Download Infectious Disease - Lemon Bay High School

LESSON 35.1
Getting Started
Infectious Disease
Objectives
35.1.1 Identify the causes of infectious disease.
35.1.2 Explain how infectious diseases are spread.
Key Questions
Student Resources
Study Workbooks A and B, 35.1 Worksheets
Spanish Study Workbook, 35.1 Worksheets
Lesson Overview • Lesson Notes
• Activity: Art Review • Assessment: Self-Test,
­Lesson Assessment
F or corresponding lesson in the
Foundation Edition, see pages 838–840.
What causes infectious
disease?
How are infectious
diseases spread?
Vocabulary
infectious disease
germ theory of disease
Koch’s postulates
zoonosis
vector
Taking Notes
Two-Column Table Use a twocolumn table to list the ways
diseases are spread and describe
each way.
Activate Prior Knowledge Make a T-Chart on the board, and label one column
Disease and the other Infectious. Then, introduce the
concept of infectious disease. Have students brainstorm a list of human diseases. (Sample answers:
common cold, influenza, strep throat, lung cancer,
measles, chicken pox, atherosclerosis, athlete’s foot,
diabetes, malaria) Write the diseases in the Disease
column. For each disease listed, call on volunteers to
identify if it is infectious or not. Tell students they will
learn more about infectious disease in this lesson.
Study Wkbks A/B, Appendix S30, T-Chart.
­Transparencies, GO15.
Figure 35–1 Examples of
Agents of Disease Infectious
diseases are caused by pathogens
and parasites—organisms that
invade a body and disrupt its
normal functions.
ThINK ABouT IT For thousands of years, people believed that
diseases were caused by curses, evil spirits, or vapors rising from
foul marshes or dead plants and animals. In fact, malaria was named
after the Italian words mal aria, meaning “bad air.” This isn’t all that
surprising, because, until microscopes were invented, most causes of
disease were invisible to the human eye!
Causes of Infectious Disease
What causes infectious disease?
During the mid-nineteenth century, French chemist Louis Pasteur
and German bacteriologist Robert Koch established a scientific explanation for infectious disease. Pasteur’s and Koch’s observations and
experiments led them to conclude that infectious diseases occur when
microorganisms cause physiological changes that disrupt normal body
functions. Microorganisms were commonly called “germs,” so this
conclusion was called the germ theory of disease. That’s unfortunate
now, because the word germ has no scientific meaning.
Agents of Disease If germ isn’t a scientific term, how should we
Infectious diseases
describe the causes of infectious disease?
can be caused by viruses, bacteria, fungi, “protists”, and parasites.
Except for parasites, most of these disease-causing microorganisms are
called pathogens. Figure 35–1 provides more information and examples of pathogens and parasites.
Viruses
Characteristics: nonliving, replicate
by inserting their genetic material
into a host cell and taking over many
of the host cell’s functions
Diseases Caused: common cold,
influenza, chickenpox, warts
Bacteria
Characteristics: break down the tissues
of an infected organism for food, or
release toxins that interfere with normal
activity in the host
Diseases Caused: streptococcus infections, diphtheria, botulism, anthrax
. Influenza Virus, Strain taken from a
Beijing 1993 epidemic (TEM 120,000)
. Mycobacterium causes tuberculosis
(SEM 10,600)
Fungi
Characteristics: cause
infections on the surface
of the skin, mouth, throat,
fingernails, and toenails;
dangerous infections may
spread from lungs to other
organs
Diseases Caused: ringworm,
thrush
. Trichophyton interdigitale
causes athlete’s foot (SEM 2800)
national science education standards
Lesson 35.1
1010
• Lesson Overview • Lesson Notes • Art Review
UNIFYING CONCEPTS AND PROCESSES
I, II, V
1010_Bio10_se_Ch35_S1_1010 1010
CONTENT
C.4.c, C.6.b, F.1
Teach for Understanding
ENDURING UNDERSTANDING The human body is a complex system. The coordinated
functions of its many structures support life processes and maintain homeostasis.
INQUIRY
GUIDING QUESTION How do people contract infectious diseases?
A.2.a
EVIDENCE OF UNDERSTANDING After completing the lesson, this assessment should
show student understanding of how a person contracts an infectious disease. Have
each student write a newspaper article describing a researcher investigating an
infectious disease that has spread in a community. The article should describe how
the researcher used Koch’s postulates to identify the pathogen and tell how the
disease spreads. Ask volunteers to share their articles with the class.
1010 Chapter 35 • Lesson 1
3/26/11 9:35 AM
Teach
Lead a Discussion
Begin a discussion of infectious disease by reviewing what students learned in earlier chapters about
viruses, bacteria, fungi, single-celled eukaryotes, and
parasites. Emphasize that many different microorganisms live in and on the body with no harmful effects.
Then, turn the discussion to Koch’s postulates.
Ask Why do you think Koch’s postulates played
an important role in the development of modern
medicine? (Sample answer: They have provided
researchers a method to follow when identifying
a pathogen that causes a specific disease. To treat
patients effectively, it’s important to know the cause
of their disease.)
Symbionts vs. Pathogens Parts of the human body provide excellent habitats for microorganisms. Fortunately, most microorganisms
that take advantage of our hospitality are symbionts that are either
harmless or actually beneficial. Yeast and bacteria grow in the mouth
and throat without causing trouble. Bacteria in the large intestine help
with digestion and produce vitamins. In fact, if all your cells disappeared, the outlines of your body and digestive tract would still be
recognizable—as a ghostly outline of microorganisms!
What’s the difference between harmless microorganisms and
pathogens that cause disease? The “good guys” obtain nutrients, grow,
and reproduce without disturbing normal body functions. The “bad
guys” cause problems in various ways. Some viruses and bacteria
directly destroy the cells of their host. Other bacteria and single-celled
parasites release poisons that kill the host’s cells or interfere with their
normal functions. Parasitic worms may block blood flow through
blood vessels or organs, take up the host’s nutrients, or disrupt other
body functions.
“Protists”
Characteristics: single-celled eukaryotes may infect
people through contaminated water and insect bites;
they take nutrients from their host; most inflict damage
to cells and tissues
Diseases Caused: malaria, African sleeping sickness,
intestinal diseases
䉲 Giardia intestinalis, causes infection of the digestive tract
(SEM 3500⫻)
Ask Why might step 3 raise ethical issues when
studying certain diseases, such as a disease that
only affects humans? (Sample answer: It would not
be ethical to inject a healthy person with a known
pathogen.)
DIFFERENTIATED INSTRUCTION
LPR Less Proficient Readers Some students may
have difficulty understanding Koch’s postulates. Help
them by writing the steps on the board in simpler
form. The following is an example.
Parasitic Worms
Characteristics: most parasites that infect humans
are wormlike; may enter through the mouth, nose,
anus, or skin; most reside in the intestinal tract
where they absorb nutrients from the host
Diseases Caused: trichinosis, schistosomiasis,
hookworm, elephantiasis
1. Find the suspected pathogen in a sick organism.
2. Grow the pathogen in culture in a lab.
3. Introduce the pathogen into a healthy organism.
4. Find the same pathogen in the second, sick
䉲 Trichinella spiralis, causes trichinosis in humans
organism.
(SEM 65⫻)
Encourage students to write the simplified steps in
their notebook for later reference.
1011
0001_Bio10_se_Ch35_S1.indd 2
Students can further explore the different kinds of pathogens using Art Review:
Agents of Disease.
6/3/09 3:50:41 PM
How Science Works
EXCEPTIONS TO KOCH’S POSTULATES
Although Koch’s postulates are very useful in identifying pathogens that cause specific diseases, scientists by necessity make exceptions to these rules. For example, scientists have never been able to culture either the bacterium that causes syphilis or the
bacterium that causes Hansen’s disease (leprosy). Some pathogens cause disease only
in humans, and for ethical reasons, these pathogens cannot be injected into healthy
individuals. HIV, the virus that causes AIDS, is an example. When researchers can’t rely
on Koch’s postulates to prove a pathogen causes a disease, they turn to other types
of experimental evidence.
Immune System and Disease
1011
LESSON 35.1
Koch’s Postulates Koch’s studies with bacteria led him to develop rules
for identifying the microorganism that causes a specific disease. These
rules are known as Koch’s postulates.
1. The pathogen must always be found in the body of a sick organism
and should not be found in a healthy one.
2. The pathogen must be isolated and grown in the laboratory in pure
culture.
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. It
should be identical to the original pathogen.
Koch’s ideas played such a vital role in the development of modern
medicine that he was awarded a Nobel Prize in 1905. Today, we know
that there can be exceptions to these rules, but they remain important
guidelines for identifying the causes of new and emerging diseases.
LESSON 35.1
Teach
How Diseases Spread
continued
Build Science Skills
Tell students that designing an experiment is a skill
that should be learned and practiced. Remind them
that most scientific experiments have an independent variable, a dependent variable, and one or more
controlled variables. Scientific experiments also have
methods for collecting and recording data. Then,
have small groups of students design an experiment
that could be used to determine how a specific
disease is spread, such as the flu or athlete’s foot.
Have each group present its experimental design to
the class, and allow students from other groups to
ask questions or propose ways to make the experiment better.
Figure 35–2 Sneezing Some
infectious diseases are spread from
person to person by sneezing.
Thousands of pathogen particles
can be released in a sneeze. infer
Why is it more beneficial to sneeze
into a tissue rather than covering
your mouth with your hand?
DIFFERENTIATED INSTRUCTION
l1 Struggling Students To reinforce the skill of
designing an experiment, have students make a
poster showing the experimental designs. Posters
may depend more on labeled drawings than text
explanations. Place posters on the classroom walls.
Have volunteers present the information on their
posters to the class.
ELL
BUILD Vocabulary
PrEFixES The prefix trans-, used
in words such as transmission,
transferred, and transportation,
comes from the Latin trans- which
means “across” or “beyond.”
Focus on ELL:
Build Background
Beginning and intermediate SPEAKERS ­
Create a Word Wall with the lesson’s vocabulary
terms: infectious disease, germ theory of disease,
Koch’s postulates, zoonosis, and vector. List
the terms on the wall, and then ask students
to add a definition and/or a drawing for each
term. Students can also add translations in their
native languages. Then, have students locate
each term in the lesson’s text. Call on students
to pronounce the term and give a definition or
description in their own words, according to
language level.
How are infectious diseases spread?
Infectious diseases can be spread in a number of ways.
Some
diseases are spread through coughing, sneezing, physical contact,
or exchange of body fluids. Some diseases are spread through
contaminated water or food. Still other diseases are spread to
humans from infected animals.
Pathogens are often spread by symptoms of disease, such as
sneezing, coughing, or diarrhea. In many cases, these symptoms
are changes in host behavior that help pathogens spread and infect
new hosts! After all, if a virus infects only one host, that virus will
die when the host’s immune system kills it or when the host dies.
For that reason, natural selection favors pathogens with adaptations
that help them spread from host to host.
Coughing, Sneezing, and Physical Contact Many bacteria and
viruses that infect the nose, throat, or respiratory tract are spread
by indirect contact. Coughing and sneezing releases thousands of
tiny droplets that can be inhaled by other people. Those droplets
also settle on objects such as doorknobs. If you touch those objects
and then touch your mouth or nose, you can transfer the pathogens
to a new home! Thus, the ability of a flu virus or a tuberculosis
bacterium to cause a host to sneeze or cough is an adaptation that
increases transmission of the pathogen from one host to another.
Other pathogens, including drug-resistant staphylococci that
cause skin infections, can be transferred by almost any kind of
body-to-body contact. They can also be transferred by contact with
towels or certain kinds of sports equipment.
Minimizing transmission of these diseases is surprisingly
simple. The most important means of infection control is thorough and frequent hand washing. If you have a cold or flu, cover
your mouth with a tissue when you cough or sneeze, and wash your
hands regularly.
Exchange of Body Fluids Some pathogens require specific kinds
of direct contact to be transferred from host to host. For example,
a wide range of diseases, including herpes, gonorrhea, syphilis, and
chlamydia, are transmitted by sexual activity. Therefore, these diseases are called sexually transmitted diseases. Other diseases, including certain forms of hepatitis, can be transmitted among users of
injected drugs through blood from shared syringes. HIV can be
transmitted through blood or sexual contact. Sexually transmitted
diseases can only be completely prevented by avoiding sexual activity.
Contaminated Water or Food Many pathogens that infect the
digestive tract are spread through water contaminated with feces
from infected people or other animals. Symptoms of these diseases often include serious diarrhea. This is another adaptation
that helps pathogens spread from one host to another, especially
in places with poor sanitation.
1012 Chapter 35 • Lesson 1
Study Wkbks A/B, Appendix S17, Word Wall.
1010_Bio10_se_Ch35_S1_1012 1012
Check for Understanding
One-Minute Response
Give students about a minute to write a quick response to the following question:
Answers
FIGURE 35–2 Sample answer: You would be better
able to contain the spread of pathogens if you
sneeze into a tissue that you then discard. If you
sneeze into your hand, the pathogens would be
transferred when you then touch something else.
1012 Chapter 35 • Lesson 1
•Why does it make sense that natural selection favors pathogens with adaptations
that help them spread from host to host? Give some examples in your response.
(Spreading from host to host allows a pathogen to survive and reproduce, even if
the original host dies. Examples include causing the host to cough or sneeze.)
Adjust Instruction
If student responses indicate they are confused, quickly review natural selection with
students. Discuss how organisms that are better-adapted to their environments are
more likely to survive, reproduce, and pass their traits on to their offspring.
3/26/11 9:35 AM
Zoonoses: The Animal Connection Many diseases that have made
headlines in recent years thrive in both human and other animal hosts.
Any disease that can be transmitted from animals to humans is called
a zoonosis (plural: zoonoses). Mad cow disease, severe acute respiratory syndrome (SARS), West Nile virus, Lyme disease, Ebola, and
bird flu are all zoonoses. Transmission can occur in various ways.
Sometimes an animal carries, or transfers, zoonotic diseases from an
animal host to a human host. These carriers, called vectors, transport
the pathogen but usually do not get sick themselves. In other cases,
infection may occur when a person is bitten by an infected animal,
consumes the meat of an infected animal, or comes in close contact
with an infected animal’s wastes or secretions.
Many of the sick children
remembered receiving
strange insect bites that
summer, which developed
into rashes. What clue
did this give Steere?
Focus students’ attention on zoonoses
transmission by vectors. Guide them to
infer that the disease may be spread by
insect bites. Students can go online to Biology.com
to gather their evidence.
Assess and Remediate
EVALUATE UNDERSTANDING
FIGURE 35–3 Vectors Vectors
are animals that harbor a
pathogen. The pathogen may
spread to a human through the
bite of the vector, or when a
person eats the vector.
Ask students to write a short paragraph that identifies five different kinds of disease-causing agents
and describes the different ways diseases are spread.
Then, have them complete the 35.1 Assessment.
REMEDIATION SUGGESTION
L1 Struggling Students If students have trouble
answering Question 2c, review how changes in host
behavior, such as coughing, help pathogens spread
and infect new hosts. Also, help students recall that
viruses need to use host cells to replicate.
䉱 Fruit bat that may carry the Ebola virus
from birds to humans
Review Key Concepts
1. a. Review List the types of organisms that can
cause disease.
b. Explain What are ways that pathogens can
cause disease in their hosts?
c. Infer If a researcher introduced a suspected
pathogen into many healthy hosts, but none
of them became sick, what could this indicate?
2. a. Review What are the ways in which infectious diseases are spread?
b. Explain How do vectors contribute to the
spread of disease?
Lesson 35.1
Students can check their understanding of lesson concepts with the SelfTest assessment. They can then take an online
version of the Lesson Assessment.
䉱 Mosquito that transfers West Nile virus
c. Apply Concepts Why do you think it’s a
beneficial adaptation for a pathogen to make
its host very sick without killing the host?
(Hint: Think about how viruses replicate.)
Description
3. Animals infected with the virus that causes
rabies often salivate excessively and are apt to
bite other animals even when unprovoked. In
a paragraph, explain how these symptoms lead
to the spread of the virus.
• Self-Test
• Lesson Assessment
Immune System and Disease 1013
0001_Bio10_se_Ch35_S1.indd 4
6/3/09 3:50:50 PM
Assessment Answers
1a. viruses, bacteria, single-celled eukaryotes,
fungi, and parasites
2b. Vectors spread disease by transporting
pathogens from one host to another.
1b. Some viruses and bacteria directly destroy
the cells of their host. Other bacteria and
single-celled eukaryotes release poisons that
kill host cells or interfere with their functions.
2c. Sample answer: The pathogen often needs
the host to stay alive for the pathogen to
reproduce or replicate. A sick host is beneficial for the pathogen if some of the host’s
behaviors, such as coughing and sneezing,
help spread the pathogen.
1c. Sample answer: It likely indicates that the
pathogen was not responsible for causing
the disease in question.
3. Sample answer: The pathogen is probably
present in the saliva. When an infected animal bites another animal, the pathogen in
the infected animal’s saliva comes in contact
with the bitten animal’s blood.
2a. coughing, sneezing, physical contact,
exchange of body fluids, contaminated
water or food, infected animals
Immune System and Disease
1013
LESSON 35.1
Contaminated water may be consumed, or it may carry pathogens
onto fruits or vegetables. If those foods are eaten without being washed
thoroughly, infection can result. In recent years, several disease outbreaks have been traced to transmission through packaged salad greens.
Bacteria of several kinds are commonly present in seafood and
uncooked meat, especially ground meat. If meats and seafood are not
stored and cooked properly, illness can result.