1. The Biology of Disease Infectious Agents Modes of Infection
Germ Theory of Disease
Defense Against Disease

2. Disease
Any change (other than an injury) that disrupts normal body functions
Inherited/genetic
Environmental factors
Infectious agents (pathogens)
Viruses
Bacteria
Protists
Fungi
Large parasites
Prions*
Incubation period
3-14 days

3. Miasma, curses, and more
“As long as (individuals) believed that microorganisms could arise from nonliving substances, scientists saw no purpose in considering how diseases were transmitted or how they could be controlled.” - Black, 1996

4. Germ Theory of Disease Refuted theory of spontaneous generation
Infectious disease is caused by germs (L. “to beget”) or pathogens.

5. Development of the Germ Theory of Disease
Ignaz Semmelweis (1840s)
Louis Pasteur (1860s)
Joseph Lister (1860s)
Robert Koch (1870s)
Dmitri Ivanovsky (1890s)
Development of the Germ Theory of Disease

6. Pathogen What it is What it causes Viruses Bacteria Protists Fungi
Noncellular particles
that invade living cells
AIDS, polio, smallpox, measles, colds, influenza, chicken pox, SARS, bird flu
Bacteria
Unicellular prokaryotes;
from Domain Bacteria
gonorrhea, botulism, pneumonia, strep throat, boils/acne, tuberculosis, meningitis, cholera, tetanus
Protists
Any eukaryote that is
NOT a plant, an animal, or a fungus;
from Kingdom Protista
malaria, amoebiasis/amoebic dysentery, African sleeping sickness
Fungi
Eukaryotic heterotrophs w/ chitinous CWs; from Kingdom Fungi
ringworm, athlete’s foot, San Joaquin Valley fever (lung disease), histoplasmosis
Worms
Parasitic animals from the
phyla Platyhelminthes & Nematoda
schistosomiasis,
beef tapeworm
Prions*
Misfolded proteins that cause other normal proteins to misfold and cause widespread damage
Mad-cow disease, Creutzfeldt-Jakob disease, scrapie

7. How do pathogens cause disease?
Rapid multiplication interferes with normal cell function
Destruction of body cells and tissues
Production of poisons or toxins that kill cells or interfere with their functions

8. Koch’s Postulates
set of rules that is used to determine whether a specific pathogen is the cause of a specific disease
Pathogen should always be found in the body of a sick organism and never in a healthy one
Pathogen should be isolated and grown in pure culture
When purified pathogens are placed in a new host, it should cause the same disease as in the first host
When the infected pathogen is isolated from the new host, it should be identical to the original pathogen

9. Discovering the cause of Lyme disease
Allen Steere (Yale University)
Lyme, Connecticut
Observations
39 children, several adults
Pain, joint inflammation
Summer-early fall
Insect bite then expanding skin rash
Problem
What is causing Lyme disease?

10. Using Koch’s Postulates
Skin rash linked to deer tick (Ixodes scapularis) bite
Spiral bacteria (Borrelia burgdorferi) found in ticks
B. burgdorferi found in patients with Lyme disease
Hypothesis: B. burgdorferi causes Lyme disease
Postulate 1
B. burgdorferi was grown in pure culture
Postulate 2
B. burgdorferi introduced into lab mice caused them to develop symptoms similar to those of children
Postulate 3
B. burgdorferi was obtained from sick mice
Conclusion: B. burgdorferi is a pathogen that causes Lyme disease
Postulate 4

11. Modes of Infection food- and water-borne ex. tapeworms, amoebiasis
airborne ex. droplets of pathogens expelled into the air via coughing,
sneezing, talking
actual contact ex. common cold, STDs
carriers/vectors:
organisms that carry pathogens from person to person ex. mosquitoes, tsetse fly

12. Two major types of defenses
INNATE (NONSPECIFIC)
IMMUNITY
Rapid responses to a
broad range of microbes
ACQUIRED (SPECIFIC) IMMUNITY
Slower responses to
specific microbes
External defenses
Internal defenses
Skin
Mucous membranes
Secretions
Phagocytic cells
Antimicrobial proteins
Inflammatory response
Natural killer cells
Humoral response
(antibodies)
Cell-mediated response
(cytotoxic
lymphocytes)
Invading
microbes
(pathogens)

13. Pathogen Awareness Project
3D model of a chosen pathogen that affects Filipinos (pref. recycled materials, NO STYRO!)
Include a write-up with the following information on an A3 sized sheet:
Characteristics of the pathogen
Modes of transmission
Incubation period
Symptoms induced
Prevention/cure
Interesting trivia/statistics
Due Oct 15th, 12NN
CAMIA
1,2 – Virus
3,4 – Bacteria
5,6 – Large parasite
7,8 – Virus
9,10 - Bacteria
CHAMPACA
1,2 – Virus
3,4 – Bacteria
5,6 – Large parasite
7,8 – Virus
9,10 – Large parasite