Chapter 20:
Viruses and Prokaryotes
Section 20-3: Diseases Caused by Bacteria and Viruses
Bacterial Diseases




Pathogens are microorganisms that cause disease
All known prokaryotic pathogens are bacteria
Louis Pasteur helped establish the germ theory of disease
by showing bacteria responsible for many human and
animal diseases
Bacterial diseases produced in 2 general ways:


Destroy living tissue of infected organism, directly or causing
tissue damage by triggering immune system (bacteria that
cause tuberculosis)
Release toxins that interfere with normal activity (bacteria that
cause diphtheria, botulism)
Common Human Bacterial Diseases
Controlling Bacteria





Physical removal – washing hands or other surfaces under
running water does not kill bacteria, but it can dislodge
them (also viruses)
Disinfectants – chemical solutions that kill bacteria
Food storage – low temperatures slow bacterial growth,
keep foods fresher than room temperature
Food processing – cooking kills bacteria
Heat sterilization – instruments are heated to above 100°
C to kill bacteria
Preventing Bacterial Diseases

Vaccines are preparations of weakened or killed
pathogens or inactivated toxins

When injected, vaccines prompt body to produce
immunity to a specific disease
Treating Bacterial Diseases

Antibiotics such as penicillin and tetracylcine block the
growth and reproduction of bacteria by disrupting
proteins or cellular processes specific to bacterial cells
without harming host

Ineffective against viral infections
Viral Diseases


Produce disease by disrupting homeostasis
Animal and plant diseases
Disease Mechanisms

Some attack and destroy specific cells, causing disease
symptoms – poliovirus

Some viruses cause infected cells to change their growth
and development patterns, sometimes leading to cancer
Preventing Viral Diseases

Vaccines







1769- Smallpox vaccine, using cowpox virus
1880s- Anthrax and rabies
1923- tuberculosis
1950s- 2 polio vaccines, one used killed viruses and one
using weakened viruses
1981- hepatitis B vaccine using recombinant DNA
2006- vaccine against human papillomavirus (HPV)
Cold and flu viruses often spread by hand-to-mouth
contact – wash hands, avoid contact with sick
people, do not cough or sneeze on hands
Treating Viral Diseases

Few antiviral drugs

Attack specific viral enzymes host cells do not have
Emerging Diseases


Pathogens reproduce quickly, evolve easily
An unknown disease that appears in a population for the
first time or a well-known disease that suddenly becomes
harder to control is called an emerging disease
Emerging Diseases

Changes in lifestyle and commerce have made this a
bigger issue

Tend to appear suddenly, resist control methods

Need better understanding of molecular structure and
genetics
“Superbugs”



Evolution has created many bacteria that are resistant to
antibiotics
In the 1940s, penicillin killed everything
Widespread use of antibiotics has allowed for natural
selection to favor resistance, and conjugation can transfer
drug-resistant genes
MRSA
New Viruses

Reproduce so quickly, so simple genetically they can jump
species (SIV to HIV)

Flu virus is always changing – new vaccines and variations
(bird flu)
Prions





1972- Stanley Prusiner investigated cause of scrapie, an
infectious disease in sheep
Experiments showed clumps of protein particles in the
brains of infected sheep.
Prusiner called particles prions, short for “protein
infectious particles”
Misfolded proteins in the brain cause a chain reaction of
misfolding in other normal proteins, clogging the brain
tissue and causing disease
Mad cow disease