Cultivation (culture) of Animal viruses:
Viruses can grow only in living cells. However the culture of viruses is possible nowadays. The most economical and convenient method of cultivating a wide variety of animal viruses is the 'chicken embryo technique'. In this technique, fertile chicken eggs incubated for 5 to 12 days are inoculated with the virus particles through the shell, aseptically. The opening may be sealed with paraffin wax. The eggs incubated at 36oC are ideal sources for the growth of viruses.
Chick embryos contain several different types of cells in which various viruses will undergo replication. The yolk sac is a general ideal medium for the growth of viruses.
Viral cultures are of three types viz., Primary cell cultures, diploid cell strains and continuous cell lines.
Primary cell culture are derived from normal tissue of an animal such as mouse, hamster, chicken and monkey or a human being. When cells from these tissues are processed and cultured the first monolayer is referred to as the primary culture. A monolayer is a confluent layer of cells covering the surface of a culture vessel.
Diploid cell strains are derived by primary cell cultures from a specific tissues like lung or kidney which is of embryonic origin. These diploid cells are the most employed host of choice for the production of human vaccine virus.
Continuous cell lines are capable of an infinite number of doublings. Such cell lines may arise with the mutation of a cell strain or more commonly from the established cell cultures from malignant tissue. Many viruses, which are difficult or impossible to grow have been cultured in continuous cell lines.