Viruses – Bacteria – Fungi – Protists – Multi-cellular – Prions -

Name ____________________________ Date ______________ Period ________
Unit 3 – Infectious Disease, Background Paper 3-2
Infectious Agents1
Viruses –
Very simple in structure, a virus consists of a strand of DNA (or RNA)
surrounded by a protein shell. Since viruses are not truly alive they cannot be
killed. Once introduced into our bodies they attack individual cells and cannot be
controlled by antibiotics. We don’t have cures for viruses. We can only help our
own body’s defenses by strengthening it to fight off the virus. The virus to the
right causes HIV – AIDS.
Bacteria –
Single celled prokaryotes (cells with no nucleus). During the 1950’s
we thought that one day soon we would be able to eliminate all diseases
caused by bacteria. The best controls for these living cells are anti-biotics.
Unfortunately bacteria have been able to evolve resistance to antibiotics to
the point where some diseases are no longer treatable.
To the left are: E. coli 0157:H7 (causes food poisoning), Strepococcus pyrogenes (causes
strep throat), Mycobacterium tuberculosis (causes tuberculosis)
Fungi –
Fungi are heterotrophic (can’t make their own food like plants).
Several species parasitize humans causing everything from ring worm to
ear infections.
Protists –
Single celled eukaryotic (with a cell nucleus) organisms causing
some of the most wide spread infections known. Malaria and dysentery are
two major protist diseases. Pictured at right are: Giardia intestinalis (causes
diarrhea), Trypanosoma brucei (causes sleeping sickness), Plasmodium gametocyte
(causes malaria)
Multi-cellular –
Not all disease causing organisms are microscopic. Many multi-cellular animals find
places inside our bodies to live, grow, reproduce, and make us ill. To the left meet: Ascaris
lumbricoides (an intestinal roundworm), Schistosoma mansoni (a parasitic worm that lives in contaminated water
Prions Unlike the other disease causing ‘agents’, prions contain no genetic information. They are
proteins manufactured in the host’s cells that have mutated into a disease causing form. The mutated
protein can then be passed from one animal to another. Mad Cow disease is probably the most
famous of the prion diseases.
Images from
Background 3-2,Disease2012
Text 2012
Greg Ballog
Page 1
Name ____________________________ Date ______________ Period ________
Title of Reading: 3-2 Infectious Agents
Points Earned
1 2 3 4 5 6 7
Concept Map of Reading (3 points)
Main Idea
A) What one question do I have about this article?
1 Point
B) Show or describe the reading to a parent or guardian (Name ___________________).
What comments or questions did they have concerning the reading?
(Biology Homework Time __________)
Background 3-2,Disease2012
Text 2012
Greg Ballog
Page 2