How are viruses grown in laboratories? | Isolation of viruses | Microbiology

Isolation of viruses is not so easy as you think it is! Viruses cannot be grown in artificial culture media, but they can be cultivated by animal inoculation, using cell lines, etc.,

Read this blog fully to know various techniques by which viruses can be isolated.

Techniques available for isolation of viruses :-

1) Animal inoculation
2) Egg inoculation
3) Tissue cultures

Animal inoculation

This technique is rarely used these days due to ethical issues. The various uses of this technique are :-

- Research use : To study viral pathogenesis or viral oncogenesis or for viral vaccine trials.

- Diagnostic use : Viruses which are difficult to be cultivated otherwise can be grown by animal inoculation. Eg., Arboviruses and coxsackie viruses.

How is it done?

- Inoculate specimens intracerebrally or intraperitoneally in infant mice and observe if the mice develops any disease or if it dies. Tissue sections of this mice is later examined by histopathological examinations.

- Coxsackie viruses are injected intracerebrally into infant mice and following changes are observed.

a) Coxsackie A virus produces flaccid paralysis

b) Coxsackie B virus produces spastic paralysis

This helps to differentiate between Coxsackie A viruses and Coxsackie B viruses.

Egg inoculation

Take a look at the picture above. Viruses are inoculated in either of 4 parts present in the egg. Those 4 parts are :-

- Yolk sac inoculation (for arboviruses)

- Amniotic sac (for influenza viruses)

- Allantoic sac (it is a larger cavity, so more viral yield can be obtained. It is used to obtain viral vaccines. Eg., Influenza vaccine, yellow fever vaccine)

- Chorioallantoic membrane (mainly for poxviruses and Herpes simplex virus. They produce something known as pocks in the membrane after inoculation, which is an indicator of virion load. More number of pocks produced indicates the presence of more virions)

This image shows pocks formation by Vaccinia viruses by inoculation into chorioallantoic membrane.

Tissue cultures

Three types of tissue culture are :-

- Organ culture

- Explant culture

- Cell line culture

Of these three types, cell line culture is the one which is used these days.

Cell line culture :-

This picture shows a tissue culture flask. The viral growth medium and cells inoculated with viruses are kept in this flask and then incubated under ideal conditions.

Types of cell lines :-

1) Primary cell lines

- They are derived from normal cells freshly taken from the organs and cultured.

- They can undergo just 5-10 divisions

- They possess diploid karyosome

- Used for isolation of viruses as well as for vaccine production

- Eg., Monkey kidney cell line, Human amnion cell line and Chicken embryo cell line.

2) Secondary (Diploid) cell lines

- They are also derived from normal cells

- They can undergo 10-50 divisions

- They possess diploid karyosome

- They are used for isolation of viruses as well as for vaccine production

- Eg., Human fibroblast cell line (Very useful for Cytomegalovirus isolation), etc.,

3) Continuous cell lines

- Derived from cancerous cell lines, so they are immortal

- So they are capable of indefinite divisions

- They usually possess aneuploid karyosome

- They are easy to be maintained in laboratories because of their capacity to undergo infinite divisions.

- Examples - HeLa cell line, HEp - 2 cell line, Mc Coy cell line, etc.,

I hope you got some idea on how viruses are cultivated in laboratories. If you have any doubts feel free to comment below! I'll get back to you as soon as possible.

Don't forget to check out my video on Coxsackie viruses, where I've described a bit about animal inoculation technique.

Reference: -

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