1. Lesson Overview
35.1 Infectious Diseases

2. THINK 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!

3. Causes of Infectious Disease
1900s, Louis Pasteur & Robert Koch established a scientific explanation for disease.
Pasteur’s & Koch’s experiments led them to conclude that infectious diseases are caused by microorganisms.
Microorganisms were commonly called “germs”
-germ theory of disease.

4. Agents of Disease
pathogens—organisms that invade the body and disrupt its normal functions.
Ex.) viruses, bacteria, single-celled eukaryotes, fungi, and parasites.

5. Agents of Disease
Viruses are nonliving particles that replicate by inserting their genetic material into a host cell
ex,) common cold, influenza, chicken pox, and warts.
Bacteria cause disease by breaking down the tissues or by releasing toxins
ex.) streptococcus, diphtheria, botulism & anthrax.
Fungus may infect the surface of the skin, mouth, throat, fingernails and toenails.
ex.) athlete’s foot & ringworm

6. Agents of Disease
The single-celled eukaryote Plasmodium causes malaria.
The single-celled eukaryote Trypanosoma brucei causes African sleeping sickness.
Both are spread to human by insects.
Giardia intestinalis causes infection of the digestive tract and is transmitted in infected water.

7. Agents of Disease
People may be infected with the roundworm from eating infected pork.
The flatworm can be contracted by people working in rice paddies.
Other parasitic worms include tapeworms and hookworms.

8. Koch’s Postulates
Koch’s studies with bacteria led him to develop rules for identifying the microorganism that causes a specific disease.
These rules are known as Koch’s postulates.
Although there are exceptions to these rules, they remain important guidelines for identifying the causes of new and emerging diseases.

10. Symbionts vs. Pathogens
Symbionts=Good Guys
Yeast and bacteria grow in the mouth and throat without causing trouble.
Bacteria in the large intestine help with digestion and produce vitamins.
Pathogens=Bad guys
Some viruses and bacteria directly destroy the cells of their host.
Other bacteria and single-celled parasites release poisons that kill the host’s cells or interfere with their normal functions.
Parasitic worms may block blood flow through blood vessels or organs, take up the host’s nutrients, or disrupt other body functions

11. Symbionts vs. Pathogens

12. Causes of Infectious Disease
What causes infectious disease?

13. Causes of Infectious Disease
What causes infectious disease?
Infectious diseases can be caused by viruses, bacteria, fungi, single-celled
eukaryotes (formerly called protists), and parasites.

14. How Diseases Spread
How are infectious diseases spread?

15. How Diseases Spread How are infectious diseases spread?
Some diseases are spread through coughing, sneezing, physical contact,
or exchange of body fluids.
Some diseases are spread through
contaminated water or food.
Still other diseases are spread to humans
from infected animals. (vectors)