Transcript Transmission and control of infectious diseases

Unit 4 - Immunology and Public Health
CfE Higher Human Biology
23. Transmission and Control of Infectious
Diseases
Learning Intentions
I can describe the transmission and control of infectious diseases.
I can state that infectious diseases caused by pathogens, transmitted by direct
physical contact, water, food, body fluids, inhaled air or vector organisms and
controlled by quarantine, antisepsis, individual responsibility, community
responsibility and vector control. Epidemiological studies of infectious diseases.
I can state that classification of spread to include sporadic, endemic, epidemic,
and pandemic. Control measures to include preventing transmission, drug therapy,
immunisation or a combination of these.
I can describe active immunisation and vaccination.
I can state that active immunity can be developed by vaccination with antigens
from infectious pathogens. Antigens from infectious pathogens, usually mixed with
an adjuvant to enhance the immune response, include inactivated pathogen toxins,
dead pathogens, parts of pathogens and weakened pathogens.
I can state that The design of vaccine clinical trials including randomised, doubleblind and placebo-controlled protocols. Importance of group size to reduce
experimental error and statistical significance.
What are Pathogens?
As we have seen, pathogens are agents which
can cause disease.
They can include many different types of
organisms including:
Viruses e.g. measles
Bacteria e.g. cholera
Fungi e.g. athletes foot
Protozoa e.g. malaria
Multicellular parasites e.g. hookworm
Viruses
A virus can only survive
outside a host for a
very short time,
however they are
responsible for many
diseases;
- AIDS
- Chicken pox
- Influenza
- Herpes
And some cases of cancer,
e.g. Cervical cancer
caused by the Human
papillomavirus (HPV)
Bacteria
Bacteria are singlecelled organisms
and can cause
diseases such as:
- Cholera
- Typhoid
- Salmonella
- Pneumonia
- Tuberculosis
Fungus
Fungi are widely
used by humans
but some can
cause diseases
like:
- Thrush
- Ringworm
- Athlete’s Foot
Protozoa
Protozoa are singlecelled organisms
which are
typically mobile.
They can cause:
- Malaria
- Sleeping sickness
- Dysentery
Malarial infestation by Plasmodium
http://www.youtube.com/watch?v=OEDh
e4MPEMc
Multicellular parasites
Short clip of tapeworms in situ
http://www.youtube.com/watch?v=JeDD0Hde
cGk
Multicellular
parasites include
tapeworms and
hookworms
(pictured).
They can cause
- Anaemia
- Diarrhoea
- Low birth weight
Pathogen Transmission
These pathogens can be transmitted in
many ways:
- Direct physical contact
- Inhaled air
- Indirect physical contact
Pathogen transmission
- Exchanging body fluids
- Faecal-oral route
- Vector organisms
Controlling Transmission
Because we know how pathogens are
transmitted we can interrupt it by the
following;
- Antisepsis – inhibiting or destroying a
microorganism by sterilising everything
that could carry a pathogen or prevent
them reaching somewhere.
Controlling Transmission
Quarantine – compulsory isolation of the
person who is infected or has been in
contact with an infected person to
prevent spreading of the disease.
The length of the
quarantine is usually
just over the length
of time it usually
takes for someone to
display symptoms
after being infected.
Individual responsibility
Knowing what we do about transmission of
pathogens there are a number of things
that can be used to prevent it;
- Good hygiene – washing hands, brushing
teeth, showering etc.
- Care in sexual health – use of condoms to
prevent sexually transmitted diseases
- Handling and storage of food – washing
hands, keeping raw and cooked food
separate and at the appropriate
temperatures.
Community responsibility
Clean water supply – our water is filtered and
chlorinated to prevent growth of
microorganisms… is everyone as lucky?
Safe food webs – for example good manufacturing
practice e.g. milk pasteurisation (heating at
72oC for 15s to kill any microorganisms),
inspection, risk analysis and traceability.
Waste disposal – keeping any refuse collected
regularly and recycled, buried or incinerated.
Community responsibility
Control of vectors – Taking care to eradicate any
animals which can carry diseases e.g.
Bubonic plague was caused by bacteria carried by
fleas on rats so being in close proximity to rats
carrying those fleas put you at high risk.
Malaria is caused by a protozoa carried by female
mosquitoes in their saliva. How could you
protect people from this animal vector? (see
page 335)
Epidemiology of infectious diseases
Epidemiology is the study of the
characteristics of an infectious disease.
We would look at:
- The location of an initial outbreak
- The pattern and speed of the spread
- The geographical distribution
Patterns of Distribution
Sporadic – occurs in scattered or isolated
instances with no connection between them
Endemic – recurs as a regular number of cases in
a particular area
Epidemic – affects an unusually high number of
people in a particular area
Pandemic – occurs as a series of epidemics
spreading across continents or the whole world
What can we hope to do with
this?
It is essential to understand how diseases
spread so that we are able to identify
appropriate control measures should an
outbreak occur.
Think of the Swine ‘flu outbreak http://www.bbc.co.uk/news/10483218
For overview of methods used to stop the
spread of infection see the following clip
https://www.youtube.com/watch?v=lEzTBzh
4NQg
Active Immunity
Immunisation is the process by which a person develops
immunity to a disease-causing organism.
• Naturally acquired active immunity
occurs when
– a person is exposed to a live pathogen,
– develops the disease,
– becomes immune as a result of the primary
immune response e.g. immunological memory.
• Artificially acquired active immunity can
be induced by a vaccine, a substance
that contains the antigen.
• A vaccine stimulates a primary response
against the antigen without causing
symptoms of the disease.
– B & T cells are produced and some persist as
memory cells. Antibodies are also formed.
Vaccines
• The pathogen is mixed with an adjuvant
• This is a chemical which increases the antigenic
response, enhancing the immune system
• Types of vaccines include
–
–
–
–
inactivated pathogen toxins (tetanus and diphtheria),
dead pathogens (polio and hepatitis A),
parts of pathogens (HPV and hepatitis B)
weakened pathogens (measles, mumps and rubella).
Clinical Trials
• A clinical trial is a type of medical
research.
• It aims to find new and improved ways
of
– preventing
– diagnosing
– Treating
– controlling illnesses.
• People are involved in the trial in a
controlled and carefully planned way.
Clinical Trials
• Clinical trials are designed to answer
questions - about a treatment or a procedure.
• The main questions are usually:
–
–
–
–
–
–
Does it work?
Is it safe?
Does it cause side effects?
How does it affect quality of life?
Does it work better than existing treatments?
What is the best dose to use?
Clinical Trials
• Vaccines are subjected to clinical trials
just like any other pharmaceutical
medicine
• They must be shown to be safe and
efficacious (effective when used in
humans)
Types of Vaccine Trials
Randomisation
Everyone taking part in a randomised
trial is put into different groups at
random. Usually decided by
computer.
There are usually two groups in a
randomised trial. Only one group has
the new treatment. The other, called
the control group, has the standard
treatment or a placebo. The
research team can then compare
results from the two groups.
One reason that trials are
randomised is so that the research
team can't choose who goes into
which group based on what they
know about their patients. For
example, they might put people who
they thought were healthier or more
unwell into a particular group. This
precaution helps to increase the
reliability of the results.
Placebo Controlled Trials
•
A placebo is a dummy treatment.
E.g. a pill that looks the same as
the drug being tested but just
contains sugar.
• People can sometimes feel better
when they have a placebo because
they think they are having a real
treatment. This is known as the
'placebo effect'.
• Comparing a group of people taking
a new treatment with a group
taking a placebo can show if the
new treatment is really having an
effect.
• A truly effective drug will show
better results than the placebo.
Double Blind Trials
• In a blinded trial, you won't know
whether you are getting the trial
treatment, or the standard
treatment or placebo. They will
both look the same. Trials need to
be 'blind' because just knowing
that you are getting a new
treatment can affect how you
respond to, and make the results
unreliable.
• Often the health professionals on
the trial who give you your
treatment are also 'blinded',
meaning they don't know which
treatment you are getting either so they can't be influenced by
what they know.
Experimental Error
• At the end of the trial, results from the
two groups, which must be of a suitable
size to reduce the magnitude of
experimental error are compared to
determine whether there are any
statistically significant differences
between the groups
Chapter23-infectious diseases and epidemiology
.
Question
Answer
What is an Infectious disease?
A disease that can be transmitted from one
person to another by direct or indirect
contact.
What cause infectious diseases?
Pathogens.
Name some types of pathogens.
Viruses(measles), bacteria,(cholera),
fungi(athletes foot), protozoa(malaria),
multicellular parasites(hookworm).
How are infectious diseases transmitted?
Physical contact, inhaled air from an
infected person, indirect contact such as
needles or cups, body fluids (kissing or in
seminal fluids in intercourse), faecal-oral
route, vector organisms(bitten by mosquito
infected with malaria).
What does it mean by saying transmission
can be controlled by quarantine?
A period of isolation for the infected person
or for someone who has been in contact
with an infected person for the incubation
period of the disease.
Chapter 23-infectious diseases and epidemiology.
Question.
Answer.
What is asepsis?
Free of live micro-organisms.
What is antisepsis?
The inhibition or destruction of microorganisms by carrying out procedures like
sterilisation, applying antiseptics, gloves
and masks.
What should individuals practice to ensure Wash hands, shower, look after teeth,
good hygiene and reduce our chance of
infection by a pathogen?
What should individuals use to protect
them against STD’s like gonorrhoea and
aids?
condoms.
What practices should individuals adopt
when handling food to prevent
transmission of microbes?
Clean hands, separate cooked and
uncooked meats, sterilise knives and work
surfaces in butcher shops and abattoirs.
Name the two procedures that prevent
the transmission of pathogens from wild
animals in drinking water.
Filtration and chlorination of water.
Chapter 23-infectious diseases and epidemiology.
Question
answer.
What do manufacturers in the UK do to
prevent transmission of pathogens from
milk and to keep food webs safe?
Pasteurise the milk by heating it to 72
degrees for 15 seconds to kill most
microorganisms including tuberculosis
causing ones.
They use inspection, risk analysis and
traceability of food sources.
What happens with our dry rubbish?
Waste disposal mechanisms are in place to
recycle, burn or bury it.
How do we control vectors?
Control of rats and their fleas that carry
bubonic plague(black death) bacterium to
humans.
Mosquito vectors carry malaria (caused by
a protozoan) and we drain stagnant water
where they breed, use chemicals like
insecticides and larvicides, introduce
sterile male mosquitoes to reduce
breeding.
Question.
Answer.
.
23-epidemiology
of infectious
diseases
What doesChapter
epidemiology
of an infectious
Where
the outbreak started,
its pattern and
disease mean?
speed of spread, its geographical
distribution.
Who does this work?
Epidemiologists. They closely watch the
spread of the disease and analyse it to find
out what caused it and what control
measures can be taken (drugs to help,
immunisation, try to stop transmission from
person to person and region to region.
How are the patterns of infectious diseases
classified?
SEEP: Sporadic, endemic, epidemic,
pandemic.
Define sporadic.
Occurs in scattered instances with no
connection between them.
Define endemic.
Recurs as a regular number of cases in a
particular area.
Define epidemic.
Simultaneously affects an unusually large
number of people in a particular area.
Define pandemic.
Occurs as a series of epidemics that spread
across continents or through the world.
Question.
Answer.
What is immunisation?
The way in which a person develops immunity to a disease
causing organism.
What is active immunity?
The protection a person gets from making their own antibodies
against pathogens.
What is naturally acquired active immunity?
If a person survives infection by a pathogen and meets the
pathogen again and is not affected by it then the person has
acquired active immunity by natural means (primary and
secondary response).
What is artificially acquired immunity?
Vaccination results in this. The person is deliberately given a
weakened or changed form of the pathogen or its toxin to act
as an antigen and start the immune response. An adjuvant is
also given to promote the activity of the antigen. This starts the
production of B cells and T cells and the formation of
antibodies-it does not cause the disease. Some B cells and T
cells stay in the body as memory cells to start the secondary
response if needed.
What are vaccine clinical trials?
Clinical trials involves testing the drugs or vaccines on humans
This can only happen when the medicines and vaccines are fully
checked for safety and that they work .
Clinical trials have 3 phases-see next slide.
What happens before clinical trials are
carried out
Testing on cells and animals in the lab takes place first and then
it is checked that it meets European protocol that helps keep
good standards.
Active immunisation and vaccination-page 332.
question
Design of phase three in the clinical trial
Answer.
.
How many groups are those who are taking part divided
into?
two
Name the two types of groups .
The test group and the control group.
Which group gets the treatment?
The test group.
What do the control group get and what is it?
A placebo that looks like the treatment but is not.
Name the 3 things in the protocol used at this stage.
Placebo-controlled, double-blind, randomised.
What is the placebo effect?
This is the effect from receiving the treatment that does
not depend on the drug or vaccine-they could show
improvement due to a psychological effect.
The placebo allows a valid comparison to be made that
takes this into account.
What is a double-blind trial?
Neither the subjects or the doctors know who is getting
what and so this eliminates bias-the doctor could act in a
different way to the patient if he knew that the patient
was getting the treatment.
What is randomisation?
Each person is put into a group at random by a computer
to further eliminate bias-a doctor might avoid putting an
ill person into the treatment group without thinking. And
this would……
How is experimental error further avoided?
Computer ensures the groups are as similar as possible –
same number of males and females, similar age groups in
each group, similar weights of people in each group
What happens next?
The results are subjected to statistical analysis and the
results from the two groups are compared to find out if
the treatment works and if it does the researchers try to
get a licence to make it and sell it.