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Teacher Notes for Infectious Diseases
PERIOD FOUR
Entry And Defense Of Infectious Agents
Transmission of infectious agents: five main routes
(20 min).

Airborne. Airborne transmission involves small evaporated or dust
particles (< 5 µm) containing an infectious agent. Mycobacterium
tuberculosis is an example of airborne transmission.

Droplet. Droplets (> 5 µm) are produced primarily from coughing,
sneezing, and talking.
Transmission occurs when droplets
containing microorganisms travel a short distance through the air and
are deposited in another person’s respiratory tract. The common cold
can be spread through droplet transmission.

Contact. Contract transmission is the most important and frequent
mode of transmission. It can be divided into two groups: (1)
transmission through direct contact of body surfaces and (2)
transmission through indirect-contact of infectious agents via
contaminated objects, such as instruments and needles. HIV is an
example of contact transmission


Common Vehicle.
Vector-borne. E.g. Dengue Fever
Non-specific mechanism of defense against infectious agents
1.
(20 min)
Physical barriers

Skin. Intact skin provides a complete external protection for our
body. The unbroken skin acts as a physical or mechanical barrier
to invaders; only when it is injured can pathogens gain entrance.
The skin's normal secretions, such as acidic perspiration from
sweat glands and fatty acids from oil glands, destroy bacteria or
inhibit their growth on its surface.

Mucus. Mucus is produced by the mucous membranes at the
openings to the respiratory, digestive, urinary, and reproductive
systems. Mucous membranes trap invaders and thus protect our
body from the invasion of foreign microorganisms and substances.

Cilia. The cilia of the cells lining the respiratory tracts sweep the
trapped dust and microbes toward the throat, where they are
swallowed or expelled by sneezing and coughing. The respiratory
system would be particularly vulnerable to airborne invaders that
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Teacher Notes for Infectious Diseases
are inhaled with each breath, were it not for the hair, mucous
membranes, and nasal chambers that serve to trap much of the
inhaled debris. The trapped invaders in the mucous lining may be
destroyed by chemical mechanisms or by the immune system.

Other. Peristalsis and the expulsion of feces remove bacteria from
the intestine, as well.
2. Chemical barriers
3.

Enzymes. Enzymes are regular constituents of body fluids such
as nasal secretions, saliva, and tears. For example, lysozymes
are active proteins that can lyse (disintegrated/destroy) bacteria.

Acidity and alkalinity. Besides enzymes, our digestive system is
also protected by digestive secretions such as acidity of the
stomach, alkalinity of the intestines, and bile acid from the liver.
The acidity and alkalinity in the gastrointestinal tract help to kill of
inactivate bacteria.

Bile acid. Synthesized in the liver and secreted into the intestine
bile acid lowers the surface tension and induces chemical changes
in bacterial cell walls and membranes that enable easier lysis
(disintegration) of bacteria more ready to be destroyed.
Microbial antagonism
Microbial antagonism is the prevention of the growth of harmful
microbes by the residential microflora at a given anatomical site.
The anti-bacterial and anti-fungal capability of these microflora has been
attributed to nutritional competition as well as the production of certain
inhibitory substances.
The effectiveness of microbial antagonism is frequently reduced
following overuse of antibiotics. The improper use of antibiotics
disturbs the balance of the microflora and permits overgrowth of the
potentially pathogenic bacteria or fungi that are resistant to the
administered antibiotics.
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Teacher Notes for Infectious Diseases
PERIOD FIVE
The Immune System And Immunity
Specific mechanism of defense against infectious diseases- the
immune system
The immune system is capable of differentiating between ‘self’ and ‘foreign’
substances and guards our body by specifically recognizing and destroying
the ‘foreign’ substances’.
Key players of the immune system
(5 min)
Antigens. An antigen is a foreign molecule that can be bound by an antibody
specifically recognizing it. Antigens must be foreign molecules that the
human body does not recognize as ‘self’ and they may be proteins, sugars,
nucleic acids, or combinations of bio-molecules. On the surface of a
bacterial cell are many molecules capable of stimulating the production of
antibodies.
Antibodies. The term ‘antibody’ refers to a protein with high specificity for an
antigen produced by a special types of white blood cells in the immune
system in response to the presence of that antigen. An antibody ‘labels’ the
antigen for destruction by the immune system.
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Teacher Notes for Infectious Diseases
White Blood Cells The white blood cells provide one of the body's main
defenses against pathogens that gain entry. White blood cells can filter
through the walls of blood vessels into the infection site, where they surround
or 'swallow' the microbes, which are then digested. White blood cells are
often killed in the process of battling pathogens. The resulting pus contains
plasma and dead white blood cells, it is the evidence that some infection has
occurred.
Steps of immune responses
(15 min)
1. The white blood cells recognize ‘foreign' molecules or so called antigens,
such as microbes, pollen grains or the toxins made by bacteria.
2. The presence of antigens in the body stimulates the immune system to
produce antibodies. Each type of antigen causes the production of new
antibodies specific to the antigen.
3. Antibodies circulate in the blood. When they encounter the particular
type of antigen which they have been produced to react with, they bind
to the antigen, forming a complex. These complexes are then destroyed.
4. After infection, some white blood cells become ‘memory cells’ that can
be stimulated to produce antibodies rapidly and in large quantities when
later exposed to the same antigens at a later date.
5. This increased production of antibodies following the second exposure to
the antigen is called the ‘memory response’. The magnitude of the
memory response increases with longer duration and higher affinity for
the antigen. Memory cells are crucial to the maintenance of immune
status of the host.
After primary exposure of antigens, some
white blood cells become “memory cells” (m).
Memory cells usually exist in an inactive state,
or a “resting state” (rest). However, when
exposed to the same antigens at a later date,
memory cells can be activated for rapid
production of antibodies in large quantities.
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Teacher Notes for Infectious Diseases
How is immunity developed
(5min)
Immunity is the condition of being immune or resistant to a particular
infectious disease, usually as a result of the presence of antibodies that are
specifically directed against the pathogen of that disease. These circulating
antibodies are normally found in blood, lymph, and other body secretions
where they readily protect against the specific pathogens that have
stimulated their production. Thus, a person is immune to a particular
infectious disease because of the presence of specific protective antibodies
that are effective against the pathogen.
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Teacher Notes for Infectious Diseases
PERIOD SIX
Vaccines And Vaccination
What are vaccines?
(3min)
Vaccines contain chemically weakened toxins or purified antigens that are
adsorbed frequently onto an aluminum salt adjuvant.
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Teacher Notes for Infectious Diseases
Why do we need vaccines?
Vaccines protect us against serious diseases like measles, mumps,
whooping cough and hepatitis.
How do vaccines work?
1.
2.
3.
4.
(5 min)
The antigens-salt adjuvant attracts white blood cells to the injection
site. (see steps a, b in the figure below)
These cells participate in the local inflammatory responses such as
redness, swelling and pain at the injection site.
Local inflammation induces immune responses to the vaccine and
stimulates the production of antibodies against the vaccine antigens.
(see steps c, d in the figure below)
A subpopulation of white blood cells become memory cells which can
rapidly produce antibodies in large quantity if the host is exposed to
the same antigens in the future.
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Teacher Notes for Infectious Diseases
Why multiple vaccine doses?
(7 min)
The goals of primary immunization are two-fold:
1.
The production of sufficient numbers of antibody-producing cells
capable of raising antibody levels above protective thresholds.
The amount and type of antibodies produced by a given antigen
depend on the site and the quantity of antigenic stimuli as well as
the number of times the person is exposed to the antigen.
2.
The induction of sufficient numbers of memory cells to allow their
recall activation many years after the primary immunization.
Prompt and effective immune response to a pathogen can be induced
upon re-exposure even years after vaccination due to the presence of
memory cells. As the antibody concentration induced from the initial
vaccine shot declines, a second booster shot of the same antigen many
months later elevates the antibody concentration to a level that protects
the host from the disease. This is the reason why booster shots are given
to protect against certain pathogens that one might encounter repeatedly
throughout life, such as Clostridium tetani, the pathogen that causes
tetanus. If boosters are not given, vaccine antibodies progressively
diminish and will lead to increased disease risk with advancing age.
Examples of how a vaccine works
(5 min). .
Hepatitis B immunization
The role of memory cells is demonstrated best by the vaccine-mediated
prevention of hepatitis B. The strong immunogenicity of hepatitis B vaccines
in infants, children and young adults allows > 90% of subjects to respond to
immunization with high antibody titers. Thus, the vaccine-induced antibodies
are expected to confer protection for more than 15 years.
Unlike the exposure to diphtheria or tetanus, natural exposure to hepatitis B
virus acts as a natural booster and induces a rapid rise of antibodies in
previously vaccinated subjects. If viral exposure occurs after antibodies
decline below protective levels, a transient infection may result during which
viral replication produces antigens sufficient to reactivate memory cells
previously induced by immunization. These memory responses ultimately
neutralize and eliminate the hepatitis B virus. Thus, exposure to hepatitis B
virus may result in transient infections in previously immunized subjects
without causing clinical symptoms or progression to chronic hepatitis.
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Teacher Notes for Infectious Diseases
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Teacher Notes for Infectious Diseases
PERIOD SEVEN
Control Of Infectious Diseases
International organizations
(5 min).

World Health Organization (WHO)
WHO assumes the mission of supporting an environment in which its
Member States strengthen the scientific and ethical foundation of health
policies and strategies and improve the performance of their health
systems functions so that they respond better to the needs of their
citizens by promoting equity, quality, efficiency and the active
involvement of civil society.

United States Center for Disease Control and Prevention (CDC)
To promote health and quality of life by preventing and controlling
disease, injury, and disability.
Example: Anthrax
In late 2001, it was discovered that Bacillus anthracis spores had been
intentionally distributed through the U.S. postal system causing 22 cases of
anthrax, including 5 deaths. To improve its response, the CDC has
established rapid response teams composed of experts in operations,
epidemiology, microbiology, data management, and communications to
facilitate the control of the disease in case of another outbreak.
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Teacher Notes for Infectious Diseases
Local organizations (15min)

Hong Kong Department of Health
It is the Government’s health adviser and agency to execute Hong
Kong’s health care policies and statutory functions. Its mission is to
protect the health of the community through promotive, preventive,
curative, and rehabilitative services.
Under the Department of Health, the Disease Prevention and
Control Division is responsible for formulating strategies and
implementing measures in the surveillance, prevention, and control
of diseases.

Hospital Authority
To meet the different needs of the patients for public hospital
services, and to improve the hospital environment for the benefit of
the patients.

Food and Environmental Hygiene Department
To ensure that food is fit for human consumption and to maintain a
clean and hygienic living environment for the people of Hong Kong.
Roles of health and community workers
They participate in the control of infectious diseases by the following
measures:






Reporting cases of communicable diseases to the proper agencies.
Educating the general public about how diseases are transmitted
and explaining proper sanitation procedures.
Identifying and attempting to eliminate reservoirs of infection
Carrying out measures to isolate infected persons.
Participating in immunization programs.
Bringing treatment to sick persons.
Through these similar measures, diphtheria, poliomyelitis, and smallpox
have been totally or nearly eliminated in most parts of the world.
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Teacher Notes for Infectious Diseases
Implementation of the vaccination program
(20 min)
Vaccination is the introduction of vaccine into the human body by oral
ingestion or by injection. A vaccine stimulates the production of antibodies
against a particular pathogen and thus protects the host from the invasion of
a particular disease.
The vaccination program in Hong Kong is covered by three main services
listed below. The medical practitioners in the private sectors also facilitate
the vaccination program.

The Family Health Service is responsible for the vaccination of
infants and pre-school children up to the age of 5. The Family
Health Service also undertakes to remind individual parents the
need to complete the immunization schedule (table 1) of their infants
and children.

The Regional Offices are responsible for carrying out the
immunization program in schools and remote sites.
The
vaccination program in the Regional Offices is carried out by teams
of inoculators under the supervision of the Community Physicians
and in accordance with a timetable for immunization campaigns.

The Government Chest Service carries out the BCG vaccination
program. The Service has teams of inoculators who visit the
maternity units in all public hospitals to provide BCG vaccination for
newborns during the first few days of life. These inoculators also
visit children in primary schools.
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Teacher Notes for Infectious Diseases
What are advantages and risks of vaccination programs?

Advantages
Immunization provides long-term protection against many diseases to
which we have little or no treatment.
The number of infectious diseases that may be prevented through
routine immunization has long included diphtheria, tetanus, pertussis,
poliomyelitis, measles, mumps, rubella and tuberculosis.
The combination of vaccine antigens has led to the development of
combined vaccines with preventive capacities against a growing
number of pathogens. For example, vaccines that combine diphtheria-,
tetanus-, acellular pertussis-, polio-, and HIB-hepatitis B.

Risks
The normal immune processes generated to protect the host can also
trigger harmful responses. Overall, the risks associated with giving an
immunization are small. More serious vaccine-induced illnesses are
much rarer than the diseases themselves. The possible risks of
vaccination are listed below.
1. Slight physical discomfort.
Most problems consisting of
short-lived aches, pains or fever.
2. Allergies.
DTP (Diphtheris, Tetanus and Pertussis triple
antigen) and tetanus vaccinations may induce allergic
responses. There is a greater possibility of developing asthma
among vaccinated subjects than among unvaccinated subjects.
DTP or tetanus vaccination appears to increase the risk of
allergies and related respiratory symptoms in children and
adolescents.
3. Vaccines fail to work properly
4. Introduction of diseases
The whooping cough vaccine:
In England, the likelihood of the whooping cough vaccine causing brain
damage was reported in the news in the mid-1970’s. The public was scared
to give the vaccines to the children. Before the report, 79% of babies were
immunized and few were getting whooping cough. After the scare, the rate
of immunization dropped to 31% in 1978. The result of the lowered
immunization rate was an outbreak of whooping cough. At the peak of the
outbreak, more than 2,000 children caught the disease every week. Over 30
children died and some were left with long-term disabilities.
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Suggested activities
Suggested Activities:
Period 1 to Period 3
1. Identifying the morphology and sizes of microorganisms, such as bacteria,
fungi, mites, etc. by using light microscopy.
2. Watching the videotapes
i) “Louis Pasteur’s legacy of hope” from the distributor Barr Media Group,
Irwindale, CA, U.S.A.
Contact Method:
Barr Media Group
12801 Schabarum Avenue, P.O. Box 7878, Irwindale, CA 91706-7878
Tel: 800-234-3878 / 818-338-7878
Fax: 818-814-2672
ii) Unseen Life on Earth – An introduction to Microbiology, Episode 12.
Microbes of Human Diseases
Contact Method:
Joanne M. Grason, Manager, Sales & Distribution
Annenberg / CPB, 401 9th Street, NW, Washington, DC 2004
Tel: 202-879-9648
Fax: 202-879-9696
e-mail: [email protected]
3. Conducting an experiment on pasteurization using simple equipment in
laboratory. Equipment required: Bunsen burner, thermometer, timer,
refrigerator, and a light microscopy with supplies. The bacterial count is
taken for every 10oC increase by streaking plates.
4. Setting up an experiment on the turbidity / bacterial count on the water
supply: water sample taken from the reservoir, tap water, and after boiled.
5. Performing an experiment on the bacterial count on the hand surface
after an outing, before and after hand washing with soap. Hands under
test must be swabbed thoroughly
6. Counting the bacterial growth on different food items in refrigerator, and
to observe the differences among perishable, semi-dried or dried food
items. Example, fresh beef and beef jerky.
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Suggested activities
Period 4 to Period 7
7. Conduct a case study on the outbreak and control of Dengue Fever and
discuss how the disease may be prevented. (Total 10 mins)
 Separate students into groups of 2-3 persons.
 Show students printed information about the symptoms, transmission,
and outbreaks of Dengue Fever.
 Allow students 5 minutes to read the material and discuss what they
think can be done to prevent the spread of the disease.
 Pick 1 group at in random to report the result of their discussion and
other groups to contribute ideas (5 min).
8. Use audiovisual materials to illustrate the immune process, including
the production of antibodies in response to an antigen, and the antigen
and the antigen-antibody reaction. (About Immune System, Corel Medical
Series, 1997, CD-ROM). (Total 15 mins)

Resources: Video of immune system and immune response.
9. Tell the stories of Jenner in the development of small pox vaccination
using the cartoon slide (Total 10 mins).
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Suggested activities
10. Study the recommended immunization table and an immunization card to
identify the types of disease that are covered by the Hong Kong
immunization program from birth to adolescence.



Ask students to bring their own immunization card to class.
Separate students into groups of 2-3 persons.
Show the recommended immunization record card on slide.

Ask students to compare their immunization record with their group
members and discuss what diseases they should be immune from
Pick one or two groups at in random to report if every member in the
group has completed the recommended immunization program.

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Suggested activities
11. Introduce the story of the whooping cough vaccination program.
Discuss the advantages and risks of vaccination to both individuals and
the community. (Total 10 mins)





Separate students into groups of 2-3 persons.
Give students reading materials about whopping cough (controversial
cases).
Ask the students if they think the parents should allow their children to
receive the whooping cough vaccination?
Allow 5 minutes for them to read the story and discuss the question.
Ask random groups to give their reasons for receiving or not receiving
the vaccination (5 min).
The Whooping Cough Vaccine:
In England, the likelihood of the whooping cough vaccine causing brain
damage was reported in the news in the mid-1970’s. The public was
scared to give the vaccines to the children. Before the report, 79% of
babies were immunized and few were getting whooping cough. After the
scare, the rate of immunization dropped to 31% in 1978. The result of the
lowered immunization rate was an outbreak of whooping cough. At the
peak of the outbreak, more than 2,000 children caught the disease every
week. Over 30 children died and some were left with long-term disabilities.
In addition to less children been vaccinated, a recent outbreak of whooping
cough in Leicestershire England exposed the problem that the disease went
unrecognized as the local general practitioner refused to believe the school
mistress who reported it, lengthening the time before a vaccination program
was introduced. This delayed response caused increase in the number of
cases. News regarding to the recent whooping cough outbreak, please see
http://news.bbc.co.uk/1/hi/uk/england/2014708.stm
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Suggested activities Appendix I
Lab Safety & Culturing Bacteria Procedures
Safety Precautions

Do not eat and drink in laboratory.

All laboratory workers should wear lab coats during working in
laboratory.

All laboratory workers should wear gloves to avoid skin contact with
biological materials.

Label all containers and biological samples properly.

Label all materials that to be autoclaved with autoclave tape.

Loosen all containers’ cap and other covers before autoclaving, to
avoid pressure accumulation inside the containers.

Autoclave* all containers, glassware and culture medium before use.

Sterilize the working bench with alcohol or bleach, and use Bunsen
burner to slightly flame all containers and pipettes during the material
transfer.

Autoclave* all biological wastes before disposal. (Do not autoclave
carcinogenic and radioactive materials)

Wash hands thoroughly before leaving the laboratory.

If your body has been contaminated with biological materials, clean
the contaminated portion with suitable disinfectant and then flush with
water. Report the issue to laboratory in charge as soon as possible.
*Autoclave methods:
Pressure cooker could be used or commercial bleaching agent could be
used to sterilize the apparatus as well.
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Suggested activities Appendix I
Culturing Bacteria
You need:
1. Pressure cooker
2. Bleaching agent
3. Test tubes
4. Conical flask
5. Petri dishes
6. Wire loop
7. Droppers
8. Bunsen burner
9. Nutrient agar
10. Nutrient broth
11. Bacteria sample
Main skills assessed:
Follow instructions
Form hypotheses/solve problems
Design and carry out experiments
Use apparatus
Record and handle data
Criticize the experiment
How to collect bacterial samples?
1. Obtain bacteria by allowing a piece of boiled potato to decompose in
water for 2 days, or
2. Collect samples of river water, pond water and tap water, and place in
separate sterile containers, or
3. Place soil in a container with just sufficient water to cover it.
Methods (Culturing bacteria)
1.
2.
3.
4.
5.
Suspend 32 g LB agar in 1 L of distilled water.
Stir the solution until all powder dissolved.
Suspend 20g LB Broth base in 1 L distilled water.
Loosen all container caps
Autoclave the LB agar solution, broth solution and test tubes 15 min.
at 121 oC .
6. Under sterilized condition, pour about 5ml LB agar medium to each
petri dish. The lids are tilted open.
7. Allow the medium to cool and set.
8. Cover one of dishes with lid, which acts as a control (dish 1).
9. Use dropper to apply 1 or few drops of bacteria sample to another
dish. (dish 2)
10. Use flame-sterilized inoculating loop to streak the plate in an angled
sequence.
11. Incubate the dishes and tubes at 37℃ for two days, and then
compare them.
12. Re-sterilize all the cultures in the autoclave before disposal
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Suggested activities Appendix I
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Suggested activities Appendix I
Alternative Method of Culturing Bacteria
1. Use millipores paper to filter the bacteria for cultivation.
2. Place the filter on an agar plate for about 10 seconds and then
remove it.
3. Incubate the agar plate at 37℃ for at least two days.
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Suggested activities Appendix II
Bacterial Count between Washed and Unwashed Hands
You need:
1.
2.
3.
4.
5.
6.
Perti dishes of sterile nutrient agar
Warm water for hand washing
Soap and paper towels
Pressure cooker
Bleaching agent
Sterile bulb pipettes
Main skills assessed:
Follow instructions
Form hypotheses/solve
problems
Design and carry out
experiments
Use apparatus
Record and handle data
Criticize the experiment
How clean are your hands?
1. Label four Petri dishes of sterile nutrient agar A, B, C, and D
2. Dish A: Take off the lid for 10 seconds then cover the lid and seal
around the rim with sticky tape.
Dish B: Take off the lid and press the fingers of an unwashed hand
onto the agar (it must not be broken up by too much pressure).
Cover the lid within 10 seconds and seal it.
Dish C: Wash your hands in warm water only (no soap). Dry them
with paper towels. Take off the lid and touch the agar as before.
Cover the lid within 10 seconds and seal it.
Dish D: Wash your hands thoroughly using warm water and soap.
Dry them with paper towels. Take off the lid, touch the agar as before,
cover the lid within 10 seconds and seal it.
3. Incubate the petri dishes upside down at 37°C for a week. Without
opening them:
a) Count the number of bacteria colonies in each dish.
b) Count the number of different colonies in each dish.
c) Design a result table
What do your results tell you about the cleanliness of washed and
unwashed hands and the effectiveness of soap as a cleaning agent?
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Suggested activities Appendix II
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Review Questions/Quizzes/Food for thought
Review Questions/quizzes/food for thought
Period 1 to Period 3
1. Why cannot antibiotics cannot control viruses?
2. Why killing mosquitoes is is important in controlling Dengue fever?
3. Why may fresh milk can only be consumed within 2 weeks after
pasteurization?
4. Why can ham can be stored for a much longer time than fresh pork?
Period 4 to Period 7
1. Can students think of more examples of infectious diseases transmitted
through the above-mentioned routes?
2. Would it be good to have a world free of microbes?
3. What if the immunization program is not available?
4. Why is small pox eradicated?
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References for Teachers and Students
Supplementary Resources
References for Teachers:
Books
1.
Burton GRW and Engelkirk PG. Microbiology for the Health Science
6th Ed., 2000, Lippincott Williams & Wilkins.
2.
Burton GRW and Engelkirk PG. Human Defense Against Infectious
Disease’ in Microbiology for the Health Sciences 6th Ed., 2000,
Lippincott Williams & Wilkins.
Articles
1.
Health and Epidemiology Bulletin (1992) by the Department of Health.
Chapter 2 & 3: Organization of Epidemiological Surveillance of
Communicable Diseases in Hong Kong –Part I & II, pp. 4-15.
2.
Hughes JM, and Gerberding JL (2002).
Lessons Learned and Future Directions.
Diseases, 8, 1013-14
Anthrax Bioterrorism:
Emerging Infectious
Websites
http://www.info.gov.hk/dh/diseases
http://www.who.int/emc/index.html
http://www.info.gov.hk/fehd
http://www.who.int/vaccines-documents/DocsPDF99/www9943.pdf
http://www.nevdgp.org.au/language/english/en_dtp.htm
http://school.discovery.com/lessonplans/programs/vaccinations/
http://www.accessexcellence.org/AE/AEC/CC/vaccines_how_why.html
CD Rom/Video Tape
1.
2.
About Immune System, Corel Medical Series, 1997
“Louis Pasteur’s legacy of hope” from the distributor Barr Media Group,
Irwindale, CA, USA
References for Students:
Websites
1.
2.
3.
http://www.info.gov.hk/dh/diseases
http://www.info.gov.hk/fehd
http://school.discovery.com/lessonplans/programs/vaccinations/
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