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MICROSCOPIC METHODS OF DETECTING VIRUSES



1. In a light microscope, the morphology of only the largest viruses, whose dimensions exceed 200 nm, is available for study. They can be painted according to Romanovsky-Giemsa and are found with immersion microscopy. Large viruses can be detected with phase contrast microscopy.

2. Smaller viruses that do not reach 200 nm, using special methods of treatment with mordant and impregnation, leading to an increase in the size of the virus, become visible with light microscopy with the immersion system. The best way is to process with Morozov silvering: for mordant use Ruge liquid (ice acid + formalin) and tannin solution with carbolic acid on heating, and then processing with a solution of silver nitrate and then its reduction. Under the microscope, the viruses are black and round in shape. When processing by Morozov's method, a smallpox virus (Paschen's body) can be detected, which reach a size of 0.2 μm.

3. If to irradiate viruses with ultraviolet waves, and then photographed them with a micro-attachment, it is possible to obtain pictures of viruses measuring about 75 nm.

To detect viruses, luminescent microscopy is also used, based on the ability of certain substances to convert short, invisible ultraviolet rays into long visible waves.

4. Electron microscopy made it possible to observe a particle of 1 nm in size. At the same time, the contrast between the particles and the medium was increased, creating shadows by dusting the smear of the preparation with heavy metals. With the help of electron microscopy, a great variety of virus morphology was discovered and the ultrastructure of virus particles was studied.

5. Viral clusters are often formed in tissues infected with viruses. These clusters of viral particles are called viral bodies or viral inclusions. They are colored by special methods and studied with the aid of a light microscope. The formation of intracellular inclusions has been noted in many viral infections. Most often they are found only in a certain tissue, but with certain diseases occur in a variety of tissues. They can be found in the cytoplasm of the cell (smallpox virus), in the nucleus (herpes virus) or in the nucleus and in the cytoplasm (measles virus). Inclusions have different values ​​(from 0.25 to 20-30 nm) and shape (round, oval, pear-shaped, fusiform, irregular).

6. The structure of inclusions and their location in cells is always characteristic of a particular pathogen of a viral infection, so their detection is used for diagnostic purposes. For example, rabies in the cytoplasm of nerve cells (mainly in the tissue of the ammon horn) reveals the Babes-Negri body. They are polymorphic (most often have a round shape), one cell or several bodies of various forms are found in one cell. With a smallpox in the cytoplasm of epithelial cells, Gvarnieri corpuscles are oval, pear-shaped, fusiform, or sickle-shaped. Viral inclusions are found in a number of other viral diseases.

7. To identify intracellular inclusions, special methods are used to process smears or cuts from tissues. Inclusions can be obtained in an experiment when viruses infect experimental animals. They can be detected in tissue culture during the artificial growth of viruses.

8. The nature of intracellular inclusions has not been fully studied. In most cases, inclusions contain a significant accumulation of viral particles detected by the electron microscope, which allows considering the inclusions as a colony of the virus. By tryptic digestion or by other methods of inclusion, it is possible to break into elementary bodies and the latter to cause diseases in the experiment with the formation of typical inclusions in the tissues. In relation to the Babes-Negri calves in the rabies believe that these bodies are the result of the deposition of nuclear colloids.

 


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