 Why do you get sick?  How do you get better?  What’s the best way for you to avoid getting sick in the first place?

 For years, people thought diseases were caused by curses, spirits, etc.  In the nineteenth century, Louis Pasteur and Robert Koch concluded that infectious diseases were caused by microorganisms (germs) = the Germ Theory of Disease

 Koch developed a series of guidelines to identify the microorganism that causes a specific disease  1. The pathogen should always be found in the body of a sick organism and should not be found in a healthy one.  2. The pathogen must be isolated and grown in the laboratory in pure culture.  3. When the purified pathogens are placed in a new host, they should cause the same disease that infected the original host.  4. The injected pathogen should be re-isolated from the second host and be identical to the original pathogen.  Disease no longer seems unavoidable consequences, but now pathogens could be identified and diseases could be prevented or cured.

The pathogen should always be found in the body of a sick organism and should not be found in a healthy one. The pathogen must be isolated and grown in the laboratory in a pure culture. When purified pathogens are placed in a new host, they should cause the same disease that infected the host. The very same pathogen should be reisolated from the second host. And it should be the same as the original pathogen. No pathogen Suspected pathogen Injection of organisms from pure culture Pathogen Dead mouse Healthy mouse Suspected pathogen grown in pure culture. Section 40-1

 Disease = any change, other than injury, that disrupts the normal functions of the body  Diseases can be inherited (ex. Hemophilia)  Diseases can be caused by materials in the environment (ex. Cigarette smoke)  Diseases can be produced by agents (ex. Bacteria, viruses, fungi) = pathogens  Pathogens = “sickness-makers”  Diseases caused by pathogens = infectious diseases, because they enter, or infect, the body

 The human body provides great conditions for pathogenic growth  You have many different microorganisms living in your body that are actually harmless or beneficial  However, some microorganisms are dangerous  Some bacteria break down body tissues and others release toxins (poisons)  Some protists, fungi, and worms are parasites that live inside you and use up your nutrients or destroy blood/nerve cells  Viruses are nonliving pathogens that use a host cell to make copies of the virus and destroy other cells

 Infectious diseases are spread  From person to person: coughing, sneezing, or physical contact ▪ Common cold, mumps, measles, influenza, STDs (AIDS), meningitis, athlete’s foot  Contaminated water and/or food ▪ Cholera, dysentery, E.coli infection, salmonellosis  Vectors: infected animals (ticks/mosquitoes) ▪ Lyme disease, malaria, West Nile virus, rabies

Viruses Protists Worms Fungi Disease Agent That Causes Disease Method of Transmission Common cold Influenza Chicken pox Measles Tuberculosis Meningitis Cholera Tetanus African sleeping sickness Malaria Amoebic dysentery Schistosomiasis Beef tapeworm Athlete’s foot Ringworm Rhinovirus Two types (A, B), plus subtypes Varicella Paramyxovirus Mycobacterium tuberculosis Neisseria meningitidis Vibrio cholerae Clostridium tetani Trypanosoma Plasmodium Entamoeba histolytica Schistosoma Taenia saginata Imperfect fungi Airborne; direct contact with infected person Airborne; droplet infection; direct contact with infected person Airborne; direct contact with infected person Droplets in air; direct contact with secretions of infected person Droplets in air; contaminated milk and dairy products Direct contact with a carrier Contaminated drinking water Contaminated wound; usually puncture wound Spread by tsetse fly Spread by Anopheles mosquitoes Contaminated drinking water Freshwater streams and rice paddies Contaminated meat Contact with infected person Exchange of hats, combs, or athletic head gear with infected person Section 40-1 Pathogen Types Bacteria

 Drugs have been developed to use against pathogens  Antibiotics = chemicals that kill bacteria without harming the cells of humans or animals )  Penicillin = interferes with the synthesis of cells walls by Eubacteria (breaks down peptidoglycan in their cell walls)  Streptomycin = interferes with bacterial growth by blocking protein synthesis in ribosomes  Antivirals = inhibit the ability of viruses to invade cells or multiply inside cells

 A series of defenses that guard against diseases = body’s protection  Nonspecific defenses = “walls” of the immune system keeping everything out  Specific defenses = “security guards” identifying and inhibiting pathogens

 Skin = most important nonspecific defense  Physical barrier  Acidic environment on surface kills bacteria  Mucus, sweat, tears and saliva  Traps pathogens and removes them from the body by cilia or destroys them using the enzyme lysozyme, which breaks down cell walls  Inflammatory response = reaction to tissue damage caused by injury or infection  Blood vessels around wound expand, white blood cells enter infected tissue and phagocytes (special WBCs) engulf and destroy bacteria, tissue becomes swollen and painful, body temperature increases (fever) to slow pathogen growth and increase circulation and activity of WBCs  Interferon = proteins that “interfere” with the virus  Proteins released by virus-infected cells to help other cells resist viral infection by inhibiting viral protein synthesis, blocking viral replication

 Pathogen: any disease causing agent  Ex. Fungus, Bacteria, Virus etc.  A series of specific defenses that attack the pathogens = immune response  Antigen = a substance that triggers the immune response (organic molecules on the surface of pathogens)  Antigens are chemicals present on the surface of viruses, bacteria, pollen grains etc.  Antibody = protein that helps destroy pathogens by binding to antigen and attracting phagocytes to engulf and destroy them

 Immunity against pathogens in the body fluids (blood/lymph)  Immunity produced by lymphocytes (type of WBC)  B lymphocytes (B cells) produce antibodies to mark pathogens and prevent future infections

 Immunity that relies on lymphocytes (cells)  Killer T cells (cytotoxic T cells) can attack infected cells and destroy their cell membranes  Killer T cells are what make organ transplants difficult, because they see the new organ as foreign and begin to attack it = rejection.

A Killer T Cell Attacking and Killing a Virus-Infected Target Cell Here, the smaller cytotoxic T cell or T c (arrow) is attacking and killing a much larger virus-infected cell. The T cell will survive while the infected cell is destroyed.

 People that survived infectious diseases, never developed the same disease again  Memory B and T cells remain capable of producing specific antibodies to that pathogen, ensuring the disease never gets a chance to develop again

 An immediate active immune response against the pathogen in a vaccine  Vaccination = injection of a weakened or mild form of a pathogen to produce immunity  Prevents serious human diseases by stimulating the immune system to create plasma cells capable of producing the specific antibodies for another possible infection  Active Immunity lasts long term (permanent)

 Antibodies produced by other animals for a pathogen are injected into the bloodstream  The antibodies will produce passive immunity against a pathogen as long as they remain in circulation (several weeks)  Antibodies from the mother are passed to the fetus through the placenta or to the infant in the mother’s milk = maternal immunity  The antibodies will produce passive immunity against most infectious diseases for the first few months of life or longer if breast-fed

 Although the immune system defends the body from potential pathogens, sometimes disorders occur  The immune system may overreact to an antigen, producing discomfort or disease  The cellular nature of the immune response is a potential weak point

 Overreaction of the immune system  Allergies occur when antigens from allergens (pollen, dust, dust mites) bind to mast cells (type of immune cell common in nasal passages)  Activated mast cells release chemicals = histamines, which increase the flow of blood and fluids to the surrounding area (sneezing, runny eyes/nose, etc)  Antihistamines = drugs used to reduce allergy symptoms by counteracting the effects of histamines  Asthma = allergic reaction where smooth muscle contractions reduce the size of air passageways in the lungs making breathing difficult

 The immune system has the ability to distinguish “self” from “nonself”  The immune system makes a mistake and attacks the body’s own cells (“it attacks itself”)  Juvenile-onset diabetes (immune system attacks insulin- producing cells in pancreas)  Myasthenia gravis (attacks neuromuscular junctions)  Multiple Sclerosis (destruction of myelin sheath – attacks nervous system)  Lupus (attacks cells and tissues resulting in inflammation and tissue damage: heart, joints, skin, lungs, blood vessels, liver, kidneys and nervous system)

 Acquired Immune Deficiency Syndrome (AIDS) = when cells of the immune system are weakened by infection  Caused by HIV (human immunodeficiency virus) and spread by contact with body fluids (drug needles, unprotected sexual intercourse, breast milk, blood during birth, blood transfusions)  HIV attaches and destroys most helper T cells, so body is more susceptible to infections  People DO NOT die from HIV/AIDS, they die from the infections they get because the HIV virus has left their immune system unable to respond to the infections

Infection; Immune system eliminates most of HIV Symptoms, such as swollen lymph nodes, are few Loss of immune function more apparent; appearance of characteristic diseases such as yeast infections Almost total loss of cellular immunity; AIDS Relative HIV concentration T cell concentration Section 40-3 Years

Treating HIV/AIDS  There are many different types of drugs being used. Each drug has a different approach:  Stop the virus from attaching to cells.  Stop the virus from creating its protein coat.  Stop the virus from replicating its genetic information.  Doctors are now treating people with HIV with drug cocktails (several different drugs at the same time)  These cocktails have dramatically increased the amount of time people are living with HIV and their quality of life – VERY expensive!

HIV/AIDS in the World Total population 2007: 6,625,000,000 Adults age with HIV/AIDS, 2005 – 38 mill New HIV infections, 2005 – 4.9 mill, 2007 – 2.5 mill Adult HIV prevalence (%), , 2007 – 0.8 Women age with HIV/AIDS, 2005 – 17.5 mill Children with HIV/AIDS, 2005 – 2.3 mill, 2007 – 2.5 mill AIDS orphans (ages 0-17), 2003 – 15 mill AIDS deaths, 2005 – 3.1 mill, 2007 – 2.1 mill The number of people with HIV/AIDS has been decreasing. Source:

Structure and Life Cycle of HIV

Upon entry of Target cells  Viral RNA genome is converted to double-stranded DNA by a virally encoded reverse transcriptase that is present in the virus particle.RNADNAreverse transcriptase  Then the genome can be transcribed.transcribed  Once the virus has infected the cell, two pathways are possible:  the virus becomes latent and the infected cell continues to functionlatent  the virus becomes active and replicates, and a large number of virus particles are liberated that can then infect other cellsactivereplicates

Genetic Variability of HIV  There are two types of HIV (HIV-1 and HIV-2)  HIV differs from many viruses in that it has very high genetic variability.  This diversity is a result of its fast replication cycle, with the generation of 10 9 to viruses every day, coupled with a high mutation rate.diversityreplication cycle  This leads to many variants of HIV in a single infected patient in the course of one day.  This variability is compounded when a single cell is simultaneously infected by two or more different strains of HIV.

 Cells multiply uncontrollably and destroy healthy tissue  Cancer begins when cells lose the ability to regulate cell growth and division  Tumor: mass of growing tissue ▪ Benign: tumors that will not spread to surrounding tissue (non cancerous) ▪ Malignant: tumors that can spread to other tissues and organs invading and destroying tissue (cancerous)  Metastasis: the spread of cancerous tumors beyond their original site to new places in the body  As cancer cells spread, they absorb nutrients, block nerve connections, and prevent proper functioning, disrupting the body’s balance

 Cancer is caused by defects in the genes that regulate cell growth and division  Inherited genes  Viruses: interfere with cell cycle (mitosis) ▪ Ex. Human papilloma virus (HPV: an STD) can lead to cervical cancer or genital warts (non cancerous)  Radiation: causes mutations in DNA ▪ Ex. X-rays, nuclear radiation, sunlight (UV Rays)  Chemicals: cause mutations in DNA ▪ Carcinogens = chemicals that cause cancer ▪ Ex. Chloroform and benzene (industrial solvents used in production of drugs, plastics and synthetic rubber, small component in gasoline), cigarette smoke

 Prevention by protecting your DNA from agents that cause cancer (not smoking, balanced diet with regular exercise)  Treatments  Surgery: remove tumors to prevent spread of cancer ▪ Problem: cancerous tumors spread, so some cancerous cell may remain in the body forming new tumors  Radiation therapy: destroy cancer cells ▪ Problem: also damages healthy cells in the vicinity and there is a limit to how much a person can have  Drug therapy (chemotherapy): using chemicals to destroy cancer cells or just stop the growth of cancer cells ▪ Problem: also damages healthy cells, uncomfortable side-effects

Blood Type of Donor A B AB O Blood Type of Recipient A B AB O Unsuccessful transfusionSuccessful transfusion Prentice Hall Biology Presentation Pro, 2002

Blood Types (review)  Humans: 4 Main types classified by their antigens  Type A: A antigensB antibodies  Type B: B antigensA antibodies  Type AB: A & B antigensno antibodies  Type O: no antigensA&B antibodies