Transmission of disease .pdf

Transmission of disease Biomedical science Benjamin Tighe Intended Learning Outcomes By the end of the session students should be able to: Explain Koch’s postulates Explain each step and give examples of the ‘chain of transmission’ De>ne the di?erent classi>ca@ons of immunity Describe the di?ere...

Transmission of disease Biomedical science Benjamin Tighe Intended Learning Outcomes By the end of the session students should be able to: Explain Koch’s postulates Explain each step and give examples of the ‘chain of transmission’ De>ne the di?erent classi>ca@ons of immunity Describe the di?erent mechanisms by which direct and indirect transmission can occur Explain the mechanisms by which the host prevents the ingress of disease Explain the mechanisms by which the host manages the ingress of disease  En mass 1-2-1 Watch this video (23) Scrubs - bacterial movement (My Cabbage episode) – YouTube Koch’s Postulates Transmission of Disease To be able to persist or live on, pathogens must be able to: 1. Leave an infected host 2. Survive transmission in the environment 3. Enter a susceptible person How do we have the or animal opportunity of spreading 4. Develop and/or multiply in infecBon in the dental surgery? the newly infected host. Put on discussion board Transmission Chain The spread of infection requires; 1. Agent 2. Reservoir 3. Exit 4. Mode of transmission 5. Portal of entry 6. Susceptible host  Pathogen The next sick Where the germ person- examples? lives - examples? How the germs How the germs get get in - examples? out- examples? Complete secBon 2 Where the germ lives - examples? in workbook Classifying Transmission of Disease 1. Horizontal 2. Vertical 3. Direct 4. Indirect Transmission of disease Horizontal Vertical Mother to child examples? Person to person examples? Complete secBon 3 in workbook and place answers on discussion board Direct and Indirect Think about – survival of Mode of pathogen in relaBon to Direct and Transmission Indirect transmission? Direct Indirect (through and (physical object or vector) contact) Kissing Touching Vehicle Vector Sexual contact Air Water Food Kissing Intercourse Oral SecreBons Body Lesions SecreBons Complete secBon 4 in workbook Indirect Transmission of Disease Vehicles Vectors Air/Droplets Water Soil Food Fomites Blood Saliva Complete secBon 5 in workbook  Transmission of infectious Droplets or dust particles agents in droplets from containing microbes remain respiratory secretions by suspended in air for long coughing, sneezing or talking periods Must be capable of surviving Droplets are too large to be outside the body and be airborne for long periods and resistant to drying quickly settle out of air e.g. measles and SARS Allows organisms to enter (severe acute respiratory upper and lower respiratory tract E.g. tuberculosis, syndrome) chickenpox, measles Waterbourne Insects Water contaminated by the Very few diseases are actually caused by excreta of animals or humans e.g. insects - most are caused by other organisms typhoid passed on when the insects feed or bite - Infec@on spread by insect faeces or secre@ons Infec@on commonly results during bathing, washing, drinking, in prepara@on or consump@on of Filthy breeding habits, feeding mechanisms food and indiscriminate travel between >lth and food make some groups of insects eHcient vectors of human parasites 4.1% of global burden of disease (WHO), causing 1.8 million deaths annually The microbe can be on the outer surface of the vector and spread through physical contact with food, surfaces, individuals Prominently include protozoa and bacteria, many of which are intes@nal parasites More vector-borne transmission Soil The most common vector is the mosquito - Infec@ons may arise from contact transfers disease through saliva when they are withdrawing blood from victim with soil such as tetanus Spores can survive in soil for long Mosquitoes are vectors for malaria, West Nile virus, dengue fever and yellow fever periods Soil can also transmit intes@nal worms e.g. hookworm Soil is a recipient of solid wastes able to contain enteric (intes@nal) pathogens in high concentra@ons Food and faecal-oral transmission Usually associated with organisms that infect the diges@ve system Enter through inges@on of contaminated food/water and shed from the body in faeces e.g. salmonella May contaminate water supply or the >sh swimming in it If a?ected individual is waiter, cook, food handler then inadequate hand-washing may contaminate food Fomites Blood and body fluids Some infections are spread when blood/fluids from an infected person comes into contact with mucous membranes or bloodstream of uninfected person e.g. through needlestick, break in the skin Particularly relevant to DCPs Diseases spread this way include Hepatitis B, Hepatitis C and HIV Passed by sexual contact including genital to genital, oral to genital, or oral or genital to anal contact e.g. chlamydia, genital herpes, genital warts, gonorrhoea, Hepatitis B, HIV, pubic lice, syphilis Saliva Contains a balanced microflora, which includes bacteria, fungi and viruses Ideal environment for growth of these organisms which acts as a good medium for transmission from host to host Some infections spread by direct contact with saliva (kissing) or indirect contact with contaminated objects (children sucking toys) e.g. CMV, glandular fever Defence against disease Defence against disease may be divided into: Preventing Ingress Dealing with Ingress Defences concerned with Defence mechanisms preven@ng ingress of which deal with the micro disease organisms once they have gained ingress PrevenBng Ingress Can you think of the ways we are able to stop ingress? Put on the discussion board  Blood brain barrier Tears Saliva Gingival crevicular Zuid Mucociliary escalator Stomach acid Skin Blood Sweat – faWy acids & salt Complete secBon 6 Scabs in workbook Mucociliary Escalator Skin The respiratory tract is lined with Has a tough outer layer of cells that mucus and tiny hairs called cilia produce keratin Microbes become trapped in the mucus and the cilia beat to remove This layer, which is constantly renewed mucus from the lungs from below serves as a mechanical This is a continual process so that barrier any particles that penetrate the lungs are trapped and swept up to the However, the alimentary and respiratory epiglottis where they are swallowed tracts along with the eyes and gingival sulcus are susceptible (as they are unkeratinised) Fatty acids and salts Saliva Glands in the skin secrete This contains many fa\y acids and lysozyme an@bacterial agents and has which kill bacteria a lavage e?ect Gingival crevicular fluid Blood An in^ammatory exudate The entry of infec@on that can be collected at through wounds is a major gingival margin or within source of infec@on gingival crevice To some extent this is prevented by the ^ushing It is another an@bacterial ac@on of blood ^ow and solu@on, containing then by the clo`ng immunological defence mechanisms mechanisms Blood brain barrier Specialised filter that surrounds brain and spinal cord and acts as a physical barrier to keep out proteins, toxins and most micro-organisms while letting in glucose Dealing with ingress Dealing with ingress of micro-organisms Immune response Variable response Please refer to immunology lectures Say what you see Immune system/ Host Response Recognises and destroys foreign substances and organisms that enter the body Can distinguish between body’s own tissues and outside substances called antigens Allows cells of immune system to identify and destroy only those enemy antigens Immune system remembers previously encountered antigens, so that body can mount a better and faster immune response next time it encounters that antigen Lymphocytes White blood cells that develop in the bone marrow and circulate throughout body in lymphatic system Divided into 2 subgroups: B and T lymphocytes B Lymphocytes – Humoral Immune Response B lymphocytes antibodies ( or immunoglobulin) (humoral immune response) 10k proteins on outside – membrane-bound antibodies Antibodies are protein molecules that attach to specific antigens When an foreign antigen enters the blood it combines with a few B-lymphocytes which then divide rapidly through mitosis forming a clone of plasma cells  These then produce mainly antibodies but also memory cells The memory cells can live for large periods of time, sometime even for life T lymphocytes Help control immune response and destroy antigens directly (cell mediated immune response) Once matured T-lymphocytes circulate the body in the blood until it meets an antigen it has the receptor site for. It is then stimulated to divide by mitosis many times forming clones. Three types of T-lymphocyte: Killer cells – cause lysis of target cells, will destroy virus infected or cancer cells. Helper cells – activate B-lymphocytes to produce antibodies. Suppressor cells – turn off immune response, e.g. turning off antibody production Phagocytosis The fraction of white blood cells known as the polymorphonuclear leucocytes carry out phagocytosis When micro-organisms invade, these cells phagocytose them (phage means to eat!) This is the bodies most direct and earliest way of dealing with invaders Immunity Condition of being protected against an infectious disease Natural immunity is present from birth and inherited from mother to offspring Acquired immunity is gained throughout life, developed in response to a disease and may be temporary (e.g. flu) or permanent (e.g. measles, mumps) Acquired Immunity – 2 types Active or Natural immunity Passive of Artificial immunity Long-lasting immunity Ready made antibodies are developed either by having injected into human body to the disease, having a develop immunity e.g. subclinical infection or by hepatitis B (body has no inoculation with killed micro- capacity to develop antibodies organisms or detoxified to these diseases) toxins e.g. polio, tetanus