INFECTIOUS DISEASES B

1 EJC H2 Biology T2W8 Infectious Diseases Part II Extension Topic A: Infectious Diseases (Part 2) 1. Introduction Pathogens have the ability to infect humans and cause diseases. This led to the development of vaccines to induce immunity against pathogens as well as antibiotics to treat bacterial infections. Edward Jenner is considered the founder of vaccinology in the West in 1796, after he inoculated a 13 year old boy with vaccinia virus (cowpox), and demonstrated immunity to smallpox. In 1798, the first smallpox vaccine was developed. Since then, a plethora of vaccines have been developed. In 1928, Alexander Flemi ng had discovered the first antibiotic, penicillin, but it took over a decade before penicillin was introduced as a treatment for bacterial infections. This was possible through the work of Florey and Chain who managed to efficiently purify the antibiotic and scale-up production. The introduction of penicillin marked the beginning of the so-called “golden era” of antibiotics. 2. Learning Outcomes a. Describe the specific (adaptive) and non -specific (innate) immune systems including active and passive, natural and acquired immunity. e. Discuss how vaccination can control disease (e.g. in the eradication of small pox), limited to vaccination stimulates immunity without causing the disease and vaccination of a high enough proportion of the population can break the disease transmission cycle. f. Discuss the benefits and risks of vaccination. g. Explain how viruses, including influenza and HIV, cause diseases in humans through the disruption of host tissue and functions (e.g. HIV and T helper cells, influenza and epithelial cells of the respiratory tract). h. Explain the mode of transmission and infection of bacterial pathogens, using Mycobacterium tuberculosis as an example. i. Describe the modes of action of antibiotics, including penicillin, on bacteria. 3. References Judith Owen, Jenni Punt, Sharon Stranford. Kuby Immunology, 7th Edition. Murphy KM, P Travers, M Walport (Eds.) Janeway’s Immunobiology. 8 th Edition. Pommerville, Jeffrey C. Alcamo’s Fundamentals of Microbiology: Body Systems.

2 EJC H2 Biology T2W8 Infectious Diseases Part II Contents 1. Introduction ............................................................................................................... 1 2. Learning Outcomes.................................................................................................... 1 3. References ................................................................................................................. 1 4. Vaccination ................................................................................................................ 3 5. Pathogens & Diseases................................................................................................ 9 a. Pathogenicity of Influenza Virus ................................ ................................ .......... 10 b. Pathogenicity of HIV ................................ ................................ ............................ 11 c. Pathogenicity of Mycobacterium tuberculosis ................................ ..................... 12 6. Mode of Action of Antibiotics ................................................................................. 14

3 EJC H2 Biology T2W8 Infectious Diseases Part II 4. Vaccination The knowledge of immunological memory has been used in medical practice to improve human health and survival through the practice of vaccination. The type of immunity described so far occurs during the course of an infection , when an immune response to antigens activates lymphocytes and antibodies are produced by plasma cells of the infected individual . This is known as natural active immunity. Natural immunity is immunity gained by being infected by pathogen (active) or by receiving antibodies from the mother across the placenta or in breast milk (passive). Differences between active immunity and passive immunity: Active Immunity Passive Immunity Antibody production Antibodies are produced by the individual’s own immune system in response to antigens introduced naturally or artificially. Antibodies are transferred to the recipient without the participation of the recipient’s immune system. Examples: (1) Fetus receives IgG antibodies from mother through transfer across the placenta. (2) Newborn receives antibodies such as IgA from mother through the breast milk. Duration of immunity Immunity conferred is long- lasting since memory cells are formed in the individual after primary immune response to antigen. Immunity conferred is short- lived since there is no formation of memory cells. Notes to self

4 EJC H2 Biology T2W8 Infectious Diseases Part II Fig. 1:. Overview of the 4 different types of immunity and their corresponding examples. Vaccination is the intentional administration of a harmless form of a pathogen in order to induce a specific adaptive immune response that protects the individual against later exposure to the pathogen due to production of memory cells. The individual should not develop disease symptoms. Vaccination is an artificial active immunity since the immune response is activated artificially by introducing antigens into the body to initiate primary immune response. Vaccination uses the property of immunological memory to provide long - lasting protection against infectious diseases. When exposed to the actual pathogen, the memory cells trigger a secondary immune response that is faster and stronger. Notes to self

5 EJC H2 Biology T2W8 Infectious Diseases Part II Fig. 2: Events that happen after vaccination. The events that happen after vaccination (Fig. 2): (1) A person is vaccinated against a specific disease. The vaccine contains either the attenuated or weakened form of pathogen or the killed pathogen. (2) The modified pathogen is no longer able to cause disease, but it can still retain immunogenic effect (i.e. ability to elicit immune response) because a characteristic surface antigen of the pathogen is still retained and can be recognised by antigen presenting cells. (3) Adaptive immune response occurs. Naïve B and T lymphocytes are activated to become effector lymphocytes. (4) The B lymphocyte with the specific BCR that is complementary in shape to the antigen undergoes clonal expansion by dividing repeatedly by mitosis to form genetically identical B lymphocytes which become either (5) memory cells or (6) antibody-secreting plasma cells. Notes to self

6 EJC H2 Biology T2W8 Infectious Diseases Part II Vaccination can prevent disease by generating a rapid and more intense immune response. (Fig. 3) (1) If the previously vaccinated individual is exposed to the virulent pathogen, (2) memory cells will quickly recognize the surface antigen of the pathogen. (3) Memory cells rapidly undergo clonal expansion and (4) they develop into antibody secreting plasma cells. (5) These plasma cells produce a large number of antibodies which are able to bind and inactivate the virulent pathogen to prevent them from infecting the healthy host cells in the individual. Fig. 3: Vaccination can prevent disease by generating a rapid and more intense immune response. Notes to self

7 EJC H2 Biology T2W8 Infectious Diseases Part II Fig. 4: Concentration of serum antibody following vaccination (primary response) and infection by virulent pathogen (secondary exposure). (Modified: Human Anatomy and Physiology, Elaine Marieb) Types of Vaccine A vaccine is a preparation of immunogenic material used to induce immunity against pathogenic organisms. Three types of vaccines: 1. Live, attenuated vaccine 2. Inactivated vaccine 3. Toxoid vaccine Live, attenuated vaccine Attenuation refers to wea