A communicable disease is a disease that is spread from one living thing to another or through the environment. Pathogens like viruses, bacteria, fungi, protozoans, and rickettsias can cause communicable diseases by entering the body, multiplying, and damaging cells, potentially causing an infection to develop if not fought off by the immune system. Communicable diseases spread through direct contact, indirect contact via contaminated objects or vectors like mosquitoes and ticks, and through airborne transmission when pathogens spread through the air. Preventing the spread involves washing hands, properly handling food, avoiding contact with ill individuals, vaccination, and other strategies.

1. What Are Communicable Diseases?
Lesson 1
When was the last time you had a cold?
How did you treat it?

2. Lesson Objectives
Lesson 1
In this lesson, you will learn to:
• Identify the types of pathogens that cause
communicable diseases
• Describe the ways in which communicable
diseases are spread
• Develop strategies to help prevent communicable
diseases

3. What Are Communicable Diseases?
Lesson 1
Microorganisms and Communicable Diseases
• Although most microorganisms—living
things too small to be seen without a
microscope—are harmless, a few can
cause communicable diseases.
• Knowing how communicable
diseases spread can help you
choose behaviors to reduce
your risk of getting them.

4. Causes of Communicable Diseases
Lesson 1
Pathogens
• Common pathogens include certain viruses, bacteria, fungi,
protozoans, and rickettsias.
• Pathogens cause diseases.
• If the body is not able to fight off an infection, a disease
develops.

5. Causes of Communicable Diseases
Lesson 1
Diseases by Type of Pathogen

6. Causes of Communicable Diseases
Lesson 1
Viruses
• Viruses by themselves are inactive—they need living cells to
reproduce.
• After a virus penetrates a cell (called the host cell), the virus
takes control of the cell to manufacture more viruses.
• The new viruses burst from the cell, usually killing it, and
take over other cells.
• Viruses usually run their course and eventually are killed by
the immune system.
• Antibiotics do not work against viruses.

7. Causes of Communicable Diseases
Lesson 1
Bacteria
• Most bacteria are harmless, and many types are essential
for life.
• When bacteria enter the body, they multiply through cell
division.
• Some bacterial pathogens, such as the ones that cause
tetanus, produce a toxin.
• Bacteria are usually destroyed by the immune system.
• Most bacterial diseases can be treated with antibiotics.

8. Causes of Communicable Diseases
Lesson 1
Other Types of Pathogens
• Fungi are plantlike organisms. Some types can cause
diseases of the skin and diseases of the mucous
membranes.
• Protozoans are single-celled organisms that are larger and
more complex than bacteria.
• Rickettsias are pathogens that resemble bacteria. Often
these organisms enter humans through the bites of insects.

9. How Communicable Diseases Are Transmitted
Lesson 1
Transmission of Communicable Diseases
• Transmission can occur through direct and indirect contact
and through breathing contaminated air.
• If you know how they are spread, you can take precautions
and avoid infection.

10. How Communicable Diseases Are Transmitted
Lesson 1
Direct Contact
• Direct contact includes touching, biting, kissing, and sexual
contact.
• Sneezing and coughing can spray infectious droplets of
saliva or mucus into a nearby person’s eyes, nose, or mouth.
• A pregnant female may also transmit an infection to her
unborn child through the placenta.

11. How Communicable Diseases Are Transmitted
Lesson 1
Indirect Contact
• Contaminated objects: Inanimate objects can become
contaminated with infectious discharges or secretions.
• Vectors: Common vectors include flies, mosquitoes, and
ticks. Lyme disease and malaria are spread by vectors.
• Water and food: Careless handling and storage of food
and water supplies that become contaminated with human
or animal feces are major sources of contamination and
illness.

12. How Communicable Diseases Are Transmitted
Lesson 1
Airborne Transmission
• Airborne transmission is different from direct contact
because the pathogens don’t settle quickly on surfaces.
• You don’t have to be close to an infected person to inhale
the pathogens.
• Diseases that are transmitted this way include chicken pox,
tuberculosis, and influenza.

13. Strategies for Preventing Communicable Disease
Lesson 1
Washing Hands
• Handwashing is the single most effective strategy for
preventing the spread of disease.
• Wash your hands before you prepare food, before you eat,
and after you use the bathroom.
• Make it a habit to wash your hands after handling animals
(especially reptiles) or animal wastes.
• When someone in your home is ill, keep hands clean to
prevent the spread of pathogens.

14. Strategies for Preventing Communicable Disease
Lesson 1
Handling Food Properly
• Foodborne illness occurs in places where food is handled
improperly.
• Always wash your hands before you handle food.
• Use paper towels, not dishcloths or sponges, to keep
surfaces and equipment clean.
• Separate raw meat from other foods. Cook food to its
proper temperature.
• Chill cold and leftover foods quickly to the proper
temperature.

15. Strategies for Preventing Communicable Disease
Lesson 1
Other Prevention Strategies
Avoid sharing eating utensils, makeup, combs and
brushes, and other personal items.
Avoid unnecessary contact with people who are ill.
Cover your mouth when you cough or sneeze.
Be sure you are vaccinated against particular
diseases as recommended by your physician.
Practice abstinence from sexual activity.
Learn to manage stress.

16. Quick Review
Lesson 1
Q. Which of the following is NOT a type of common
pathogen and the disease it causes?
1. Viruses: influenza, bacteria, tuberculosis
2. Cortex: pathenogens, bacteria, cirrhosis
3. Fungi: athlete’s foot, protozoans, malaria
4. Rickettsias: typhus, bacteria, tuberculosis

17. Quick Review - Answer
Lesson 1
A. 2. Cortex: pathenogens, bacteria, cirrhosis
Types of common pathogens and the diseases they cause
do NOT include cortex—pathenogens, bacteria, cirrhosis.
Click Next to attempt another question.

18. Quick Review
Lesson 1
Q. Pathogens can spread through direct and indirect
contact and through breathing contaminated air. Which of
the following is NOT a habit you can adopt to limit
their spread?
1. Washing your hands
2. Inspecting your throat for redness and mucus
3. Covering your mouth when you cough or sneeze
4. Being sure you are vaccinated against particular
diseases as recommended by your physician

19. Quick Review - Answer
Lesson 1
A. 2. Inspecting your throat for redness and mucus
Pathogens can spread through direct and indirect contact
and through breathing contaminated air. Habits that can
be adopted to limit their spread does NOT include
inspecting your throat for redness and mucus.
Click Next to attempt another question.

20. Quick Review
Lesson 1
Q. Your risk of getting a communicable disease is less if
you
1. eat a balanced diet.
2. participate in regular physical activity.
3. avoid the use of tobacco, alcohol, and
other drugs.
4. All of the above

21. Quick Review - Answer
Lesson 1
A. 4. All of the above
Your risk of getting a communicable disease is less if you
eat a balanced diet; participate in regular physical activity;
avoid the use of tobacco, alcohol, and other drugs.
Click Next to attempt another question.

22. Quick Review
Lesson 1
Choose the appropriate option.
Q. The fungus that causes athlete’s True
foot lives in warm, moist places.
It is a pathogen that can be
easily caught at the gym or in False
communal showers.

23. Quick Review - Answer
Lesson 1
A. True. The fungus that causes athlete’s foot lives in
warm, moist places. It is a pathogen that can be easily
caught at the gym or in communal showers.

24. Lesson 1
End of Lesson 1
Click Home to view the Main menu.

25. Quick Review - Answer
Lesson 1
A. Correct! Types of common pathogens and the diseases
they cause do NOT include: cortex—pathenogens,
bacteria, cirrhosis.

26. Quick Review - Answer
Lesson 1
You have answered the question incorrectly. Go back to try
again, or click Next to view the correct answer.

27. Quick Review - Answer
Lesson 1
A. Correct! Pathogens can spread through direct and
indirect contact and through breathing contaminated air.
Habits that can be adopted to limit their spread does
NOT include: inspecting your throat for redness and
mucus.

28. Quick Review - Answer
Lesson 1
You have answered the question incorrectly. Go back to try
again, or click Next to view the correct answer.

29. Quick Review - Answer
Lesson 1
A. Correct! Your risk of getting a communicable disease is
less if you do all of the following: eat a balanced diet;
participate in regular physical activity; avoid the use of
tobacco, alcohol, and other drugs.

30. Quick Review - Answer
Lesson 1
You have answered the question incorrectly. Go back to try
again, or click Next to view the correct answer.

31. Quick Review - Answer
Lesson 1
A. Correct! The fungus that causes athlete’s foot lives in
warm, moist places. It is a pathogen that can be easily
caught at the gym or in communal showers.

32. Quick Review - Answer
Lesson 1
You have answered the question incorrectly. Go back to try
again, or click Next to view the correct answer.

33. What Are Communicable Diseases?
Lesson 1
Microorganisms and Communicable Diseases
• Although most microorganisms—living
things too small to be seen without a
microscope—are harmless, a few can
cause communicable diseases.
• Knowing how communicable
A communicable
diseases spread A communicable
can help you
disease is a disease
disease is a disease
choose behaviors to reduce
that is spread from
your risk ofthat is spread from
getting them.
one living thing to
one living thing to
another or through
another or through
the environment.
the environment.

34. Causes of Communicable Diseases
Lesson 1
Pathogens
• Common pathogens include certain viruses, bacteria, fungi,
protozoans, and rickettsias.
• Pathogens causeAdiseases.
A pathogen
pathogen
is an organism
is an organism
• If the body that causesto fight off an infection, a disease
that causes
is not able
develops. disease.
disease.

35. Causes of Communicable Diseases
Lesson 1
Pathogens
• Common pathogens include certain viruses, bacteria, fungi,
protozoans, and rickettsias.
• Pathogens cause diseases.
• If the body is not able to fight off an infection, a disease
develops.
An infection is a
An infection is a
condition that occurs
condition that occurs
when pathogens
when pathogens
enter the body,
enter the body,
multiply, and
multiply, and
damage body cells.
damage body cells.

36. Causes of Communicable Diseases
Lesson 1
Pathogens
• Common pathogens include certain viruses, bacteria, fungi,
protozoans, and rickettsias.
• Pathogens cause diseases. virus is a
A virus is a
A
piece of genetic
piece of genetic
• If the body is not able to fight off invade
material that invade
material that an infection, a disease
develops. living cells to
living cells to
reproduce.
reproduce.

37. Causes of Communicable Diseases
Lesson 1
Pathogens
• Common pathogens include certain viruses, bacteria, fungi,
protozoans, and rickettsias.
Bacteria
Bacteria
• Pathogens cause diseases.
are single-celled
are single-celled
microorganisms.
• If the body is not able to fight off anmicroorganisms.
infection, a disease
develops.

38. Causes of Communicable Diseases
Lesson 1
Bacteria
• Most bacteria are harmless, and many types are essential
for life.
• When bacteria enter the body, they multiply through cell
division.
• Some bacterial pathogens, such as the ones that cause
tetanus, produce a toxin.
Toxin is a
Toxin is a
• Bacteria are usually destroyed by thethat kills system.
substance immune
substance that kills
cells or interferes
cells or interferes
• Most bacterial diseases can be their functions.
with treated with antibiotics.
with their functions.

39. How Communicable Diseases Are Transmitted
Lesson 1
Indirect Contact
• Contaminated objects: Inanimate objects can become
contaminated with infectious discharges or secretions.
• Vectors: Common vectors include flies, mosquitoes, and
ticks. Lyme disease and malaria are spread by vectors.
Vector is an
Vector is an
• Water and food: usually an
organism, Careless handling and storage of food
organism, usually an
and water supplies such become contaminated with human
arthropod, such as a
arthropod, that as a
tick, that
tick, that
or animal feces are major sources of contamination and
illness. carries and transmits
carries and transmits
pathogens to humans or
pathogens to humans or
other animals.
other animals.