Question

Explain the method of animal virus culture by using the ‘Chicken Embryo Technique’.

Answer 1

Hint: Viruses are obligate intracellular parasites i.e. they cannot live outside the living cells. So, in order to study them, we cannot grow them in normal lab conditions as they are dead once outside the cell. So, methods like the chicken embryo technique are used.

Complete answer:
Viruses cannot be cultured in a normal culture or agar plate. So, in order to observe the properties of viruses they are grown in living organisms or in chicken embryos. This is very helpful for preparing vaccines against viruses.
The chicken embryo technique is performed as follows.
- Viruses are injected into the chicken embryo which is 1- 2 weeks old.
- Before injecting, the shell and needle are thoroughly sterilized to prevent contamination.
- Once the virus is injected inside, the shell is sealed with wax or gelatin.
- The egg is incubated for 2- 3 days after which the egg is broken and the virus is extracted from it for observation.
On the basis of where the virus is injected into the chicken embryo, there are different types of chicken embryo cultivation like amniotic inoculation, yolk sac inoculation, allantoic inoculation, etc.

Note:
- One disadvantage of the chicken embryo technique is that different viruses need to be inserted into different portions of the chicken embryo.
- The animals used for growing viruses are mice, guinea pigs, hamsters, rabbits, etc. Newly born animals are inoculated with viruses because they are more susceptible to infection.
- The effects of the virus are studied by observing the symptoms shown by infected animals. But this method is expensive and some viruses cause infection without any symptoms. Also, it is difficult to maintain the animals.