14. Differences between viruses & bacteria
1. They are obligatory intracellular parasites
They can not be cultivated on artificial culture
media.
can only replicate inside living cells.
15. 2. Viruses contain only one type of nucleic acid
(DNA or RNA), never both.
16.
17. 3. They can not be cultivated on artificial
culture media.
18. 4. They are not susceptible to antibacterial
agents.
19. Diagnosis of viral infections
Diagnosis of viral infections
A- Direct methods
A- Direct methods
I. Direct detection
I. Direct detection
of viruses and //or
of viruses and or
their components
their components
II. Isolation of
II. Isolation of
viruses
viruses
B- Indirect methods
B- Indirect methods
I. Serology
I. Serology
II. Skin tests
II. Skin tests
20. A- Direct methods
A- Direct methods
I. Direct detection of viruses & / or their
components:
1. Light microscopy:
Examination of large viruses
as Poxviruses
Detection of giant cells
in Herpes infection
Detection of inclusion bodies
e.g. Negri bodies in nerve
cells in rabies
21. 2. Electron microscopy (EM):
Large number of viruses in the sample.
Size and shape of viruses.
22. 3. Immunoelectron microscopy (IEM):
Sample (unknown virus) + known specific antibody
aggregation of unknown virus particles
e.g. hepatitis A virus in stools
26. 6. Nucleic acid hybridization:
A highly sensitive and specific method.
Viral nucleic acid in sample + Specific labeled probe
hybridization
fluorescence
27. 7. Polymerase chain reaction (PCR)
Amplification of a specific sequence of nucleic acid
Detection e.g. by gel electrophoresis.
28. A- Direct methods
A- Direct methods
II. Isolation of viruses:
• Obligatory intracellular parasites
• Replicate only in living susceptible
cells
a. Laboratory animals
b. Embryonated eggs
c. Cell culture (tissue culture)
29. Cultivation of viruses
a. Laboratory animals:
Used in:
• Isolation of coxsackie viruses by inoculation in
white suckling mice.
• Rabies virus inoculation in mice.
• For research.
31. Cultivation of viruses
c. Cell culture (tissue culture)
The most widely used method
Tissues + trypsin → separate cells
Cells + growth media in
flat-sided bottles
monolayer culture
33. Types of cell lines
Primary cell
lines
Diploid cell
lines
Continuous cell
lines
Prepared
from
Organ
fragments
Human fibroblasts
derived from
embryonic tissues
Tumor cells
Examples
Monkey kidney
Number of
Passages
(subcultures)
5-10
Human embryo lung
HeLa cells from
tissue
carcinoma of cervix
50-100
Unlimited
34. Detection of Virus Replication in Tissue Culture:
1- Cytopathic Effect (CPE):
i- Cell death or lysis
37. 3- Inclusion bodies
Site of virus assembly or degenerative changes
Their location and appearance are diagnostic for a
particular virus.
a- Intracytoplasmic: e.g.
Rabies (Negri bodies)
. b- Intranuclear: e.g
Herpes viruses
c- Both: e.g. Measles virus and CMV
40. 6. Interference phenomenon:
Monolayer + rubella virus → no change for
weeks
Add CPE-producing virus → NO CPE
(due to interference)
7- Detection of viral antigens
41. 8- Direct fluorescent antibody staining of
infected cells (DFA):
:Neutralization test- 9
Monolayer + unknown virus + known specific Ab
NO CPE (due to neutralization)
42. Diagnosis of viral infections
Diagnosis of viral infections
A- Direct methods
A- Direct methods
I. Direct detection
I. Direct detection
of viruses and //or
of viruses and or
their components
their components
II. Isolation of
II. Isolation of
viruses
viruses
B- Indirect methods
B- Indirect methods
I. Serology
I. Serology
II. Skin tests
II. Skin tests
43. B- Indirect methods
B- Indirect methods
I. Serological diagnosis:
Detection of antiviral antibodies
2 serum samples
acute phase & 2-3 weeks later,
to demonstrate a rising titer
(4 fold increase or more is diagnostic).
Only one sample may be used in the acute
stage to detect IgM
44. I. Serological diagnosis:
Serological methods include:
Neutralization test
Complement fixation test
Haemagglutination inhibition test
Indirect IF
ELISA
RIA
45. II. Skin tests
Used as an indication of cell-mediated immunity (CMI)
in some viral infections, e.g. mumps.
47. 1) Viruses differ from bacteria in all of the
following EXCEPT:
a) Viruses are very small in size.
b) Viruses are obligatory intracellular parasites.
c) Viruses contain both DNA and RNA.
d) Viruses cannot be cultivated on artificial
culture media.
e) Viruses are not susceptible to antibiotics.
48. 2) Sites of viral assembly in tissue culture are
called:
a)Plaques
b)Inclusion bodies
c) Viral capsid
d)CPE
e)Areas of transformation
49. 3) Regarding continuous cell lines, all of the
following are true EXCEPT:
a)They allow unlimited number of passages.
b)They are prepared from tumor cells.
c) After viral inoculation, they should be
sterilized by autoclaving.
d)They are used for isolation of viruses.
e)HeLa cell line is an example of continuous cell
lines.
50. 4) PCR may be used to diagnose viral infections
by detecting:
a)Antiviral IgM antibodies
b)Viral antigens
c) Rising titer of antiviral antibodies
d)Viral nucleic acid
e)CPE produced by the virus in tissue culture
51. 5) Direct detection of viruses and/or their
components can be done by all of the
following EXCEPT:
a)Fluorescent microscope
b)Electron microscope
c) Light microscope
d)PCR
e)Biochemical reactions
52. 6) Cultivation of viruses can be done on:
a)Blood agar
b)Tissue culture
c) MacConkey’s medium
d)Nutrient broth
e)Anaerobic media
54. 1) Viruses differ from bacteria in all the
following EXCEPT:
a) Viruses are very small in size.
b) Viruses are obligatory intracellular parasites.
c) Viruses contain both DNA and RNA.
d) Viruses cannot be cultivated on artificial
culture media.
e) Viruses are not susceptible to antibiotics.
55. 2) Sites of viral assembly in tissue culture are
called:
a)Plaques
b)Inclusion bodies
c) Viral capsid
d)CPE
e)Areas of transformation
56. 3) Regarding continuous cell lines, all of the
following are true EXCEPT:
a)They allow unlimited number of passages.
b)They are prepared from tumor cells.
c) After viral inoculation, they should be
sterilized by autoclaving.
d)They are used for isolation of viruses.
e)HeLa cell line is an example of continuous cell
lines.
57. 4) PCR may be used to diagnose viral infections
by detecting:
a)Antiviral IgM antibodies
b)Viral antigens
c) Rising titer of antiviral antibodies
d)Viral nucleic acid
e)CPE produced by the virus in tissue culture
58. 5) Direct detection of viruses and/or their
components can be done by all of the
following EXCEPT:
a)Fluorescent microscope
b)Electron microscope
c) Light microscope
d)PCR
e)Biochemical reactions
59. 6) Cultivation of viruses can be done on:
a)Blood agar
b)Tissue culture
c) MacConkey’s medium
d)Nutrient broth
e)Anaerobic media