Download Pathogens How Do They Cause Disease?

Pathogens
How Do They Cause
Disease?
I. Overview
A.  Pathogens
1. definition: a disease-causing agent
a. disease: a disturbance in the state of health such that the affected organism experiences some loss of
normal function (“dis” ease) b. parasite: an organism that lives in or on another
organism (the host) and causes change to the host
B.  Non-Pathogenic Parasites
1. Most parasitic relationships are not disease-causing a. A certain strain of E. Coli lives in the human intestines and creates a waste product we
call vitamin K, which is needed to make certain blood-clotting factors
b. Sloths have dozens of types of fungi that
live in their fur and feed on dead cells and other parasites.
Hi.
II. How Pathogens Cause Disease
A.  Types of Pathogens
1. bacteria: single celled prokaryotic organisms
2. viruses: non-living entities
3. fungi: eukaryotic heterotrophs
4. protists: single cell eukaryotes
5. worms: multicellular eukaryotic organisms
B. How Diseases are Spread
1. Physical Contact
a. Direct Contact
I. When a healthy person touches a person with a disease
b. Indirect Contact I. When a healthy person touches an object that
a person with a disease has contaminated
II. When a sick person sneezes or coughs and the contaminated particles are carried in
the air
2. Infected Animals
a. Animals that carry infection from person to person are called vectors
b. Infection can be carried through mosquitos, ticks, sheep, and wild animals
3. Contaminated Food and Water
a. Contaminated water carries a wide range of disease
b. Undercooked food can carry bacteria and other protists
C.  How Bacteria Cause Disease 1. they must stick to a certain cell type
2. they must be able to colonize, or penetrate the cell’s
surface 3. penetrating the cell surface can result in the destruction of the cell or will allow the bacteria to move
inside the cell
4. once colonized or inside a cell, bacteria often produce
toxins: poisonous substances that cause disease
D. How Viruses Cause Disease
1. They must invade a cell (its host) to reproduce
a. Lytic Infections I. The virus enters a cell, uses the cell’s resources to make copies of itself, and causes
the cell to burst, releasing more virus to the
organism
II. Examples: Common Cold, Influenza
b. Lysogenic Infections
I. A virus integrates its DNA into the DNA of the host
cell, forcing the host cell to replicate the viral DNA with
every regular DNA replication.
II. Examples: HIV, Hepatitis B
c. the mass killing of cells can cause a wide range of disease
I. since intestinal cells reproduce rapidly any infection of these
cells does not last long and no permanent damage is done
Ex: Stomach Flu and Rotavirus
II. viral infection of neurons, which cannot be replaced can cause
permanent damage including paralysis
Ex: Encephalitis and Viral Meningitis
III. viral infection of immune system cells can disable a person’s
ability to defend itself against pathogens
Ex: Lupus and HIV
E. How Fungi Cause Disease
1. Fungi thrive in warm, moist environments
2. Microscopic fungi normally colonize dead skin and hair
3. Occasionally the fungus can invade the skin or can be
inhaled, causing infection through the release of toxins
4. Organisms typically host helpful bacteria that help kill
off fungi
5. Examples: Athlete’s Foot, Jock Itch, Ringworm
F.  How Protists Cause Disease
1. Protists commonly invade the blood stream (Malaria and
African Sleeping Sickness) or the intestines (Dysentery)
2. How do Protists cause disease?
a. Protists are large enough that the body tries to fight
them off, causing illness
b. Protists can release waste that causes a severe reaction or infection.
3. Nutrients meant for the host are used by the protist,
and any disease related to lack of nutrients may occur
G. How Worms Cause Disease
1. Animals generally get worms by ingesting their eggs,
which then mature inside the warm, nutrient rich body
2. Worms latch onto tissue and consume cells and nutrients
intended for the host, often leading to nutrient deficiency
3. Some worms burrow into tissue and cause infection in the
host.