Health: The Ultimate Treasure · Lesson 3 of 8
Signs, Symptoms, and Types of Disease
“Learn how signs and symptoms reveal illness, what pathogens are, and how diseases are classified by cause and spread.”
• Distinguish a symptom from a sign of illness. • Define disease and explain how it can disturb normal body or mind function. • Define pathogens and identify major pathogen groups discussed in the chapter. • Distinguish communicable diseases from non-communicable diseases. • Explain why the cause of a disease helps determine whether it can spread from person to person.
How Do We Know That We Are Unwell?
Our bodies usually follow familiar patterns: we have a normal range of temperature, energy, appetite, breathing, movement, and other functions. When something is wrong, the change may be felt by the person or detected by someone else. Doctors use both kinds of information to understand what might be happening.
A change or problem that the person experiences, such as pain, tiredness, dizziness, or nausea.
A change that can be observed or measured, such as fever, rash, swelling, or high blood pressure.
| Example | Sign or symptom? | Why |
|---|---|---|
| Headache | Symptom | The person feels it. |
| High body temperature | Sign | It can be measured with a thermometer. |
| Skin rash | Sign | It can be observed. |
| Dizziness | Symptom | It is mainly experienced by the person. |
| Swelling | Sign | It can usually be seen or examined. |
What Is a Disease?
A disease is a condition in which the normal functioning of the body or mind is disturbed. Sometimes one organ is mainly affected; in other cases an entire organ system may be involved. Diseases do not all have the same cause. Some result from infection, while others are connected with nutrition, lifestyle, environment, or other factors.
A condition that interferes with the normal working of the body or mind.
Pathogens Cause Infectious Disease
Many communicable diseases are caused by organisms or infectious agents called pathogens. The chapter introduces several kinds: bacteria, viruses, fungi, protozoa, and worms. These are not all alike. A virus behaves differently from a bacterium, and a worm is very different from a single-celled protozoan. What they have in common is that some members of these groups can cause disease.
A disease-causing organism or infectious agent.
| Pathogen group | Examples of diseases from this chapter |
|---|---|
| Viruses | Common cold or influenza, chickenpox, measles, Hepatitis A, dengue |
| Bacteria | Tuberculosis, cholera, typhoid |
| Protozoa | Malaria |
| Worms | Ascariasis |
| Fungi | Included as a pathogen group; no specific disease example is developed in the chapter table |
Two Broad Groups of Disease
A useful first classification asks whether the disease is caused by a pathogen and can spread between people. Communicable diseases are infectious diseases that can pass from one host to another through routes such as air, contact, contaminated food or water, or vectors. Non-communicable diseases do not spread in this way and are not caused by pathogens.
A disease caused by a pathogen that can spread from one person or host to another, directly or indirectly.
A disease that is not caused by an infectious pathogen and does not spread from person to person in the way an infection does.
Problem
Classify influenza, typhoid, diabetes, asthma, and chickenpox as communicable or non-communicable.
- 1.Influenza is caused by a virus and spreads between people, so it is communicable.
- 2.Typhoid is caused by bacteria and can spread through contaminated food or water, so it is communicable.
- 3.Chickenpox is caused by a virus and spreads between people, so it is communicable.
- 4.Diabetes and asthma are not infections passed from one person to another, so they are non-communicable.
Duration Is Another Useful Clue
Some illnesses last only a short time, while others continue for months or years and may require regular care. Duration does not by itself tell us whether a disease is communicable. A disease can be long-lasting without being infectious, and an infectious disease may be brief or prolonged. Later we will study chronic non-communicable diseases in more detail.
Not every disease is caused by 'germs'. Nutrient deficiencies, lifestyle factors, environmental conditions, and other biological causes can also disturb normal body function.
Quiz
Which is a symptom rather than a sign?
Which statement best defines a disease?
Which of these is a pathogen group named in the chapter?
Which pair contains two communicable diseases?
Why is the cause of a disease important when classifying it?
Practice Problems
- Write one example each of a sign and a symptom and explain the difference.
- Explain why a person can have a disease even when no pathogen is involved.
- Create a two-column classification for these conditions: influenza, diabetes, typhoid, asthma, measles, dengue.
- Why is it incorrect to say that every long-lasting disease is non-communicable?
- Describe the relationship among the terms disease, pathogen, communicable disease, and non-communicable disease.
Key Takeaways
• Symptoms are felt by the person; signs can be observed or measured. • A disease disturbs normal body or mind function. • Pathogens include disease-causing bacteria, viruses, fungi, protozoa, and worms. • Communicable diseases are caused by pathogens and can spread between hosts. • Non-communicable diseases are not infectious and do not spread from person to person in the same way.