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PowerLecture:
Chapter 18
Life at Risk:
Infectious Disease
Learning Objectives



Differentiate between the microorganisms
that normally live on and in you and those
which cause infection and disease.
List the general characteristics of viruses,
bacteria, and other parasites.
Describe the different patterns of infectious
disease and how you can protect yourself.
Impacts/Issues
Virus, Virus Everywhere
Virus, Virus Everywhere
West Nile virus is a virus with historical
and present-day importance.



In 324 B.C. it quite possibly killed
Alexander the Great.
In 1999 West Nile virus
was discovered in the U.S.,
the first time it had ever
been seen in the Western
Hemisphere.
Figure 18.15
Virus, Virus Everywhere

Avian (bird) flu, caused by the H5N1 virus,
is rapidly spreading around the globe,
evidence that no place is safe when it
comes to infectious disease.
Video: West Nile Virus
 This
video clip is available in CNN Today
Videos for Anatomy and Physiology, 2003,
Volume VII. Instructors, contact your local
sales representative to order this volume,
while supplies last.
Video: Bird Flu
CLICK
TO PLAY

From ABC News, Environmental Science in the Headlines, 2005 DVD.
Useful References for Impacts/Issues
The latest references for topics covered in this section can be found at
the book companion website. Log in to the book’s e-resources page at
www.thomsonedu.com to access InfoTrac articles.
 CDC:
West Nile Virus
 CDC: Avian Influenza
 InfoTrac: Avian Flu, West Nile Virus, and
Lyme Disease. Robert Charles Moellering Jr.
et al. Patient Care for the Nurse Practitioner,
April 2006.
How Would You Vote?
To conduct an instant in-class survey using a classroom response
system, access “JoinIn Clicker Content” from the PowerLecture main
menu.
 Killing
mosquitoes is the best defense
against West Nile virus. Some people object
to spraying, fearing harmful effects on health
or wildlife. Would you support a spraying
program in your area?


a. Yes, spraying pesticides to kill mosquitoes is
an effective way to limit the spread of this
disease.
b. No, the pesticides used to control the virus do
more harm than good.
Useful References for
How Would You Vote?
The latest references for topics covered in this section can be found at the book
companion website. Log in to the book’s e-resources page at
www.thomsonedu.com to access InfoTrac articles.

InfoTrac: Suit over West Nile Spraying Goes
Forward against City. New York Law Journal, June
13, 2005.
 InfoTrac: Study Claims Risks of West Nile Spraying
Exaggerated. Pesticide & Toxic Chemical News,
May 3, 2004.
 InfoTrac: A Global Market Isn’t as Easy as It Looks.
Business Week, Sept. 3, 2001.
 Maine Environmental Policy Institute: Overkill
Section 1
Some General Principles
of Infectious Disease
Some General Principles of
Infectious Disease
The body is home to a great many “friendly”
microorganisms.



Many species of microorganisms colonize the
epithelial tissues of the skin, mouth, nasal
cavity, conjunctiva, GI tract, urethra, and
vagina.
All possess some sort of adhesion proteins on
their surfaces that allow them to “stick” to our
tissues; pathogens, on the other hand, often do
not have this ability to “stick.”
conjunctivae of eyes
nasal cavity and
nasopharynx
mouth
skin
intestinal tract
urethra
vagina (females)
Fig. 18.1, p.340
Some General Principles of
Infectious Disease
Different types of pathogens cause disease
in different ways.



An infection occurs when a pathogen enters
cells or tissues and multiplies; if this growth
interferes with normal body function, then it is
termed a disease.
Infectious diseases are those diseases that can
be passed from one person to another.
Some General Principles of
Infectious Disease

Pathogens produce disease in different ways.
•
•
•
•
Some bacteria produce toxins, chemicals that are
poisonous to human tissues; the disease botulism is
caused by a bacterial toxin produced by Clostridium
botulinum.
Septic shock is another condition resulting from
bacterial toxins.
Viruses cause disease by invading and destroying
body cells; others become latent in the cell, only
manifesting some time after infection.
Some pathogenic fungi release enzymes to digest
human tissues; parasitic worms and protozoa may
damage tissues directly or trigger harmful immune
responses.
Some General Principles of
Infectious Disease
To cause an infection, pathogens must meet
several requirements.


Pathogens must have a host, an organism that
a pathogen can infect; a reservoir is a place
where the organism
can survive and
remain infectious,
including other
organisms (carriers),
soil, and water.
Some General Principles of
Infectious Disease
•
•
•

The pathogen must have a way to leave the reservoir
and enter a host, attach to the host’s body, and enter
the tissues.
Pathogens must have some way to avoid the host’s
defenses so that it can reproduce inside the host.
The pathogen finally must be able to return to a
reservoir or move to a new host.
Infectious diseases are sometimes grouped
according to reservoirs; a zoonosis is an
infectious disease carried by animals that can
also infect humans.
Some General Principles of
Infectious Disease
Emerging diseases present new challenges.



Emerging diseases are those that only
recently have begun to infect humans or which
were present only in limited areas previously.
Factors influencing the emergence of new
diseases include increased human population
density, ease of travel, and such medical
concerns as antibiotic resistance.
Some General Principles of
Infectious Disease

Many of these diseases are viral; examples
include West Nile virus, SARS virus, Ebola virus,
and Lyme disease.
Figure 18.2
Video: Germs in Pakistan
CLICK
TO PLAY

From ABC News, Human Biology in the Headlines, 2006 DVD.
Video: Mask of Technology
CLICK
TO PLAY

From ABC News, Human Biology in the Headlines, 2006 DVD.
Useful References for Section 1
The latest references for topics covered in this section can be found at
the book companion website. Log in to the book’s e-resources page at
www.thomsonedu.com to access InfoTrac articles.
 Centers
for Disease Control and Prevention
 CDC: Emerging Infectious Diseases
 InfoTrac: Antibiotics Alter the Normal
Bacterial Flora in Humans. Biotech Week,
April 7, 2004.
 InfoTrac: Botulism. Jeremy Sobel. Clinical
Infectious Diseases, Oct. 15, 2005.
Section 2
Viruses and
Infectious Proteins
Viruses and Infectious Proteins
A virus is a tiny, noncellular pathogen that
can infect the cells of almost every other
organism.



A virus consists of a DNA, or RNA, core
surrounded by a protein coat (capsid); some
viruses additionally have an outer lipid envelope.
Viruses can replicate only after infecting a cell
and taking over that cell’s metabolic machinery.
viral
RNA
protein
subunits
of coat
a
rodlike virus
Fig. 18.3a, p.342
spike
proteins
b
polyhedral virus
Fig. 18.3b, p.342
DNA
protein
coat
sheath
tail
fiber
c
complex virus
Fig. 18.3c, p.342
viral coat
(proteins)
viral
enzyme
spike
proteins
viral
RNA
d
envelope
enveloped polyhedral virus
Fig. 18.3d, p.342
Viruses and Infectious Proteins
Viruses multiply inside a host cell.


Replication of a virus involves five basic steps:
•
•
•
•
•
A virus recognizes, and attaches to, a host cell.
The virus, or its genetic core, enters the cell.
Viral DNA, or RNA, directs the host cell in producing
copies of viral nucleic acids and in making viral
enzymes and other proteins.
Viral nucleic acids and proteins are assembled into
new viral particles.
Newly formed viruses are released from the infected
cell.
a An enveloped DNA virus
particle contacts the plasma
membrane of host cell and
fuses with it.
coat surrounded by envelope
viral DNA
DNA virus particle
b Once inside the
cytoplasm, viral DNA
and viral coat separate.
plasma
membrane
of host cell
d Host machinery
replicates
viral DNA.
f Many new virus
particles assembled.
e Genetic information translated
into viral proteins
c Host metabolic
machinery transcribes
the viral genes.
viral
DNA
some
proteins
for viral
coat
other
proteins
for viral
envelope
g Viral envelope
proteins become
inserted into host’s
plasma membrane.
h Particles leave nucleus,
move to plasma membrane.
nuclear
envelope
j The finished particle
is equipped to infect a
new potential host cell.
i Virus particles bud from plasma
membrane. Their viral coat becomes
wrapped in protein-spiked membrane,
which becomes the viral envelope.
Fig. 18.4, p.342
Viruses and Infectious Proteins


A cell will serve as a host for the synthesis of
new viral particles only if the original virus can
recognize and lock onto the cell’s surface.
Some viruses do not kill their host cells outright
but enter a period of latency.
•
•
One example is the herpes virus, introduced
previously as an example of a sexually transmitted
disease.
Epstein-Barr virus (EBV) is also a herpes virus; it
causes infectious mononucleosis.
Viruses and Infectious Proteins
•
Retroviruses are RNA viruses that use an enzyme
called reverse transcriptase to synthesize a DNA
molecule for insertion into the host DNA; the
integrated form is called a provirus. HIV is a
retrovirus.
Figure 18.14a
Viruses and Infectious Proteins
Prions are infectious proteins.


Prions are small, infectious proteins linked to
several rare, fatal degenerative diseases of the
nervous system.
•
•
Prions are misfolded versions of normal proteins
found on brain neurons and other cell types.
Prions can bind to normal proteins and refold them,
creating clumps of protein in the brain, destroying
brain tissue.
Viruses and Infectious Proteins

BSE (bovine spongiform encephalitis) or “mad
cow disease” affects cows and can cause
variant Creutzfeldt-Jakob disease (vCJD) in
humans; prions are also associated with a long
known human-only version of CJD.
Figure 18.5b
Useful References for Section 2
The latest references for topics covered in this section can be found at
the book companion website. Log in to the book’s e-resources page at
www.thomsonedu.com to access InfoTrac articles.
 InfoTrac:
Cannibals to Cows: The Path
of a Deadly Disease. Newsweek, Mar.
12, 2001.
 InfoTrac: Cold Sore Virus Can Evade
Immune System. UPI NewsTrack, July
17, 2006.
Video: Mad Cow Victim
 This
video clip is available in CNN Today
Videos for Anatomy and Physiology, 2003,
Volume VII. Instructors, contact your local
sales representative to order this volume,
while supplies last.
Section 3
Bacteria—
The Unseen Multitudes
Bacteria—The Unseen Multitudes
Bacteria are prokaryotic cells.


Structural features appear rather simple
compared to more complex cells.
•
•
There is no nucleus or other membrane-bound
organelles.
Most bacteria have a cell wall that makes them
strong, semirigid, and gives them shape; coccus,
bacillus, and spirillum (spirochete) are common cell
shapes.
DNA
capsule
bacterial flagellum
pilus
plasma
membrane
cell wall
ribosomes in
cytoplasm
cytoplasm
Fig. 18.6, p.344
Bacteria—The Unseen Multitudes
•
Bacterial flagella allow for motility; pili help bacteria
attach to objects or each other.
Figures 18.7 and 18.14b
Animation: Prokaryotic Body Plan
CLICK
TO PLAY
Bacteria—The Unseen Multitudes

Bacteria reproduce by prokaryotic fission, a
process that can be repeated every 20 minutes.
•
•

The chromosome is a single, circular DNA.
Some bacteria possess plasmids, small circles of
extra DNA; plasmids may allow for fertility and for the
transfer of drug resistance.
Streptococcus is a species of bacteria that
causes respiratory tract infections and strep
throat; these bacteria possess the ability to
transfer genes.
Animation: Prokaryotic Fission
CLICK
TO PLAY
Bacteria—The Unseen Multitudes
Bacteria play both positive and negative
roles in human society.




Some bacteria are useful, such as those used
to make cheese and therapeutic drugs, but
most are notorious for the diseases they cause.
Antibiotics are the products of some bacteria
and fungi that can be used to kill other bacteria.
Antibiotics do not work against viruses; rather,
body defenses such as interferons may block
replication of viruses inside cells.
Bacteria—The Unseen Multitudes
A biological backlash to antibiotics is under
way.



Because antibiotics have been both overused
and in some cases inappropriately prescribed,
large numbers of bacterial species that were
once susceptible to antibiotics are now resistant
to their effects.
Staphylococcus aureus
may soon be resistant to
all available antibiotics.
Figure 18.12
Bacteria—The Unseen Multitudes
Bacteria cause some important emerging
and reemerging diseases.


Lyme disease, caused
by the spirochete
Borrelia burgdorferi, is
an important emerging
disease in the
United States.
Figure 18.8a
Bacteria—The Unseen Multitudes

Tuberculosis (TB), caused by Mycobacterium
tuberculosis, is a reemerging disease.
•
•
Antibiotics had made TB rare by the 1970s in
developed nations, but many factors have since
allowed the number of TB cases to rise.
In some areas of the world, all new cases of TB are
antibiotic resistant.
Figure 18.8b
Video: Salon Infections
 This
video clip is available in CNN Today
Videos for Biology, 2003, Volume VII.
Instructors, contact your local sales
representative to order this volume, while
supplies last.
Useful References for Section 3
The latest references for topics covered in this section can be found at the book
companion website. Log in to the book’s e-resources page at
www.thomsonedu.com to access InfoTrac articles.
 InfoTrac:
Overdoing Antibiotics. Harvard
Health Letter, Nov. 2002.
 InfoTrac: Chronic Middle Ear Infections
Linked to Resistant Biofilm Bacteria. PR
Newswire, July 11, 2006.
Section 4
Infectious Fungi,
Protozoa, and Worms
Infectious Fungi, Protozoa, and Worms
Parasitic fungi and protozoa are small but
potentially dangerous.


Common fungal infections include yeast
infections, ringworm, and athlete’s foot.
•
•
Fungi in athlete’s foot and ringworm
release enzymes that degrade keratin
in skin; inflammation can also occur.
Yeast infections occur in the vagina
and other mucous membranes
following changes to the chemistry
of the organ system.
Figure 18.9a
Infectious Fungi, Protozoa, and Worms

Several protozoa are important pathogens.
•
•
Entamoeba histolytica causes
amoebic dysentery; it enters
the body in food and water
contaminated with feces.
Giardia intestinalis causes
giardiasis; it typically enters
the body through water.
Figure 18.9b-c
Infectious Fungi, Protozoa, and Worms
•
Trypanosoma brucei is transmitted by the tsetse fly
to humans, where it invades the central nervous
system and causes African sleeping sickness;
untreated, it is fatal.
•
Cryptosporidium parvum, which causes
cryptosporidiosis, is an emerging disease in the U.S.;
this organism is highly resistant to common
disinfectants.
Figure 18.9d
Infectious Fungi, Protozoa, and Worms
Worms also can be a serious threat.



Pinworms are small, white roundworms that
are easily transferred as eggs from the anal
area of one person (usually a child) to the
mouth of a new host via contaminated fingers.
Other notorious worms such as tapeworms,
hookworms, whipworms, and the large Ascaris
intestinal worms can cause damage to body
tissues and organs.
Animation: Life Cycle of a Beef Tapeworm
CLICK
TO PLAY
Useful References for Section 4
The latest references for topics covered in this section can be found at
the book companion website. Log in to the book’s e-resources page at
www.thomsonedu.com to access InfoTrac articles.
 Structural
Genomics of Pathogenic Protozoa:
African Trypanosomiasis
 InfoTrac: Dark Fungi Emerging as Cause of
Lethal Infections. Nancy Walsh. Family
Practice News, May 15, 2006.
Section 5
Malaria: Efforts to
Conquer a Killer
Useful References for Section 5
The latest references for topics covered in this section can be found at
the book companion website. Log in to the book’s e-resources page at
www.thomsonedu.com to access InfoTrac articles.



CDC: Malaria
WHO: Malaria
InfoTrac: Fatal Inaction: There Is a Silver Bullet for
Africa’s Malaria Epidemic. Joshua Kurlantzick.
Washington Monthly, July–Aug. 2006.
 InfoTrac: Push for New Tactics as War on Malaria
Falters. Celia W. Dugger. The New York Times,
June 28, 2006.
Malaria: Efforts to Conquer a Killer


Malaria kills nearly 3 million people
annually, mostly children in Africa; 110
million new cases arise each year.
The cause of the disease is a protozoan
called Plasmodium, which is transmitted by
the female Anopheles mosquito.
Animation: Life Cycle of Plasmodium
CLICK
TO PLAY
a Plasmodium zygotes
sporozoite
develop in the gut of
female mosquitoes. They
become sporozoites,
which migrate to the
insect’s salivary
glands.
b Mosquito bites human,
bloodstream carries the
sporozoites to liver.
e Some of the
merozoites enter
liver, cause more
malaria episodes.
g Female
mosquito bites,
sucks blood from
infected human.
Gametocytes in blood
enter her gut and mature
into gametes, which
fuse to form zygotes.
f Others develop
into male, female
gametocytes that
are released into
bloodstream.
male gametocyte in red blood cell
sporozoites
c Sporozoites
reproduce in liver
cells.
merozoite
d Offspring
(merozoites) enter
blood, invade red blood
cells and reproduce.
They can do so over a
prolonged period. Disease
symptoms (fever, chills,
shaking) become more and
more severe.
Fig. 18.10, p.347
a Plasmodium zygotes
sporozoite
develop in the gut of
female mosquitoes. They
become sporozoites,
which migrate to the
insect’s salivary
glands.
b Mosquito bites human,
bloodstream carries the
sporozoites to liver.
e Some of the
merozoites enter
liver, cause more
malaria episodes.
g Female
mosquito bites,
sucks blood from
infected human.
Gametocytes in blood
enter her gut and mature
into gametes, which
fuse to form zygotes.
f Others develop
into male, female
gametocytes that
are released into
bloodstream.
male gametocyte in red blood cell
sporozoites
c Sporozoites
reproduce in liver
cells.
merozoite
d Offspring
(merozoites) enter
blood, invade red blood
cells and reproduce.
They can do so over a
prolonged period. Disease
symptoms (fever, chills,
shaking) become more and
more severe.
Stepped Art
Fig. 18.10, p.347
Malaria: Efforts to Conquer a Killer
The symptoms of the disease are periodic
bouts of severe chills, high fever, sweats,
and shaking leading to debilitation and
possibly anemia over time.




Individuals who inherit one copy of the gene for
sickle-cell anemia are partially protected from
the effects of malaria.
Many strains of Plasmodium are resistant to
drug therapy; drugs are also expensive.
Current efforts seek to devise a malaria
vaccine.
Section 6
Patterns of
Infectious Diseases
Patterns of Infectious Diseases
Infectious pathogens spread in four ways.


There are four general ways by which infectious
diseases can move between hosts:
•
•
Direct contact with a pathogen by touching the
infected person.
Indirect contact, as by touching doorknobs or
tissues previously in contact with the infected
person; this could include food and water.
Patterns of Infectious Diseases
•
Inhaling pathogens that have been released by
coughs and sneezes from the infected person; this is
the most common mode of transmission.
•
Contact with a vector, such as mosquitoes, flies,
fleas, and ticks, which can transfer the pathogen;
these vectors are often called disease vectors.
Figure 18.11
Patterns of Infectious Diseases

Nosocomial infections are hospital acquired
infections affecting 5-10% of all hospitalized
patients each year; most are acquired by direct
contact.
Patterns of Infectious Diseases
Diseases occur in four patterns.




During an epidemic, disease rates increase
above predicted levels; cholera is an example.
When epidemics occur in several countries
around the world in a given time frame, a
pandemic is declared; AIDS is an important
example.
A sporadic disease breaks out irregularly and
affects few people; whooping cough manifests
this way.
Patterns of Infectious Diseases

An endemic disease occurs more or less
continuously; the common cold may be the best
known example.
Virulence is a measure of the damage a
pathogen does.



Virulence is the relative ability of a pathogen to
cause serious disease; how fast the pathogen
invades tissues, how severe the damage is,
and where the damage is all help define
virulence.
Antibiotic resistance in certain bacteria has
made those microbes highly virulent.
Patterns of Infectious Diseases
There are many public and personal
strategies for preventing disease.



Prevention is the best way to combat infectious
disease; hand washing is probably the single
most important preventative tool.
Public health measures include vaccination
programs, ensuring standards for safe water,
food, and medical supplies, and dissemination
of correct and current information.
Blood
Preventative measures:
• Avoid/prevent needle sharing/
IV drug abuse
• Maintain pure public blood
supplies
• Vaccination programs
against blood-borne
pathogens
(e.g., hepatitis B)
Respiratory tract
Preventative measures:
• Hand washing
• Cover mouth when
coughing or sneezing
• Proper disposal of
used tissues
• Vaccination programs
GI tract
Preventative measures:
• Hand washing
• Proper food storage,
handling, and cooking
• Good public sanitation
(sewage, drinking water)
Skin
Preventative measures:
• Hand washing
• Limit contact with items
used by an infected
Fig. 18.13, p.349
Infectious
Diseases:
Global
Health
Threats
Video: Whooping Cough Immunization
 This
video clip is available in CNN Today
Videos for Anatomy and Physiology, 2004,
Volume VIII. Instructors, contact your local
sales representative to order this volume,
while supplies last.
Video: Global AIDS
 This
video clip is available in CNN Today
Videos for Biology, 2003, Volume VII.
Instructors, contact your local sales
representative to order this volume, while
supplies last.
Useful References for Section 6
The latest references for topics covered in this section can be found at
the book companion website. Log in to the book’s e-resources page at
www.thomsonedu.com to access InfoTrac articles.
 InfoTrac:
The Science of Clean Water.
Elettra Ronchi. OECD Observer, Mar.
2003.
 InfoTrac: Pandemic Dilemma: Who Gets
the Shot? Chicago Tribune, June 27,
2006.