Medical virology

1.Morphology and physiology
of the virus.
A virus (from the Latin. virus-poison) — the
simplest form of life, a microscopic particle
that is a molecule of nucleic acids (DNA or
RNA), enclosed in a protein shell and can
infect living organisms.

Distinguishing features of viruses:
1.contain only one type of nucleic acid (RNA or DNA);
2.they do not have their own protein synthesis and energy
systems;
3.do not have a cellular organization;
4.they have a disjointed method of reproduction (the
synthesis of proteins and nucleic acids occurs in different
places and at different times);
5.obligate parasitism of viruses is realized at the genetic
level;
6.viruses pass through bacterial filters.

Viral particles can exist in two
forms:
1.extracellular (virion)
2.intracellular (virus).

In shape, there are: round, rod-shaped,
convoluted, in the form of regular
polygons, 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 shell-
a capsid, which consists of capsomers.

Functions of the capsid:
 Protection of genetic material (DNA or
RNA) of the virus from mechanical and
chemical damage.
 Determination of the potential for
infection of the cell.
 At the initial stages of infection of the cell:
attachment to the cell membrane, rupture
of the membrane and introduction of the
genetic material of the virus into the cell.

The nucleic acid and the capsid
shell make up the nucleocapsid.
The nucleocapsid complex of the
virion is covered with the outer
shell – supercapacitor.

The supercapsid (additional lipoprotein) shell is
formed from the plasma membrane of the host cell.
It occurs only in relatively large viruses (flu, herpes).
This outer shell is a fragment of the nuclear or
cytoplasmic membrane of the host cell, from which
the virus exits into the extracellular environment.
Sometimes the outer shells of complex viruses
contain carbohydrates in addition to proteins, for
example, in pathogens of influenza and herpes.

The structure of DNA and RNA - containing viruses is not fundamentally
different from the NC of other microorganisms.
DNA can be:
1. double-chain;
2. single-stranded;
3. annular;
4. double-chain, but with one shorter chain;
5. two-chain, but with one continuous chain and the other fragmented
chain.
RNA can be:
1. single-thread;
2. linear two-thread;
3. linear fragmented;
4. ring; containing two identical single-stranded RNA.

Viral proteins are divided into:
1.genomic-nucleoproteins. Provide replication of
viral nucleic acids and virus reproduction
processes. These are enzymes that increase the
number of copies of the parent molecule, or
proteins that synthesize molecules on the
nucleic acid matrix that provide the
implementation of genetic information;

1.capsid shell proteins are simple
proteins that have the ability to self-
assemble. They are formed into
geometrically regular structures that
distinguish several types of symmetry:
spiral, cubic (they form regular
polygons, the number of faces is strictly
constant) , or mixed;

1.supercapsid shell proteins are complex proteins that are
diverse in function. Through them, the interaction of a virus
with a sensitive cell. Among the proteins of the supercapsid
shell, there are:
a) anchor proteins (one end of them is located on the surface,
and the other goes deep; providing contact with the virion cell);
b) enzymes (can destroy cell membranes);
с) hemagglutinins (cause hemagglutination);
d) elements of the host cell.

Interaction of the virus
with the host cell:

There are four types of interaction:
1. productive viral infection (interaction that results in the reproduction of the
virus, and the cells die);
2. abortive viral infection (an interaction in which the virus does not reproduce,
but the cell restores the impaired function);
3. latent viral infection (the virus reproduces, but the cell retains its functional
activity);
4. virus-induced transformation (an interaction in which a cell infected with a
virus acquires new properties not previously inherent in it).
After adsorption, virions penetrate through endocytosis or as a result of fusion of
the viral and cell membranes. The resulting vacuoles containing whole virions or
their internal components fall into the lysosomes, where deproteinization is
performed, i.e.," Stripping " of the virus, as a result of which the viral proteins
are destroyed. The nucleic acids of viruses released from proteins penetrate
through cellular channels into the cell nucleus or remain in the cytoplasm.

Influenza A, B, C viruses
(Orthomyxoviridae family)

Flu viruses (lat. Influenzavirus) — four monotypic genera of viruses from
the family of orthomyxoviruses (Orthomyxoviridae)
Alphainfluenzavirus
Monotypic genus, former name: Flu A. Type A influenza virus
It causes outbreaks of flu every year, often epidemics, periodically
pandemics. This is due to the high degree of variability of the virus: a type
A virus is susceptible to both antigenic shift (shift) and antigenic drift. In
2018, influenza viruses of the subtypes A (H1N1) and A (H3N2) circulate
among people.
The natural reservoir of the influenza A virus is waterfowl. Sometimes it is
transmitted to other birds, as a result it can infect poultry, from them -
domestic animals and then people, leading to epidemics and pandemics.

In birds, the virus
infects the epithelial
cells in the digestive
tract, in humans - the
epithelial cells of the
respiratory tract.

Within the species Influenza A virus, several serotypes have been identified
(observed in nature)
H1N1, which caused the pandemic of the Spanish influenza in 1918 and swine
flu in 2009 (according to the old classification, there are three sero-types:
Hsw1N1, H0N1 and H1N1;
H1N2, endemic to humans, pigs and birds;
H2N2, which caused the pandemic of Asian flu in 1957;
H3N2, which caused the Hong Kong flu pandemic in 1968;
H5N1, which caused the bird flu pandemic in 2004;
H6N1, detected in a single patient, was cured;
H7n2
H7n3
H7N7 is associated with human conjunctivitis and has a high epizootic
potential;
H7N9, responsible for six epidemics in China, now has a high pandemic
potential among other influenza A serotypes;
H9N2
H10N7
H17N10
H18N11

Betainfluenzavirus
Monotypic genus, formerly known as Influenzavirus
B. of the influenza Virus type "B".
The "B" type flu virus changes by type of drift, but
not by shift. It is not subdivided into subtypes, but can
be subdivided into lines. In 2018, influenza type b
viruses are circulating in the V/Yamagata and
V/Victoria lines.

The natural reservoir of Influenzavirus B is
human. The virus affects the upper and lower
respiratory tract, the symptoms are similar to
those caused by a type "A" virus. It has a limited
number of lines, which is probably why most
people acquire immunity to Influenzavirus B at an
early age. This species is only variable in
hemagglutinin, ha antigen drift is not as active as
in Influenzavirus A.

The "B" flu virus causes epidemics, but it is quite rare, once
every 4-6 years, they develop slowly compared to those caused
by the "A" virus and usually cover 8-10 % of the population
The "B" type of flu virus is similar to the "A" type of virus,
they are difficult to distinguish under an electron microscope.
The shell of virions " B " contains 4 proteins: HA, NA, NB and
BM2. BM2 is a proton channel that is used by decapitati virus
(in a cage). The NB protein is considered an ion channel, but
this is not a prerequisite for virus replication in cell culture.
The virus genome consists of eight RNA fragments

Gammainfluenzavirus
Monotypic genus, former name:
Influenzavirus C. influenza Virus type "C".
Flu virus "C" is detected in patients less often
than "B" and "A", it usually leads to mild
infections, is not dangerous for humans and
does not pose a problem for public health.

The natural reservoir of Influenzavirus C is
human, it also infects pigs and in experiments
can be transmitted between pigs. Affects the
upper respiratory tract, mainly in children, the
clinical symptoms are weak. Serological studies
have revealed the global prevalence of type "C"
virus. Most people get immune to it at an early
age.

The type "C" virus is not characterized by an
antigenic shift and it changes slightly[.
Influenzavirus C is much more stable than the "A"
type virus and the high degree of cross-reactivity
observed among them isolates these species from
each other.
The "C" flu virus causes scattered diseases and
almost never produces epidemic outbreaks.

Parainfluenza virus
(Paramyxoviridae
family)

Paramixoviruses (lat. Paramyxoviridae is a
family of viruses in the order Mononegavirales.
Parainfluenza virus
Parainfluenza refers to acute respiratory viral
infections.
The disease is characterized by damage to the
upper respiratory tract and moderate
intoxication.

Taxonomic position. Pathogens of human
parainfluenza are
viruses belonging to the family Paramyxoviridae, the
genus Respirovirus (serotypes
HPIV-1 and HPIV-3) and the genus Rubulavirus
(serotypes HPIV-2, HPIV-4).
Diseases in children
people are caused by parainfluenza viruses of
serotypes 1, 2 and 3, and the main
the pathogen for humans is the parainfluenza virus
serotype 3.

For the first time human
parainfluenza viruses were isolated
in 1956-1957 by R. M. Chanock
from nasopharyngeal swabs of
children with influenza-like illness by
infection of cell cultures.

Structure of the virus. The virion has a spherical shape with a
diameter of 150 nm.
The genome of human parainfluenza viruses is represented by a
single-stranded
UN-fragmented molecule minus-RNA.

The life cycle of the virus. Parainfluenza virus that has entered
the body
binds HN-spikes with sialic acid of the cell membrane. Then with
using the F-protein, the virus envelope merges with the cell
membrane, and the nucleocapsid
penetrates into the cell cytoplasm without the formation of
endosome. Transcription, the synthesis of
protein and genome replication occur directly in the cell's
cytoplasm.
The genome is transcribed into mRNA for the synthesis of viral
proteins and a complete
plus-a matrix for the formation of genomic RNA.

Child genomes interact
with L -, P-and NR-proteins, resulting in the formation of
nucleocapsids.
At the same time, HN and F proteins are embedded in the
cell membrane, and M-protein
it is located opposite them on the inner side of the cell
membrane. Then
nucleocapsids are surrounded by a supercapsid shell
made of a pre-modified cell membrane. The yield of
virions from the cell is by budding. The scheme of the life
cycle of the parainfluenza virus is presented on
figure

Epidemiology. The source of
infection in parainfluenza is patients
people with severe symptoms of the
disease or with an asymptomatic
course
infections.

The mechanism of infection is aerogenic, the main
route of infection transmission
- air-drop. The virus is most intensively released into
the external environment in
the first 2-3 days of the disease. The disease is
widespread. Children are more likely to get sick
before
5 years. There is no seasonality, but an increase in
the incidence is observed in the spring and
in autumn.

Pathogenesis. The entrance gate of infection is the
mucous membranes
upper respiratory tract (pharynx and larynx). The virus
after adsorption penetrates into the
epithelial cells of the respiratory tract, multiplies in them,
causes death
cells and inflammation. For a short time it is noted
of viremia. The decay products of the cells determines the
toxicity of the body.
The disease can be accompanied by bacterial
complications.

Clinic. The incubation period for parainfluenza is from 1
to 6 days.
When parainfluenza affects the larynx (laryngitis,
laryngotracheitis), bronchi (bronchitis),
the mucous membrane of the nose (rhinitis). The disease is
accompanied by an increase in
body temperature up to 38 ° C, weakness, runny nose,
tickling or sore throat, cough. The duration of the disease
is 5-7 days. The cough may persist for up to 2 weeks or
more.

Immunity. After the disease
develops fragile and
short-term type-specific
immunity. Possible repeated
diseases.

Laboratory diagnostics. The study material for
parainfluenza
serves as mucus or flushing from the respiratory tract,
sputum. To isolate the virus
they use cell culture. Indication of the virus is carried out
by cytopathic
action and hemadsorption. Virus identification is
performed using
RTGA, RSK, RN.
Modern methods of diagnosis of parainfluenza are RT-
PCR reverse
transcription and ELISA.

Treatment. For the treatment of
parainfluenza, symptomatic agents are
used
(antipyretic and antitussive agents, as
well as vitamin preparations).
Prevention. Means of specific prevention
of parainfluenza
absent.

Coronaviruses and acute
respiratory syndromes
(MERS and SARS)
Middle Eastern respiratory
syndrome (MERS)
Severe acute respiratory
syndrome (SARS)

Coronaviruses are RNA-coated viruses
that cause respiratory diseases of
varying severity from the common cold
to fatal pneumonia.
Coronavirus infections in humans most
often cause cold symptoms.

Three of the 7 coronaviruses cause much more severe
than other coronaviruses, and sometimes fatal
respiratory infections in humans, they have caused
major outbreaks of deadly pneumonia in the 21st
century:
SARS-Cov2 is a new coronavirus that is the identified
cause of the 2019 coronavirus disease (COVID-19) that
originated in the city of Wuhan, China in late 2019 and
has spread worldwide.
IN 2012, the mers-CoV coronavirus was identified as the
cause of Middle Eastern respiratory syndrome (MERS).
In late 2002, SARS-CoV was identified as the cause of an
outbreak of severe acute respiratory syndrome (SARS)

These coronaviruses, which cause
severe respiratory infections, are
zoonotic pathogens that first
infect infected animals and then
are transmitted from animals to
humans.

Middle East respiratory syndrome
(MERS)
Middle East respiratory syndrome
(MERS) is a severe acute
respiratory disease caused by
MERS coronavirus (MERS-CoV).

MERS -CoV virus transmission pathways
MERS-CoV can be transmitted from person to
person through direct contact, by airborne
droplets (particles > 5 microns), or by aerosol
(particles < 5 microns). The fact of human-to-
human transmission was established by the
development of infection in people who had the
only risk factor - close contact with people with
MERS.

Clinical implications
The incubation period of MERS-CoV is about 5 days.
Diagnostics
Reverse transcription PCR (RT-PCR) of upper and
lower respiratory tract secretions and blood serum
MERS should be suspected in patients who have an
unexplained acute febrile respiratory infection of the
lower respiratory tract and who have at least one of the
following signs within 14 days of the onset of symptoms:

- Travel or stay in areas where MERS has recently
been registered or transmission may have occurred
- Stayed in medical institutions where cases of MERS
were recorded
- Close contact with a suspected MERS patient
The MERS virus should also be suspected in patients
who have had close contact with a suspected mers
patient and who have fever, regardless of whether
they have respiratory symptoms.

Severe acute respiratory syndrome (SARS)
Severe acute respiratory syndrome (SARS) is
a severe, acute respiratory disease caused by
SARS coronavirus (SARS-CoV).
SARS is much more severe than other
coronavirus infections. SARS is a flu-like
disease that sometimes leads to progressive
severe respiratory failure.

Adenovirus infection
Adenovirus infection is a group of human infectious
diseases caused by adenoviruses. They belong to the
group of acute respiratory viral infections (ARVI) and
are characterized by damage to the mucous
membranes of the upper respiratory tract,
conjunctiva, and lymphoid tissue. There is a fever with
moderate symptoms of intoxication.

Etiology
For the first time, an adenovirus (namely, a virus of
the genus Mastadenovirus of the family
Adenoviridae) was isolated by Robert Huebner and
W. Rowe in 1953 during surgery on the tonsils and
adenoids of children. Currently, there are more than
40 known varieties. Adenovirus is resistant to the
external environment and to the action of organic
solvents.

Epidemiology
The source of infection is a patient with any
form of adenovirus infection or a healthy
virus carrier. There is a great risk of
infection from patients at the beginning of
the disease, i.e. during the first two weeks.
However, it also happens that the virus
continues to be released in the next 3-4
weeks during the recovery period.

The infection is transmitted by airborne
and fecal-oral route. Children aged 6
months to 5 years are most susceptible to
it. Children under 6 months are not
susceptible to infection due to the presence
of transplacental immunity, i.e. received
from the mother. After the disease, there is
a type-specific immunity

Epidemic outbreaks are recorded throughout
the year, especially in winter, and in the form
of sporadic cases in the warm season. Infection
is facilitated by close communication of
children. Organized children's groups often
get sick-undulating, for 10-12 days. All types of
adenoviruses are characterized by the
presence of a common complement-binding
antigen.

Clinical implications
The incubation period is from 1 day to 2 weeks. The
disease begins acutely, with a rise in temperature.
Characteristic is a tetrad of symptoms: rhinitis-
pharyngitis-conjunctivitis-fever. There are also
symptoms of General intoxication — weakness,
lethargy, headache, lack of appetite, drowsiness.
Laboratory diagnostics is ineffective. In General
blood tests, non-specific changes (lymphocytosis,
leukopenia), flushes from the nasopharynx are not
widely used in practical medicine.

Pathogenesis
The infection enters the body through the mucous membranes of
the upper respiratory tract, less often-the intestines or
conjunctiva. The virus enters epithelial cells and cells of
lymphoid tissue, affects the cytoplasm and the nucleus, where
viral DNA replication occurs. The affected cells stop dividing and
die. Viruses penetrate other cells of the mucous membranes and
lymph nodes, as well as into the blood. This is accompanied by
massive exudative inflammation on the part of the mucous
membranes, i.e. the accumulation of fluid in them. Conjunctivitis
appears. Further, the pathological process involves internal
organs (lungs, bronchi, intestines, kidneys, liver, spleen), as well
as the brain, mesenteric lymph nodes.

Prevention
Proper diet
Ventilation.
Air humidification.
nose washing
Hardening

Drug-based prevention measures
 Vaccination, or inoculation.
 Nose washing. You can, as already mentioned, make a
saline solution yourself, or you can buy a ready-made
mixture in a bottle with a convenient spout at the
pharmacy.
 Vitamin and mineral complexes. By themselves, they do
not treat or protect against infection, but they help to
maintain normal immunity.
 Antiviral agents

Methods of laboratory diagnostics of viral
infections
Methods of laboratory diagnostics of viral infections are
divided into several large groups.
- Direct methods that consist in detecting the virus itself or
antibodies to it directly in the biological material.
- Indirect methods-consist in artificial development of the
virus in significant quantities, and its further analysis.

The most relevant diagnostic methods in everyday
practice include:
Serological methods of diagnosis-detection of certain
antibodies or antigens in the patient's blood serum as a
result of the antigen-antibody reaction (AG-at). That is,
when searching for a specific antigen in a patient, the
corresponding artificially synthesized antibody is used,
and, accordingly, Vice versa-when detecting antibodies,
synthesized antigens are used.

The reaction immunofluorescence (RIF)
Based on the use of dye-labeled antibodies. In the
presence of a viral antigen, it binds to labeled
antibodies, and a specific color is observed under
the microscope, which indicates a positive result.
With this method, unfortunately, it is not
possible to interpret the result quantitatively, but
only qualitatively.

The possibility of quantitative determination
is provided by enzyme immunoassay
(ELISA). It is similar to a REEF, but the
markers used are not dyes, but enzymes that
turn colorless substrates into colored
products, which makes it possible to
quantify the content of both antigens and
antibodies.

- Wash away non-binding antibodies and
antigens.
- Add a colorless substrate, and in the wells with
the antigen that we determine, staining will
occur, because there will be an enzyme
associated with the antigen, after which the
intensity of the glow of the colored product is
evaluated on a special device.

Reaction of indirect (passive) hemaglutination
(RPGA).
The method is based on the ability of viruses to bind
red blood cells. Normally, red blood cells fall to the
bottom of the tablet, forming a so-called button.
However, if there is a virus in the biological material
under study, it will bind the red blood cells into a so-
called umbrella that will not fall to the bottom of the
hole.

If the task is to detect antibodies, it is
possible to do this by using the
hemagglutination inhibition reaction
(GIR). Various samples are buried in the
well with the virus and red blood cells. If
there are antibodies, they will bind the
virus, and the red blood cells will fall to
the bottom to form a "button".

Now we will focus on the
methods of diagnostics directly
of nucleic acids of the studied
viruses, and first of all on PCR
(Polymerase Chain Reaction) .

The essence of this method is to detect a specific fragment of
DNA or RNA of the virus by repeatedly copying it under
artificial conditions. PCR can only be performed with DNA, that
is, for RNA viruses, a reverse transcription reaction must first be
performed.
Directly PCR is carried out in a special device called an
amplifier, or thermal cycler, which maintains the necessary
temperature regime. The PCR mixture consists of added DNA,
which contains the fragment of interest, primers (a short
fragment of nucleic acid, a complementary DNA target, serves as
a seed for the synthesis of a complementary chain), DNA
polymerase, and nucleotides.

- Denaturation is the first stage. The
temperature rises to 95 degrees, the DNA
strands diverge relative to each other.
- Annealing of primers. The temperature is
lowered to 50-60 degrees. Primers find a
complementary section of the chain and link
to it.
- Synthesis. The temperature is raised again
to 72, which is the operating temperature for
DNA polymerase, which builds daughter
chains based on primers.

The cycle is repeated many times. After 40 cycles, a single
DNA molecule produces 10 * 12 degree copies of copies of
the desired fragment.

During real-time PCR, synthesized copies of the
DNA fragment are marked with a dye. The device
registers the intensity of the glow and plots the
accumulation of the desired fragment in the course
of the reaction.
Modern methods of laboratory diagnostics with
high confidence can detect the presence of the virus-
pathogen in the body, often long before the first
symptoms of the disease appear.

Medical virology

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