1. Causes of Communicable Diseases
A disease is an unhealthy condition of the body or mind. There are two basic types of disease. A communicable disease, such as a cold, is a disease that spreads from person to person. A noncommunicable disease, such as cancer, is a disease that doesn’t spread from person to person- you can’t catch it from somewhere else.

2. Causes of Communicable Diseases
Communicable diseases are caused by pathogens (germs). An infection results when germs invade the body, multiply, and cause harm to body cells. Sometimes the body can fight off an infection, if it cannot, disease occurs.

3. Disease-Causing Germs
Viruses- smallest and simplest of disease-causing organisms. Viruses cause colds, the flu, measles, rabies and AIDS.
Bacteria- One-celled organisms similar to plants. Bacterias cause strep throat, tuberculosis, Lyme disease, and whooping cough.

4. Disease-Causing Germs (cont.)
Fungi- One- or many-celled primitive plants such as molds. Fungi cause Athlete’s foot, jock itch, ringworm, and vaginitis.
Protozoa- One-celled organisms similar to animals. Protozoa cause malaria, dysentery, and toxoplasmosis.

5. How Germs Are Spread
Direct contact. Germs can be passed on to you if you touch an infected area on another person (i.e. skin infection and rashes). Some germs, such as the virus that causes AIDS, are spread through direct sexual contact.

6. How Germs Are Spread (cont.)
Indirect contact. Germs may be passed on to you when someone sneezes or coughs near you. Germs may also be shared if you share cups, eating utensils, or other personal items with a sick person.

7. How Germs Are Spread (cont.)
Contact with animals. You can get an infection from an animal or insect bite. The germ that causes rabies is spread that way.
Other contact. You can get an infection from eating or drinking contaminated food or water. Salmonella, a type of food poisoning, is spread this way.

8. The Body’s Defenses
Even though you are exposed to millions of germs each day, you aren’t sick all the time. This is because your body has strong barriers to keep germs out. Your skin & mucous membranes are your body’s first line of defense.

9. The Body’s Defenses (cont.)
Skin covers the outside of your body and mucous membranes cover the inner parts of your body such as your nose, throat and mouth. Both of these act to keep germs out of your body.
Saliva, tears, and gastric juices all contain chemicals that attack and destroy certain germs.
If germs do get into the body, the body responds with general reactions.

10. General Reactions
General reactions are referred to as “general” because they are the same no matter what germ has entered your body.
Special blood cells surround germs and destroy them.
A chemical is released that stops viruses from reproducing.
Fever kills some germs and makes it hard for others to reproduce.

11. The Immune System
If germs somehow get past the barriers and then survive the general reactions, your body has another line of defense- your immune system. This is a group of cells, tissues and organs that fights specific germs.

12. The Immune System (cont.)
Lymphocytes, white blood cells that attack germs, are an important part of the immune system. When germs enter your body, some lymphocytes multiply and attack them. Other lymphocytes produce antibodies, chemicals that are specifically manufactured to fight a particular invading substance. If the same germ enters your body again, your immune system “remembers” how to produce the correct antibodies, giving you resistance to infection, or immunity.

13. The Immune System Response
Each type of germ carries unique chemicals, called antigens, on its surface. Your immune system recognizes these antigens as invaders.
For each antigen, your immune system produces an antibody. This antibody is specifically produced to fight that antigen.
Each antibody attaches to an antigen like a key in a lock. This kills the germ, makes it harmless, or marks it for attack by other lymphocytes.