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

In the summer of 1975, many children in Lyme, CT developed a rare form of childhood arthritis

Allen Steere realized the children developed their problems after having a skin rash from a deer tick bite

Steere’s colleague, Dr. Burgdorfer, found an unusual spiral-shaped bacterium in the ticks and the child patients

Steere injected lab mice with the bacterium and they developed similar symptoms = Lyme Disease

So, Lyme disease is caused by a bacterium

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 Suspected pathogen

Injection of organisms from

pure culture

Pathogen

Dead mouse Dead mouse

Dead mouse

Healthy 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 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 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

SkinWound

Bacteria enter the wound

Phagocytes move into the area and engulf the bacteria and cell debris

Capillary

Section 40-2

A series of specific defenses that attack the pathogens = immune response Humoral immunity Cell-mediated immunity Permanent immunity

Antigen = a substance that triggers the immune response (organic molecules on the surface of pathogens)

Antibody = protein that helps destroy pathogens by binding to antigen and attracting phagocytes to engulf and destroy them

Pathogen:Pathogen: any any disease causing agentdisease causing agent Ex. Fungus, Bacteria, Ex. Fungus, Bacteria,

Virus etc.Virus etc. Antigen:Antigen: any any

substance that substance that triggers an immune triggers an immune response. response. Antigens are chemicals Antigens are chemicals

present on the surface present on the surface of viruses, bacteria, of viruses, bacteria, pollen grains etc.pollen grains etc.

Antibody:Antibody: a protein a protein that helps to destroy that helps to destroy pathogens.pathogens.

Antigen-binding

sites

Antigen Antibody

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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 B Cell (a.k.a. B-lymphocyte) is activated by antigens on

the pathogen (will eventually produce antibodies.) Macrophage (a type of phagocyte): engulfs pathogen and

then displays the antigens on its surface. T Cell: binds to activated macrophage (one with the

antigens on surface) and then becomes a helper T cell (or a killer T cell).

Helper T Cell: helps the activated B cell to begin producing antibodies.

Antibodies bind to the pathogen marking them for destruction by other immune cells like phagocytes.

Bacteria With Antigens on Surface

Macrophage

T cell

B cell

A large phagocyte called a macrophage engulfs a bacterium

Circulating antibodies bind to bacterial antigens, helping other immune cells to identify and destroy bacteria

Active B cells proliferate to produce clones of memory cells

Helper T cell assists the activated B cell to develop into an antibody-producing plasma cell

T cell, activated by macrophage, becomes a helper T cell

Antigens are displayed on surface of macrofage after digestion of bacterium

T cell binds to activated macrophage

Section 40-2

Bacterial antigens also stimulate B cells

Plasma cell produces large amounts of antibody proteins, released intothe bloodstream

Immunity that relies on lymphocytes (cells) Killer T cells (cytotoxic T cells) can attack

infected cells and destroy their cell membranes T cells bind to activated macrophages and become

Helper T cells Helper T cells activate Killer T cells. Killer T Cells (a.k.a. cytotoxic T cells) bind to infected

cells, disrupt their cell membranes which causes the contents of the infected cell to leak out and it dies.

Killer T cells are what make organ transplants difficult, because they see the new organ as foreign and begin to attack it = rejection. Rejection can be limited by finding donors that are well

matched to the recipients and by administering drugs to the recipient that will suppress the cell-mediated immune response.

Macrophage

T Cell

Helper T Cell

Killer T Cell

Infected CellAntigens are displayed on surface of macrophage

T cell binds to activated macrophage

T cell, activated by macrophage, becomes a helper T cell

Helper T cell activates killer T cells and B cells

Killer T cells bind to infected cells, disrupting their cell membranes and destroying them

Section 40-2

Here, the smaller cytotoxic T cell or Tc (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

Interval between exposures

First exposure

Second exposure

Time

Ant

ibod

y C

once

ntra

tion

Section 40-2

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 immunefunction moreapparent; appearanceof characteristic diseases such asyeast infections

Almost total loss of cellular immunity; AIDS

Relative HIV concentration

T cell concentration

Section 40-3

Years

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!

ACQUIRED IMMUNODEFICIENCY SYNDROME ACQUIRED IMMUNODEFICIENCY SYNDROME (AIDS)(AIDS)

Worldwide HIV infection, 1999

HIV virus particle

Total population 2007: 6,625,000,000Total population 2007: 6,625,000,000Adults age 15-49 with HIV/AIDS,Adults age 15-49 with HIV/AIDS, 20052005 – 38 mill – 38 millNew HIV infections,New HIV infections, 20052005 – 4.9 mill, – 4.9 mill, 20072007 – 2.5 mill– 2.5 millAdult HIV prevalence (%),Adult HIV prevalence (%), 20052005 - 1.1, - 1.1, 20072007 – 0.8– 0.8Women age 15-49 with HIV/AIDS, Women age 15-49 with HIV/AIDS, 20052005 – 17.5 mill – 17.5 millChildren with HIV/AIDS, Children with HIV/AIDS, 20052005 – 2.3 – 2.3 millmill,, 20072007 – 2.5 – 2.5

millmill

AIDS orphans (ages 0-17), AIDS orphans (ages 0-17), 20032003 – 15 mill – 15 millAIDS deaths,AIDS deaths, 20052005 – 3.1 mill, – 3.1 mill, 20072007 – 2.1 mill– 2.1 mill

The number of people with HIV/AIDS has been The number of people with HIV/AIDS has been decreasingdecreasing..Source: http://hivinsite.ucsf.edu/global?page=cr-00-01Source: http://hivinsite.ucsf.edu/global?page=cr-00-01

 

Viral RNA genome is converted to double-stranded DNA by a virally encoded reverse transcriptase that is present in the virus particle.

The viral DNA is then integrated into the cellular DNA by a virally encoded integrase, along with host cellular co-factors, so that the genome can be transcribed.

Once the virus has infected the cell, two pathways are possible: the virus becomes latent and the infected cell

continues to function the virus becomes active and replicates, and a large

number of virus particles are liberated that can then infect other cells

HIV-1 is the virus that was initially discovered and termed LAV. It is more virulent, relatively easily transmitted, and is the cause of the majority of HIV infections globally.

HIV-2 is less transmittable than HIV-1 and is largely confined to West Africa.

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 109 to 1010 viruses every day, coupled with a high mutation rate and recombinogenic properties of reverse transcriptase.

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

Section 40-4

includes a knowledge of

which may include a

including including

which may consist of

which are classified as

The Study of Cancer

Symptoms Causes Treatments

Benign Malignant X-rays Sunlight Nuclear radiation

Surgery

Tumor Viruses Radiation Chemicals

Drug therapy

Radiation therapy

Blood Type of Donor

A

B

AB

O

Blood Type of Recipient

A B AB O

Unsuccessful transfusion Successful transfusion

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Blood Types (review)Blood Types (review)

Humans: Humans: 4 Main types classified by their antigens4 Main types classified by their antigens Type A: Type A: A antigensA antigens B antibodiesB antibodies Type B: Type B: B antigensB antigens A antibodiesA antibodies Type AB: Type AB: A & B antigensA & B antigens no antibodiesno antibodies Type O: Type O: no antigensno antigens A&B antibodiesA&B antibodies