Viruses cultivation

Human viruses Cultivation of human viruses 13 Further reading... 

Fig. 5.7 A chick embryo showing the inoculation routes for virus cultivation.

Virus cultivation is more complex than bacterial cultivation because viruses are, by themselves, nonreplicating. Virus must be grown on a host cell substrate, which can be animal tissue, embryo, or ex vivo cells the host substrate determines the cultivation technology. In the United States, only Japanese encephahtis virus vaccine is still produced from infected mature animals. Worldwide, many vaccines are produced in chicken embryos, an inexpensive substrate. The remainder of vaccines are produced from ex vivo cultivated animal cells. Some virus-like particle vaccines are made by recombinant DNA techniques in either microbial or animal cells, for example, hepatitis B virus vaccine, which is made in yeast as mentioned above, or in Chinese hamster ovary cells. An interesting synopsis of the development of rabies vaccine technology from Pasteur s use of animal tissues to modern use of ex vivo cells can be found in Sureau [1987]. 

The cultivation of viruses from material taken from lesions is an important step in the diagnosis of many viral diseases. Studies of the basic biology and multiplication processes of human viruses also require that they are grown in the laboratory under experimental conditions. Human pathogenic viruses can be propagated in three types of cell systems. 

Experimental animals sueh as miee and ferrets have to be used for the cultivation of some viruses. Growth of the virus is indicated by signs of disease or death of the inoculated animal. 

There are known to be about 30,000 disease-causing agents (fungi, viruses, nematodes, bacteria) in 3,000 types of cultivated plants. More than 10,000 species of arthropods (insects, ticks, arachnids) affect agricultural plants and animals. Along with agriculture, pesticides are also widely used in forestry and fisheries, in energy and railroads (to clear plants), in construction (to protect wood structures), etc. 

With animal viruses, the initial host may be a whole animal which is susceptible to the virus, but for research purposes it is desirable to have a more convenient host. Many animal viruses can be cultivated in tissue or cell cultures, and the use of such cultures has enormously facilitated research on animal viruses. 

Classification of animal viruses Most of the animal viruses which have been studied in any detail have been those which have been amenable to cultivation in cell cultures. As seen, animal viruses are known with either single-stranded or doublestranded DNA or RNA. Some animal viruses are enveloped, others are naked. Size varies greatly, from those large enough to be just visible in the light microscope, to those so tiny that they are hard to see well even in the electron microscope. In the following sections, we will discuss characteristics and manner of multiplication of some of the most important and best-studied animal viruses. 

One of the most obvious benefits of plants is the potential for production scale up, leading to the production of virtually limitless amounts of recombinant antibody at minimal cost Plants are easy to grow, and unlike bacteria or animal cells their cultivation is straightforward and does not require specialist media, equipment or toxic chemicals. It has been estimated that plantibodies could be produced at a yield of 10-20 kg per acre at a fraction of the cost associated with production in mammalian cells [2,18] The use of plants also avoids many of the potential safety issues associated with other expression systems, such as contaminating mammalian viruses or prions, as well as ethical considerations involving the use of animals. 

Viral vaccines are cultivated on inanimate media. Some examples include hepatitis b vaccine, influenza virus vaccine, measles virus vaccine, rabies vaccine, rubella vaccine, and yellow fever vaccine. The viral vaccines are available as lyophilized powder for reconstitution, or suspension for injections,... 

Taking into account process integration, i.e. - cultivation and product purification, particle locaHsation is an important issue. Strategies to produce a secreted particle, either by manipulation of its composition or by co-expression of NS protein(s) will be also discussed, since this can lead to an easier purification process and to a decrease in product losses due to intracellular proteolysis. The production of Rotavirus-Hke particles and Bluetongue virus-like particles production will be used as examples to illustrate this point. 

Enders, J.,T. Weller, and F. Robbins, Cultivation of the Lansing strain of poliomyelitis virus in cultures of various human embryonic tissues. Science, 1949.109 85-7. 

John F. Ender (1897-1985), Thomas H. Weller (1915- ), and Frederick C. Robbins (1916- ) publish Cultivation of Polio Viruses in Cultures of Human Embryonic Tissues. The report by Enders and coworkers is a landmark in establishing techniques for the cultivation of poliovirus in cultures on non-neural tissue and for further virus research. The technique leads to the polio vaccine and other advances in virology. 

A classic way to produce viral vaccines consists of cultivating cells on an appropriate static support, infecting them with virus, collecting and purifying the virus produced and formulating the vaccine. 

In such a system, a species-specific virus is used. In the case of soy cultivation, this virus is Baculovirus anticarsia, which specifically kills a caterpillar found on the soy - Anticarsia gemmatalis - a defoliating pest that substantially reduces farming productivity. With this bioinsecticide,... 

In a similar way, sarcoma growth factors (SGFs e.g. ESG) can be obtained by the serum-free cultivation of murine sarcoma virus transformed 3T3 cells or transformed rat kidney cells. Nerve growth factor (NGF) is produced in excess by the human melanoma cell line A375 and fibroblast growth factor (FGF) is secreted by fibrosarcoma cells (Todaro et al., 1979). 

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