Viruses are obligate intracellular parasites that can only replicate inside living host cells. There are several methods for cultivating or growing viruses, including inoculation into animals, embryonated eggs, and cell/tissue culture. Inoculation into animals allows study of viral replication and disease but is expensive and difficult. Embryonated eggs are widely used as they are inexpensive and support growth of many viruses. Tissue/cell culture has replaced eggs for many viruses as it is more convenient and sensitive. Various cell types, including primary cultures, continuous cell lines, and explant cultures can support viral growth. Detection of viral growth involves monitoring for cytopathic effects, hemadsorption, interference, transformation, or metabolic inhibition.

1. VIRUSES
intracellular
❖ Viruses are obligate
parasites.
❖ They multiply only inside the living
host cells. Animals ,plants ,humans ,
bacteria, fungus ,protozoa and algae
are the natural hosts of viruses.

2. ❖Viruses are host specific and grow only in
selective hosts. Virologists use only a suitable
hostsystemfor cultivation of a virus.
❖Viruses cannot grow in artificial media .They
cannot grown in non-living culture or on agar plates
alone , they must require living cells to support their
replication.
❖There is no universal cell that will support all
viruses.

3. Main purpose of virus cultivation
❖ To isolate and identify viruses in
clinical samples.
❖ To prepare viruses for vaccine
production.
❖ To do research on viral structure
, replication , genetics and
effects on host cells.

4. ❖ Reed and colleagues (1900) used human
volunteers for their pioneering work on yellow fever . Due to
the serious risk involved , human volunteers are used only
when no other method is available and when virus is relatively
harmless.
❖ Monkeys were used for the isolation of the poliovirus by
Landsteiner and Popper (1909). However, due to
their cost and risk to handlers, monkeys find only limited
applications in virology.
❖ The use of white mice, pioneered by Theiler (1903)
extended thescope of animal inoculation greatly.

5. ❖ Good Pasture in 1931 first used the embryonated
hen’s egg for the cultivation of virus and this method is
further developed by Burnet.
❖The first application of tissue culture in virology was by
Steinhardt and colleagues (1913), who maintained
the vaccinia virus in fragments in rabbit cornea.
❖Maitland (1928) used chopped tissue in nutrient
media for cultivation of vaccinia viruses.
❖The turning point which made tissue culture the most
important method for cultivation of virus was the
demonstration by Enders, Weller and Robins (1949),
that poliovirus till then considered a strictly neurotropic
virus,could be grown in tissue culture of non-neural origin.

6. METHODS FOR CULTIVATION OF VIRUSES
Inoculation of virus
into animals.
Inoculation of virus
into embryonated eggs.
Tissue culture.

7. ❖Viruses which are not cultivated in
embryonated egg and tissue culture are
cultivated in laboratory animals. e.g: mice,
guinea pig , hamester , rabbits and
primates are used.
❖The selected animals should be healthy
and free from any communicable diseases.
❖Suckling mice (less than 48 hours old) are
most commonly used.
1). Inoculation of Virus in
Animals

8. Different ways of inoculation in mice are:
1) Intracerebral.
2) Subcutaneous.
3) Intraperitoneal.
4) Intranasal.

9. 1). Intracerebral
➢It occurring or
introduced
within
or
administered into the
cerebrum. It means
when a diseased blood
vessel within the brain
bursts allowing blood
to leak inside the brain.

10. 2). Subcutaneous
❖A subcutaneous
injection is an
injection in which a
needle is inserted
just under the skin.

11. 3). Intraperitoneal
❖ Intraperitonium injection is the
into the
injection of a substance
peritonium (body cavity).

12. 4). Intranasal
✓It lying within or administered by way
of the nasal structure.

13. Advantages and disadvantages
of animal inoculation :
Advantages :
❖ Production of antibodies can be identified.
❖Diagnosis , pathogenesis and clinical
symptoms are determined.
❖ Primary isolation of certain viruses.
❖Mice provide a reliable model for
studying viral replication.
❖Used for the study of immune
responses,epidemology and oncogenesis.

14. Disadvantages :
❖Expensive and difficulties in maintaince
of animals.
❖Difficulty in choosing of animals for
particular virus.
❖Some human viruses cannot be grown
in animals or can be grown but do not
cause diseases.
❖Mice do not provide models for vaccine
development.

15. 2). Inoculation of virus into
embryonated egg
The process of cultivation of viruses in
embryonated eggs depend upon the
type of egg being used.
Egg provide a suitable means for :
i. The primary isolation and
identification of viruses.
ii. The production of vaccines.
iii. The maintaince of stock culture.

16. After incubation , the egg is broken and virus is
isolated from tissue of egg.
For inoculation , eggs are first prepared for cultivation ,
the sheel surface are first prepared for cultivation , the
shell surface is first disinfected with iodine and
penetrated with a small sterile drill.
Viruses are inoculated into chick embryo of 7-12
days old.

17. Inoculation of virus into
embryonated eggs

18. ▪ Virus growth and multiplication in
the egg embryo is indicated by the
death of the embryo , by embryo cell
damage , or by the formation of
typical pocks or lesions on the egg
membrane.
▪ Viruses can be cultivated in
various pats of egg like :
1). Chorioallantoic membrane (CAM)
2). Allantoic cavity
3) Amniotic sac
4) Yolk sac Pock

19. 1). Chorioallantoic
membrane (CAM)
▪ Inoculation is
growing poxvirus.
▪ After incubation
mainly for
and visible
lesions called pocks are
observed , which is grey white
area in transparent CAM.
▪ Herpes simplex virus is also
grown.
▪ Single virus gives single pocks.
▪ This method is suitable for
plaque studies.

20. Plaque : A clear area in a lawn of
host cells that results from the lysis of
host cells by viruses.

21. 2). Allantoic cavity:
❖Inoculation is mainly done for
production of vaccine of
influenza virus , yellow fever ,
rabies.
❖Most of avaian viruses can be
isolated using this method.
❖Allantoic inoculation is a quick
and easy method that yields
large amounts (8-15ml) of
virus-infected egg fluids.

22. 3). Amniotic sac :
▪ Inoculation is mainly done
for primary isolation of
influenza virus and the
mumps virus.
▪ Growth and replication of
virus in egg embryo can be
detected by
haemagglutination assay.
▪ The virus is introduced
directly into the amniotic fluid
that bathes the developing
embryo.

23. 4). Yolk sac inoculation:
❖ It is
method
also a simplest
for growth and
multiplication of virus.
cultivation
viruses
of
and
❖ It is inoculated for
some
some
bacteria ( Chlamydia ,
interference
Rickettsiae ).
❖Immune
mechanism can be
detected in most of avian
viruses.

24. Advantages of inoculation into
embryonated egg
❖ Widely used method for the isolation of virus and
growth.
❖ Cost effective and maintenance is much easier.
❖ The embryonated eggs are readily available.
❖ They are free from contaminating bacteria and
many latent viruses.
❖ Ideal substrate for the viral growth and replication.
❖ less labor is needed.
❖ Widely used method to grow virus for some
vaccine production.
❖ Defense mechanisms are not involved in
embryonated eggs.

25. Disadvantage of inoculation into
embryonated egg
• The site of inoculation for varies with
different virus . That is , each virus
have different sites for growth and
replication.

26. 3). Tissue culture
❖Cultivation of bits of tissues and organs in
vitro had been used by physiologists and
surgeons for the study of morphogenesis
and wound healing.
❖Before the advent of cell culture , animal viruses
could be propagated only on whole animals or
embryonated chicken eggs.

27. ✓ Cell cultures have replaced
embryonated eggs as preferred
type of growth medium for
many viruses.
✓Cell culture consists of cells
grown in culture media in the
laboratory.

28. There are three types of tissue culture:
1) Organculture.
2) Explantculture.
3) Cell culture.

29. 1). Organ culture
Example: Tracheal ring organ culture is employed for the isolation of
coronavirus, a respiratory pathogen.
Organ culture is useful for the isolation of some viruses which appear
to be highly specialized parasites of certain organs.
Small bits of organs can be maintained in vitro for days and weeks,
preserving their original architecture and function. Formalin is used for
the preservation.

31. 2). Explant culture
The explants taken from laboratory animals such as mice , rabbit , guineapigs
, hamester and man can be grown in petri dishes.
An explant is aseptically transferred into a sterile petri dish by using a fine
tipped forceps and then a coverslip is placed over that explant.
Enough volume of medium is poured into the petri dish , which is then
incubated at 37 ⁰C untill cell growth.
Example : Adenoid tissue explant culture were used for the isolation of
adenoviruses.
A small portion of tissue excised from animal’s body is explant.

32. Explant culture

33. 3). Cell culture
The essiential constitutents of the growth medium are physiologic amounts of
essiential amino acids and vitamins , salts , glucose and a buffering system
generally consisting of bicarbonate in equilibrium with atmosphere containing
about 5% carbon dioxide.
Tissues are dissociated into the components of cells by the
action of proteolytic enzymes such as trypsin and
mechanical shaking.
This is the type of culture routinely employed for growing
viruses.

34. Antibiotics are added to prevent the bacterial
contaminants and phenol red as indicator.
Such media will enable most cell types to multiply with
a division time of 24-48 hours.
The cell suspension is dispensed in bottles , tubes or
petri dishes.
The cell adhere to the glass surface and on incubation ,
divide to form a confluent monolayer sheet of cells
covering the surface within about a week.
This is supplemented with up to 5% calf or fetal calf
serum.

35. Based on their origin , chromosomal
characters and the number of generations
through which they can be maintained , cell
culture are classified into three types :
Some fastidious virus grow only in suchroller
cultures.
Cell culture tubes may be incubated in a
sloped horizontal position , either as
‘stationary culture’ or may be in special ‘roller
drums’ to provide better aeration.

36. Types of cell culture
1).Primary cell culture.
2). Continuous cell
lines.

38. 1). Primary cell culture
Examples : Kidney cells of monkey and man , embryo
cells , alveolar cells , macrophages and amniotic cells
are usually grown in primary cell cultures.
It is capable of only limited growth and hence it can
be subcultured once or twice.
The cell culture established directly from cells taken
from animal’s tissue is called primary culture.

39. Primary cell cultures are widely used for the isolation
of animal viruses and cultivation of viruses for vaccine
production.
The culture vessel is incubated at 37⁰C for a few days to
get a primary culture.
A small volume of cell suspension is aseptically
transferred to a culture flask or petri dish containing
nutrient medium , with the help of pipette.

40. Secondary cell cultures are used for the isolation of wide group of animal
viruses and growing fastidious viruses. Some secondary cultures are usedfor
vaccine production.
Examples : Human embryonic kidney cells and skin fibroblast cells.
As secondary cell cultures can be maintained and subcultured for 20-50 times
, they are called semi-continuous cells.
The cell culture established from primary cell culture are called secondary
culture or sub-culture.

41. The fragments of monoculture grow into large
monolayers. These are called secondary culture.
It is then cut into small fragments. 2or 3fragments are
inoculated into a roller drum containing nutrient medium
and the roller drum is incubated at 37⁰Cfor few days.
Monolayer produced as a result of primary cell culture is
detached from the bottom of the culture flask by adding
trypsin or EDTA.

42. ➢ Animal cells capable of indefinite growth are
called continuous cell lines or cell lines.
➢ These are the cells of a single type , usually
derived from cancer cells , that are capable of
continuous serial cultivation indefinitely.
➢ Standard cell lines derived from human
cancers , such as HeLa , HEp – 2 and KB cell
lines have been used in laboratories
throughout the world for many years.

43. ❖These cell lines may be maintained by
serial subcultivation or stored in the cold (
-70⁰C ) for use when necessary.
❖Some cell lines are now permitted to be
used for vaccine manufacture, for example
: Vero cells for rabies vaccine.

44. Advantages of cellculture
❖Relative ease, broad spectrum, cheaper
and sensitivity
Disadvantage of cellculture
❖The process requires trained technicians
with experience in working on a full time
basis.
❖State health laboratories
laboratories do not isolate
and hospital
and identify
viruses in clinical work.
❖Tissue or serum for analysis is sent to
central laboratories to identify virus.

45. Detection of virusgrowth
• The following methods are available to
detect the virus growth in the cell or tissue
cultures.
a). Cytopathic effect.
b). Haemadsorption.
c). Interference.
d) Transformation.
e)Immunofluorescence.
f). Metabolic inhibition.

46. ❖Many viruses cause morphological changes
in cultured cells in which they grow. These
changes can be readily observed by
microscopic examination of the cultures.
❖These changes are known as ‘cytopathic
effects’ (CPE) and the viruses causing CPE
are called ‘cytopathogenic viruses’.
❖The CPE produced by different groups of
viruses are characteristic and help in
presumptive identification of virus isolates.

47. • For example, enteroviruses produce
rapid CPE with crenation of cells and
degeneration entire cell sheet ; measles
virus produce syncytium formation;
herpes virus causes discrete focal
degeneration; adenovirus produce large
granular clumps of grapes.

49. ❖When hemagglutinating viruses (such as
influenza and parainfluenza viruses) grow
in cell cultures, their presence can be
indicated by the addition of guinea pig
erythrocytes to the cultures.
❖If the viruses are multiplying in the cultures,
the erythrocytes will adsorb onto the surface
of cells. This is known as
‘hemadsorption’.

51. 3). Interference
• The growth of first virus will inhibit second
virus infection due
effect. This property
to some inhibitory
of cell cultures is
celled interference. it is useful to detect
the growth of non-cytopathic viruses in cell
cultures

52. 4). Transformation
• If oncogenic viruses are inoculated into
cell cultures, the infected cell grow fast
and produce microtumours in the culture.
This is called transformation. It indicated
the presence of oncogenic viruses in the
culture.

53. 5). Immunofluorescence test
• Some cell from the cell culture are stained
with a fluorescent dye conjugated antiserum
and viewed under an UV microscope.
• Viral antigen present on the cell surface bind
with the antiserum.
• Fluorescence from the cell is the positive
indication for presence of virus in the cell.
This is a widely used method in diagnostic
virology.

54. ImmunofluorescenceAssay

55. 6). Metabolic inhibition
❖ In normal cell cultures, the medium
turns acid due to the cellular
metabolism.
❖When viruses grow in cell cultures , the
cell metabolism is inhibited and there is
no acid production.
❖This can be made out by the indicator
(phenol red) incorporated in the
medium.

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