Virus classification

1. VIRUS
DR.VINUTHA M G
FINAL YR PG SCHOLAR
GAMC, BANGALORE

2. CONTENTS
• GENERAL PROPERTIES OF VIRUSES
• VIRUS HOST INTERACTIONS
• POX VIRUS
• HERPES VIRUS
• ADENO VIRUS
• PICORNA VIRUS
• ORTHOMYXO VIRUS
• PARAMYXO VIRUS

3. GENERAL PROPERTIES OF VIRUSES
• DEFINITION
Virus-poison
Smallest
Obligate
Intracellular
Infective agent
Nucleic acid ( DNA/RNA)
Non living/living

4. CONTD…
• MORPHOLOGY
Size- 20-300nm
Smallest-parvo
Largest – small
Electron microscope
Mimi virus
Mama virus
Bacteriophage

5. CONTD..
• STRUCTURE
Nucleic acid core- genome
Capsid –protein coat
Nucleocapsid
Capsomers – protein subunits
Envelope – lipoprotein
Peplomers – spikes of proteins

6. CONTD..

7. CONTD..
• SYMMETRY
Icosahedral:
papova, picorna, adeno(non enveloped)
Herpes, tago (enveloped)
Helical:
Enveloped, RNA viruses
Complex:
Pox virus

8. CONTD..

9. CONTD..
• SHAPES
Pox-brick
Rabies-bullet
TMV-rod
Irregular
Pleomorphic

10. CONTD..
• CHEMICAL PROPERTIES
NUCLEIC ACID- single/double stranded
DNA/RNA
VIRAL PROTEIN & LIPIDS

11. CONTD..
• SUSCEPTIBILITY TO PHYSICAL AND CHEMICAL
AGENTS
TEMPERATURE:
Heat labile
Seconds- 56 deg
Minutes-37 deg

12. CONTD..
Days -4 deg
Hep.B-60 deg -1hr
Long term storage—70 deg
Lyophilisation
Freeze drying

13. CONTD..
PH:
Viable – 5-9
Killed-extreme acidity & alkalinity
Enteroviruses- resistant acidic
Rhinoviruses- susceptible
LIPID SOLVENTS:
Chloroform,ether & detergents-enveloped v.
Resistants – naked v.

14. CONTD..
RADIATIONS:
Sunlight, UV, ionising radiations
VIRAL HAEMAGGLUTININ:
Haemagglutinin spikes- peplomers
Influenza, para influenza, mumps, enterovirus,
reovirus

15. REPLICATION OF VIRUSES
1. Adsorption/attachment-random
collision, ligands . Eg. Influenza, hiv
2. Penetration/viropexis – phagocytosis
Envelope+ Pls.mem-nuc.pla(cyto)
3. Uncoating – stripping, lysosomal
enzymes
4. Biosynthesis – nuclues/
cytoplasm/both (differs)
a. Transcription of mRNA from viral
nucleic acid
b.Translation of mRNA to early
proteins
c.Replication and synthesis of late
proteins
5. Maturation – n.a+ capsid-daughter
virions- nucleus/cytoplasm-?
Envelop
6. Release – budding from cell
membrane

16. CONTD..
• CULTIVATION OF VIRUSES
1. Animal inoculation:
2. Embyonated egg inoculation
a. CAM
b. Allantoic cavity
c. Amniotic sac
d. Yolk sac Inoculation

17. CONTD..
3. Tissue culture
a. Organ culture-tracheal ring in corona v.
b. Explant culture- rare
c. Cell culture
i. Primary cell cultures
ii. Diploid cell strains
iii. Continous cell lines

18. CONTD..
• DETECTION IN CULTURES
1. Cytopathic effects:
a. Synctium- measles, RSV
b. Cell necrosis & Lysis- Entero V.
c. Cellular clumping-Adeno V.
2. Haemadsorption:Orthomyxo, Paramyxo
3. Interference- Rubella

19. CONTD..

20. CONTD..
4. Transformation: Oncogenic V.
5. Immunofluorescence:
stain- fluoroscent microscope- v. antigen
6. Electron microscopy:
ultra thin section of infected cells
7. Detection of Enzymes:
Culture fluids- retro virus- reverse
transcriptase

21. CONTD..

22. NOMENCLATURE OF VIRUSES:
Nomenclature
1. Families- Viridae
2. Subfamilies – Virinae
3. Genera- Virus
4. Viral species: A group of
viruses sharing the same
genetic information and
ecological niche (host)
• Common names are used
for species
• Subspecies are designated
by a number
Example
Retroviridae
Orthoretrovirinae
Lentivirus
Human immunodeficeincy virus
HIV
HIV1 & HIV2

23. CONTD..
• Nucleic acid- DNA/RNA
• Symmetry of capsid- 3
• Enveloped/Naked
• Genome architecture-ds/ss
• Baltimore classification
Viruses were divided into six groups based on
the their nucleic acid and m-RNA production.

24. CONTD..
1- ds-DNA viruses.
2- ss-DNA viruses.
3- ds- RNA viruses.
4- ss-RNA viruses with positive strands( positive
polarity).
5- ss-RNA viruses with negative strands(negative
polarity).
6- ss-RNA viruses associated with the enzyme
reverse transcriptase.

26. TRANSMISSION OF VIRAL INFECTIONS
1.Respiratory tract
2.Alimentary tract
3.Skin
4.Genital tract
5.Conjunctiva
Influenza, para infl, RSV,
MMR, Rhino, CMV
Polio, Adeno, HAV, HEV, Rota
Herpes simplex, Arbo,
Papilloma, Rabies, HBV
Herpes simplex, HBV, HCV,
HIV, Papilloma
Adeno, Entero

27. VIRUS HOST INTERACTIONS
1. Cytocidal infection
cell death- polio
2. Cell transformation
HBV, HCV, EBV
3. Latent infection
Herpes simplex, Varicella-Zooster, Oncogenic

28. CONTD..
4. Inclusion bodies
Virus spfc. Intracellular globular masses
Light microscope
Cytoplasm(DNA V)/Nuclues(RNA)/Both
e.g:Rabies-Negri bodies
Vaccinia- Guarneiri B.
Moll.Cont-Molluscum

30. HOST RESPONSE TO VIRAL INFECTION
NON SPECIFIC RESPONSES
• Age- Rotavirus
• Hormones-Cortico steroids
• Malnutrition
• Body temp.-natural defence
• Phagocytosis- Macrophages
• Interferons- Glycoproteins
alpha, beta & gamma
IMMUNOLOGICAL RESPONSES
• AMI
IgG & IgM-Blood & tissue
IgA- Mucosal surfaces
• CMI
i.Cytolysis- cytotoxic, T, NK
ii.ADCC
iii.ACMC

31. LABORATORY DIAGNOSIS OF VIRAL
INFECTIONS
1.Detection of specific antibodies
Nuetralisation, ELISA, haemagglutination
inhibition, CFT, LAT & IF
2. Isolation of Virus
3.Direct demonstration of virus & its components
a. PCR
b. Viral antigens-ELISA, RIA, LA

32. CONTD..
c. Light microscopy- Incusion bodies
d. Fluorescent Microscopy- Direct/ Indirect
e. Immunoelectron microscopy
f. Electron microscopy
SPECIMEN VIRUSES
Faeces Rota, HAV, Adeno, Norwalk,
Astro
Vesicular fluid Herpes simplex, Varicella
zooster
CSF Entero, Varicella zooster
Urine CMV

33. POX VIRUS
CLASSIFICATION
Poxviridae
2 sub families-Chordo(Vertebrates, 4/8) &
Entomo(insects)
Largest
Light microscope
Replicate- cytoplasm

34. CONTD..
MORPHOLOGY
Complex virus
Enveloped
Double stranded DNA
RESISTANCE
Months- room temp.- protected from sunlight
Cold/freeze- yrs

35. CONTD..
Susceptible- UV
Resitant-1%phenol
Readily inactivated- Formalin
ANTIGENIC STRUCTURE
Nucleoprotein
LS antigen
Agglutinogen
Haemagglutinin

36. CONTD..
CULTIVATION
CAM-Chick embryo
Tissue cultures- Cytopathic effects
Guarneiri bodies- eosinophilic inclusion bodies
HUMAN INFECTING POX V.
1.VARIOLA
Smallpox

37. CONTD..
Epidemic, Eradicated
2 forms- Florid-v.major- India
Alastrium-V .minor- Latin america

38. CONTD..
2.MOLLUSCUM CONTAGIOSUM
Benign epidermal tumour like lesion
Arms, legs, buttocks, genital areas
Contagious, sexual transmission
Molluscum bodies-hyaline acidophilic i.b. in
epidermal cells

39. HERPES VIRUS
Herpesviridae
3 subfamilies
a. Alpha-HHV1-HSV1
HHV2-HSV2
HHV3-VZV
cercopithecine HV1-herpes BV/HVs
b. Beta- HHV5-CMV
HHV 6a, 6b & 7

40. CONTD..
c. Gamma- HHV4-EBV
HHV8-Kaposi’s sarcoma with v.
MORPHOLOGY
Icosahedral, DNA V.
Lifelong latent inf.
Envelop
Tegument
Cowdry type A

41. CONTD..
• HERPES SIMPLEX VIRUS:
Natural host- Man
2 types-1&2
1- oral & ocular lesions
2- genital infections

42. CONTD..
INFECTIONS
a.HSV-1:
Acute gingivostomatitis, herpes labialis,
keratoconjuctivitis, eczema herpeticum,
encephalitis, dendritic keratitis
b.HSV-2:
Genital herpes, neonatal herpes, aseptic
meningitis

43. CONTD..
PATHOGENESIS:
• Primary infection(Skin, Oral mucous membranes,
eyes)-Vesicle formation-lymph nodes-
lymphadenitis
• Retrograde intraaxonal flow-sensory root ganglia-
settle within neurons in ganglia
• Trigeminal(HSV 1) & Sacral (HSV 2)
• Herpes virus DNA-Host cell genome
• Reactivated by various stimuli

44. CONTD..
• VARICELLA –ZOOSTER
Varicella- chicken pox
Zooster- shingles
Chicken pox:
primary infection-non Immune
Zooster:
reactivation of latent infection

45. CONTD..

46. CONTD..
• VARICELLA:
Commenest childhood exanthemata
Respiratory route
Source-patient
IP-7-23days
Vesicular rash on trunk
Macule, papule, vesicle, pustule & scab
Centripetal

47. CONTD..
Varicella pneumonia-adults
Uneventful disease
Life long immunity
May cross placenta- viremia in pregnant
women- may infect foetus-congenital
malformations
Pneumonia

48. CONTD..
• HERPES ZOOSTER:
Herpein- creep
Zoster- girdle
Varicella- childhood
Zoster- old age & in persons who had earlier
varicella infected
Virus – remain latent in sensory ganglia

49. CONTD..
• CYTOMEGALOVIRUS
Strict host specificity
Inapparent
Prolonged latency
Occasional reactivation
Carries v. lifelong
Shed- urine, saliva, semen, cervical sec., tears &
breast milk

50. CONTD..
PATHOGENESIS:
Transmitted transplacentally
Congenital – inapparent/ cytomegalic inclusion
disease(fatal)
Hepatospleenomegaly, jaundice,
thrombocytopenic purpura, microcephaly &
Chorioretinitis
Excreted- urine & saliva

51. CONTD..
Postnatal infection
Inapparent
Sexual intercourse, blood transfusion, organ
transplantation
Infectitious mononucleosis
Hepatitis/pnuemonitis

52. CONTD..
• EPSTEIN BARR VIRUS:
Affinity- lymphoid tissues
B lymphocytes-receptors CD21 molecules- EBV
B lymphocytes-Transformed- multiply
continously
CLINICAL MANIFESTATIONS:
Ubiquitous
Lifetime

54. CONTD..
80-90% children- 3yrs
Source- saliva- oropharyngeal infection
Intimate oral contact
Oncogenic properties- burkitt’s lymphoma &
nasopharyngeal CA
1.Infectitous mono nucleosis/ Glandular fever
2.Infections in immunocompromised hosts
3.EBV-ass. malignancies

55. CONTD..
1.Glanular fever:
Self limiting disease
Children & young adults
Fever, sore throat, lymphadenopathy, abnormal
lymphocytes in PBS, subclinical hepatitis
IP-4-7 weeks
Lasts for 2-3 weeks

56. CONTD..
Activates B lympho.-secretion of
immunoglobulin(IgM high levels)
2. Infections in immunocompromised hosts
Progessive lymphoproliferative disease in
immunodeficient children, transplant
recipients & AIDS patients.
3. EBV-ass. malignancies

57. CONTD..
Burkitt’s lymphoma:
malignant neoplasm of B lympho. ( tumour of
jaw)
Endemic/ sporadic type
Nasopharyngeal CA:
B cell Lymphoma:
Recipients of transplants & HIV infected pts.
May develop EBV with B cell Lymphoma

58. CONTD..
• HUMAN HERPES VIRUS 6 & 7:
CD4+ T lymphocytes, Macrophages
Saliva
Asymptomatic
Exanthum subitum/
roseola infactum
& mononucleosis with
cervical lymphadenopathy

59. CONTD..
• HUMAN HERPES VIRUS 8:
Causitive factor for Kaposi’s sarcoma
Commonest tumour in HIV infected
PCR

60. ADENO VIRUS
Adeno- adenoid
Adenoviridae
Non enveloped
Icosahedral
DNA, repplicate in nucleus
CLASSIFICATION:
2 genera

61. CONTD..
Aviadenovirus & Mastadenovirus
Human adeno virus-7 species (A-G)
PATHOGENESIS:
Respiratory, eye, GIT & Urinary
Conjunctiva/ nasal mucosa
Faeco oral-children
IP-5-7days

62. CONTD..
Conjunctiva/ pharynx/s.i-lymph nodes
Acute febrile pharyngitis-C
Acute respiratory disease-B
IMMUNITY:
Long lasting immunity
Maternal antibodies protect infants

63. PICORNA VIRUS
Pico-Small
RNA-RNA
ssRNA -+
Non-enveloped
CLASSIFICATION
Enterovirus – enteric tract, 4 spcs A-D, poliov.-C,
rhinoV.
Parecho virus-Echovirus
Hepatovirus-HAV

64. CONTD..
Apthovirus-Foot and mouth disease
Cardiovirus
ENTERO VIRUSES: Polio V., Cocksackievirus,
ECHO V. & Entero V.
Polio v .:
Human entero virus C
Affinity for nervous tissue
Poliomyelitis

65. CONTD..
Based on nuetralisation: 3 strains
1- common & endemic
Each type- 2 spcf. Antigen C (coreless/capsid) &
D/N( dense/native)
PATHOGENESIS:
Virus-mouth-multiplies in lymphatic tissues of
oropharynx & intestine-Bloodstream-spinal
cord & brain-destroys the anterior horn cells
of spinal cord

66. CONTD..
Spread- droplet infc.
CLINICAL FEATURES:
IP-10 days ( 4days-4weeks)
Earliest- fever, malaise, headache, drowsiness,
constipation & sorethroat (1-5days)
4 types
1.Inapparent infc: (90-95%)
asymptomatic, stool/throat/both

67. CONTD..
2. Minor illness (4-8%):
Mild influenza like illness
3.non-paralytic PM(1-2%):
Headache, neck stiffness & backpain-aseptic
meningitis
4.Paralytic PM(0.1-2%):
Flaccid paralysis-spinal/bulbar/bulbospinal

68. CONTD..
Cocksackie V.:
Similar to polio virus in properties.
Similar to other entero virus in morphology.
2 groups: A & B
A:
i. Aseptic meningitis
ii. Herpangina(Vesicular pharyngitis)
iii. Hand-foot and mouth disease

69. CONTD..

70. CONTD..

71. CONTD..

72. CONTD..
B:
i. Epidemic myalgia(Bornholm D.)- fever+stitch
like pain in abdomen. Sporadic/epidemic
ii. Myocarditis & pericarditis
iii. Aseptic meningitis- with paralysis
iv. Juvenile Diabetes: B4 assc.
v. Neonatal infc.: Transplacental passage-
hepatitis, myocarditis, meningoencephalitis &
adrenocortical involvement
vi. Post viral fatigue syndrome

73. CONTD..
Echo V.:
Entericcytopathic human orphan viruses
Orphan v.
Alimentary tract
Faeco-oral route
Asymptomatic
Clinical syndromes

74. CONTD..
Aseptic meningitis, paralysis, rash
Fever, respiratory disease, infantile diarrhoea,
pericarditis & myocarditis
Common cause- aseptic meningitis
Entero viruses.:
Pneumonia & bronchitis
Acute hemorrhagic conjuctivitis
Meningitis & encephalitis

75. CONTD..
RHINO VIRUS:
Rhine-nose
Common cold
Nose, throat, rarely faeces
Acid labile
Droplet infc.-URTI
2-4days

76. CONTD..
Profuse watery discharge with nasal obstruction
Sneezing
Cough
Headache
Sore throat
Malaise
Subside-a week

77. ORTHOMYXO VIRUS
Ortrho-free
Myxa-mucous
Spherical/ filamentous
Enveloped
Ss, segmented RNA
Influenza –pigs, horse, birds
3 serotypes-a,b,& c

78. CONTD..

79. CONTD..
Matrix protein-M 1-2
2 surface glycoprotein-HA(H1-3) & NA(N1 &2)
Antigenic drift-minor antigenic changes either
H/N/both
Antigenic shift- major antigenic changes H/N
Epidemics & endemics-A
Sporadic, rarely epidemic-B
Inapparent infc.-C
1-2 yrs protection

80. CONTD..
PATHOGENESIS:
Enters-rs
Ciliated EP cells of RS-NA hydrolyse mucus film
lining of RS -expose spc. Mucoprotein
receptors for viral adsorption-death &
sloughing of ciliated EP (bacterial infc.)
IP-1-4days
Subclinical

81. CONTD..
Acute respiratory disease
Mild Coryza- fulminating pneumonia
Abrupt onset
Chills, fever, sore throat, non-productive cough,
myalgia, headache & maliase
Uncomplicated- resolves in 7 days
Extra pulmonary lesions- guillian barr synd.,
reye’s synd.(B), fatty liver

83. PARAMYXO VIRUS
Morphologically similar to OMV
Ss RNA
Helical nucleocapsid
Enveloped spherical
Single piece genome
No antigen shift/drift

84. CONTD..
Paramyxoviridae
6 genera
Respiro-HPiV 1,3
Rubula-HPiV 2,4a, 4b, mumps
Morbilli-measles
Pneumo-RSV
Meta pnuemo-HMpV

85. CONTD..
PARAINFLUENZA V.
Respiratory infc.-children
F protein
Droplets & contact with respiratory secr.
IP-2-6days
Ubiquitous
URTI
Severe-croup(laryngotracheobronchitis)

86. CONTD..
MUMPS V.:
Epidemic parotitis- mainly childhood
Saliva/aerosols
Respiratory tract
IP-16-18 days
Virus-multiplies in URT & lymph nodes-blood
stream-spreads to salivary glands, testes,
ovaries, pancreas, kidneys & brain

87. CONTD..
Non suppurative inflammation
Complications- meningitis, meningoencephalitis,
orchitis, oophoritis, pancreatitis & nephritis
Lifelong immunity
MEASLES V.
Highly infectious childhood disease
Respiratory secretions
HA +, NA -, FP +, MP +

88. CONTD..
Inhalation
IP-10-12days
Virus- multiplies in lymphoid tissue of RS-
invades blood(primary viraemia)-RES-
multiplies-Secondary viraemia- transported to
EP surfaces-skin, mouth, RS, Conjunctiva
High Fever,cough, conjunctivitis, koplik’s
spots(buccal mucosa)

89. CONTD..
Decline of 1-2 days, widespread maculopapular
rash-appears first on neck-body
Rash-delayed hypersensitivity
Post measles encephalitis & subacute sclerosing
panencephalitis(SSPE)-complications
RSV:
Pleomorphic
HA -, NA -, GP +, FP +

90. CONTD..
Highly contagious
IP-4-6days
Virus- multiplies in mucous membrane of nose,
throat, spread to LRTI- Bronchiolitis &
pneumonitis
HUMAN META PNEUMO VIRUS:
Respiratory pathogen
RS-children, similar to RSV