Infectious Agents Pathogen an organism that causes disease

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. Copyright © 2010 Pearson Education, Inc.

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 Nucleoid region containing circular DNA chromosome Flagellae Spherical (cocci) Plasmid Spiral (spirochetes) 1 µm Copyright © 2010 Pearson Education, Inc. Figure 18. 1

Infectious Agents - Bacteria § Bacteria reproduce through binary fission. 1 2 Copyright © 2010 Pearson Education, Inc. 3 4 Figure 18. 2

Infectious Agents - Bacteria § Bacteria can reproduce rapidly. § Under ideal conditions a population can double in 20 minutes Noon 2 bacteria Chicken salad sandwich 2: 00 p. m. 128 bacteria 4: 00 p. m. 8192 bacteria 8: 00 p. m. Over 33 million bacteria Copyright © 2010 Pearson Education, Inc. Figure 18. 3

Infectious Agents - Bacterial diseases are caused by toxins secreted by bacteria. Copyright © 2010 Pearson Education, Inc. Table 18. 1

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 Staphylococcus aureus (MRSA) has recently caused the deaths of otherwise healthy young athletes. Copyright © 2010 Pearson Education, Inc.

Infectious Agents - Viruses § Viruses consist of nucleic acid surrounded by a protein sheath or coat, and are not classified as living organisms because they. . 1. Cannot reproduce by themselves; require a host cell 2. Are not composed of cells 3. Also do not have cytoplasm or organelles, and cannot produce toxins Copyright © 2010 Pearson Education, Inc.

Infectious Agents - Viruses § The genome of a virus can be DNA or RNA. Surface protein Membrane envelope Reverse transcriptase Capsid 0. 01 µm Genome: Single-stranded DNA or RNA or Double-stranded DNA or RNA Copyright © 2010 Pearson Education, Inc. Figure 18. 4

Infectious Agents - Viruses § Viral replication is carried out by hijacking the host cell’s transcription and translation processes. 3 2 1 RNA Reverse transcription Transcription and translation DNA Host cell Viral genomes (RNA) 4 Viral proteins Copyright © 2010 Pearson Education, Inc. Figure 18. 5

Infectious Agents - Viruses PLAY Animation—Structure and Reproduction of Viruses Copyright © 2010 Pearson Education, Inc.

Infectious Agents - Viruses Examples of Viral Diseases Copyright © 2010 Pearson Education, Inc. Table 18. 2

Infectious Agents - Eukaryotic Pathogens § Protozoans, worms, and some fungi can infect animals, including humans. Copyright © 2010 Pearson Education, Inc. Table 18. 3

Infectious Agents - Prions § A prion is a misfolded protein. (a) Normal prion protein has more helical regions. (b) Misfolded prion protein has more pleated regions. Amino acid chain 0. 001 µm Copyright © 2010 Pearson Education, Inc. Figure 18. 6

Transmission of Infectious Agents § Common Methods of Transmission (a) Direct contact (c) Indirect contact Copyright © 2010 Pearson Education, Inc. (b) Vector-borne (d) Inhalation (e) Ingestion Figure 18. 8

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. Copyright © 2010 Pearson Education, Inc.

The Body’s Response to Infection: The Immune System Pathogens 3 Lines of Defense § Nonspecific Physical 1 Nonspecific § Skin, Mucous § Nonspecific Cellular § Macrophage, Phagocytes Skin 2 Nonspecific § Specific § Antibodies § Lymphocytes: § B-Cells, T-Cells Copyright © 2010 Pearson Education, Inc. Macrophage 3 Specific Lymphocytes Figure 18. 9

The Body’s Response to Infection: The Immune System - Skin and Mucous Membranes Nonspecific Immune Response § Skin § Sheds, takes pathogens with it § Has low p. H, repels microorganisms § Glands in skin secrete chemicals to slow bacterial growth § Mucous Membranes § Mucous traps pathogens § Can be sneezed, coughed away Copyright © 2010 Pearson Education, Inc.

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 Copyright © 2010 Pearson Education, Inc. Figure 18. 10

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 Copyright © 2010 Pearson Education, Inc.

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) Copyright © 2010 Pearson Education, Inc.

The Body’s Response to Infection: The Immune System - Inflammation Copyright © 2010 Pearson Education, Inc.

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 Copyright © 2010 Pearson Education, Inc. Figure 18. 11

The Body’s Response to Infection: The Immune System - Fever Nonspecific Immune Response § Fever – temperature above range of 9799º F § Macrophages can release pyrogens, which cause temperature to increase § Increased temperature inhibits bacterial growth § Increases metabolism of healthy cells Copyright © 2010 Pearson Education, Inc.

The Body’s Response to Infection: The Immune System - The Third Line of Defense: Lymphocytes Specific Immune Response § 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. Copyright © 2010 Pearson Education, Inc.

The Body’s Response to Infection: The Immune System - The Third Line of Defense: Lymphocytes Specific Immune Response Tonsils and adenoid: Type of lymph node Thymus: Where some lymphatic cells go to mature Bone marrow: Produces some lymphatic cells Spleen: Stores and purifies blood; contains high concentration of lymphocytes Lymph nodes: Store cells and filter out bacteria and other unwanted substances to purify the lymphatic fluid; become swollen and painful when infection occurs Lymphatic vessels: Transport fluid from tissues to lymph nodes Copyright © 2010 Pearson Education, Inc. Figure 18. 12

The Body’s Response to Infection: The Immune System - The Third Line of Defense: Lymphocytes § B and T cells produce antigen receptors that fit on a portion of a particular antigen. (a) B lymphocyte (b) T lymphocyte B-cell receptors Antibodies B cell T-cell receptors T cell Viruses Bacteria Antigen Virus-infected cell Copyright © 2010 Pearson Education, Inc. Figure 18. 13

The Body’s Response to Infection: The Immune System - The Third Line of Defense: Lymphocytes Specific Immune Response § 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 Copyright © 2010 Pearson Education, Inc.

The Body’s Response to Infection: The Immune System - The Third Line of Defense: Lymphocytes Specific Immune Response § 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 Copyright © 2010 Pearson Education, Inc.

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 Copyright © 2010 Pearson Education, Inc.

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. Copyright © 2010 Pearson Education, Inc.

The Body’s Response to Infection: The Immune System - Self vs. Non-self § When the immune system is not selftolerant, it can result in auto-immune disease – when the system attacks some part of the body. § Multiple sclerosis is 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. Copyright © 2010 Pearson Education, Inc.

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) Copyright © 2010 Pearson Education, Inc.

The Body’s Response to Infection: The Immune System - Humoral and Cell-Mediated Immunity § Humoral Immunity – B cells produce: 1. Antibodies 2. Clonal copies of themself, providing long-term immunity B-cell receptors B cell Antigen Antibodies Clonal population Copyright © 2010 Pearson Education, Inc. Figure 18. 17

Specific Host Defense: Humoral Immunity 1 Clonal Selection: 1) Ag binds specific Ab only 2) Clonal Proliferation 3) Plasma Cell or Memory Cell 4) Ab Produced 5) Memory for next encounter with pathogen 2 3 -5 Copyright © 2010 Pearson Education, Inc.

Specific Host Defense: Humoral Immunity Memory Cells 1) Inject Rabbit with tetanus toxin 2) Primary response: Several days for Clonal Proliferation (Plasma and Memory Cells) 3) Secondary Response: Faster and Stronger (have memory cells) Copyright © 2010 Pearson Education, Inc.

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 Copyright © 2010 Pearson Education, Inc.

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 Copyright © 2010 Pearson Education, Inc.

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 Copyright © 2010 Pearson Education, Inc.

The Body’s Response to Infection: The Immune System - Humoral and Cell-Mediated Immunity Macrophage presents antigen to T cell Viruses T-cell receptors Virus antigen 1 Memory cells will help the body respond more quickly if the pathogen is encountered again. 2 Cytotoxic T cells attack and kill body cells that have become infected with a pathogen. 3 Helper T cells secrete a substance that enhances humoral immunity (B cells) and cell-mediated immunity (T cells). Body cell Clonal population Copyright © 2010 Pearson Education, Inc. Virus Interleukin 2 amplifies immune response. Figure 18. 18

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. Copyright © 2010 Pearson Education, Inc.

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 Copyright © 2010 Pearson Education, Inc.