Download Unit 4 Student Summary Notes

Higher Human
Biology
Unit 4:
Immunology and
Public Health
Learning Objectives
By the end of this topic, you should be able to:
• explain that the immune system of the human body has the capacity to
protect against pathogens, some toxins and cancer cells;
• explain the different types of non-specific defences.
• explain that epithelial cells on the body surface and cavity linings form
a physical barrier;
• state that these barriers can produce secretions that defend against
infection.
• state when and why an inflammatory response might occur;
• describe the steps involved in the inflammatory response.
• explain the cellular basis of inflammation.
• describe how phagocytes respond to a pathogenic infection;
• describe the role of natural killer cells in response to a pathogen.
• explain the function of natural killer cells.
1. The Immune System
Our bodies are able to defend themselves against disease causing
pathogens, toxins and cancer cells via the immune system.
There are two types of immune response which work together to
achieve this special defence system: Non-specific (Innate)
Specific
THINK! What does each of these responses mean in
practice? Discuss with your partner and write your ideas
below.
Non-specific:
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Specific:
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Non-Specific Responses
Our skin is the single largest barrier against all bacteria and viruses. It is
composed of layers and layers of epithelial cells which enable this type
of physical protection.
The mucous membranes which line the body’s digestive and
respiratory tracts are also important in this first line defence system as
they secrete chemical substances which act to prevent bacterial growth
and prevent viral entry to the body.
Match the secretions listed below to their defensive role in the
body.
Mucus
Contains lysozyme to digest the bacterial walls
Tears/Saliva
Ensures a low pH on the skins surface to
prevent bacterial growth
Acid
Traps microorganisms in the lining of the
airway
Sweat
Destroys harmful microorganisms which are
swallowed
The second line of defence occurs when a harmful microorganism
manages to get into the body, most often via a physical injury such as a
cut on the skin.
The immune system issues an alert to non-specific cells which are
recruited to the affected area to promote an inflammatory response.
THINK!
What are the 3 main symptoms we associate with
inflammation?
Discuss with your partner and note your ideas below.
Symptoms include: 1.________________________________________
2.________________________________________
3.________________________________________
Inflammation is caused by special cells found in connective tissue called
mast cells. They release large quantities of a chemical called
histamine which promotes the vasodilation of blood vessels and
increases the permeability of surrounding capillaries.
(This is what causes the red appearance and swelling at the injured
site!)
Cells Involved
1. Cytokines
Cytokines are special cell-signalling protein molecules
which are released by cells at the site of injury.
Cytokines are involved in BOTH non-specific and specific
responses to recruit specialised white blood cells to assist
in the fight against the invading microorganism.
2. Phagocytes
Phagocytes are specialised white blood cells which are
involved in the non-specific response. Two main
examples of phagocytes in the body are neutrophils
and monocytes.
They are described as being motile due to their ability to
move towards a foreign pathogen.
Phagocytes engulf the pathogen and destroy it using digestive
enzymes which are located in the cytoplasm.
This process is called PHAGOCYTOSIS and is outlined in four stages
as shown in the diagram below.
3. Natural Killer Cells
Natural killer cells (NK cells) are involved in the non-specific response
to viral infection and cancer cells in the body.
NK cells cause pores to be created in the target cell via the production of
perforin and granzyme which trigger a genetically controlled ‘selfdestruct’.
This programmed cell death is called APOPTOSIS.
Summary
• The immune system in the human body has the capacity to protect
itself against invaders.
• These invaders are pathogens, some toxins and cancer cells.
• Innate immunity is an inborn, non-specific ability to resist infection by a
pathogen.
• Examples include: skin epithelial cells, mucus membranes, ciliated
cells, lysozyme in tears.
• The cells involved in the immune response are the white blood cells
like phagocytes and lymphocytes.
• Epithelial cells on the body surface and cavity linings form a physical
barrier. These cells produce secretions that defend against infections.
• Phagocytes carry out phagocytosis, the process by which solid
particles are taken up by a cell.
• Mast cells release histamines.
• The release of histamine by mast cells causes vasodilation and
increased capillary permeability.
• The increased blood flow in capillaries results in the accumulation of
phagocytes.
• Increase blood flow results in the delivery of antimicrobial proteins and
clotting elements to the site of infection.
• NK cells are a type of lymphocytes.
• Natural killer (NK) cells induce the pathogen to produce self-destructive
enzymes in apoptosis.
• Phagocytes and NK cells release cytokines which stimulate the specific
immune response.
• Apoptosis is a process where a cell is degraded in order for it to be
ultimately engulfed and recycled.
Learning Objectives
By the end of this topic, you should be able to:
• explain the different types of specific cellular defences in the human body.
• explain the action of lymphocytes in response to infection or tissue damage.
• explain the immune surveillance theory.
• explain the clonal selection theory.
• explain the role of phagocytes, T lymphocytes and B lymphocytes during antigen
presentation.
• list the different types of lymphocytes.
• explain 'self' and 'non-self' recognition in the immune system
• list the different types of T cells;
• explain the functions of cytotoxic T cells;
• explain the functions of T helper cells.
• state the functions of B lymphocytes.
• describe what is meant by immunological memory;
• explain that T and B lymphocytes can form memory cells;
• state the benefits of having memory cells;
• understand what primary and secondary response to infection is.
1. Specific Cellular Defences
If the non-specific defences fail to get rid of the invading pathogen our
body switches to its’ third line of defence: the specific immune response!
This is brought about by lymphocytes of which there are 2 main types:
- T lymphocytes (T cells)
- B lymphocytes (B cells)
Immune Surveillance
Immune surveillance is a theory to explain how the
immune system continuously patrols the body not only to
recognise and destroy invading pathogens but also to
destroy host cells that become cancerous via the detection
of new antigens (a molecular marker found on the surface
of cells) by T lymphocytes.
A group of white blood cells called leucocytes are the
main cells involved in this process.
They release cytokines into the blood stream to recruit
large numbers of phagocytes and T cells to the site of
injury to fight off the invading microorganism.
Clonal Selection
The clonal selection theory states that the body has large number of
lymphocytes each with a single type of membrane receptor specific for
one antigen. Essentially each lymphocyte can only be activated by one
type of antigen and when this occurs the lymphocyte will respond by
dividing repeatedly to form a ‘clonal population’ of identical
lymphocytes.
This is the process of clonal selection.
2. Antigen Presentation
T Lymphocytes
There are two main groups of T cells in the body which are involved in
the specific response and antigen presentation;- helper T cells (TH cells)
- cytotoxic T cells ( TC cells)
Helper T cells can be regarded as the main regulators of the immune
system. Their main task is to activate B cells and cytotoxic T cells as
they themselves cannot destroy an infected cell.
It is important that the helper T cells are themselves being activated.
This happens when a phagocyte has engulfed a pathogen and
displays fragments of its antigens on its surface for recognition by the
TH cells- which in turn will trigger the formation of a clone of activated
TH cells and a clone of memory TH cells which will release cytokines to
stimulate cytotoxic T cells and B cells.
This is the process of antigen presentation and is shown in the
diagram below:
Cytotoxic T cells also undergo this clonal activation process once they
recognises a specific antigen and will move to the site of infection to
attack infected cells by releasing chemicals to cause lysis or induce
apoptosis.
B Lymphocytes
The presence of a foreign antigen stimulates the production of
antibodies by B cells. Antibodies are Y-shaped protein molecules with
receptor binding sites which are specific to a particular antigen as
shown below:
An antibody response can occur as a direct response upon contact
between a B cell and the antigen, however in most cases it is a TH cell
that is involved by releasing cytokines to stimulate a clone of
activated B cells for immediate antibody production and a clone of
memory B cells for future use.
Antibodies work by inactivating the toxic component of the foreign
pathogen upon the establishment of an antibody-antigen complex in
order for phagocytosis to occur.
3. Self vs Non-Self Antigens
A unique property of the body's specific cellular defence is its ability to
differentiate between the body's own cells, recognised as “self,” and
foreign cells, or “non-self.” Moreover, every person, with the exception of
identical twins, has a unique antigen signature recognised only by their
own cells as being 'self' and therefore safe.
THINK
What might be the expected immune response in a patient
who has received a blood transfusion or an organ transplant?
Can we control our natural response? Note your ideas:
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Cells bearing non-self antigens are attacked by the immune system.
When this system breaks down and the immune system stops identifying
'self' antigens as safe, autoimmune disorders occur.
Choose one of the autoimmune diseases listed below and
produce either a written report (300-400 word) or a
PowerPoint presentation on the disease you have chosen.
- Rheumatoid Arthritis
- Type 1 Diabetes
- Multiple Sclerosis
THINK
Based on your knowledge so far of the immune system, what
do you think happens during an allergic reaction?
Discuss your ideas with your partner and note them in the
space provided below.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
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4. Immunological Memory
Primary Response:
In the primary response several days elapse before a significant
number of antibodies appear in the bloodstream.
It is often not quick or large enough to prevent the person suffering the
symptoms of the disease.
The primary immune response can take between 10-17 days from
initial exposure until selected lymphocytes generate the maximum
effector cell response. During this time the affected individual may
become ill.
Secondary Response:
If the person survives the initial infection and is exposed to the same
antigen at a later time, the secondary response is initiated.
This time antibody production:
• is much more rapid;
• is at a higher concentration;
• is maintained for a longer time;
• has a greater affinity for the antigen.
Memory cells can proliferate and differentiate rapidly if they meet the
same antigen. As a result, the person usually does not suffer the
disease symptoms.
Below is a summary of the primary and secondary responses:
Summary
• Immune surveillance explains:
– how some white blood cell constantly circulate and monitoring the tissues,
– when these tissues become damaged or invaded, a variety of cells release
cytokines,
– the process recruits specific white blood cells to the site of infection or tissue
damage.
• An antigen is defined as a molecule recognised as foreign by an organism and
which elicits an immune response.
• The clonal selection theory explains that:
– the body has a wide range of lymphocytes; each consists of a single type of
membrane receptor specific for one antigen;
– if a receptor is activated by the binding of an antigen, the lymphocyte
repeatedly divides, resulting in a clonal population of lymphocytes.
• The role of phagocytes, T lymphocytes and B lymphocytes during antigen
presentation is:
– phagocytes engulf pathogens and display part of the antigen on their surface,
– helper T cells, the major regulators of the immune system, are activated by
the phagocyte antigen,
– active B cells, cytotoxic T cells as well as other immune cells are activated by
the helper T cell.
• Cells bearing non-self antigens are attacked by the immune system.
• T lymphocytes have specific surface proteins that allow them to distinguish
between the surface molecules of the body's own cells and cells with foreign
molecules on their surface.
• Failure in regulation of the immune system leads to a T lymphocyte immune
response to self cells (autoimmune disease).
• There are four possible blood groups among humans: A, B, AB and O.
• The antigens on the red blood cells of different blood groups are as follows:
- blood group individuals A possess A antigens;
– blood group B individuals possess B antigens;
– blood group AB individuals possess both A and B antigens;
– blood group O individuals possess no antigens - since they have no antigens
to stimulate an immune response blood group O can be given to any other
blood group and is known as the universal donor.
• If exposed to different blood groups the following antibodies will be produced:
– A individuals will produce anti-B antibodies;
– B individuals will produce anti-A antibodies;
– AB individuals will not produce any antibodies - they are said to be universal
recipients because they can receive blood from any other blood group without
producing antibodies;
• Individuals will produce both types of antibody and can therefore only receive blood
from other O individuals.
• Autoimmunity occurs when the immune system fails to recognise its own cells
as 'self' and treats them as if they were foreign, 'non-self' cells by attacking and
destroying them.
• An allergy occurs when the immune system makes a mistake and misidentifies a
harmless substance as a harmful one.
– the B cells cause the body to produce large quantities of antibodies;
– these attach themselves to specialised cells in the connective tissue;
– this sensitises the body to the allergen and causes an allergic reaction when
the allergen next enters the body.
• T lymphocytes are produced in the bone marrow and mature within the thymus
gland.
• Cytotoxic T cells detect and kill cells in the body which are harbouring pathogens.
• They do this by secreting toxic chemicals into the cells.
• Because the T cells themselves are directly involved in the immune response, this
is called the cellular response.
• T helper cells produce chemicals which activate B lymphocytes so that they
produce antibodies.
• They also increase the rate of phagocytosis.
• Antibodies and antigens bind together. When this happens, a complex forms
making the antigen harmless.
• B lymphocytes are produced and mature in the bone marrow and carried by the
blood to the lymph nodes.
• When they come into contact with a foreign antigen the B cells differentiate and
secrete large quantities of antibodies into the lymph and blood.
• Because the antibodies act at a distance from the parent B-lymphocytes, this
response is known as the humoral response.
• Memory cells are formed if some of the T and B lymphocytes produced in response
to antigens by clonal selection can survive long term.
• Two clones of cells are formed:
– effector cells which are short-lived and responsible for the primary immune
response;
– memory cells are long-lived and responsible for the secondary immune
response.
• The primary immune response occurs when the body is infected by a pathogen for
the first time.
• The secondary immune response occurs when the body is subsequently infected
by the same pathogen.
• The primary response is slower and produces fewer antibodies than the secondary
response.
Learning Objectives
By the end of this topic you should be able to:
• explain that the immune system is at the centre of much of the research in public
health;
• explain that infectious diseases continue to be a major threat to the health of the
world's population;
• describe the causes of infectious diseases;
• compare the transmission methods of different pathogens;
• explain how the transmission of infectious diseases can be controlled.
• list the organisms that cause infectious diseases;
• give examples of some infectious diseases.
• explain how infectious diseases are transmitted by direct and indirect physical
contact, water, food, body fluids, inhaled air or vector organisms.
• explain how the transmission of infectious disease can be controlled.
• explain the work of an epidemiologist;
• explain the process of disease surveillance;
1. What is Health and Disease?
The term health takes a person's physical, mental and social well-being into
account. A person of good health is not only free from disease but is also mentally
and physically able to deal with everyday life.
The term disease is used to describe a problem in the body (or the mind) that leads
to poor health. Diseases can be categorised into five general groups: • deficiency
• hereditary
• mental
• pathogenic
• physiological
Infectious Disease
An infectious disease causes harm to the body and can be transmitted between
people both directly and indirectly.
THINK
Infectious diseases are spread by direct and indirect contact between
people. Work with your shoulder partner to provide examples of these
transmission methods and discuss which method is easily controlled.
Direct:______________________________________________________________
___________________________________________________________________
___________________________________________________________________
Indirect:____________________________________________________________
___________________________________________________________________
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Infectious diseases are caused by many different pathogens as shown in the table
below:
Type of Pathogen
Virus
Bacteria
Fungi
Protozoa
Parasite
Example
Measles, HIV
Cholera, MRSA
Athletes Foot, Candida
Malaria
Loa Loa worm, Hookworm
Choose 2 different pathogens and compare their transmission and
survival. Try to think of a preventative measure which can be taken to
control the spread of the disease and complete the table below with your research.
Pathogen 1:
Example
of Disease
Mode of
Transmission
How
Pathogen
Survives?
Preventative
Measure/
Control
Pathogen 2:
2. Control of Infectious Diseases
The transmission of infectious disease can be controlled by various measures
including:
• quarantine – compulsory isolation
• antisepsis – sterilisation techniques to destroy or inhibit pathogen spread
• individual responsibility – good daily practices i.e. hand washing, teeth brushing
• community responsibility – quality control procedures for water supply, food
manufacturing and waste disposal. (immunisation*)
• control of vectors- control the numbers of the organisms which spreads the
disease known as vectors.
For example, to control mosquitoes which transmit malaria;
- releasing sterile males into the population
- use of chemical controls
- removal of stagnant water breeding grounds
Use the internet to research the mosquito’s life cycle and transmission of
malaria. What are the current methods being used to control the spread
of the disease? Are there other associated problems?
Present your findings in a PowerPoint presentation.
3. Epidemiology
Epidemiology is the study of infectious disease spread patterns and associated
characteristics. It is through epidemiology that control measures are suggested for
infectious diseases’.
There are four key terms used to describe the spread patterns for such diseases:
- Sporadic
- Endemic
- Epidemic
- Pandemic
With your partner discuss what each of these terms means in practice
based on your own knowledge from the recent events surrounding swine
flu in 2009. Use the provided match cards to help.
Summary
• The immune system is at the centre of much of the research in public health.
• The term health takes an individual's physical, mental and social well-being into
account and is more than just the absence of disease.
• A disease causes a problem in the body or mind that leads to poor health.
• Diseases may be acute ('short and sharp') or chronic (persistent).
• Diseases can be categorised into five general groups: deficiency, hereditary,
mental, pathogenic and physiological disease.
• Infectious diseases are caused by pathogens such as viruses, bacteria, fungi,
protozoa and multicellular parasites.
• Malaria is transmitted between human hosts by the female Anopheles mosquito known as a vector.
• The transmission of an infectious diseases is the passing on of a disease from an
infected host individual or a group to another individual or group.
• Infectious diseases are transmitted by direct physical contact, water, food, body
fluids, inhaled air or vector organisms.
• Control of disease transmission:
– Quarantine, involves the containing of an infectious disease by isolating
infected and exposed persons from the remainder of the population.
– Antisepsis, a way to prevent disease infection through inhibition or arresting
the areas of growth of the infection.
– Individual responsibility can be achieved by changing personal behaviour.
– Community responsibility where all communities can provide an adequate,
year-round supply of high-quality water.
– Control of vectors, a method to limit or removal of mammals, birds, insects or
other arthropods which transmit disease pathogens.
• Epidemiologists study the occurrence and distribution of diseases
• The outbreaks of disease can occur on different levels.
• Sporadic is when the disease occurring occasionally, singly or in scattered
instances.
• An endemic disease is persistent in a population, but at a low level.
• A disease becomes epidemic when its incidence suddenly increases above the
normal endemic level.
• A pandemic is an epidemic over a very wide area, such as a continent or the world.
Learning Objectives
By the end of this topic you should be able to:
• explain active immunisation and vaccination;
• explain what a vaccine is
• describe the effect of a vaccine on the immune system immediately after
vaccination and when the body comes into contact with the same pathogen
after vaccination.
• explain the importance of vaccine clinical trials;
• describe the process of clinical trials of vaccines;
• describe how all vaccine clinical trials apply randomised, double-blind, placebo controlled
protocols.
• explain what is meant by herd immunity;
• describe the benefit of herd immunity to non-immune individuals;
• describe the importance of herd immunity in reducing the spread of diseases
• understand how public health medicine works.
• explain that in most countries, the policy in public health medicine is to establish
herd immunity in a number of diseases;
• explain the differences in health standards between the developed and
developing countries
1. Immunisation and Vaccines
Immunisation is the process by which our immune system goes through in order to
protect our bodies from a disease causing microorganism.
This can be achieved through natural means by surviving infection and creating
memory cells for subsequent exposure (a good example is the childhood chicken
pox) or by artificial means such as vaccination.
In creating antibodies for protection we say the person has active immunity to the
disease.
A vaccine contains an agent that resembles a diseasecausing microorganism.
It contains antigens from infectious pathogens, which could
be inactivated pathogen toxins, dead pathogens, fragments
of pathogens or attenuated (weakened) pathogens.
As the antigens are identical to the known pathogen, they
stimulate a primary response making B memory cells.
If the person encounters the real pathogen, memory B cells
will produce a faster secondary response, i.e.
immunological memory thus protecting the individual from illness.
Form of Antigen in Vaccine Examples of Diseases to which
Active Immunity Forms
Dead Pathogen
Hepatitis A, Polio
Inactivated Pathogen
Diphtheria, Tetanus
Fragments of Pathogen
Hepatitis B, HPV
Attenuated Pathogen
Measles, Mumps, Rubella, Smallpox
The MMR vaccination has been highly controversial due to a report linking
it with autism in children. Read through the case study provided and note
your own views on the triple vaccination giving evidence to support your
view.
Notes:______________________________________________________________
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2. Clinical Trials for Vaccination
Like any new product which will be made for public use, vaccines must first be
rigorously tested in the laboratory and in clinical trials. This is to ensure the
safety of the product and ensure it will be fit for its purpose (efficacy).
Prior to human clinical trials, the vaccine is first tested on cell cultures and
animals in the laboratory to allow vaccine researchers a better understanding as to
how the treatment works and any side effects which may be associated with it.
This pre-clinical stage can take up to a decade and only once approval from the
regulatory authority is granted and protocols are drawn up and independently
checked and approved by an ethics committee, can clinical trials begin.
Protocols which must be checked and approved include:
• target groups for the trials;
• number of subjects involved in these trials;
• other treatments to be compared with;
• further collection and interpretation of data.
In addition, all clinical trials must be designed to incorporate randomisation of test
subjects, experimental error, placebo effects and include a double-blind trial.
Why must clinical trials be designed according to the above protocols?
Discuss your ideas of what each protocol might mean with your partner to
explain the reason behind their compulsory aspect of all human clinical
trials. Note your ideas below:
___________________________________________________________________
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___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
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Phases of Clinical Trials
There are 4 main phases of clinical trials and they can only progress if each stage
has proven to be successful. Each stage is summarised in the diagram below:
3. Herd Immunity
When a large portion of a community is immunised against an infectious disease it
drastically reduces the likelihood of an un-immunised individual coming into
contact with the disease.
Theoretically, un-immunised individuals have a degree of protection which is
provided by the majority of the community who have likely been mass vaccinated.
This is known as herd immunity.
THINK
Why is herd immunity beneficial to pregnant women or young infants?
What is the outcome of mass vaccination to many diseases?
Answer:_____________________________________________________________
___________________________________________________________________
___________________________________________________________________
Use the internet to research which countries have COMPULSORY mass
vaccination programs and find out the average number of cases recorded
for that disease last year. Compare your findings to a country without
compulsory vaccination programs and create a bar chart from your statistics
4. Pathogen Evasion Mechanisms
One of the most difficult aspects of creating vaccines is the continuous changes
which disease causing microorganisms undergo through genetic recombination
and mutations enabling new antigens to be displayed on their surface continually.
This ensures the pathogen avoids the effects of immunological memory and can
cause serious harm to the body if susceptible. These new strains of the pathogen
arse said to show ANTIGENIC VARIATION.
A new strain of a pathogen in this way is often genetically and immunologically
distinct as it has adapted for survival and has a selective advantage over
previous versions.
Examples of pathogens which undergo this evasive technique are outlined in the
table below:
Pathogen
Virus
Protozoa
Protozoa
Example
Influenza
Trypanosomiasis brucei
Plasmodium falciparum
Illness Caused
Flu
African Sleeping Sickness
Malaria
The graph below focuses on the Trypanosome species whom undergo this antigenic
variation continuously. You can clearly see how one mutation will give rise to the
continuation of the infection making it difficult to treat and control as the rate of
change occurs in a matter of days.
Direct Attack
Tuberculosis
Within connective tissue there resides special
phagocytic cells called macrophages. It is these
particular cells which strains of bacteria are able to
manipulate to evade the immune response by
blocking the release of toxic enzymes once they
have been engulfed.
This is how the bacteria Mycobacteria tuberculosis is able to induce tuberculosis
(TB) in humans.
The bacteria is able to ‘hide’ from the hosts’ immune response and survive the
immune onslaught.
HIV
HIV is a very aggressive and very clever virus which
not only attacks the TH cells but is able to successfully
manipulate the host cell into creating viral
DNA/RNA.
HIV is particularly dangerous as it lowers the white blood
cell count in the body making opportunistic infections extremely
dangerous to the individual.
At this stage the person is said to have AIDS as their immune system no longer
functions normally and their life expectancy is decreased drastically.
Use the resources to research HIV.
Create an information poster targeted at 16-25 year olds which will
provide clear information about how the virus is transmitted, how it
survives against the immune system and ways in which to control the
spread of the virus.
Summary
Antigenic variation
• Pathogens like viruses, bacteria and protozoa can evolve mechanisms to evade
the host immune system.
• Antigenic variation is a process by which a pathogen can alter its surface proteins.
• Antigenic variation can be different in different pathogens (viruses, bacteria,
protozoa).
• Antigenic variation occurs in diseases like malaria and trypanosomiasis.
• It is one of the reasons why they are still so common in many parts of the world.
• Antigenic shift can occur when two strains of the pathogen recombine, a process
exemplified by influenza A.
• Antigenic drift is a result of genetic point mutations.
• The absence or failure of some component of the immune system results in
increased susceptibility to infection.
HIV and AIDS
• HIV attacks lymphocytes and is the major cause of acquired immunodeficiency in
adults.
• HIV is transmitted by the direct exchange of body fluids through:
– sexual intercourse,
– sharing needles,
– blood transfusions and
– from mother to child across the placenta and through breast milk.
• There is no vaccine or cure for HIV/AIDS.
• Infection can be prevented by measures such as practising safe sex and life can
be prolonged with the use of drugs (for those who can afford them).
• Education is the main measure used to prevent HIV/AIDS.
TB
• Tuberculosis (TB) is a contagious, airborne disease caused by either
Mycobacterium tuberculosis or M. bovis (from animals - mainly in developing
countries).
• Mycobacterium tuberculosis or M. bovis can survive within phagocytes and avoids
immune detection.
• Only people with the active form of the disease are infectious but the infection can
lie dormant for years and become active when the host has been weakened.
• TB spreads rapidly in areas of high poverty when people live in close proximity
and are malnourished.
• It is common in developing countries but is reappearing in inner cities in developed
countries.
• A vaccine is available (BCG) and control plans such as DOTS are also used.
• Drug resistance in cases of TB is common as many people fail to complete the 6-8
month long course of medication.
• The use of DOTS is helping with this problem.