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Community Health and Infectious Diseases 社區健康與傳染病 K.N. Leung 梁國南 Department of Biochemistry, and Food and Nutritional Sciences Programme ,CUHK 香港中文大學生化系、食品及營養科學課程 Lecture Outline Concepts of Health and Disease Human Pathogens and Infections Prevention of Infectious Diseases Microbial Control and Public Health Emerging and Reemerging Infectious Diseases WHO Definition of Health “Health is a state of complete physical, mental and social well-being, and not merely the absence of disease and infirmity.” Community Health the participation of the community in health care programs. “A healthy community is one that embraces the belief that health is more than merely an absence of disease. A healthy community includes those elements that enable people to maintain a high quality of life and productivity.” - Department of Health, USA Definition of Disease (1) Dis-ease: opposite of ease, when something is wrong with a bodily function. (2) “An impairment of health due to an interruption, cessation or disorder of body functions.” Mother is the First Microbiology Instructor! Antonie van Leeuwenhoek (1632-1723) “Father of Microbiology” Founders of Microbiology and Modern Medicine Louis Pasteur (1822-1895) Robert Koch (1843-1910) Types of Disease Infectious vs. Non-infectious Infectious disease a disease caused by a pathogenic microorganism Communicable disease an infectious disease that is transmissible from one human to another, either directly or indirectly Contagious disease a communicable disease that is easily transmitted from one person to another The World’s Most Common Causes of Death from Infectious Diseases Tetanus 2.50% Hepatitis B Measles Malaria Tuberculosis 5% 4% Others 26% 7% Respiratory Infections (3.9 million) 9% 11% 18% AIDS 17.50% Diarrheal diseases Data from The World Health Report 2002 Infection invasion of the body tissues by living organisms Types of Infection Acute vs. Chronic Latent vs. Persistent Clinical vs. Subclinical Hospital-acquired vs. Community-acquired Causes of Infectious Disease PATHOGENS IN OUR ENVIRONMENT Viruses Bacteria Fungi Protozoa Parasitic worms Most micro-organisms are harmless, only a few are pathogenic Typical Structure of a Virus Envelope proteins (often as receptors for host cell) Lipid envelope derived from host cell membrane Capsid protein Viral nucleic acid (double or single-stranded) Nucleoprotein 20-300 nm in diameter Typical Structure of a Bacterium Flagellum (confers motility) Capsule (mainly polysaccharides) Cell wall Pili (adhere to host cell surface) Circular DNA genome Cell membrane Plasmids (DNA that code for toxin production or antibiotic resistance) Different Types of Bacteria Streptococcus that causes sore throats Legionella pneumophila that causes Legionnaire’s disease Campylobacter jejuni that causes food poisoning FACTORS AFFECTING THE EXTENT & SEVERITY OF AN INFECTION Factors related to micro-organisms: e.g. Dose, Pathogenicity, Route of entry Intrinsic host factors: e.g. Age, Sex, Immune competence, Genetic makeup, Previous infections, Nutritional & emotional states Extrinsic factors: e.g. Infections in community, Hygiene & sanitation, Medication used, Environmental pollution ROUTES OF ENTRY OF INFECTIOUS ORGANISMS Through the skin or mucus membrane 1) by direct close contact: e.g. Venereal disease (花柳病); AIDS (愛滋病) 2) by contamination of abrasions and wounds: e.g. Rabies (狂犬病); Tetanus (破傷風) 3) by inoculation: insect bite – Malaria (瘧疾); syringe – serum hepatitis (血清性肝炎) ROUTES OF ENTRY OF INFECTIOUS ORGANISMS By ingestion of contaminated food and water: e.g. Cholera (霍亂); Infective hepatitis (傳染性肝炎) By inhalation of dust and aerosols-borne pathogens: e.g. Influenza (流行性感冒); Tuberculosis (肺結核) SARS (嚴重急性呼吸道症候群) The Human Immune System 人體的免疫系統 骨髓 幹細胞 病毒 細菌 真菌 寄生蟲 癌細胞 花粉 Lymphocytes 淋巴細胞 B cells: ~10-15% of blood lymphocytes T cells: ~70-80% of blood lymphocytes Phagocytes 吞噬細胞 Include Macrophages & Granulocytes Immune Mechanisms Innate (Non-specific) Immunity Acquired (Specific) Immunity Resistance not improved by repeated antigen exposure Without memory Fast response Resistance improved by repeated antigen exposure With memory Slow response Physical barriers: Skin, Mucus membrane Biochemical factors: Complement, Humoral Immunity: (B cells + Antibodies) Acute phase proteins, Lysozyme Chemical barriers: Acid in stomach, Mucus in saliva Cellular factors: Phagocytes, NK cells, Eosinophils Cell-mediated Immunity: (T cells + Accessory cells + Cytokines) Normal Resistance to Microbial Infection Epithelium Bac teri um Ba ct er iu m First barriers to infection Physical Mechanical Chemical/Biochemical Normal flora sIgA Intraepithelial lymphocytes Invading microbe (Inflammatory stimulus) Second line of defense Macrophages Subepithelial lymphocytes Dendritic cells Innate immunity Adaptive Immunity T cells Antibodies Inflammatory mediators Reinforcement Infectious Disease: Dynamic Interaction and Balance of Various Factors HOST PATHOGEN ENVIRONMENT Chain of Infection (Infectious Disease Cycle) The pathogen Exit from host Reservoir (Source of pathogen) Susceptibility of the host Mode of transmission Prevention of Infectious Diseases breaking the chain of infection Isolation and Quarantine - remove the source of infection Increase host resistance - vaccination and immunopotentiation Modify environment - improve sanitation, eradication of vectors Isolation and Quarantine Separation of ill infected patients in hospitals (Isolation) or infected suspects in their homes, or in community-based facilities (Quarantine) Voluntary basis or mandatory to protect public’s health Invention of Vaccination Variolation in Ancient China Variolation introduced to Europe (1721) by Lady Mary Montagu From Variolation to Vaccination (1796) Edward Jenner: “Father of Immunology” Discovery of smallpox vaccine Vaccination against smallpox in 1796 Eradication of smallpox in 1979 Principle of Vaccination Vaccination Antibody titer Toxoid 1st Exposure Natural infection Primary Antibody Response Toxin 2nd Exposure Memory cell formation Time Secondary Antibody Response STRATEGIES FOR VACCINATION Killed Organism Natural Infectious Agent Live Attenuated Organism Protein subunits DNA for Protective Antigens Recombinant proteins Protective Antigens Synthetic Peptides VACCINES CURRENTLY AVAILABLE FOR HUMANS Live attenuated Polio (小兒痲痺) Measles (痲疹), Mumps (痄腮) & Rubella (德國痲疹) (MMR) BCG (TB肺癆) Subunit Hepatitis B (乙型肝炎) Haemophilus B (流感杆菌性腦膜炎) Inactivated Influenza (流感), Rabies (狂犬病) Hepatitis A (甲型肝炎) Cholera (霍亂) Pertussis (百日咳) Toxoid Tetanus (破傷風) Diphtheria (白喉) Newly Developed Vaccines Conjugate vaccine for Haemophilus influenzae type b (Hib) Oral vaccine for Rotavirus Bacterial Meningitis Viral Gastroenteritis Microbial Control Methods Physical Agents: Dry heat (incineration) and moist heat (autoclaving and Pasteurization) Radiation (gamma irradiation and UV irradiation) Chemical Agents: Gases (ethylene oxide, beta-propiolactone) Disinfectants and antiseptics (alcohols, chlorine compounds) Mechanical Removal Methods: Filtration and sanitization Disinfectants Commonly Used in Hospitals 60 - 90% Alcohols (Ethanol, Isopropanol) Chlorine compounds (Halazone, Hypochlorite) Glutaraldehyde Iodine and iodophors Phenolic compounds (Lysol, Cresol) Quaternary Ammonium Compounds Action of Antibiotics Inhibit protein synthesis: Tetracycline Erythromycin Chloramphenicol Inhibit nucleic acid synthesis: Nalidixic acid Rifampicin Inhibit synthesis of essential metabolites: Sulfonamide Inhibit cell wall synthesis: Penicillins Cephalosporins Change cell membrane permeability: Polymyxin Antibiotic Resistance Mechanisms Antibiotics are broken down by enzymes Antibiotics are removed from cell via pumps Antibiotic Altered receptor sites do not allow antibiotics to fit Decreased cell membrane permeability does not allow antibiotics to enter Personal Protection Against Infectious Diseases Wash hands frequently Wear cap, gloves and gowns Wear face masks (N95/Surgical) Cook and store foods properly Observe healthy lifestyles Stay up-to-date on immunizations Strategies to Improve Public Health Better cooperation between the public and private health sectors Maintain and improve vector control programs Increase monitoring and surveillance programs Promote education of the public for community health matters Increase research in public health and infectious diseases Major Public Health Agencies International Local (HKSAR) Hospital Authority 醫管局 Department of Health 衛生署 Centre for Health Protection 衛生防護中心 World Health Organization 世界衛生組織 Centres for Disease Control and Prevention, USA 美國疾病控制 及預防中心 Surveillance & Epidemiology Branch 監察及流行病學 處部 Food and Environmental Hygiene Department 食物及環境 衛生署 “New viruses and drug-resistant bacteria are reversing human victories over infectious diseases” Time Sept. 12, 1994 Dengue Fever (登革熱) An acute viral disease caused by infection with dengue virus which is transmitted through mosquito bites Sept. 2002 : First local cases detected in Hong Kong The Human Immunodeficiency Virus (HIV) 人體免疫缺陷病毒 HIV-1 major cause of AIDS HIV-2 less harmful What is AIDS ? AIDS is a transmissible disease caused by infection with HIV which impairs or destroys the body’s immune system. Death may result from wasting syndromes, opportunistic infections and cancers Transmitted by (1) sexual contact (2) blood-borne and (3) maternal route Global Summary of HIV/AIDS Epidemic No. of cases People living with HIV/AIDS 39.4 million New HIV infection in 2004 4.9 million Deaths due to HIV/AIDS in 2004 3.1 million Cumulative AIDS deaths since 1980s ~34 million From the Joint United Nations Programme on HIV/AIDS (UNAIDS) - Figures in December 2004 Structure of HIV gp120 gp41 ss RNA Protease Reverse transcriptase What Causes The Immune System to Collapse in AIDS? Direct killing of HIV-infected CD4+ T cells or indirect lysis of uninfected CD4+ T cells Life-threatening immune suppression What is Avian Influenza (Bird Flu) (禽流感)? An infectious disease of birds caused by certain type A flu virus Infected birds shed virus in saliva, nasal secretions and feces Mainly infect birds but occasionally affect humans Can cause high fever, chest infection, respiratory and multi-organ failure and death in humans The Influenza Viruses (A, B, C) Types A and B viruses cause widespread outbreaks in humans Type C viruses cause only mild upper respiratory tract infection in humans Type A viruses can infect several animal species, including birds, pigs, horses, seals and whales Type B and C viruses do not affect domestic animals Influenza A Virus (甲型流感病毒) 病毒基因 血凝素 Hemagglutinin (H1 – H15) Segmented RNA 神經氨酸酵素 Neuraminidase (N1 – N9) 膜蛋白 Matrix protein Human Infection with Flu and Avian Flu Viruses Virus strain Year Location Effects Human Flu H1N1 H2N2 H3N2 H1N1 1918 1957 1968 1977 Spain? Asia Hong Kong Russian 40 - 50 million deaths > 1 million deaths Virus still circulating Virus still circulating Avian Flu H5N1 1997 Hong Kong H9N2 1999 H7N7 2003 Highly pathogenic for birds & humans Hong Kong Mild infection in humans Not highly pathogenic in birds Netherlands Highly pathogenic for bird Emergence of “new” influenza viruses by genetic recombination? Human flu virus (XX) XY New flu virus (XY) Pig (Blender) Avian flu virus (YY) Human Severe Acute Respiratory Syndrome (SARS) 嚴重急性呼吸道症候群 Worldwide Cases 8,098 probable cases & 774 deaths (By Dec. 2004 Source: CDC) What is SARS? A highly contagious and sometimes fatal respiratory infection First appeared in China in Nov. 2002, then spread to > 30 countries Causative agent (SARS-CoV) was identified in late March 2003 Transmitted mainly by close person-to-person contact via respiratory droplets or via air-borne route (?) Incubation period ranged from 2 to 11 days Symptoms include high fever (>38.0°C >24 h), chills, body aches, dry cough, breathing difficulties; Diarrhea is seen in ~10 - 20% patients; Most patients develop pneumonia SARS-CoV Virus (沙士冠狀病毒) 病毒基因 RNA 膜蛋白 Membrane protein 刺蛋白 Spike Protein Treatment and Prevention of SARS No specific treatment for SARS Anti-viral drugs: (a) inhibit virus entry to target cells (b) block virus-induced cell fusion (c) inhibit virus replication Immunosuppressants (e.g. corticosteroids) Development of SARS vaccines Know More About Communicable Diseases www.info.gov.hk/dh/diseases/CD/CD_index.html www.who.int/vaccines-diseases/ THE END Thank you for your attention!