Infectious DiseaseInfectious Disease

Disease that can pass from one person to another

Also known as communicable diseases

1860s1860s Joseph Lister

British surgeon hypothesized that microorganisms cause infections

Used carbolic acid to wash his hands and instruments before surgery/ covered patients bandages with it after surgery

This reduced the deaths from infections from 45% to 15%

Louis Pasteur French scientist showed

that microorganisms causes certain diseases

Showed that killing these microorganisms could prevent spread of the diseases

Led to pasteurization (heating process widely used today to kill microorganisms in foods like milk)

PathogensPathogens

Pathogens Micro-organisms that enter the body & multiply to cause disease

4 major groups of pathogens: Bacteria Virus Fungi Protists

BacteriaBacteria Single-cell micro-organisms

Release toxins

Examples Escherichia coli, a type of bacteria, is a

leading cause of food-borne illnesses Tetanus – bacteria on objects/soil Staphylococcus and Streptococcus can

cause skin and respiratory infectionsStaph

VirusVirus Smallest parasite

Enter cells, multiply & take over

Examples: Influenza virus causes flu West Nile virus Human Immunodeficiency Virus (HIV) 

HIV

FungiFungi Not all are harmful

Mushroom/ yeast/ mold/ fungi

Some cause rashes Ringworm & athlete’s foot

Spreading Infectious Spreading Infectious DiseaseDisease

Pathogens need food and a place to live & reproduce Your body may the perfect place for this!

You can become infected by a pathogen in one of several ways: Physical contact with infected person Contact with contaminated object Environmental sources Contact with contaminated animals

Person-to-Person Transfer Person-to-Person Transfer Direct physical contact (kissing, hugging, shaking hands)

Ex: If you kiss someone with a cold sore, cold sore viruses can get into your body too.

Indirect contact (sneeze, cough) Ex: If a person with pneumonia sneezes, pathogens get into the air. If

someone else inhales them, they may catch pneumonia too. Colds, flu and tuberculosis can spread by coughing and sneezing.

Animal BitesAnimal Bites If an infected animal bites a

person then it can pass the pathogen to that person.

Examples: Rabies (dogs,raccoons) Lyme disease (ticks) Malaria (mosquitoes)

Contaminated Object Contaminated Object Some pathogens can survive for a time

outside a person’s body.

Water and food can become contaminated.

People can pick up pathogens by using objects that have been touched by an infected person.

Examples: Colds and flu Tetanus bacteria

Environmental Environmental Sources Sources

Some pathogens occur naturally in the environment.

Examples: Bacteria causing tetanus live in

soil/water Bacteria causing botulism (severe

form of food poisoning) lives in soil

www.nature.com

The Body’s DefensesThe Body’s Defenses

Your body has 3 first-lines of defense against pathogens which trap and kill most pathogens with which you come into contact. Skin Breathing passages Mouth and stomach

Go to http://www.diseasedetectives.org/online_activities and complete the following:

“Disease Detectives”choose 3 occupations involving infectious disease and summarize what each does

“Microbe Gallery”Choose 3 and answer:

What it is ,where it is found and 2 other factsLISTEN TO THE 3 STORIES LISTED BELOW AND WRITE 2 THINGS YOU LEARN FROM EACHwrite 2 things you learn from each story (total of 4)

http://m.youtube.com/watch?v=sYoCIfeVcFk

http://m.youtube.com/watch?v=1uBh7Z8QXUE

http://m.youtube.com/watch?v=HZcjGedqRR8

THIS CAN ALL BE DONE ON IPAD OR PAPER

Now what???

Part 2

General DefensesGeneral Defenses Despite the barriers, pathogens can still get into your body.

Cells of the body release chemicals that trigger an inflammatory response when they are damaged. (2nd line of defense) Fluid and certain types of white blood cells leak from blood

vessels into nearby tissues to fight the pathogens. All white blood cells fight disease but it is the phagocytes

that are involved in the inflammatory response. Phagocytes engulf the pathogen & breaks it down to

destroy it. During the inflammatory response, blood vessels widen to

increase blood flow, making the area red & swollen.

The Immune SystemThe Immune System If the infection by a pathogen is severe enough to cause a fever, it

triggers the 3rd line of defense- the immune response. Cells of the immune system distinguish between different kinds of

pathogens and react to each with a specific defense. White blood cells that do this are called lymphocytes (T-lymphocytes

and B-lymphocytes aka T-cells and B-cells). T-cells distinguish one kind of pathogen from another by

recognizing markers (called antigens) on each pathogen. These are markers on cells that the immune system recognizes either as part of your body or coming from outside your body. Each person’s antigens are different from other peoples’.

B-cells produce chemicals called antibodies to destroy the pathogens. Antibodies lock onto antigens like puzzle pieces. When antibodies

bind to the antigen of a pathogen, they mark it for destruction.

Preventing Infectious Preventing Infectious DiseaseDisease

As people recover from some diseases, they develop immunity to the diseases. Immunity is the body’s ability to destroy pathogens before

they can cause disease. 2 kinds of immunity: active and passive

Active immunity: occurs when a person’s own immune system produces antibodies in response to the presence of a pathogen Ex: chicken pox; unlikely to get them again once you’ve had

them Usually lasts for many years and sometimes for life

Active immunity can be gained by having the disease or by being vaccinated against it. A vaccine is made of pathogens that have been weakened or

killed but can still trigger the immune response.

Preventing Infectious DiseasePreventing Infectious Disease

Passive immunity Occurs when the antibodies that fight the pathogen come from

another source rather than from the person’s own body. Ex: If bitten by a dog, a rabies shot is given which contains

antibodies to the rabies antigen. Usually lasts no more than a few months.