Title 5. GROWTH AND CULTIVATION OF VIRUS.pdf ✅

PHARMD GURU Page 1 Viruses are obligate intracellular parasites, which cannot be grown on inanimate culture media. Three methods are used for the cultivation of viruses. 1. Laboratory animals 2. Embryonated eggs 3. Tissue culture 1. LABORATORY ANIMALS: It is one of the oldest methods for cultivation of viruses. Reed and colleagues (1900) used human volunteers for their pioneering work on yellow fever. Due to the serious risks involved, human volunteers are used only when no other method is available and viruses are harmless. Landsteiner and Popper (1909) used monkeys for isolation of the poliovirus. However, due to their cost and risk to handlers, monkeys find less application in virology. The poliomyelitis virus after intraspinal or intracerebral inoculation in monkeys causes a typical paralytic disease. The use of white mice, pioneered by Theiler (1903) extended the scope of animal inoculation. Mice are still the most widely employed animals in virology. Infant (suckling) mice are very susceptible to coxsackie and arboviruses. Other animals such as rabbits, guinea pigs and ferrets are used in some situations. Small pox virus may be inoculated in the scarified skin or cornea of rabbits. The growth of the virus in inoculated animals may be indicated by death, disease or visible lesions. Sometimes immunity in an experimental animal may interfere with the growth of viruses in the animal. Animal inoculation is also used for the study of pathogenesis, immune response and epidemiology. 2. EMBRYONATED EGGS: The embryonated hen's egg was first used for cultivation of viruses by Goodpasture (1931) and the method was further developed by Burnet. The embryonated egg offers several sites for the cultivation of viruses (Fig. 3.6). Fertile chicken eggs incubated for 5 to 12 days can be inoculated through the shell aseptically. The opening may be sealed with paraffin wax and the egg incubated at 36oC for the time required for the growth of the virus. The duration of incubation GROWTH AND CULTIVATION OF VIRUS
PHARMD GURU Page 2 may depend on the type of viruses and the route of inoculation. Viruses may kill the chick embryo or produce specific evidence of viral activity such as production of pocks on chorioallantoic membrane and haemagglutinating activity in the harvested amniotic and allantoic fluid. These effects help in the identification of the virus. Inoculation into the allantoic cavity provides a rich yield of influenza and some paramyxoviruses. Inoculation into the amniotic sac is employed for the primary isolation of the influenza virus. Yolk sac inoculation is used for the cultivation of some viruses, chlamydiae and rickettsiae. Yellow fever (17 D strain) and rabies (Flury strain) are other vaccines produced from chick embryo and vaccinia and herpes viruses from the chorioallantoic membrane. Advantages and disadvantages of this method are summarised as follows: ADVANTAGES OF EMBRYONATED EGGS: 1) The eggs are much simpler to handle than animals. 2) Eggs are very economical and easily available. 3) They are clean and bacteriologically sterile.