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35.1 Infectious Disease
Objectives: Know…
1)…the differences between viruses
and bacteria.
2)…the differences in how viruses
and bacteria cause disease.
Vocabulary
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Infectious Disease
Germ Theory of Disease
Koch’s Postulates
Zoonosis
Vector
Infectious Disease
• Changes to body physiology
that disrupt normal body
functions caused by
microorganisms
• Germ Theory of Disease:
microorganisms cause
disease
Causes of Infectious
Disease
• What causes infectious disease?
• Infectious diseases can be caused
by viruses, bacteria, fungi, single
celled eukaryotes (protists), and
parasites.
• These “Agents of Disease” are all
called “pathogens” except for
parasites.
Viruses
• Viruses invade and
replicate in living
cells, killing the cells
in the process and
upsetting homeostasis
• Examples: HIV,
Common cold, Flu,
chickenpox, and warts
Bacteria
• Cause disease by
breaking down tissues
(killing cells) or
releasing toxins that
upset homeostasis
• Example: botulism,
anthrax, diptheria, and
Strep.
Fungi
• Can infect
the skin,
mouth,
throat, and
nails
• Example:
athlete’s foot
Single-Celled Eukaryotes
• Used to be called
“Protists”
• Example: Giardia ( an
infection of the
intestines)
Parasites
• Example: trichinosis
Robert Koch
• Louis Pasteur and
Robert Koch
established a
scientific
explanation for
infectious disease.
• Nobel prize in 1905
for his work
Koch’s Postulates
• Rules for identifying the microorganism
that causes a specific disease
• 1) The pathogen must be found in a sick
organism, but not in a healthy one
• 2) The Pathogen must be isolated and
grown in the laboratory in a pure culture
Koch’s Postulates
• 3) When the cultured pathogens are
introduced into a healthy host, they should
cause the same disease that infected the
original host.
• 4) The injected pathogen must be isolated
from the second host, and should be
identical to the original pathogen.
Symbionts vs. Pathogens
• Not all bacteria cause
disease, most live in a
symbiotic relationship
with us.
• Pathogens upset
homeostasis
How Diseases Spread
• How are infectious
diseases spread?
• Coughing, sneezing,
physical contact, or
exchange of bodily
fluids
How Diseases Spread
• Contaminated
water or food.
How Diseases Spread
• Spread from infected
animals to humans
• These diseases are
called: Zoonoses
(zoonosis)
• Vectors: animals that
carry a disease from
an animal host to a
human host
Question #1
• List the Types of organisms that can cause
disease. (Hint: There are five)
Question #2
• What are the ways that pathogens can cause
disease in their host?
Question #3
• What are the ways infectious diseases are spread?
Question #4
• How do vectors
contribute to the
spread of disease?
• Give one example.
Answer #1
• Viruses, bacteria, single-celled eukaryotes, fungi,
and parasites.
Answer #2
• Some viruses and
bacteria directly
destroy the cells of
their host. Other
bacteria and singlecelled eukaryotes
release poisons that
kill host cells or
interphere with their
function.
Answer #3
• Infectious diseases are
spread through
coughing, sneezing,
physical contact,
exchange of bodily
fluids, contaminated
water or food, or
infected animals.
Answer #4
• Vectors spread disease by transporting pathogens
from one host to another.