Infectious Agents

1. Infectious Agents • Pathogen – an organism that causes disease • A pathogen that can be spread from one organism to another is contagious. • A pathogen is infectious when it finds a tissue that will support its growth. • A parasite obtains nutrients and shelter from an organism while contributing nothing. • Bacteria and viruses are the most common infectious microbes.

2. Infectious Agents - Bacteria • Bacteria are single-celled prokaryotes, are very diverse, and can be categorized into 3 basic shapes Pili Rod shaped (bacilli) Gelatinous capsule Cell wall Plasma membrane Flagellae Nucleoid regioncontaining circularDNA chromosome Spherical (cocci) Spiral (spirochetes) Plasmid 1 µm Figure 18.1

3. Infectious Agents - Bacteria • Bacteria reproduce through binary fission. 1 2 3 4 Figure 18.2

4. Infectious Agents - Bacteria Noon2bacteria Chicken saladsandwich 2:00 p.m.128bacteria 4:00 p.m.8192bacteria 8:00 p.m.Over33millionbacteria • Bacteria can reproduce rapidly. • Under ideal conditions a population can double in 20 minutes Figure 18.3

5. Infectious Agents - Bacteria Bacterial diseases are caused by toxinssecretedby bacteria. Table 18.1

6. Infectious Agents - Bacteria • Bacterial infections are usually treated with antibiotics. • Many bacteria – including those which cause gonorrhea, ear infections, and TB – have become resistant to antibiotics. • This is likely due to natural selection through overuse. • Methicillin-resistant Staphylococcusaureus (MRSA) has recently caused the deaths of otherwise healthy young athletes.

7. Infectious Agents - Viruses • Viruses consist of nucleic acid surrounded by a protein sheath or coat, and are not classified as living organisms because they.. • Cannot reproduce by themselves; require a host cell • Are not composed of cells • Also do not have cytoplasm or organelles, and cannot produce toxins

8. Infectious Agents - Viruses Surfaceprotein Membraneenvelope Reversetranscriptase Capsid Genome: 0.01 µm Single-strandedDNA or RNA or Double-strandedDNA or RNA • The genome of a virus can be DNA or RNA. Figure 18.4

9. Infectious Agents - Viruses • Viral replication is carried out by hijacking the host cell’s transcription and translation processes. 3 2 1 Reversetranscription Transcription andtranslation RNA DNA 4 Viral genomes(RNA) Hostcell Viral proteins Figure 18.5

10. Infectious Agents - Viruses PLAY Animation—Structure and Reproduction of Viruses

11. Infectious Agents - Viruses Examples of Viral Diseases Table 18.2

12. Infectious Agents - Eukaryotic Pathogens • Protozoans, worms, and some fungi can infect animals, including humans. Table 18.3

13. Infectious Agents - Prions (a) Normal prion protein has morehelical regions. (b) Misfolded prion protein hasmore pleated regions. Amino acid chain 0.001 µm 0.001 µm • A prion is a misfolded protein. Figure 18.6

14. Transmission of Infectious Agents (a) Direct contact (b) Vector-borne (c) Indirect contact (d) Inhalation (e) Ingestion • Common Methods of Transmission Figure 18.8

15. Transmission of Infectious Agents - Ingestion • Spongiform encephalopathy can be spread by ingestion of food containing misfolded prions. • Cows can become infected by eating feed made from infected cows. • Humans who eat infected cows can become infected. • Prions occur in the nervous system; these parts are not commonly eaten in the US, but meat can be exposed during processing.

16. The Body’s Response to Infection: The Immune System Pathogens 1 Nonspecific Skin 2 Nonspecific Macrophage 3 Specific Lymphocytes 3 Lines of Defense • Nonspecific Physical • Skin, Mucous • Nonspecific Cellular • Macrophage, Phagocytes • Specific • Antibodies • Lymphocytes: • B-Cells, T-Cells Figure 18.9

17. The Body’s Response to Infection: The Immune System - Skin and Mucous Membranes • Skin • Sheds, takes pathogens with it • Has low pH, repels microorganisms • Glands in skin secrete chemicals to slow bacterial growth • Mucous Membranes • Mucous traps pathogens • Can be sneezed, coughed away Nonspecific Immune Response

18. The Body’s Response to Infection: The Immune System - White Blood Cells Nonspecific Immune Response • White blood cells: macrophages and phagocytes • Engulf and digest invasive organisms • Also digest old red blood cells and cellular debris • Can release chemicals to stimulate production of more white blood cells Figure 18.10

19. The Body’s Response to Infection: The Immune System - White Blood Cells Nonspecific Immune Response • natural killer cells • Attack tumor cells and virus-infected cells • Release chemicals that break apart cell membranes

20. The Body’s Response to Infection: The Immune System - Inflammation Nonspecific Immune Response • Inflammation: response which produces redness, warmth, swelling, and pain • After tissue injury, damaged cells release histamine • Histamine causes vasodilation which increases blood flow (redness) • More blood in area brings more oxygen and nutrients, also more fluid (swelling/pain)

21. The Body’s Response to Infection: The Immune System - Inflammation

22. The Body’s Response to Infection: The Immune System – Defensive Proteins Nonspecific Immune Response • Interferons – produced by infected cells • Bind to healthy cells • Stimulate production of anti-viral chemicals • Complement proteins – class of about 20 different proteins • Can coat surface of bacteria to facilitate phagocytosis • Can make holes in bacterial membrane Figure 18.11

23. The Body’s Response to Infection: The Immune System - Fever • Fever – temperature above range of 97-99º F • Macrophages can release pyrogens, which cause temperature to increase • Increased temperature inhibits bacterial growth • Increases metabolism of healthy cells Nonspecific Immune Response

24. The Body’s Response to Infection: The Immune System - The Third Line of Defense: Lymphocytes • Lymphocytes are a specific defense because they recognize specific antigens. • Lymphocytes travel throughout the body in spaces between the cells and are carried in the blood and lymphatic system. Specific Immune Response

25. The Body’s Response to Infection: The Immune System - The Third Line of Defense: Lymphocytes Tonsils and adenoid: Type oflymph node Thymus: Where some lymphaticcells go to mature Bone marrow: Produces somelymphatic cells Spleen: Stores and purifiesblood; contains highconcentration of lymphocytes Lymph nodes: Store cells andfilter out bacteria and otherunwanted substances to purify thelymphatic fluid; become swollenand painful when infection occurs Lymphatic vessels: Transportfluid from tissues to lymph nodes Specific Immune Response Figure 18.12

26. The Body’s Response to Infection: The Immune System - The Third Line of Defense: Lymphocytes (a) B lymphocyte (b) T lymphocyte B-cell receptors Antibodies T-cell receptors B cell T cell Viruses Bacteria Antigen Antigen Virus-infected cell • B and T cells produce antigen receptors that fit on a portion of a particular antigen. Figure 18.13

27. The Body’s Response to Infection: The Immune System - The Third Line of Defense: Lymphocytes • B cells • Recognize small organisms such as bacteria • Produce antibodies • T cells • Respond to larger organisms, virally infected cells, body cells that have gone awry and transplanted tissues • Attack antigen directly Specific Immune Response

28. The Body’s Response to Infection: The Immune System - The Third Line of Defense: Lymphocytes • Passive Immunity– short-term immunity, lasts as long as antibodies are in bloodstream. • Ex: Given antibodies as antitoxin • Active Immunity – long-term, caused by exposure to antigen and production of B and T cells. Example: Vaccinations/memory Specific Immune Response

29. The Body’s Response to Infection: The Immune System - Allergy • Allergy – immune response that occurs even though no pathogen is present • Body reacts to a non-harmful substance as if it were pathogenic • Common allergies include ragweed pollen and peanuts • Asthma might be caused by allergy

30. The Body’s Response to Infection: The Immune System - Self vs. Non-self • B- and T-cells must be able to distinguish between body cells and other cells. • All cells of an individual have characteristic proteins, like an ID badge. • Developing lymphocytes are tested to insure they do not bind to body cells. • Normal immune system is self-tolerant.

31. The Body’s Response to Infection: The Immune System - Self vs. Non-self • When the immune system is not self-tolerant, it can result in auto-immune disease – when the system attacks some part of the body. • Multiple sclerosisis the result of T cells attacking a protein on neurons. • Insulin-dependent diabetes is when T and B cells attack the insulin-producing cells in the pancreas.

32. The Body’s Response to Infection: The Immune System - Humoral and Cell-Mediated Immunity • Humoral Immunity: provided by antibodies produced by B cells, extracellular pathogens • Cell-Mediated Immunity: provided directly by T cells, intracellular pathogens (viruses)

33. The Body’s Response to Infection: The Immune System - Humoral and Cell-Mediated Immunity B-cellreceptors B cell Antigen Antibodies Clonalpopulation • Humoral Immunity – B cells produce: • Antibodies • Clonal copies of themself, providing long-term immunity Figure 18.17

34. Specific Host Defense: Humoral Immunity 1 Clonal Selection: • Ag binds specific Ab only • Clonal Proliferation • Plasma Cell or Memory Cell • Ab Produced • Memory for next encounter with pathogen 2 3-5

35. Specific Host Defense: Humoral Immunity Memory Cells • Inject Rabbit with tetanus toxin • Primary response: Several days for Clonal Proliferation (Plasma and Memory Cells) • Secondary Response: Faster and Stronger (have memory cells)

36. Specific Host Defense: Humoral Immunity Vaccines: 1) Give an innocuous dose of tetanus toxin -Not a toxic level, primes immune system 2) Actual encounter with tetanus is stronger and faster

37. The Body’s Response to Infection: The Immune System - Humoral and Cell-Mediated Immunity • Vaccinations attempt to take advantage of long-term immunity through exposure to parts of antigens • Produces population of memory cells • Some antigens, such as flu, mutate quickly and require frequent vaccinations • Some antigens are difficult to make vaccines for

38. The Body’s Response to Infection: The Immune System - Humoral and Cell-Mediated Immunity • Cell-Mediated Immunity– T lymphocytes divide to make different types of cells, some of which directly attack pathogens

39. The Body’s Response to Infection: The Immune System - Humoral and Cell-Mediated Immunity Macrophage presentsantigen to T cell. T cell Viruses T-cell receptors Virus antigen 1 2 3 Memory cellswill help the body respondmore quickly if the pathogenis encountered again. Cytotoxic T cellsattack and kill body cellsthat have becomeinfected with a pathogen. Helper T cellssecrete a substance that enhanceshumoral immunity (B cells) andcell-mediated immunity (T cells). Body cell Interleukin 2 amplifies immune response. Clonalpopulation Virus Figure 18.18

40. The Body’s Response to Infection: The Immune System - AIDS Weakens the Immune System • Acquired Immune Deficiency Syndrome (AIDS) is caused by the Human Immunodeficiency Virus (HIV). • HIV kills or disables helper T cells. • Loss of helper T cells causes immune deficiency; individuals can become infected by pathogens to which they should be immune. • Opportunistic infections occur when the immune system is weakened. • HIV is only transmitted through contact with bodily fluids: semen, blood, vaginal fluids, and occasionally breast milk.

41. 18.3 The Body’s Response to Infection: The Immune System PLAY Animation—The Body’s Response to Infection PLAY Animation—HIV: The AIDS Virus