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What is Influenza?
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The Influenza disease/illness, nicknamed
‘The flu’ is caused by a myxovirus.
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It exists in a number of forms usually called
type A, B and C. Most influenza outbreaks
are of type A. Type B is less common but
causes world-wide epidemics. Type C is very
rare.
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Influenza viruses infect the parts of the body
involved with breathing commonly, the
respiratory tract but it can also reach the
lungs.
Form and structure of influenza virus
The myxovirus is a helical
enveloped RNA
Virus with a protein shell and
Lipid membrane.
There are two glycoproteins
on the membrane, a
haemagglutinin
(H) and a neuraminidase (N).
The haemagglutinin assists
viral entry into the cells of the
respiratory epithelium while the
neuraminidase also facilitates
release of new virions from
infected cells.
What is a virus?
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Viruses are intra cellular parasites
Viruses lack enzymes for metabolism and have no
ribosomes or other equipment for making their own
proteins.
Every virus consists of, at least, a core of nucleic
acid (DNA or RNA) surrounded by antigenic protein.
It is the nucleic acid that provides the genetic code
the virus needs to reproduce.
The energy and raw material required for
reproduction of the virus must come from the a cell in
the host that it invades.
So…viruses don’t have their own cell metabolism.
How the virus enters Human cells
An Influenza-virus invades the epithelial tissue of the respiratory
tract. It recognises suitable cell by interactions between protein or
glycoprotein called Ligands on its surface and receptor on host
cell membrane.
Ligands bind only to specific receptors of cells in their host range.
A viral infection begins when the genome of a virus makes its way
into cell.
How the virus causes the disease
Uses the cell’s reproductive system to reproduce itself causing the disease
and turning the cell into a virus-making machine.
Releases RNA host cell then follow code on nucleic acid to make new viral
proteins.
Within a very short period, it produces hundreds of new viruses. It takes about an
hour for the virus to kill the infected cells.
After a periods of virus production the cell dies, and its cell membrane disintegrates
by a progress called lysis. The heavy mucus produced during a cold or flu is
largely made up of lysed cells.
4 features of Immune System
Specificity – each antigen has unique molecular
structure which stimulates production of particular
antibody.
Diversity –has ability to respond to millions of kinds of
invaders
Memory – it remembers antigens it has encountered
acquired immunity
Self/ non-self – ability to distinguish body’s own
molecules from foreign molecules.
Trigger of immune response
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An immune response is triggered when the
body detects the presence of foreign material
The body detects molecules by chemicals on
surface of their cells. Proteins,
carbohydrates, glycoprotein and glycolipids
are used to distinguish cells. Cells with
different chemicals on surface – ANTIGENS
are recognise by immune system as nonself or foreign cells.
Immune response: Phagocytosis
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Granulocytes
Macrophages
For phagocytosis to take place micro-organism needs to adhere to
cell surface membrane of phagocyte.
Opsonisation aids this by coating virus in opsonin which the
phagocytic cells receptors can bind easily to.
Cytokines chemicals make them more efficient
Ingest foreign cells some become embedded in macrophage alerts
T and B cells to the invasion y a particular pathogens.
Lymphocytes
Small white blood cells formed from cells in
bone marrow called stem cells.
One type develops B Lymphocytes which
secrete antibodies into blood fluid.
Humoral response
Other type develops into T Lymphocytes which
attack pathogens. Cell mediated response
T Lymphocytes
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T lymphocytes divide to form clones when they meet particular
antigens. Some become memory cells.
T – killers: activated by antigen, they attach to antigen on
infected cell killing the cells by making holes in its surface
membrane.
T - helpers: activated by contact with infected body cell. They
help other cells to destroy the virus. When bind to infected cell
secrete chemicals cytokines which stimulate macrophages
and B cells.
T- cells make molecules T –cell surface receptors, but not
called antibodies because they are not released from cell.
Antigen has to be attached to body cell before T – cells
respond.
B lymphocytes
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When B –cells are stimulated Clonal proliferation
occurs by mitosis.
Plasma cells which secretes antibodies
Some B –cells become memory cells
Takes days to produce effective amount of
antibodies in blood stream so Micro-organism have
time to form large populations.
Destroys antigens by neutralising antigen
Bind to antigens activating different events which
destroy micro-organism on which antigen is present.
Antibodies
Variable region is the part combine
with antigen.
Antibodies secreted into body fluids
bind to and destroy organisms
which are
outside your own cell.
Antibodies:
 Destroys antigens by
neutralising antigen
 Bind to antigens activating
different events which destroy
micro-organism on which antigen
is present
Transmission
Influenza virus is an air borne infection
Pathogens are passed into the atmosphere in tiny
droplets of saliva, mucus and water.
Smaller droplets remain suspended in air – human
breath and mucus
Those that fall to ground dry out quickly expose
pathogens to air currents that circulate
pathogenladen air around room.
Usually spreads from person to person but
animals can carry it.
Symptoms
fever
headache
Aching joints
and muscles
dry cough
sore throat
Tiredness
Shivering
Treatment
Most medicines that kill "germs" do so by interfering with the way metabolism and other life
functions take place. Since a virus is not actually alive, in one way of perceiving life, a
Virus cannot be killed. Most viruses can only be tolerated as best we can while they create
their havoc and move on to another.
There are only a few Antiviral drugs
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Some inhibit the production of viral DNA or RNA by altering the host cell's DNA.
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Others prevent enzymes essential for the production of new virus particles from working.
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A 3rd group prevent the virus particles from entering the cells in the first place
Immunity
Acquired Immunity: immune system remembers antigens it has
encountered and can react more promptly and effectively on
subsequent exposures.
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Vaccination
Aims to achieve the effect of the primary response, leaving a
population of memory cells for a strong secondary response
without having to suffer the illness.
Some vaccines less effective as pathogens their target
Pathogen is variable so vaccine against 1 form is useless
against other form.
Overview
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Cause:
influenza virus
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Symptoms
sore throat, head ache, fever, shivering,
tiredness, aching joints and muscles, dry
cough
droplet infection
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Transmission:
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Secondary
infections:
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Period of illness: up to 7 days
viral and bacterial pneumonia