Immune System:Bacteria & Viruses

How They Infect and Cause Disease

Page 134

Pathogens

“Sickness-Makers!”

Disease-causing agent

Germ Theory of Disease

The idea that infectious diseases are caused by microorganisms, or germs

Koch’s Postulates

series of guidelines used to identify the microorganism that causes a specific disease

Koch’s Continued1. The pathogen NEEDS to be found in the Sick Patient

(and should not be found in a healthy one)

2. The pathogen MUST be isolated and grown in the lab in pure culture.

3. When the cultured pathogens are placed in a new host, they should cause the same disease.

4. The injected pathogen should be isolated from the 2nd host. It should be identical to the original pathogen.

Why are these rules important? Because identifying pathogens that cause disease is the first step toward preventing or curing the symptoms they produce.

Agents of Disease

1. Viruses

2. Bacteria

3. Protists

4. Worms

5. Fungi

Virus

They invade and replicate w/in living cells.

They 1.) attach to the surface of a cell,2.) insert their DNA, and 3.)take over many of the functions of the host cell

(e.g.; the common cold, influenza, smallpox, and warts)

Bacteria

Bacteria cause disease by breaking down the tissues of the infected organism for food or by releasing toxins that harm the body

(e.g.; streptococcus infections, diphtheria, botulism, and anthrax)

Most bacteria are harmless to humans

Protists

Protists live in the bloodstreams of vertebrate animals & feeds off the nutrients in the host organism's blood.

(e.g.; Trypanosoma causes African sleeping sickness – found in the water, Malaria is caused by Plasmodium – injected by mosquitoes)

Worms

Flatworms and roundworms are also responsible for a number of serious human diseases

(e.g.; Contact worms directly by stepping on them, eating them out of raw meat, worms frequently infect people working in rice fields)

Fungi

Infects by penetrating the outer layers of skin.

Other types of fungi infect the mouth, the throat, and even the fingernails and toenails.

(e.g.; Ringworm and Athletes Foot)

How Diseases are Spread

1. Physical Contact (coughing/ sneezing)

2. Contaminated Food or Water

3. Infected Animals

Vectors

animal that carries disease-causing agents from person to person

Two types of lymphocytes

• B Lymphocytes (memory B Cells): provide immunity against antigens and pathogens in the bodily fluids

• T Lymphocytes (T cells): provide defense against abnormal cells and pathogens inside living cells

Concept Maps on page 133