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Defense Against Infectious Diseases

Defense Against Infectious Diseases. 6.3. 6.3. Pathogens An organism or virus that causes a disease Viruses, bacteria, fungi, protozoa, flatworms, and roundworms can all be pathogens. Examples include: Viruses – Rhinovirus (causes the common cold), HIV, HCB (Hepatitis B virus)

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Defense Against Infectious Diseases

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  1. Defense Against Infectious Diseases 6.3

  2. 6.3 • Pathogens • An organism or virus that causes a disease • Viruses, bacteria, fungi, protozoa, flatworms, and roundworms can all be pathogens

  3. Examples include: • Viruses – Rhinovirus (causes the common cold), HIV, HCB (Hepatitis B virus) • Bacteria – Staphylococcus (causes strep throat), Vibrio Cholerae (causes cholera), Myobacterium tuberculosis (causes TB) • Fungi – Candida (yeast infections), Trichophyton (fungus that causes ringworm)

  4. The Common Cold

  5. Methods of transmission • Cuts in the skin • Mouth, Nose, and Eyes • Vectors (animals that transmit disease) • Sexual Transmission • IV Drug Use • Blood Transfusions • Food and Water

  6. 6.3 • Barriers to infections • First line of defense: prevent pathogens from entering the blood stream • Skin • The skin is a tough, impenetrable physical barrier • Skin has a lower pH which make it inhospitable for many bacteria • Sweat has lysozymes (special enzymes) that destroy bacteria

  7. When Skin is Broken • When the skin is broken we lose the primary line of defense for our body. • Cuts in the skin are sealed by blood clotting • Clotting factors are released from the platelets in the blood. • Thrombin – Hormone that triggers a cascade of reactions that convert fibrogen to fibrin.

  8. 6.3 • Mucous membranes • Traps pathogens because it is sticky • Cilia in the throat sweep up bacteria and allow them to be swallowed and then destroyed by acid in the stomach • Contains phagocytes (white blood cells that ingest and destroy pathogens)

  9. 6.3

  10. 6.3 • Cellular Defense • Second line of defense is the non-specific immune system - a host of quick, non-specific methods of killing microbes that have entered the body. • Leucocytes = general category of white blood cells • Phagocytes: large, irregularly-shaped leukocyte cells that remove bacteria, viruses, cellular debris and dust particles.

  11. 6.3 • Are constantly changing shape, and they flow over pathogens, surrounding and ingesting them through the process of phagocytosis to form a phagosome • Enzymes within the lysosome of the phagosome break down the pathogen • Different phagocyte cells work in different locations: • neutrophils circulate in the blood • macrophages are found in lymph, tissue fluid, lungs and other spaces, where they kill microbes before they enter the blood

  12. 6.3

  13. https://www.youtube.com/watch?v=CEOV-SFTlpY

  14. Now that you have gotten infected • Antibiotics • Work on bacteria, not viruses • Antibiotics block specific metabolic pathways found in bacteria, but not in eukaryotic cells (such as our own) • Examples: RNA replication, transcription, translation, 70S ribosome function and cell wall formation • Since viruses do not metabolize on their own (they use our cell’s metabolic machinery) they are not effected by the antibiotics

  15. 6.3 • Antibiotics: Types • _____-static: (bacteriostatic, fungistatic) stop further growth but don’t kill existing microbes. • Buys time for immune system to catch up and target microbes. • _____-cidal: (bacteriocidal, fungicidal) kills microbes

  16. Antibiotic resistance • Some bacteria develop a gene mutation that makes them naturally resistant to antibiotics • Resistance can be transferred from strain to strain and sometimes from species to species • Bacteria that have a resistance mutation survive when antibiotics are used and other bacterium die

  17. Resistant bacteria pass on their genes for resistance to offspring • Proportion of resistant bacteria increases in each generation • This is an excellent example of natural selection and evolution

  18. 6.3 • Antigen and Antibodies

  19. 6.3 • Antigen and Antibodies • Antigens • Large molecules on the outer surface of cells • All living cells as well as viruses have antigens • All cells in one organism will have the same type of antigen (which is genetically controlled) • Therefore, the antigen acts as identification marker for cells • If a pathogen enters the body the immune system will detect the foreign antigen and begin to attack

  20. 6.3 • Antibodies (also called immunoglobulin) • Proteins that bind to the specific antigen on a pathogen to help to destroy it • Each has a variable region that is antigen specific (similar to enzyme specificity)

  21. 6.3 Youtube.com Specific Immunity: Antibodies https://www.youtube.com/watch?v=Ys_V6FcYD5I

  22. 6.3 • Antibody production • Many types of b-cells exist • Each type recognizes one specific antigen and responds by dividing to form a clone • This clone then secretes numerous copies of a specific antibody against the antigen • Cloning and antibody production is always initiated by the binding of a t-cell (another type of white blood cell) to the b-cell

  23. 6.3

  24. 6.3 • HIV and Aids • HIV, or Human Immunodeficiency Virus, was first noticed by the CDC (center for disease control) in 1981 • The U.S. origin of the disease was traced back to “patient zero”, a french flight attendant who slept with hundreds of men throughout the country

  25. 6.3 • HIV and AIDS • HIV can remain hidden in the body for years • It survives by invading and killing T-Cells • When enough T-cells have been destroyed, the immune system begins to fail and AIDS, or Acquired Immune Deficiency Syndrome, has begun • Aids patients do not die from the virus itself, but rather from the diseases that take hold of the body in the absence of a proper immune system • Many anti-viral drugs are now available for AIDS patients

  26. Effect of HIV on Immune System • The HIV virus limits the number of active lymphocytes in an organism • This makes it much harder for the organism to fight off possible infectious pathogens • Lose the ability to produce antibodies • Leads to the development of AIDS

  27. 6.3 • The drugs usually do not work alone, however, and must be administered in combinations called “cocktails” • The drugs do not destroy the virus completely, but rather slow down the rate of replication • After a few years, the drugs tend to lose their affect and the patient must begin a new drug regime • Sides effects of the drugs can be horrible and include hallucinations, insomnia, and severe depression

  28. 6.3 • HIV is transmitted through vaginal fluid, semen, blood, and sometimes breast milk • Sexual contact and IV drug use (sharing of dirty needles) are the most common ways that these bodily fluids are passed from person to person • The social implications of AIDS are numerous and devastating, especially in southern Africa where the number of cases is disproportionate to other areas of the world

  29. 6.3 • As a result of the large numbers of people with the disease and no health care in these nations there are many orphaned children • Having AIDS or having family members with the disease also provides a social stigma that may make it hard to get a job • Having AIDS may also make it hard to obtain health insurance

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