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 coldInfluenza

Chicken pox

Measles

Tuberculosis

Meningitis

CholeraTetanusAfrican sleeping sicknessMalariaAmoebic dysenterySchistosomiasisBeef tapeworm

Athlete’s foot

Ringworm

RhinovirusTwo types (A, B), plus subtypesVaricella

Paramyxovirus

Mycobacterium tuberculosisNeisseria meningitidisVibrio choleraeClostridium tetaniTrypanosoma

PlasmodiumEntamoeba histolyticaSchistosomaTaenia saginata

Imperfect fungi

Imperfect fungi

Airborne; direct contact with infected personAirborne; droplet infection; direct contact with infected personAirborne; direct contact with infected personDroplets in air; direct contact with secretions of infected personDroplets in air; contaminated milk and dairy products

Direct contact with a carrier

Contaminated drinking waterContaminated wound; usually puncture wound

Spread by tsetse fly

Spread by Anopheles mosquitoes

Contaminated drinking waterFreshwater streams and rice paddies Contaminated meat

Contact with infected personExchange 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 ingrowth and increase circulation and activity of WBCs

Interferon = proteins that “interfere” with the virus creases (fever) to slow pathogen 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

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.

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

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