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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 26 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. 27 28 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. 29 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. 30 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. 31 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. 32 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. 33 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. 34 Teacher Notes for Infectious Diseases 35 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. 36 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. 37 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. 38 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. 39 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. 40 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). 41 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. 42 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 43 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. 44 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 45 Suggested activities Appendix I 46 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. 47 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? 48 Suggested activities Appendix II 49 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? 50 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/ 51