Cultivation of viruses:
Since viruses are obligate parasites and moreover, they reproduce only in the living system, it is very difficult to deal with them. Thus culturing of plant virus is usually done on the susceptible host. The host plants are raised from healthy seeds, under controlled conditions, inside a glass house. To isolate a virus and bring it into pure culture, usually the dilution end point method is followed.
Animal viruses are usually propagated in the embryonated eggs, plasma clots, tissue culture, etc. Chick embryonated eggs technique is one of the most economical and convenient method for cultivating a wide variety of viruses. Fertile or embryonated hen's eggs incubated for 5-12 days are inoculated through the shell aseptically. The opening is then sealed with paraffin wax and the egg incubated at thirty six degree Celsius for the time required for growth of the virus. This technique is particularly used in the production of viruses for vaccines against small pox, yellow fever, influenza, and other diseases and in immunologic tests and other studies.
In plasma clot technique, viruses are inoculated into the plasma clot of blood. In it the plasma serves as host for virus growth. From this technique viruses can be obtained free from the host cells.
Tissue culture technique is more effective for the cultivation of some viruses. This technique is widely used for the isolation and propagation of viruses from clinical material and for the commercial production of vaccines. Some viruses can not be cultivated in cell culture and must be grown in animals. Mice, guinea pigs, rabbits and primates are used for this purpose.