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Infectious RNA and the reconstruction of viruses Evidence that the RNA of viruses is the genetic material, provided us with the same TMV. First of all, scientists managed to change the TMV particles by removing the protein component from their composition. In this state, viruses

The Threat of Viruses One of the books on viruses is very aptly titled "Viruses are the enemies of life." And not only influenza viruses, but also other viruses that infect humans, “on the conscience” of tens of thousands, and maybe millions of lives. Rubella should be considered an unsafe disease. it

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Chapter 10 The world of viruses and its evolution Per. G. Janus Viruses were discovered as something completely unremarkable, namely an unusual variety of infectious agents, and possibly a special kind of toxins that cause plant diseases, such as tobacco mosaic. Since these agents

1. Morphology and structure of viruses

Viruses are microorganisms that make up the kingdom of Vira.

Features:

2) do not have their own protein-synthesizing and energy systems;

3) do not have a cellular organization;

4) have a disjunctive (separated) mode of reproduction (the synthesis of proteins and nucleic acids occurs in different places and at different times);

6) viruses pass through bacterial filters.

Viruses can exist in two forms: extracellular (virion) and intracellular (virus).

The shape of the virions can be:

1) rounded;

2) rod-shaped;

3) in the form of regular polygons;

4) filiform, etc.

Their sizes range from 15–18 to 300–400 nm.

In the center of the virion is a viral nucleic acid covered with a protein coat - a capsid, which has a strictly ordered structure. The capsid is made up of capsomeres. Nucleic acid and capsid make up the nucleocapsid.

The nucleocapsid of complexly organized virions is covered with an outer shell, the supercapsid, which can include many functionally different lipid, protein, and carbohydrate structures.

The structure of DNA and RNA viruses does not fundamentally differ from the NCs of other microorganisms. Some viruses have uracil in their DNA.

DNA can be:

1) double-stranded;

2) single-stranded;

3) ring;

4) double-stranded, but with one shorter chain;

5) double-stranded, but with one continuous and the other fragmented chains.

RNA can be:

1) single-strand;

2) linear double-strand;

3) linear fragmented;

4) ring;

Viral proteins are divided into:

1) genomic - nucleoproteins. Provide replication of viral nucleic acids and virus reproduction processes. These are enzymes, due to which the number of copies of the parent molecule increases, or proteins, with the help of which molecules are synthesized on the nucleic acid matrix that ensure the implementation of genetic information;

2) proteins of the capsid shell - simple proteins with the ability to self-assemble. They add up to geometrically regular structures, in which several types of symmetry are distinguished: spiral, cubic (form regular polygons, the number of faces is strictly constant) or mixed;

3) proteins of the supercapsid shell are complex proteins, diverse in function. Due to them, the interaction of viruses with a sensitive cell occurs. They perform protective and receptor functions.

Among the proteins of the supercapsid shell, there are:

a) anchor proteins (at one end they are located on the surface, while at the other they go into the depth; they provide contact of the virion with the cell);

b) enzymes (can destroy membranes);

c) hemagglutinins (cause hemagglutination);

d) elements of the host cell.

- These are the smallest particles of life, they are 50 times smaller than bacteria. Usually viruses cannot be seen in a light microscope, since their individuals are more than half the wavelength of light. Resting individuals of a virus are called virion. Viruses exist in two forms: resting, or extracellular (viral particles, or virions), and reproducing, or intracellular (complex "virus - host cell").

The forms of viruses are different, they can be filiform, spherical, bullet-shaped, rod-shaped, polygonal, brick-shaped, cubic, while some have a cubic head and process. Each virion consists of nucleic acid and proteins.

In the virions of viruses, only one type of nucleic acid is always present - either RNA or DNA. Moreover, both one and the other can be single-stranded and double-stranded, and DNA can be linear or circular. RNA in viruses is always only linear, but it can be represented by a set of RNA fragments, each of which carries a certain part of the genetic information necessary for reproduction. By the presence of a particular nucleic acid, viruses are called DNA-containing and RNA-containing. It should be especially noted that in the kingdom of viruses, the function of the custodian of the genetic code is performed not only by DNA, but also by RNA (it can also be double-stranded).

Viruses have a very simple structure. Each virus consists of only two parts - core and capsid. The core of the virus, which contains DNA or RNA, is surrounded by a protein coat - capsid (lat. capsa- "receptacle", "box", "case"). Proteins protect the nucleic acid, and also cause enzymatic processes and minor changes in proteins in the capsid. The capsid consists of a certain way stacked of the same type of protein molecules - capsomeres. Usually this is either a spiral type of laying (Fig. 22), or a type symmetrical polyhedron(isometric type) (Fig. 23).

All viruses are conditionally divided into simple and complex. Simple viruses consist only of a core with nucleic acid and a capsid. Complex viruses on the surface of the protein capsid they also have an outer shell, or supercapsid, containing a bilayer lipoprotein membrane, carbohydrates and proteins (enzymes). This outer shell (supercapsid) is usually built from the membrane of the host cell. material from the site

On the surface of the capsid there are various outgrowths - spikes, or "carnations" (they are called fibers), and shoots. With them, the virion attaches to the surface of the cell, into which it then penetrates. It should be noted that on the surface of the virus there are also special attachment proteins, binding the virion with specific groups of molecules - receptors(lat. recipio-“I receive”, “I accept”), located on the surface of the cell into which the virus penetrates. Some viruses attach to protein receptors, others to lipids, and others recognize carbohydrate chains in proteins and lipids. In the process of evolution, viruses "learned" to recognize cells that are sensitive to them by the presence of special receptors on the cell surface of their hosts.

Viruses. Morphology and physiology of viruses

G. Minsk

LECTURE #8

TOPIC: ʼʼRNA - and DNA-containing viruses. HIV AIDS

Specialty - Nursing

Prepared by the teacher - Protko L.I.

Presentation plan:

3. HIV - AIDS. Epidemiology and pathogenesis. Prevention

4. Influenza virus. Epidemiology and pathogenesis. Immunity, prevention

5. Hepatitis viruses. Epidemiology and pathogenesis. Immunity, prevention

Viral diseases arose in ancient times, but virology as a science began to develop in late XIX century.

In 1892ᴦ. Russian botanist D.I. Ivanovsky, studying the mosaic disease of tobacco leaves, found that this disease is caused by the smallest microorganisms that pass through finely porous bacterial filters. These microorganisms are called filterable viruses. Subsequently, it was shown that there are other microorganisms that pass through bacterial filters, in connection with which the filtered viruses began to be called simply viruses.

A great contribution to the study of viruses was made by virologists: M.A. Morozov, N.F. Gamaleya, L.A. Zilber, M.P. Chumakov, A.A. Smorodintsev, V.M. Zhdanov and others.

Viruses - ϶ᴛᴏ non-cellular form of existence of living matter. Οʜᴎ are very small. According to the figurative expression of V.M. Zhdanov ʼʼtheir size in relation to the sizee of medium bacteria can be compared with the size of a mouse in relation to an elephantʼʼ. It became possible to see viruses only after the invention of the electron microscope.

Today, many methods are used to study viruses: chemical, physical, molecular biological, immunobiological and genetic.

All viruses are divided into those affecting humans, animals, insects, bacteria and plants.

Viruses have a wide variety of forms and biological properties, but they all have common features buildings. Mature particles of viruses are called virions.

Unlike other microorganisms that contain both DNA and RNA, the virion contains only one of the nucleic acids - either DNA or RNA.

Nucleic acid of viruses should be single-stranded and double-stranded. Almost all viruses containing RNA have single-stranded RNA in their genome, and those containing DNA have double-stranded DNA. In accordance with the two types of genetic substance, viruses are divided into RNA- and DNA-containing. DNA-containing ones include 6 families, RNA-containing ones - 11 families.

The structure of the virion. At the center of the virion is a nucleic acid surrounded by a capsid. The capsid is made up of protein subunits called capsomeres. The mature virus is chemically a nucleocapsid. The number of capsomeres and the way they are stacked are strictly constant for each type of virus. Capsomeres are stacked in the form of a polyhedron with uniform symmetrical faces - a cuboidal shape (adenovirus). Spiraling is characteristic of influenza viruses. There may be a type of symmetry in which the nucleic acid has the form of a spring around which capsomeres are stacked, in this case the virus has a rod-shaped form - a virus, sickening tobacco leaves.

The phage has a complex type of symmetry: the head is cuboidal, and the process is rod-shaped.

Τᴀᴋᴎᴍ ᴏϬᴩᴀᴈᴏᴍ, based on the method of packing, viruses are divided into cuboidal, spherical, rod-shaped and spermatozoic forms.

Some viruses, which have a more complex structure, have a shell, which is commonly called peplos. It is formed when the virus leaves the host cell. In this case, the viral capsid is enveloped by the inner surface of the cytoplasmic membrane of the host cell and one or more layers of the supercapsid membrane are formed. Only some viruses have such a shell, for example, rabies, herpes viruses. This shell contains phospholipids that are destroyed under the influence of ether. Τᴀᴋᴎᴍ ᴏϬᴩᴀᴈᴏᴍ, acting on ether, it is possible to distinguish a virus that has a peplos from a virus with a ʼʼnaked capsidʼʼ.

In some viruses, capsomeres in the form of spikes protrude from the outer lipid layer of the envelope (these spikes are blunt). Such viruses are called peplomers (influenza virus).

The nucleic acid of the virus is the carrier of hereditary properties, and the capsid and the outer shell have protective functions, as if they contribute to the penetration of the virus into the cell.

Virus size. Viruses are measured in nanometers. Their value fluctuates in a wide range from 15-20 to 350-400 nm.

Methods for measuring viruses.

1. Filtration through bacterial filters with a known spore size

2. Ultracentrifugation - large viruses settle faster

3. Photographing viruses with an electron microscope

Chemical composition viruses. The amount and content of DNA and RNA viruses are not the same. For DNA, the molecular weight ranges from 1‣‣‣10 6 to 1.6‣‣‣10 8 , while for RNA it ranges from 2‣‣‣10 6 to 9.0‣‣‣10 6 .

Proteins in virions were found in a small number. Οʜᴎ are composed of 16-20 amino acids. In addition to the capsid proteins, there are also internal proteins associated with the nucleic acid. Proteins determine the antigenic properties of viruses, and also, due to the dense packing of polypeptide chains, protect the virus from the action of host cell enzymes.

Lipids and carbohydrates are found in the outer envelope of complex virions. The source of lipids and carbohydrates is the shell of the host cell. The polysaccharides that make up some viruses determine their ability to cause erythrocyte agglutination.

Virus enzymes. Viruses do not have their own metabolism, so they do not need metabolic enzymes. At the same time, some viruses revealed the presence of enzymes that facilitate their penetration into the host cell.

Detection of viral antigens. Viral antigens in infected host cells can be detected using the immunofluorescence method. Preparations containing cells infected with viruses are treated with specific immune luminescent sera. When viewing the particles, a characteristic glow is observed. The type of virus is determined by the correspondence of the specific luminescent serum that caused the glow.

The introduction of the virus into the cell, its interaction with the host cell and reproduction(reproduction) are composed of a series of successive stages.

Stage 1. Begins with the process of adsorption due to virion and cell receptors. In complex virions, receptors are located on the surface of the envelope in the form of spike-like outgrowths, in simple virions, on the surface of the capsid.

Stage 2. Penetration of the virus into the host cell proceeds differently for different viruses. For example, some phages pierce the shell with their offshoot and inject the nucleic acid into the host cell. Other viruses enter the cell by drawing in the viral particle with the help of the vacuole, ᴛ.ᴇ. at the site of introduction, a depression forms in the cell membrane, then its edges close and the virus enters the cell. This retraction is called viropexis.

Stage 3. ʼʼundressing of the virusʼʼ (disintegration). It is important to note that in order to reproduce itself, the viral nucleic acid is released from the protein coats that protect it. The undressing process may begin during adsorption, or it may occur when the virus is already inside the cell.

Stage 4. At this stage, the replication (reproduction) of nucleic acids and the synthesis of viral proteins occur. This stage occurs with the participation of DNA or RNA of the host cell.

Stage 5. Assembly of the virion. This process is provided by the self-assembly of protein particles around the viral nucleic acid. Protein synthesis may start immediately after viral nucleic acid synthesis, or after an interval of several minutes or several hours. Some viruses self-assemble in the cytoplasm. Others have host cells in the nucleus. The formation of the outer shell always occurs in the cytoplasm.

Stage 6. The exit of the virion from the host cell occurs by leakage of the virus through the cell membrane or through the hole formed in the host cell.

Types of interaction between virus and cell. The first type - a productive infection - is characterized by the formation of new virions in the host cell.

The second type, an abortive infection, essentially consists in the interruption of nucleic acid replication.

The third type is characterized by the incorporation of a viral nucleic acid into the DNA of the host cell; there is a form of coexistence of the virus and the host cell (virogeny). In this case, synchronous replication of viral and cellular DNA is ensured. In phages, this is called lysogeny.

Microscopic examination. With individual viral infections in the cytoplasm or nuclei of the cells of the host organism, specific intracellular bodies are observed - inclusions of diagnostic value. The sizes of viral particles and inclusion bodies can be artificially increased by special methods of processing preparations with mordant and impregnation and observed with immersion microscopy. Smaller virions, lying beyond the visibility of an optical microscope, are detected only with electron microscopy. Exist different points vision for intracellular inclusions. Οʜᴎ the authors believe that they are an accumulation of viruses. Others believe that they arise as a result of the cell's reaction to the introduction of viruses.

Virus genetics. Modification in viruses is determined by the characteristics of the host cell in which the virus reproduces. Modified viruses acquire the ability to infect cells similar to those in which they were modified. In different viruses, modification manifests itself in different ways.

Mutation - in viruses occurs under the influence of the same mutagens that cause mutation in bacteria. A mutation occurs during the replication of nucleic acids. Mutations affect various properties of viruses, for example, sensitivity to temperature, etc.

Genetic recombination in viruses can occur as a result of the simultaneous infection of a host cell with two viruses, while the exchange of individual genes between the two viruses can occur and recombinants are formed containing the genes of two parents.

Genetic reactivation of genes sometimes occurs when an inactivated virus is crossed with a full-fledged virus, which leads to the rescue of the inactivated virus.

Spontaneous and directed genetics of viruses has great importance in the development of the infectious process.

Resistance to environmental factors. Most viruses are inactivated by high temperatures.
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However, there are exceptions, for example, the hepatitis virus is heat-resistant.

Viruses are not sensitive to low temperatures. Ultraviolet rays of the sun have an inactivating effect on viruses. Scattered sunlight acts on them less actively. Viruses are resistant to glycerol, which makes it possible to preserve them in glycerol for a long time. Οʜᴎ are resistant to antibiotics.

Acids, alkalis, disinfectants inactivate viruses. At the same time, some formalin-inactivated viruses retain their immunogenic properties, which makes it possible to use formalin to obtain vaccines.

animal susceptibility. The range of susceptible animals for some viruses is very wide, for example, many animals are susceptible to rabies viruses. Some viruses infect only one type of animal, for example, the canine distemper virus only infects dogs. There are viruses to which animals are not sensitive - the measles virus.

Organotropism of viruses. Viruses have the ability to infect certain organs, tissues and systems. For example, the rabies virus infects the nervous system.

Isolation of viruses in the environment. From a sick body, viruses can be excreted in feces, for example, the polio virus, the rabies virus is excreted in saliva.

The main ways of transmission of viruses. Airborne, food, contact-household, transmission.

Antiviral immunity. The human body has an innate resistance to certain viruses. For example, a person is not susceptible to the canine distemper virus.

Antiviral immunity is determined by both cellular and humoral protective factors, nonspecific and specific.

nonspecific factors. A powerful inhibitor of viral reproduction is a protein substance - interferon. In a healthy body, it is contained in a small amount, and viruses contribute to the production of interferon and its amount increases significantly. It is nonspecific, as it blocks the reproduction of various viruses. At the same time, it has tissue specificity, ᴛ.ᴇ. cells of different tissues form unequal interferon. It is believed that its mechanism of action is essentially that it prevents protein synthesis in the host cell and thereby stops the reproduction of the virus.

Specific factors of antiviral immunity include virus-neutralizing antibodies, hemagglutinating and precipitating.

The main methods for the study of viruses.

1. Hemagglutination reaction, hemagglutination delay reaction, indirect hemagglutination reaction. Complement fixation reaction

2. Neutralization reaction of viruses in tissue culture

3. Immunofluorescence method

4. Histological method - detection of inclusions

5. Biological method

Viruses. Morphology and physiology of viruses - concept and types. Classification and features of the category "Viruses. Morphology and physiology of viruses" 2017, 2018.

Viruses are microorganisms that make up the kingdom of Vira.

Features:

2) do not have their own protein-synthesizing and energy systems;

3) do not have a cellular organization;

4) have a disjunctive (separated) mode of reproduction (the synthesis of proteins and nucleic acids occurs in different places and at different times);

6) viruses pass through bacterial filters.

Viruses can exist in two forms: extracellular (virion) and intracellular (virus).

The shape of the virions can be:

1) rounded;

2) rod-shaped;

3) in the form of regular polygons;

4) filiform, etc.

Their sizes range from 15–18 to 300–400 nm.

In the center of the virion is a viral nucleic acid covered with a protein coat - a capsid, which has a strictly ordered structure. The capsid is made up of capsomeres. Nucleic acid and capsid make up the nucleocapsid.

The nucleocapsid of complexly organized virions is covered with an outer shell, the supercapsid, which can include many functionally different lipid, protein, and carbohydrate structures.

The structure of DNA and RNA viruses does not fundamentally differ from the NCs of other microorganisms. Some viruses have uracil in their DNA.

DNA can be:

1) double-stranded;

2) single-stranded;

3) ring;

4) double-stranded, but with one shorter chain;

5) double-stranded, but with one continuous and the other fragmented chains.

RNA can be:

1) single-strand;

2) linear double-strand;

3) linear fragmented;

4) ring;

Viral proteins are divided into:

1) genomic - nucleoproteins. Provide replication of viral nucleic acids and virus reproduction processes. These are enzymes, due to which the number of copies of the parent molecule increases, or proteins, with the help of which molecules are synthesized on the nucleic acid matrix that ensure the implementation of genetic information;

2) proteins of the capsid shell - simple proteins with the ability to self-assemble. They add up to geometrically regular structures, in which several types of symmetry are distinguished: spiral, cubic (form regular polygons, the number of faces is strictly constant) or mixed;

3) proteins of the supercapsid shell are complex proteins, diverse in function. Due to them, the interaction of viruses with a sensitive cell occurs. They perform protective and receptor functions.

Among the proteins of the supercapsid shell, there are:

a) anchor proteins (at one end they are located on the surface, while at the other they go into the depth; they provide contact of the virion with the cell);

b) enzymes (can destroy membranes);

c) hemagglutinins (cause hemagglutination);

d) elements of the host cell.

The interaction takes place in a single biological system at the genetic level.

There are four types of interaction:

1) productive viral infection (interaction resulting in the reproduction of the virus, and the cells die);

2) abortive viral infection (interaction in which the reproduction of the virus does not occur, and the cell restores the impaired function);

3) latent viral infection (there is a reproduction of the virus, and the cell retains its functional activity);

4) virus-induced transformation (an interaction in which a cell infected with a virus acquires new properties that were not previously inherent in it).

After adsorption, virions enter the body by endocytosis (viropexis) or by fusion of the viral and cell membranes. The resulting vacuoles, containing whole virions or their internal components, enter the lysosomes, in which deproteinization is carried out, i.e., the “undressing” of the virus, as a result of which the viral proteins are destroyed. The nucleic acids of viruses freed from proteins penetrate through cell channels into the cell nucleus or remain in the cytoplasm.

Nucleic acids viruses implement the genetic program to create viral offspring and determine the hereditary properties of viruses. With the help of special enzymes (polymerases), copies are made from the parent nucleic acid (replication takes place), and messenger RNAs are synthesized, which are connected to ribosomes and carry out the synthesis of daughter viral proteins (translation).

After a sufficient number of virus components accumulate in the infected cell, the assembly of progeny virions begins. This process usually occurs near cell membranes, which sometimes take a direct part in it. The composition of newly formed virions often contains substances characteristic of the cell in which the virus replicates. In such cases, the final step in the formation of virions is their enveloping with a layer of cell membrane.

The last step in the interaction of viruses with cells is the release or release of daughter virus particles from the cell. Simple viruses lacking a supercapsid cause cell destruction and enter the intercellular space. Other viruses that have a lipoprotein envelope exit the cell by budding. At the same time, the cell long time maintains viability. In some cases, viruses accumulate in the cytoplasm or nucleus of infected cells, forming crystal-like clusters - inclusion bodies.

The main methods of cultivation of viruses:

1) biological - infection of laboratory animals. When infected with a virus, the animal becomes ill. If the disease does not develop, then pathological changes can be detected at autopsy. Animals show immunological changes. However, not all viruses can be cultivated in animals;

2) cultivation of viruses in developing chicken embryos. Chicken embryos are grown in an incubator for 7-10 days and then used for cultivation. In this model, all types of tissue buds are susceptible to infection. But not all viruses can multiply and develop in chicken embryos.

As a result of infection, the following can occur and appear:

1) death of the embryo;

2) developmental defects: formations appear on the surface of the membranes - plaques, which are accumulations of dead cells containing virions;

3) accumulation of viruses in the allantoic fluid (detected by titration);

4) reproduction in tissue culture (this is the main method of culturing viruses).

There are the following types of tissue cultures:

1) transplanted - cultures of tumor cells; have high mitotic activity;

2) primary trypsinized - subjected to primary treatment with trypsin; this treatment disrupts intercellular communication, resulting in the release of individual cells. The source is any organs and tissues, most often embryonic (they have high mitotic activity).

Special media are used to maintain tissue culture cells. These are liquid nutrient media of complex composition containing amino acids, carbohydrates, growth factors, protein sources, antibiotics and indicators for assessing the development of tissue culture cells.

The reproduction of viruses in tissue culture is judged by their cytopathic action, which is of a different nature depending on the type of virus.

The main manifestations of the cytopathic action of viruses:

1) virus reproduction may be accompanied by cell death or morphological changes in them;

2) some viruses cause cell fusion and the formation of multinuclear syncytium;

3) cells can grow, but divide, resulting in the formation of giant cells;

4) inclusions appear in the cells (nuclear, cytoplasmic, mixed). Inclusions can be colored pink color(eosinophilic inclusions) or in blue (basophilic inclusions);

5) if viruses with hemagglutinins multiply in tissue culture, then in the process of reproduction the cell acquires the ability to adsorb erythrocytes (hemadsorption).

Antiviral immunity begins with the presentation of the viral antigen by T-helpers.

Dendritic cells have strong antigen-presenting properties in viral infections, and Langerhans cells in herpes simplex and retroviral infections.

Immunity is aimed at neutralizing and removing the virus, its antigens and virus-infected cells from the body. Antibodies formed during viral infections act directly on the virus or on cells infected by it. In this regard, there are two main forms of participation of antibodies in the development of antiviral immunity:

1) neutralization of the virus with antibodies; this prevents the reception of the virus by the cell and its penetration inside. Opsonization of the virus with antibodies promotes its phagocytosis;

2) immune lysis of virus-infected cells with the participation of antibodies. When antibodies act on antigens expressed on the surface of an infected cell, complement is added to this complex, followed by its activation, which causes the induction of complement-dependent cytotoxicity and the death of the virus-infected cell.

Insufficient concentration of antibodies can enhance the reproduction of the virus. Sometimes antibodies can protect the virus from the action of proteolytic enzymes of the cell, which, while maintaining the viability of the virus, leads to an increase in its replication.

Virus-neutralizing antibodies act directly on the virus only when it, having destroyed one cell, spreads to another.

When viruses pass from cell to cell along cytoplasmic bridges without contact with circulating antibodies, the main role in the development of immunity is played by cellular mechanisms associated primarily with the action of specific cytotoxic T-lymphocytes, T-effectors, and macrophages. Cytotoxic T-lymphocytes directly contact the target cell, increasing its permeability and causing osmotic swelling, membrane rupture and release of contents into the environment.

The mechanism of the cytotoxic effect is associated with the activation of membrane enzyme systems in the area of ​​cell adhesion, the formation of cytoplasmic bridges between cells, and the action of lymphotoxin. Specific T-killers appear within 1-3 days after infection with the virus, their activity reaches a maximum after a week, and then slowly decreases.

One of the factors of antiviral immunity is interferon. It is formed at the sites of virus reproduction and causes specific inhibition of the transcription of the viral genome and suppression of the translation of viral mRNA, which prevents the accumulation of the virus in the target cell.

The persistence of antiviral immunity is variable. With a number of infections (chicken pox, mumps, measles, rubella), immunity is quite stable, and repeated diseases are extremely rare. Less stable immunity develops with infections of the respiratory tract (flu) and intestinal tract.