Viral cultivation unlike the cultivation or culture of other microbial forms including bacteria and fungi is quite unique and different from the usual routine cultivation techniques undertaken in the conventional microbiology laboratory (both in the hospital and in an academic institution). One of the major reasons for this is because viruses unlike other microbes exist as a living thing inside a living host cell. Viruses only replicate inside a living cell including those of humans, plants, animals, other mammals and microbes as well. They are obligate intracellular parasites that engage in a close relationship with their host; and this allows viruses to take over the cellular and replication machinery of their host cell to their own advantage.
Virtually all the materials required for viral replication including cellular energy are provided by the viral-infected host cell. They rarely replicate independent of a living host cell. Thus, the culture of viruses requires the culture of living host cells as hosts for the unperturbed growth and replication of the virus being propagated. Viruses cannot grow and replicate in non-living culture media or agar plates as is applicable to bacteria and fungi that can readily be propagated in such growth medium. These are some of the factors that distinguish viral replication from the propagation or cultivation of prokaryotic and eukaryotic cells in the laboratory. Several reasons exist for the cultivation of viruses in the laboratory. Some of the major reasons for viral cultivation are highlighted in this section.
- Viruses are cultivated in order to prepare viruses used for the production of vaccines – that are used as prophylaxis and preventive measures for some infectious diseases.
- To isolate pathogenic viruses from clinical samples as an aid in the diagnosis of viral infections.
- To identify and classify viruses from clinical samples and other viral-laden samples.
- Viruses are cultivated in order to study their host-parasite relationship.
- To study the genetics of viruses inclusive of their structures and replication patterns.
- They are cultivated for other research purposes especially in studying the efficacy of novel antiviral drugs.
Viruses can be cultivated in vitro and in vivo – depending on the discretion of the researcher and the type of viral cultivation to be undertaken. The in vivo viral cultivation techniques include: the use of a natural viral host, experimental animals, transgenic animals and embryonated eggs. In vivo viral cultivation techniques are generally undertaken in living host cells which include embryonated eggs, experimental animals and transgenic animals as aforementioned. However, this is not the case for the in vitro viral cultivation technique – which is usually carried out in cell culture or tissue culture plates that contain living cells of animals that support the growth of the virus(s) being propagated. Organ culture (performed for viruses that attack specialized organs of the body) and explant culture (which are rarely performed) are two other methods or techniques of cell culture that can be used to cultivate viruses in the laboratory. Generally, viral cultivation can be divided into three (3) main groups.
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