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Higher Human Biology Unit 4 Immunology & Public Health KEY AREA 4: Active Immunisation and Vaccination Higher Human Biology We are going to build on the knowledge and skills that you developed during N5 and will learn about the following Immunology & Public Health key areas : - Key Area 1 – Non-specific Defences Key Area 2 – Specific Cellular Defences Key Area 3 – Transmission and Control of Infectious Diseases Key Area 4 – Active Immunisation and Vaccination and the Evasion of Specific Immune Responses by Pathogens Physiology & Health Learning Intentions KEY AREA 4 – Active Immunisation and Vaccination a)Active Immunity b)Pathogen Evolution 4a) Active immunisation and vaccination Immunisation is the process by which a person develops immunity to a disease-causing organism Active immunity refers to the protection gained as a result of the person’s body producing its own antibodies Naturally Acquired Active Immunity is when the person has acquired active immunity by natural means (e.g. they have survived the infection by a pathogen, and if exposed to this antigen again, a secondary immune response occurs) Artificially Acquired Active Immunity is when the person has received a vaccination to trigger an immune response creating an immunological memory 4b) Vaccinations Vaccinations are made from antigens from infectious pathogens that are usually mixed with an adjuvant. An adjuvant is a chemical substance that promotes the activity of the antigen and enhances the immune response The vaccine is usually a weakened or altered form of the pathogen or toxin e.g. - Inactivated pathogen toxin (e.g. Diphtheria, Tetanus) - Dead pathogen (e.g. Hepatitis A, Poliomyelitis) - Parts of pathogens (e.g. Hepatitis B, HPV (Human Papilloma virus) - Weakened pathogens (e.g. Rubella, mumps and measles) 4c) Vaccine Clinical Trials Vaccines are subjected to clinical trials to establish their safety and efficacy (capable of producing the intended result) before being licenced for use Clinical Trials involve testing on cells and animals in the lab, and once protocols have been approved then testing on humans can take place During a clinical trial, then subjects are split into groups in a randomised way in which neither the subjects nor the researchers know which group they are in e.g. 2 groups (test group, control group) 4d) Clinical Trial Design Placebo Effect Control group given a “sham” treatment to see if it improves their condition due to the psychological effect of thinking it works Double-blind Trial Neither the subjects nor the researchers know who is receiving what to eliminate bias Randomised Information about each individual is hidden, so groups are made randomly and not based on current health to eliminate bias Sample group size must be suitable to reduce the magnitude of experimental error At the end of the trial results are compared to determine whether there are any statistically significant differences between the groups 4e) Herd Immunity If a large percentage of a population are immunised, nonimmune individuals are protected as there is a lower probability that they will come into contact with infected individuals – this form of protection is called Herd Immunity Herd immunity is important in reducing the spread of diseases and in protecting vulnerable and non-vaccinated individuals For Herd immunity to be effective, only a minority of the population can be left unvaccinated. The percentage of immune individuals in a population above which a disease no longer manages to persist is called the herd immunity threshold Herd Immunity Threshold depends upon:-The pathogen’s virulence – its capacity to cause disease -The efficacy of the vaccine (it effectiveness) -The contact parameters for the population (degree of population density that affects the pathogen’s ability to spread) 4f) Public Health Immunisation Programmes In most countries, the public health policy for combating common diseases is to use mass vaccination programmes to create herd immunity. Widespread vaccination is not always possible: In developing countries due to malnutrition and poverty, or In developed countires when vaccines are rejected by a percentage of the population due to negative publicity about the vaccine e.g., MMR 4g) Pathogenic Evolution Many pathogens have evolved mechanisms that evade the specific immune system which has consequences for vaccination strategies Antigenic Variation Some pathogens can change their antigens which means they can avoid the effect of immunological memory e.g. Malaria, Trypanosomiasis, Influenza 4g) Pathogenic Evolution - Antigenic Variation 4h) Pathogenic Evolution Influenza Virus The influenza virus evolves to produce new antigens which avoid the human body’s immunological memory. This allows the virus to re-infect the person as the new antigens are not recognised. This is why influenza is a major public health problem, and high-risk individuals (those with an underlying health condition e.g., asthma, diabetes or those belonging to other risk groups e.g., the elderly, the young and pregnant women who may have weakened immune systems) need to be vaccinated every year with a new version of the vaccine to give protection 4i) Pathogenic Evolution Trypanosomiasis (African Sleeping Sickness) Trypanosoma brucei is a protozoan (unicellular animal) that causes a fatal neurological disease called Trypanosomiasis (“Sleeping Sickness”) when it gains access to the bloodstream of humans and some other mammals. The pathogen is surrounded by a coat of glycoprotein that varies in chemical composition depending on which of the genes that code of the variations are switched on. The infected host responds by making antibodies against the antigen (the glycoprotein in the pathogen’s coat), which kills 99% of protozoa but 1% of them shed their coat, switch on different genes to code for a different variation of the glycoprotein and thus the host has to produce new antibodies. Eventually this cycle results in death of the host. 4j) Pathogenic Evolution Malaria Plasmodium falciparum is a protozoan (unicellular animal) that causes malaria. The malaria pathogen is found in red blood cells of humans and shows great antigenic variation to avoid the host’s immune response. Individual pathogenic cells produce a protein that is transported to an infected red blood cell’s surface, making the red blood cell adhere to the lining of the blood vessel preventing it from being removed and destroyed. The parasite can switch off the genes for this protein, making it impossible for the host to produce antibodies within the limited time available. This antigenic variation has prevented scientists from producing an effective vaccine, and Malaria continues to kill millions of people annually. 4k) Direct Attack on Immune System The absence or failure of some component of the immune system results in increased susceptibility to infection e.g. If a pathogen interferes with the host cell’s phagocytic response, the pathogen manages to block an essential step in the immune system and brings it to a halt An Immunodeficiency Disease results from the absence or failure of some component of the immune system which leaves the person susceptible to infection 4l) Direct Attack on Immune System – AIDS & HIV AIDS (Acquired Immune Deficiency Syndrome) is a deficiency disease caused by HIV (Human Immunodeficiency Virus) as HIV attacks lymphocytes AIDS & HIV • HIV attacks helper t lymphocytes, attaching itself to specific receptors on the helper T cell surface. • Helper T cells activate B cells and Cyto-toxic T cells, as the number of helper T cells drops, the body’s immune response decreases • Individuals are left more susceptible to opportunistic infections such as pneumonia, or influenza. • This immune-compromised state arises many years after the initial infection and it is at this point the person is suffering from AIDS 4m) Direct Attack on Immune System - Tuberculosis Mycobacterium tuberculosis is a bacterium that causes tuberculosis. It is an intracellular pathogen as it can survive inside phagocytes preventing lysosomes fusing with the vesicle, the enzymes produced to break it down are not effective as there are unable to breakdown the waxy cell wall As the pathogen remains alive inside the macrophage it avoids immune detection Physiology & Health Questions KEY AREA 4 – Active Immunisation and Vaccination 1.Testing Your Knowledge 1 Page 335 Q3 2. Testing Your Knowledge 2 Page 345 Q’s 1-3 3.What you should know Page 345 Q’s 1-12 4.Applying Knowledge Page 346 Q1-6 5.Quick Quiz