shape
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17. ICOSAHEDRAL CAPSID
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18. HELICAL CAPSID
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19. COMPLEX CAPSID
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20. CAPSID SHAPES
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21. Size of viruses
 Viruses vary in diameter from 20-300nm
 1nm=10-9m
 Considerably smaller than most bacteria
 Cannot be seen with the compound light
microscope
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22. Cont..
 However, some viruses (e.g. vaccinia virus) are
slightly larger than the smallest bacteria
 The poxviruses (e.g. Smallpox) are largest in size
and measure around 330x230x100nm
 The smallest viruses are picorna (e.g. Polio) and
parvoviruses (e.g. Warts) which measure
between 20-40nm
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23. Viral Nucleic Acid
 Viruses posses single nucleic acid
 Some are DNA, others are RNA
 Some are double stranded, others are single
stranded
 Some are linear, others are circular
 Some have +ve polarity, others have –ve
polarity
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24. Classification
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25. Criteria for viral classification
 Nucleic Acid classification
1. DNA Viruses
2. RNA Viruses
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26. DNA vs RNA
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27. Cont..
 Nature classification
1. Linear/Circular
2. Segmented/ Non-segmented
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28. Cont..
 Strandedness classification:
1. Single-stranded (ss)
2. Double-stranded (ds)
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29. Strandedness
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30. Strandedness
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31. Cont..
 Polarity classification:
1. Sense strand (Positive) viruses
2. Antisense strand (Negative) viruses
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32. Cont..
 Presence of an envelop classification:
1. Enveloped viruses
2. Non-enveloped viruses
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33. Enveloped vs Non-enveloped virus
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34. Pathogenesis
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35. Preservation of viral infectivity
 Viruses are more sensitive to environmental
changes than other organisms.
 Their infectivity is affected by:
1. Temperature
2. pH
3. Lipid solvents
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36. Mr. Ejakait
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37. Replication of viruses
 Viruses are obligatory intracellular parasites.
 They make use of the metabolic machinery of
the host cell to undertake replication.
 The virus undergoes a sequence of events to
enable this replication in the host cell.
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38. Replication process
1. Attachment of virus to host cell
2. Penetration
3. Uncoating
4. Transcription
5. Translation
6. Genome replication
7. Assembly of virons
8. Release
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39. Steps in viral replication
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40. Steps in viral replication Cont..
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41. Mr. Ejakait
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Easy replication explanation

42. Viral replication video
 Viral replication video
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43. Viral pathogenicity
 Viruses gain access to the host through:
 Skin
 Mucous membrane
 Respiratory tracts
 Gastrointestinal tract
 Genital tract
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44. Cont..
 Infection caused by viruses are either:
1. Localized: at or near the site of entry
2. Generalized: involve one or more target
organs
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45. Medically significant Viruses
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46. 1. DNA viruses
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47. DNA viruses
 Adenoviruses
 Poxviridae
 Papovaviruses
 Parvoviruses
 Herpesviruses
 Herpes simplex virus
 Varicella-zoster virus
 Cytomegalovirus (CMV)
 Epstein-Barr (EB) Virus
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48. Adenoviruses
 Derive their name from human adenoid tissue
from which they were first isolated.
 Adenovirus infections of humans include:
 Acute respiratory disease, Soar throat,
Pneumonia, keratoconjuctivitis, swimming
pool conjuctivitis
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49. Mr. Ejakait
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KERATOCONJUCTIVITIS SWIMMING POOL CONJUCTIVITIS

50. Poxviridae
 This is the family of virus belonging to the
causative agent of Smallpox.
 Other diseases associated with this family of
viruses include:
 Cowpox, Buffalopox, Tanapox
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51. Smallpox
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52. Smallpox
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53. Cowpox 53
COW’S URDER HUMAN HAND
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54. Papovaviruses
 They are small double stranded DNA viruses.
 The most significant virus of this family is the
Human Papilloma Virus (HPV).
 Other diseases associated with these viruses
include:
 Genital warts, Skin warts
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55. Male genital warts
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56. Female genital warts 56
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57. Herpes viruses
 The family Herpesviridae consist of more than
80 viruses with considerable diversity.
 Till to date 7 different herpes viruses have been
isolated whose natural host is man.
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58. Herpes simplex virus
 Divided into 2 types:
 Type 1 virus (HSV-1): infects regions of body
above the waist
 Type 2 virus (HSV-2): affects genital and anal
regions
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59. HSV-1
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60. HSV-2
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61. Varicella zoster virus
 This is the virus responsible for 2 diseases of
man:
 Varicella zoster
 Herpes zoster
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62. Cont..
1. Varicella zoster
 Commonly known as Chickenpox
 Varicella is contagious, generalized
disease.
2. Herpes zoster
 Commonly known as shingles
 Characterized by unilateral, painful, vesicular
eruption localized to the dermatone
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63. Varicella Zoster (Chicken pox)
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64. Herpes zoster (Shingles) 64
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65. Epstein-Barr (EB) Virus
 This virus was discovered by Epstein and Barr.
 Epstein-Barr virus has been linked to Burkitt’s
lymphoma which is a form of malignancy.
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66. Burkitt's lymphoma
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67. 2. RNA viruses
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68. RNA viruses
 Human Immunodeficiency Virus (HIV)
 Arboviruses
 Rubella
 Picornaviridae
 Orthomyxoviridae
 Paramyxoviridae
 Rhabdoviridae
 Rotavirus
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69. Human immunodeficiency
Virus (HIV)
 Belongs in the RNA virus family of retroviruses
 The virus leads to the Acquired
Immunodeficiency syndrome (AIDS) diseases
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70. HIV
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71. Arboviruses
 These are viruses which multiply in blood
sucking arthropods and transmitted to
vertebrates by bite.
 Diseases caused by this family of viruses
include:
 Dengue, Yellow fever, Chikungunya
 Most of these present with hemorrhagic fever
symptoms
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72. Dengue Fever Chikungunya rash
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73. Rubella virus
 Also known as the German measles
 Rubella diseases is important because of the
severe congenital malformations it can cause in
the child if the mother contracts infection
during the first trimester of pregnancy
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74. Mr. Ejakait
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75. Picornaviridae
 These viruses are the smallest and hence the
name pico (small) RNA viruses
 Member of this family include:
 Polioviruses
 Hepatitis A virus
 Rhinoviruses
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76. Mr. Ejakait
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Poliomyelitis

77. Orthomyxoviridae
 This is the family of influenza viruses.
 Within this family viruses have been grouped
into three genera: Influenza A, B and C
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78. Mr. Ejakait
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79. Paramyxoviridae
 This group of viruses include:
 Parainfluenza virus,
 Mumps virus,
 Measles virus
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80. Mr. Ejakait
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Mumps Measles

81. Rhabdoviridae
 Rabies virus belongs to this family.
 Rabies is primarily a disease of animals who can
transmit it to man through their bite.
 Hydrophobia is the typical feature of disease
wherein patient goes into convulsion while
attempting to drink water.
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82. Rabies
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83. Rotavirus
 Is the single most important agent of infantile
gastroenteritis throughout the world
 The rotavirus vaccine is currently under use in
Kenya.
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84. Rotavirus
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85. Mr. Ejakait
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GE Effect of rotavirus Rotavirus vaccine

86. THE END
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