Transcript Unit 3 – Infection and Response

Unit 3
Revision
Pathogens and types of diseases
What are pathogens?
Pathogens are microorganisms that
cause infectious disease.
Pathogens may be viruses, bacteria,
protists or fungi.
Communicable diseases are diseases
that are caused by pathogens, they
can be passed on/spread.
Non-communicable diseases are
diseases such as diabetes, heart
disease and cancer. They are
caused by other factors such as
radiation or lifestyle.
The spread of diseases can be
reduced or prevented by:
simple hygiene measures
destroying vectors
isolation of infected individuals
vaccination.
How do pathogens spread?
They may infect plants or animals and can be spread by …
- direct contact,
- by water or
- by air
- by vectors (animals usually insects that
spread disease)
- contaminated food
What is the difference between an epidemic and a
pandemic?
Epidemic – When a disease spreads rapidly to many
people.
Pandemic – When a disease spreads globally.
Pathogens
Communicable
and types
disease
of diseases
- questions
- Questions
1.
What does Communicable disease mean?
2.
What is the other type of disease? Explain its meaning.
3.
What is a pathogen?
4.
Give 4 examples of pathogens.
5.
How do bacteria cause disease?
6.
How do viruses cause disease?
7.
Give 4 ways in which pathogens spread?
8.
How can the spread of diseases can be reduced or prevented?
9.
What is the difference between an epidemic and a pandemic?
Pathogens - read the next 4 pages and
then fill in the table on slide 8
Summary
•
Our bodies provide an excellent environment for many microbes which can make us ill once they are inside us. Our bodies need to stop most
microbes getting in and deal with any microbes which do get in. Vaccination can be used to prevent infection.
Pathogens
•
Microorganisms that cause infectious disease are called pathogens.
•
Disease occurs when large numbers of pathogenic micro-organisms enter the body.
Bacteria
•
Not all bacteria are pathogens.
•
Pathogenic bacteria reproduce rapidly inside the body and may produce poisons (toxins) which make us feel ill.
•
Example: E.coli produces toxins that cause fever symptoms when we have food poisoning.
Viruses
•
Viruses are much smaller than bacteria.
•
All viruses are pathogens.
•
Viruses also produce toxins and they damage the cells in which they reproduce, leading to illness.
•
Viruses replicate by invading cells, reproducing inside them and bursting them.
•
This causes damage to tissues, leading to illness.
Examples:
–
–
HIV damages white blood cells, reducing immunity and leading to AIDS.
Influenza virus causes aches and fever symptoms.
Viral diseases
Measles is a viral disease showing symptoms of fever
and a red skin rash. Measles is a serious illness that can
be fatal if complications arise. For this reason most
young children are treated by vaccinations against
measles. Transmission - The measles virus is spread by
inhalation of droplets from sneezes and coughs.
HIV initially causes flu-like symptoms. Once diagnosed HIV
is treated with anti-viral drugs, this slows the replication of
the virus, but cannot stop it.. Eventually the virus enters the
lymph nodes and attacks the body’s immune system cells
resulting in the development of AIDS. AIDS is when the
body’s immune system is no longer able to deal with other
infections or cancers.
Symptoms of AIDS include
•
•
•
•
•
•
•
•
•
Weight loss
Fatigue
Diarrhoea
Night sweats
Thrush
Rapidly progresses to the final stage
Dementia
Cancers (Kaposi’s sarcoma)
Death
HIV is spread by sexual contact or exchange of body fluids
such as blood which occurs when drug users share needles.
Tobacco mosaic virus (TMV) is a
widespread plant pathogen
affecting many species of plants
including tomatoes. Symptoms - it
gives a distinctive ‘mosaic’ pattern
of discolouration on the leaves
which affects the growth of the
plant due to lack of
photosynthesis.
Transmission from plant to plant
TMV is very easily transmitted
when an infected leaf rubs against
a leaf of a healthy plant, by
contaminated tools, and
occasionally by workers whose
hands become contaminated with
TMV after smoking cigarettes.
The virus can also contaminate
seed coats, and the plants
germinating from these seeds can
become infected.
Treatment is to prevent the
spread – e.g. cleaning tools.
Bacterial diseases
Gonorrhoea is a sexually transmitted disease (STD)
with symptoms of a thick yellow or green discharge
from the vagina or penis and pain on urinating. It is
caused by a bacterium and was easily treated with
the antibiotic penicillin until many resistant strains
appeared. Gonorrhoea is spread by sexual contact.
The spread can be controlled by treatment with
antibiotics or the use of a barrier method of
contraception such as a condom.
Salmonella food poisoning is caused by bacteria.
Transmission is due to bacteria eaten in food, or on
food prepared in unhygienic conditions. In the UK,
poultry are vaccinated against Salmonella to control
the spread.
Symptoms - Fever, abdominal cramps, vomiting and
diarrhoea are caused by the bacteria and the
toxins they secrete.
Treatment.
If you have salmonella and a healthy immune system,
your doctor may let the infection pass without giving
any medicines. For serious infections antibiotics can
also be prescribed.
Pain killers can be used to reduce temperature and
relieve cramping. As with any infection that causes
diarrhea, it's important to drink plenty of liquids to
avoid dehydration.
Fungal diseases
Rose black spot is a fungal
disease.
Symptoms
Purple or black spots develop
on leaves, which often turn
yellow and drop early. It
affects the growth of the
plant as photosynthesis is
reduced.
Transmission
It is spread in the
environment by water or wind.
Treatment
Rose black spot can be
treated
by using fungicides and/or
removing and destroying the
affected leaves.
Protist diseases - malaria
The pathogens that cause malaria are protists.
What is Malaria?
It is a disease caused by a single celled parasite called Plasmodium.
The malarial protist has a life cycle that includes the mosquito.
symptoms …
Malaria causes recurrent episodes of fever and can be fatal.
•
Chills
•
Fever
•
Exhausting sweats
•
Headache
•
Muscle aches
•
Tiredness
Transmission is by a vector – in this case mosquitoes.
The spread of malaria is controlled by preventing the vectors,
mosquitos, from breeding and by using mosquito nets to avoid being
bitten.
Life cycle of Plasmodium
First of all, a mosquito bites a human who is infected with malaria.
It sucks up human blood containing the Plasmodium parasite.
Plasmodium parasites reproduce and travel to the mosquitoes salivary
glands.
When the mosquito bites another human, the parasites are injected
into the new victim and travel to the liver causing liver damage. They
then infect red blood cells. The parasite bursts the red blood cells
(causing raging fever and exhausting sweats) releasing even more
parasites. The parasites remain in the blood ready to be ingested
when a female mosquito lands to feed.
If the victim is bitten by a mosquito during this phase, the mosquito
will pick up the parasites and the whole cycle may start again ….
Most at risk are…
•
Infants
•
Children under 5
•
Pregnant women
•
Those who are HIV positive
- because all of these have weak immune systems
Prevention…
Nets are hung over beds, to prevent night-time mosquito
bites. Since mosquitoes do most of their biting at night, nets
can reduce malaria transmission by as much as 90% in areas
with high usage. They are impregnated with a long-lasting
insecticide to both kill and repel mosquitoes.
Habitat Reduction involves reducing mosquito breeding by
draining the standing water in which their eggs hatch.
Mosquitoes can lay eggs in very small amounts of water, so
removing stagnant water from locations like old tires, mud
puddles, or deep holes can cut down on transmission.
Mosquitoes lay their eggs in so many locations, however, that
habitat reduction is effective only on a household level, not a
national level.
Indoor Residual Spraying (IRS) is exactly what it sounds like.
The inside walls and other surface in houses are sprayed with
pesticides designed to last for a long time. IRS does not
prevent the mosquitoes from biting, but it kills them
afterward, when they land on household surfaces, and stops
mosquito reproduction and malaria transmission. To be
effective, IRS must be applied to at least 70% of households in
an area.
Drugs - Preventative treatment is provided to the two groups
most at risk for death from malaria, pregnant women and
infants. They get either steady or intermittent doses of the
same drugs that treat malaria. It cannot keep them from
becoming infected, but it will eliminate the malaria parasites
that cause symptoms.
Name of
disease
Type of
pathogen
Salmonella bacteria
Gonorrhoea
Rose black
spot
Malaria
TMV (tobacco
mosaic virus)
HIV
Measles
Transmission/ how
to prevent spread
Symptoms
Treatments
Human defence systems - 1
The immune system is split into non-specific and specific
defence systems.
Bacteria and viruses (pathogens) have antigens on their
outer cell surface; this makes it recognisable to our body
that they are invaders and don’t belong.
Non-specific defence systems of the human body involves
barrier defence and inflammation and phagocytosis. This is
fast acting and does not distinguish one pathogen from
another.
Barrier defences
The human body defends itself against the
entry of pathogens.
• The skin is a barrier and produces antimicrobial secretions.
• The nose traps particles which may contain pathogens.
• The trachea and bronchi secrete mucus which traps
pathogens and cilia waft the mucus to the back of the throat
where it is
swallowed.
• The stomach produces acid which kills the majority of
pathogens which enter via the
mouth.
The immune system
The immune system defends our bodies against invading pathogens.
The immune system consists of many different types of white blood
cells. The two main types are
1. Phagocytes – these carry out phagocytosis
2. Lymphocytes – these make antibodies and antitoxins.
Pathogens are recognised by the body due to their
antigens and also by the fact that the body cells under
attack release chemicals, such as histamine.
If a pathogen manages to get through the barrier
defences and enters the body the immune system
tries to destroy the pathogen.
White blood cells help to defend against
pathogens by:
1. phagocytosis
2. antibody production
3. antitoxin production.
Human defence systems - 2
1. Phagocytosis – by phagocytes
If a pathogen manages to get through the barrier defences
and enters the body the immune system tries to destroy the
pathogen.
White blood cells help to defend against
pathogens by:
1. phagocytosis
2. antibody production
3. antitoxin production.
3. Antitoxin production - by lymphocytes
Antitoxins are made by lymphocytes. They
neutralise any toxins the bacteria have produced
which are making us feel ill.
2. Antibody production - by lymphocytes
Lymphocytes are SPECIFIC – they only
recognise one specific pathogen (by the
ANTIGENS on the pathogen).
Lymphocytes release ANTIBODIES –
proteins that fit the antigens on the
pathogen.
Antibodies can either kill the pathogen
themselves or ‘label’ the pathogen to be
ingested by a phagocyte.
Antibodies can work in 2 ways –
1. Punching holes in microbes Or
2. sticking them together so they
can’t move and they can be
engulfed by phagocytes
Human defence systems - 3
Immunity and vaccinations
Natural Immunity – by a natural infection
The first time a pathogen invades our immune system a
specific white blood cell comes across the pathogen, it will
make an antibody to match that microbe’s antigen. The
antibodies will coat the pathogen and kill it or make it easier
to find by phagocytes. Memory cells are made and circulate
in the blood for many years, so that if the pathogen enters a
second time they make more antibodies faster. This means
that the pathogen will be killed before it causes disease.
Herd immunity occurs when the vaccination of a
significant portion of a population provides a
measure of protection for individuals who have not
developed immunity.
It arises when a high percentage of the population
is protected through vaccination against a virus or
bacteria, making it difficult for a disease to
spread because there are so few susceptible
people left to infect.
Human defence systems - questions
Defence Mechanisms
What prevents pathogens entering the body?
How do we deal with disease?
You will
need to be
able to
explain
what a
graph is
showing
you.
Practice
with this
one.
White blood cells are part of the ____________________
what three things do they do to defend the body?
1.
2.
3.
Immunity
Describe how a natural infection
causes immunity.
What is an antigen?
Advantages of vaccination
What is an antibody?
What is used to make a vaccine?
Disadvantages of
vaccination
How can antibodies kill
pathogens?
What can vaccines protect
against?
What do memory cells do?
How do vaccines work?
What is the difference between
antibodies and antitoxins?
Why is it necessary to continue to develop new
vaccinations and medicines?
Antibiotics and painkillers
Using drugs to treat disease
Antibiotics, such as penicillin, are medicines that help to
cure bacterial disease by killing infective bacteria inside
the body. It is important that specific bacteria should be
treated by specific antibiotics.
The use of antibiotics has greatly reduced deaths from
infectious bacterial diseases.
However, the overuse and misuse of antibiotics has caused
some strains of bacteria to become resistant to
antibiotics. This is of great concern, as if it is not slowed
people will begin to die of bacterial infections again.
Antibiotics cannot be used to kill viral pathogens, which
live and reproduce inside cells.
It is difficult to develop drugs which kill viruses without
also damaging the body’s tissues.
Some medicines, including painkillers, help to relieve the
symptoms of infectious disease, but do not kill the
pathogens.
Alexander Fleming discovered antibiotics by accident. His lab was often a mess, however,
this proved to be very fortunate. In 1928, Fleming was tidying his lab and came across a pile
of petri dishes, which contained bacteria that he had forgotten he had been growing. Before
placing the petri dishes into cleaning fluid, Fleming decided to take a look at them. One in
particular made him stop and think. On closer examination, he realised that mould was
growing on it. In itself this was nothing unusual but, on this particular sample, all around the
mould the bacteria he had been growing was dead.
Fleming wondered if it was the mould, a strain called Penicillium notatum, that had killed
the bacteria. Fleming knew that he needed to test his prediction and, therefore, set up a
control experiment. The experiment consisted of a petri dish, which contained the mould
and bacteria, and one that did not. When he came back to look at the petri dishes, he
observed that the bacteria around the mould were dead but that they continued to grow in
the petri dish that did not contain the mould. He concluded that his prediction must be
right.
Traditionally drugs were extracted from plants and microorganisms.
• The heart drug digitalis originates from foxgloves.
• The painkiller aspirin originates from willow.
• Most new drugs are synthesised by chemists in the pharmaceutical industry.
However, the starting point may still be a chemical extracted from a plant.
Antibiotic resistance
Overuse and inappropriate use of antibiotics has increased the rate of
development of antibiotic resistant strains of bacteria.
Pathogenic bacteria mutate, producing resistant strains.
Antibiotics kill individual pathogens of the non-resistant strain, the resistant
ones survive and reproduce, passing on their resistance to their offspring, so
the population of the resistant strain increases.
Many strains of bacteria, including MRSA, have developed resistance to
antibiotics as a result of natural selection.
What can be done?
Doctor’s should only prescribe antibiotics when necessary – and not for viruses.
It is important that if you are prescribed antibiotics you take the whole course.
A lot of people will stop taking the antibiotic when they feel better.
If you do this, you leave a few bacteria inside your body.
These will reproduce, increasing the chance of some developing
resistance.
Scientists are trying to develop new versions of the antibiotics.
Some antibiotics are developed but not used – just in case
Testing new drugs
New medical drugs have to be tested and trialled before being
used to check that they are safe and effective.
New drugs are extensively tested for toxicity, efficacy and dose.
Preclinical testing is done in a laboratory using cells, tissues and
live animals.
Clinical trials use healthy volunteers and patients.
• Very low doses of the drug are given at the start of the clinical
trial.
• If the drug is found to be safe, further clinical trials are carried
out to find the optimum dose for the drug.
• In double blind trials, some patients are given a placebo, which
does not contain the drug.
• Patients are allocated randomly to groups so that neither the
doctors nor the patients know who has received a placebo and
who has received the drug until the trial is complete. This is
useful so researchers can compare the group taking the drug to a
control group (without the drug). This helps them to decide if
any differences are due to the drug.
Antibiotics and painkillers
Who discovered the first antibiotic?
What did he see that made him think that the mould made an antibacterial substance?
Using drugs to treat disease
1.
What type of pathogen do antibiotics kill?
2. Explain the statement “It is important that specific
bacteria should be treated by specific antibiotics.”
Traditionally drugs were extracted from plants and microorganisms.
Give two examples of drugs extracted from plants.
1
3. Why cant antibiotics be used to treat flu?
4. Why are viruses difficult to kill?
2
5. Why is it difficult to develop drugs that kill viruses?
6. What do painkillers do?
7. Name two painkillers.
8. What are the disadvantages of painkillers?
Antibiotic resistance
1. What has caused the swift development of antibiotic resistance?
2. How do bacteria become resistant to antibiotics?
Testing new drugs
1. What are the three main things that drugs are tested for
before they are used on patients?
2.
What are drugs tested on before people?
3.
List the stages of testing that follows on people. Explain
each stage.
4.
What is a double blind trial?
5.
Why do researchers carry out double blind trials?
6.
What is a placebo?
3. How doe the population of resistant strains increase?
4. Name a resistant strain of bacteria.
What can be done?
Describe how we can slow the development of resistance.
A reminder – how
to grow microbes
Growing Microoganisms
•
Microorganisms = organisms that can only be viewed
with a microscope.
•
Eg bacteria, viruses and fungi.
•
Uncontaminated cultures of microorganisms are
required for investigating the action of disinfectants
and antibiotics.
•
It is important that the culture is not contaminated
with other microorganisms that may compete for
nutrients or produce toxins.
•
Careful procedures are required to prevent
potentially pathogenic microorganisms being
released into the environment.
Culturing microorganisms
•
To study microorganisms, they need to be cultured.
•
They need to be provided with the conditions they
need to reproduce quickly:
–
Nutrients
–
Warmth
–
Moisture
•
Bacteria and fungi can be grown in special media
called agar.
•
This provides them with:
–
Carbohydrate
–
Protein or amino acids
–
Water
•
When agar is heated up it is liquid.
•
It can be poured into a Petri dish.
–
A circular plastic or glass dish with a lid:
Growing Microoganisms cont.
The agar solidifies when left to cool.
Petri dishes and culture media must be sterilised before use to kill unwanted microorganisms
Inoculating loops are used to transfer microorganisms to the media.
These must be sterilised by passing them through a flame:
The lid of the Petri dish should be secured with adhesive tape to prevent microorganisms from
the air contaminating the culture.
In school and college laboratories, cultures should be incubated at a maximum temperature of
25oC.
This greatly reduces the likelihood of growth of pathogens that might be harmful to humans.
In industrial conditions higher temperatures can produce more rapid growth. 40oC would
produce the maximum amount of growth without killing the bacteria.
Monoclonal antibodies – triple award only
What are monoclonal antibodies?
Polyclonal antibodies are a collection of many different types of
antibodies
Monoclonal antibodies are a collection of a single type of antibody
that is isolated and cloned.
What are Monoclonal antibodies used for?
Monoclonal antibodies have a wide range of applications:
• Used in pregnancy testing kits
• Used to treat cancer
• Diagnostic tools for AIDS
How are monoclonal antibodies made?
B lymphocytes are the cells that produce antibodies.
A lymphocyte can divide several times to make clones of itself.
But once it starts to make antibodies, it becomes a B lymphocyte
and can’t divide anymore .
To get round this problem in a laboratory, a B lymphocyte is fused
with a cancer cell (tumour cell). This creates a hybridoma.
Tumour cells are long-lived and divide outside the body.
Making Monoclonal Antibodies
B lymphocytes are extracted from mice.
B lymphocytes are short-lived and do not divide outside the body,
to enable them to divide and produce antibodies they are fused
with tumour cells.
Tumour cells are long-lived and divide outside the body.
If B lymphocytes are fused with tumour cells a cell called a
hybridoma is produced. These cells are long-lived cells that can
divide outside the body and produce antibodies.
Detergent is added to a mixture of mouse B-lymphocytes and
tumour cells to break down cell-surface membranes of both cells
to help them fuse.
Once produced the hybridoma cells divide so there are lots of
clones. All of the clones make the same type of antibody. These
antibodies have come from cells cloned from a single cell and are
called monoclonal antibodies. The antibodies produced are
identical and can be used in several ways
Monoclonal antibodies have to be made in living cells because
antibody proteins are far too complicated to be synthesised
chemically in the laboratory.
Monoclonal antibodies are used in pregnancy tests
1.
hCG hormone is detected during a
pregnancy test. hCG hormone is found in
pregnant women’s urine.
2.
Antibodies for hCG are bound to a
coloured bead (blue)
3.
When urine is applied to the specified area
any hCG will bind to the antibody on the
beads, forming an antigen-antibody
complex.
4.
Urine then moves up the stick to the test
strip carrying any beads with it
5.
The test strip contains antibodies to hCG
that are stuck in place
6.
The strip turns blue if hCG is present
because the immobilised antibody binds to
any hCG. If no hCG is present, the beads
will pass through the test area without
binding to anything, and so it won’t go
blue.
If you are still unclear watch this video!
https://www.o2learn.co.uk/o2_video.php?vid=1630
Monoclonal antibodies are used in targeting cancer cells
1.
2.
3.
4.
5.
6.
7.
Different cells in the body have different surface
antigens
Cancer cells have antigens called tumour markers
that are not found on normal body cells.
Monoclonal antibodies can be made that will bind
to the tumour markers.
Anti-cancer drugs can also be attached to the
antibodies
When antibodies come into contact with the cancer
cells they will bind to the tumour markers
This results in the drug accumulating in the body
where there are cancer cells.
Therefore the side effects of an antibody-based
drug are lower then other drugs because they
accumulate near specific cells.
Monoclonal antibodies – triple award only
The development of monoclonal antibodies has provided society with the power and
opportunity to treat diseases. However with this power and opportunity comes responsibility.
The use of monoclonal antibodies raises some ethical issues.
Production involves the use of mice. These mice are used to produce both antibodies and
tumour cells. The production of tumour cells involves deliberately inducing cancer in mice.
Despite specific guidelines drawn up to minimise any suffering, some people still have
reservations about using animals in this way.
Humanising Monoclonal Antibodies
Antibodies made from mouse cells can trigger an immune response in a patient.
Recent techniques use genetic engineering to ‘humanise’ hybridomas – replacing much of the
antibody with the corresponding human antibody structure to prevent causing a harmful
immune response in patients.
To eliminate the need for humanisation of the antibody, transgenic mice can be used. In this
case, a human gene is placed in the mice to that they can produce human antibodies rather than
mouse antibodies. This raises the whole debate surrounding the ethics of genetic engineering.
Monoclonal antibodies have been used successfully to treat a number of diseases, including
cancer and diabetes, saving many lives. There have also been some deaths associated with their
use in the treatment of multiple sclerosis.
Testing for the safety of new drugs presents certain dangers. In march 2006, six healthy
volunteers took part in the trial of new monoclonal antibody (TGN1412) in London. Within
minutes they suffered multiple organ failure, probably as a result of T cells overproducing
chemicals that stimulate an immune response or attacking the body tissues. All the volunteers
survived, but it raises issues about the conduct of drug trials.
The potential advantages of using monoclonal antibodies in the treatment of cancer are great
because monoclonal antibodies only bind to the specific cancer cells that need treatment.
Healthy cells are not affected at all. In contrast conventional drug treatment is carried all around
the body in the blood and can have a devastating effect on healthy cells as well as cancer cells.
Radiotherapy treatment is targeted on the area of the body affected by the cancer but still
usually affects the healthy tissue in the area as well.
However monoclonal antibodies create more side effects than expected. Doctors and scientists
thought they would act like a 'magic bullet' affecting only the diseased tissue. It hasn't quite
worked out like that and monoclonal antibodies are not yet as widely used or as successful as
everyone hoped.
Society must use the issues raised here, combined with current scientific knowledge about
monoclonal antibodies, to make decisions about their production and use. We must balance
the advantages that a new medicine provides with the dangers that its production and use
might bring. Only then can we make informed decisions at an individual, local, national, and
global level about the ethical use of drugs such as monoclonal antibodies.
Monoclonal antibodies – questions
1. What are monoclonal antibodies?
2. How are they different from polyclonal antibodies?
3. What is a B lymphocyte?
4. Why can’t B lymphocytes be used to make monoclonal antibodies?
5. Why do monoclonal antibodies have to be made in living cells?
6. How is a hybridoma created?
7. List four ways monoclonal antibodies can be used in science and medicine.
8. Why are cells from cancer tumours used to fuse with the B cells?
9. Why is detergent added to the mixture of B cells and tumour cells?
10. Create a table listing the advantages and disadvantages of using monoclonal antibodies.
11. List the ethical concerns surrounding the production of monoclonal antibodies.
12. List the ethical concerns surrounding the use of monoclonal antibodies.