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Defense Against Infectious Disease Topic 6.3 Types of Pathogens Cause Disease Virus influenza, polio, mumps, measles Bacteria pneumonia, strept throat, syphilis, cholera, whooping cough Fungi athlete's foot, ringworm yeast infection Protozoan amoebic dysentery, sleeping sickness, malaria Pathogens Barriers to Infection • Pathogens are organisms or viruses that cause a disease. • The skin and mucous membranes form a barrier that prevent most pathogens from ever entering the body. (primary response) The Skin • Outer layer of skin is tough and forms the first layer of defense (primary response). Dry skin also inhibits bacterial growths. • Sebaceous glands in the skin secrete lactic acid and fatty acids which make the surface of the skin acidic preventing bacteria growth. • Fatty acids and waxes have antimicrobial properties • Bacteria on the skin as well as in the mucous membranes prevent other bacteria from growing • lysozymes in sweat and saliva (mucous membranes) keep bacterial growth in check Mucous Membranes • Mucous membranes are soft areas of the skin that are kept moist with mucus. • Mucous traps bacteria in sticky mucus that is slightly acidic. (vagina, nasal passages, trachea, urethra) • Cilia sweeps mucous up to be swallowed to kill bacteria. • Contain macrophages and phagocytes that destroy pathogens. (primary response) Blood Clotting • A blood clot is the response of the body to seal up wounds to prevent passage of pathogens. • Platelets that are responsible for blood clotting are constantly circulating within the blood among erythrocytes and leukocytes. • Clotting process begins with the release of clotting factor from either damaged tissue or platelets. Blood Clotting • Clotting factors form a series of reactions where the product of one step is the substrate of the next. • This prevents clotting from happening spontaneously. • Enzyme thrombin converts soluble fibrinogen to insoluble fibrin Macrophages (phagocytes) • Macrophages make up some of the leukocytes within the blood. • Macrophages engulf pathogens and ingest them by phagocytosis (endocytosis). • Macrophages are able to move from blood capillaries towards certain tissues to sites of infection. • Large numbers of Macrophages at a site of infection forms pus. • This type of response is referred to as non-specific/first line of defense response. • The macrophage only identifies the pathogen as “notself” and eliminates it. Antibodies and Antigens • Foreign antigens are proteins found on cell walls of pathogenic bacteria or fungi and protein coats of viruses (most organisms have antigens) • Different pathogens may have several different types of antigens on the surface of their cell membrane • Antibodies are proteins made by the immune system that recognize and bind to foreign antigens on pathogens • Each antibody only binds to one type of antigen. Antigen-Antibody Antigen-Antibody Developing Natural (True) Immunity • Antibodies are made by lymphocytes called Bcells. • There are over 1015 types of antibodies. • Few B-cells exist at one time. • B-cells will produce antibodies if they encounter an antigen that their antibody binds to. • If an antigen is found they then multiply and produce many clone cells. • Antibody production by B-cells usually depends on the help of other types of lymphocytes including macrophages and helper T-cells. Types of Immunity • Passive: acquiring antibodies that were produced in another organism. – Example: breast milk, placenta-fetus, antibiotics. • Active: – Leads to the production of memory cells. Antibodies are produced by the infected organism. – Example: vaccines, overcoming a sickness • Natural – Acquiring immunity through contraction of a disease or illness • Artificial: – Acquiring immunity through methods other than your own immune system. Antibiotic use • Antibiotics work on prokaryotes (bacteria) only. Inhibits DNA replication, cell wall formation, protein synthesis • Humans are eukaryotic so our cells are not affected • Viruses “hide” inside our eukaryotic cells so antibiotics are ineffective on them as well. Development of Penicillin • Penicillin is produced by fungi. • Fungi compete with bacteria for food • Penicillin is made in fungi when food is scare and competition is increased • Discovered by Alexander Fleming in 1928 • Florey and Chain figured out how to get fungi to continuously produce penicillin and then tested it on mice…and then humans Development of Penicillin Antibiotic resistance • Some strains of bacteria have developed a resistance to antibiotics. • Already had a gene that promoted resistance • Kills off all non-resistant bacteria which means less competition for them! • Must only take antibiotics when needed and complete the entire course of antibiotics • Farmers should reduce the use of antibiotics in farming AIDS (Acquired Immunodeficiency Syndrome) • AIDS is an example of a syndrome (a group of symptoms that are found together). • Individuals with AIDS have low numbers of lymphocytes as well as weight loss and usually a variety of other diseases caused by viruses, bacteria, fungi, and protozoa which eventually lead to death. Cause of AIDS • HIV (human immunodeficiency virus) causes AIDS. • The virus infects a type of lymphocyte (t-cells) that plays a vital role in antibody production. • Over a period of years these lymphocytes are destroyed and antibodies can no longer be produced. • Without the production of antibodies the body is susceptible to pathogens that normally wouldn’t harm you. Transmission of AIDS • Blood Transfusions • Mother to child : – Across the placenta from a mother to a baby – Through cuts from child birth – In milk during breast feeding • Blood on hypodermic needles that is shared by intravenous drug users • Through small cuts or tears from vaginal, anal or oral sex.