The 21st century is a century that is taking leaps and bounds in the field of technological progress, science and medicine are rapidly developing. The current level of progress allows us to implement what previously seemed impossible to man. The post-industrial stage of human development is aimed at high technology, innovation in all areas.
Medicine is developing especially fast: most diseases that were previously considered incurable are now not such. So, for example, the cultivation of viruses allows you to create preventive drugs: vaccines and serums that prevent epidemics of plague, smallpox and other deadly diseases.
What is cultivation?
Cultivation (from lat. Cultivo - cultivate) is the process of breeding and growing something in artificial conditions. In medicine, and more specifically in epizootology - a private branch of veterinary medicine, cultivation is the main process that allows you to study the effect of the virus on a living organism.
Based on the information received, pharmacists produce antiviral drugs, create methods that allow in the future to counteract the identified microorganisms. Isolation of viruses from infected material also allows you to save them for future use.
History of Epizootology
Back in 1879, the French scientist W. Gaultier made the first attempt to cultivate a virus. His choice fell on a disease such as rabies: he isolated a non-cellular agent of this disease by infecting a rabbit with the blood of a sick dog.
In 1919, the German A. Levenshtein managed to infect herpes virus taken from a human rabbit. A year later, his compatriot V. Grüter confirmed the experience of his colleague and proved that such cultivation on rabbits is possible.
In 1925, two scientists - F. Parker and B. Nye - proved that the vaccinia virus is able to reproduce in the tissues of animals. 6 years later, Woodruff and E. Goodpaster said that the cultivation of smallpox virus in birds can be carried out on the shell of chicken embryos, thereby opening up a new method for the reproduction of viruses to the scientific world.
Cell infection process
The process of cultivation of the virus is impossible without the presence of a responsive cell. When a cell is found (it can be cells of chicken embryos, parts of tissues, organs, or even whole animals), the nucleic acid of the virus is introduced into it, which reprograms the genetic information of the desired cell, replacing it with its own. Usually a harmful particle manages to settle in the cell, even despite the antiviral defense system and interferons produced by the body.
After the virus has penetrated the cell membrane, it begins to multiply, passing through 3 stages. First, the genome of the fixed virus is transcribed, which means the transfer of information from the DNA system to RNA, which is subsequently synthesized at an accelerated rate. The next stage is the formation and maturation of proteins, which will serve as a framework for daughter viral bodies.
At the last, final stage, newly synthesized viral bodies increase in quantity. When there are too many of them, they rupture the membrane and exit the cell in which the virus was initially fixed. It should be noted that the formation of virions (daughter bodies of a given microorganism) does not always lead to the death of the host cell. Some are able to bud from the membrane without causing it to rupture, while the cell continues to produce viral bodies.
Microbiology and its methods
Over time, biology, as a science, developed and absorbed new facts. Complicating gradually, different directions began to budge from it: biomechanics, hydrobiology, virology, space biology, and many others. A section such as microbiology studies the vital processes of microorganisms, including through infection of an experimental laboratory animal with a virus. Thus, in microbiology, the cultivation of viruses is considered one of the main ways of obtaining information, being a key tool of the biological research method.
In addition to the biological method, the essence of which is to study the action of the virus on the animal’s body and its subsequent cultivation, there are several others. In many cases, chicken embryos are infected with harmful microorganisms, since a rather large proportion of the viruses known to science today can replicate in this particular form of life. However, most often biologists use tissue cultures as a working material, since they are most productive as a method of cultivation.
Virus and tissue culture
Tissue culture is a certain system of cells in the form of a suspension. This is a layer of a certain size, usually in one cell, which is placed on the glass of the vessel. Primary monolayer fabric is used more often than others. It is quite difficult to achieve monolayerness, first the selected tissue (usually the tissue of the heart, placenta or kidneys of animals) needs to be crushed.
After grinding, biologists use a protein-cleaving enzyme, trypsin, which separates tissue cells, destroying the intercellular connection between them. After the separation of cells is achieved, it is necessary to wash them from the enzyme and place them in a nutrient medium to ensure the growth of the resulting cell culture. This medium may be medium 199, which is characterized by a high content of glucose, salts and various vitamins. The nutrient medium changes after 2-3 days.
In addition to primary tissue for the cultivation of viruses, so-called digestible tissues are also used, which, in turn, are divided into normal and tumor. They are more resistant than primary, and are able to reproduce for a long time. The organs of animals can serve as normal tissues: ram kidney, monkey heart. HeLa cells, originally isolated from cervical cancer, or Hep-3 cells, taken from lymph cancer, are usually taken as tumor tissues.
Virus and chicken embryos
Most viruses known to science can be grown in chicken embryos. They are very viable and resistant to negative external influences. The period at which the embryo becomes infected depends on the objectives of the study and the type of virus, but usually does not exceed two weeks. So, for example, to cultivate the influenza virus, you need a 9-10-day embryo, and in order to grow the mumps virus, a weekly embryo is enough.
When working with a chicken embryo, all its rudiments of tissues are infected. The effectiveness of cultivation can be seen at the final stage: it can be the death of the embryo, as well as developmental defects in the form of plaques consisting of viral particles - virions on the shells of the embryo.
In any case, this method of cultivation and indication of viruses has a significant drawback, consisting in the need to open the embryo to capture the reproduced virus. Also, the obtained substance has a high concentration of protein, which must be removed in order to remove a pure infectious agent for the further production of medicines.
Virus and animal organisms
Currently, the use of laboratory animals as biological material due to its inhumanity has been limited since 1986 by the European Convention for the Protection of Vertebrate Animals. Despite this, many types of animals: mice and rats, ferrets and rabbits, sheep, dogs and monkeys - are still used in laboratory works and experiments, since some viruses can only replicate in living organisms.
The cultivation of viruses in animals is carried out in different ways: to reproduce neurotropic viruses (rabies, encephalitis), the brain of an animal is infected, to create respiratory (flu) intranasal infection is produced, for dermatotropic (smallpox) - cutaneous and subcutaneous infection.
Most often rodents are used for cultivation: mice and rats, Syrian hamsters, and mumps. They are infected with neurotropic infectious agents, adenoviruses, lymphocytic choriomeningitis by introducing a harmful microorganism into the brain or abdominal cavity.
Some harmful microorganisms develop much faster in the bodies of young individuals, so mostly newborn rats and Syrian hamsters are infected with oncogenic viruses. It is also impossible to do without them during the cultivation of Coxsackie viruses. It is worth noting that the biological method of cultivating viruses in microbiology also has its flaws. Firstly, the organisms of laboratory animals are contaminated by viruses, which is why they experience malaise. Secondly, to get a pure infectious agent, you need to pass it through other cell cultures, which increases the duration of the study.
Infection success rates
The cultivation and indication of viruses are two inextricable processes. Indication allows you to understand whether the microorganism could get along in the infected cell and whether it succeeded in developing further. You can talk about the fact of replication if the animal has the main signs of the disease, as well as if the organs and tissues have undergone pathomorphological changes. Often a hemagglutination reaction is used as an indication, which shows the degree of spread of the virus based on the hemagglutinin protein secreted by it.
Modern features of the cultivation of viruses
Progress does not stand still, innovative methods and technologies appear in all scientific fields. Microbiology and virology are no exception. Now, instead of simply placing the cell culture on the vessels, the roller method is used, in which the material used is located on several cylindrical surfaces that rotate around the circle and are periodically washed by the nutrient medium. This method is good in that it increases the number of cells obtained and requires less consumption of nutrient material.
General conclusion
To cultivate viruses, that is, to create them in artificial environments, people began recently. At first, animal organisms were infected in order to study the principle of action of infectious agents and the development of drugs against them. Thanks to microbiology, virology and epizootology, mankind has got rid of such deadly dangers of diseases such as plague, tuberculosis, rabies, measles.
Now for the cultivation of viruses, mainly separate tissue cultures and chicken embryos are used. Through various manipulations, living cells become infected, and viral bodies mature in them, which then go beyond the cell space. Ripe viruses are collected by biologists for further study.