35.1 Infectious Disease

Key Questions

  • What causes infectious disease?

  • How are infectious diseases spread?

Vocabulary

  • infectious disease

  • germ theory of disease

  • Koch's postulates

  • zoonosis

  • vector

Taking Notes

Two-Column Table Use a two- column table to list the ways diseases are spread and describe each way.

THINK ABOUT IT about it For thousands of years, people believed that diseases were caused by curses, evil spirits, or vapors rising from foul marshes or dead plants and animals. In fact, malaria was named after the Italian words mal aria, meaning “bad air.” This isn't all that surprising, because, until microscopes were invented, most causes of disease were invisible to the human eye!

Causes of Infectious Disease

What causes infectious disease?

During the mid-nineteenth century, French chemist Louis Pasteur and German bacteriologist Robert Koch established a scientific explanation for infectious disease. Pasteur's and Koch's observations and experiments led them to conclude that infectious diseases occur when microorganisms cause physiological changes that disrupt normal body functions. Microorganisms were commonly called “germs,” so this conclusion was called the germ theory of disease. That's unfortunate now, because the word germ has no scientific meaning.

Agents of Disease If germ isn't a scientific term, how should we describe the causes of infectious disease? Infectious diseases can be caused by viruses, bacteria, fungi, “protists”, and parasites. Except for parasites, most of these disease-causing microorganisms are called pathogens. Figure 35–1 provides more information and examples of pathogens and parasites.

An illustration showing five agents of diseases.

FIGURE 35–1 Examples of Agents of Disease Infectious diseases are caused by pathogens and parasites—organisms that invade a body and disrupt its normal functions.

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Table of Contents

Miller & Levine Biology
About the Authors
Changing the World of Biology Education
Contents
Diversity of Life: A Visual Guide DOL•1–DOL•64
Labs and Activities
Features
UNIT 1 The Nature of Life
1 The Science of Biology
2 The Chemistry of Life
Unit Project
UNIT 2 Ecology
3 The Biosphere
4 Ecosystems and Communities
5 Populations
6 Humans in the Biosphere
Unit Project
UNIT 3 Cells
7 Cell Structure and Function
8 Photosynthesis
9 Cellular Respiration and Fermentation
10 Cell Growth and Division
Unit Project
UNIT 4 Genetics
11 Introduction to Genetics
12 DNA
13 RNA and Protein Synthesis
14 Human Heredity
15 Genetic Engineering
Unit Project
UNIT 5 Evolution
16 Darwin's Theory of Evolution
17 Evolution of Populations
18 Classification
19 History of Life
Unit Project
UNIT 6 From Microorganisms to Plants
20 Viruses and Prokaryotes
21 Protists and Fungi
22 Introduction to Plants
23 Plant Structure and Function
24 Plant Reproduction and Response
Unit Project
UNIT 7 Animals
25 Introduction to Animals
26 Animal Evolution and Diversity
27 Animal Systems I
28 Animal Systems II
29 Animal Behavior
Unit Project
UNIT 8 The Human Body
30 Digestive and Excretory Systems
31 Nervous System
32 Skeletal, Muscular, and Integumentary Systems
33 Circulatory and Respiratory Systems
34 Endocrine and Reproductive Systems
35 Immune System and Disease
Unit Project
A Visual Guide to The Diversity of Life
HOW TO USE THIS GUIDE
THE TREE OF LIFE
Bacteria
Protists
Fungi
Plants
Animals
Appendices
Appendix A Science Skills
Appendix B Lab Skills
Appendix C Technology & Design
Appendix D Math Skills
Appendix E Periodic Table
Glossary
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C
D
E
F
G
H
I
J
K
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M
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P
Q, R
S
T
U
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W
X, Y, Z
Index
A
B
C
D
E
F
G
H
I
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K
L
M
N
O
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Q
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U
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