section studying viruses and prokaryotes 18.1 study guide · chapter 18 viruses and prokaryotes ......

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18.1STUDYING VIRUSES AND PROKARYOTES

Study Guide

KEY CONCEPT

Infections can be caused in several ways.VOCABULARYvirus viroidpathogen prion

MAIN IDEA: Viruses, bacteria, viroids, and prions can all cause infection.

1. In the top left side of the Y shape below, write the characteristics of bacteria.

2. In the top right side of the Y shape below, write the characteristics of viruses.

3. At the bottom of the Y shape below, write the characteristics that both bacteria andviruses share. Then lightly cross out those characteristics at the top of the Y.

Bacter ia Viruses

Both

4. All living things share four characteristics of life. What are they?

Unit 6 Resource Book Study Guide 27McDougal Littell Biology

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STUDY GUIDE, CONTINUED

5. Write the description for each of the infectious particles in the spaces provided on thechart below. Include what they are made of and their range of sizes in your descriptions.

Infectious Particle Description

Virus

Viroid

Prion

Vocabulary Check

virus pathogen viroid prion

6. Does not have genes

7. Includes infectious bacteria

8. Made of only RNA

9. Any living thing or particle that can cause infectious disease

10. Made only of protein

11. Infects plants

12. Made of genetic material surrounded by a protein coat

13. Can contain RNA or DNA but is not living

28 Study Guide Unit 6 Resource BookMcDougal Littell Biology

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Power Notes

Eukaryotic cells:10,000—100,000 nm

Prion:

Size range:

Prokaryotic cells:200—10,000 nm

Virus:

Size range:

Viroid:

Size range:

Unit 6 Resource Book Power Notes 29McDougal Littell Biology

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Reinforcement

KEY CONCEPT Infections can be caused in several ways.

Any living organism or particle that can cause infectious disease is called an infectiousagent, or pathogen. Some pathogens are living organisms, while others are nonliving.Some bacteria, for example, can cause disease. Bacteria are prokaryotic cells and areclearly living. They have genes and can reproduce, use nutrients and energy, grow anddevelop, and respond to their environments. Viruses, on the other hand, have only someof the properties that characterize life. Like living cells, viruses have genes and canreproduce. Unlike cells, however, viruses cannot reproduce on their own. Instead, theyneed living cells to help them reproduce and make proteins. Viruses are also muchsmaller than most cells. While viruses have key traits similar to living cells, they alsohave many differences. Here are some examples of nonliving pathogens.

• A virus is an infectious particle made only of a strand of DNA or RNA surroundedby a protein coat.

• A viroid is an infectious particle that causes disease in plants. It is made ofsingle-stranded RNA without a protein coat. Viroids are passed by seeds or pollen.

• A prion is an infectious particle made only of proteins that can cause other proteinsto fold incorrectly, so the protein does not work properly.

Prions are unusual in that they are infectious, but have no genetic material. Theyplay a part in certain diseases of the brain such as mad cow disease. Prion diseasescan incubate for a long time with no noticeable effect on their host. However, oncesymptoms appear, they worsen quickly and are always fatal, because the body hasno immune response against a protein.

1. How are bacteria unlike viruses, viroids, or prions?

2. How are prions unlike bacteria, viruses, and viroids?

3. How is the target host of a viroid-caused infectious disease different than the hosts ofthe other pathogens mentioned?

4. All of the pathogens mentioned above are microscopic. Why might it be a benefit fora pathogen to be small?

30 Reinforcement Unit 6 Resource BookMcDougal Littell Biology

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18.2VIRAL STRUCTURE AND REPRODUCTION

Study Guide

KEY CONCEPT

Viruses exist in avariety of shapesand sizes.

VOCABULARYcapsid lytic infection prophagebacteriophage lysogenic infection

MAIN IDEA: Viruses differ in shape and in ways of entering host cells.

1. Sketch the three common shapes of viruses, and give an example of a virus that existsin each shape.

2. Name the three parts of the structure of a typical enveloped virus.

3. What must viruses do before they can reproduce?

4. How does a virus identify its host?

5. How do the structures of bacteriophages help them infect host cells?

6. What are two ways that viruses that infect eukaryotes enter their host cells?


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MAIN IDEA: Viruses cause two types of infections.

7. In the top left side of the Y shape below, write the characteristics of a lytic infection.

8. In the top right side of the Y shape below, write the characteristics of a lysogenicinfection.

9. At the bottom of the Y shape below, write the characteristics that both types of infectionshave in common. Then lightly cross out those characteristics at the top of the Y.

Lytic in fection

Both

Lysogen ic in fection

Vocabulary Check

capsid bacteriophage lytic infection lysogenicinfection

prophage

10. Virus that infects bacteria

11. Viral DNA plus host cell DNA

12. Protein shell of a virus

13. Infection where virus combines its DNA with host cell’s DNA

14. Infection where host cell bursts, releasing viral offspring


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Power Notes

Events Lytic Cycle Lysogenic Cycle

1.

2.

3.

4.

Event 1

Enveloped VirusExample:

Sketch:

Helical VirusExample:

Sketch:

Polyhedral VirusExample:

Sketch:

Event 2

Event 3

Event 4

Final outcome

The bacteriophage attaches andinjects its DNA into a cell.

The bacteriophage attaches andinjects its DNA into a cell.


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Reinforcement

KEY CONCEPT Viruses exist in a variety of shapes and sizes.

Viruses have simple basic structure. A single viral particle, called a virion, is made upof genetic material surrounded by a protein shell called a capsid. Capsids can havedifferent shapes. In some viruses, the capsid itself is surrounded by a lipid envelope.A lipid envelope is the protective outer coat of a virus, from which spiky structures ofproteins and sugars may stick out. Viruses can be helical like a spring, many-sided, orenveloped. Bacteriophages, or viruses that attack bacteria, have a many-sided capsidwith a long protein tail and spiky footlike fibers.

There are two basic types of viral infections: lytic and lysogenic.

• A lytic infection is an infectious pathway in which the host cell bursts, releasingthe new viral offspring into the host’s system, where each then infects another cell.

• In a lysogenic infection, the virus makes a prophage, or provirus, which is theviral DNA combined with the host cell’s DNA. The prophage is copied and passedon to daughter cells, with the host’s own DNA. Although this process doesn’tdestroy the cell, it can change some of the cell’s traits. The prophage can remainas a permanent gene within its host, or a trigger such as stress can activate theprophage, which then uses the cell to produce new viruses.

1. What is a capsid?

2. What are three different shapes that viruses may have?

3. Is a bacteriophage a virus or a bacteria? Explain.

4. What type of infectious pathway is associated with a prophage, or provirus? Explain.

5. In which type of infectious pathway is it more likely that the host will be aware thatthey are infected? Explain.


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18.3VIRAL DISEASES

Study Guide

KEY CONCEPT

Some viral diseases can be prevented with vaccines.VOCABULARYepidemicvaccineretrovirus

MAIN IDEA: Viruses cause many infectious diseases.

1. What is the body’s first defense against infection?

2. What are two ways viruses enter the body?

3. How do some viruses trick cells into letting them in?

4. Why is it not easy to find a cure for the common cold?

5. Why must a new flu vaccine be made every year?

6. Why might a person who has AIDS have a hard time fighting off normally harmlessmicroorganisms?

MAIN IDEA: Vaccines are made from weakened pathogens.

7. Describe how a vaccine works to protect people against infection.


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Vocabulary Check

epidemic vaccine retrovirus

8. Contains RNA and uses a special enzyme to make a DNA copy

9. Rapid outbreak of an infection that affects many people

10. Stimulates the body’s own immune response against invadingmicrobes

Identify the InfectionUse Figure 18.10 to determine what infection is being described.

11. Disease caused by the bite of an infected animal

12. Disease caused by the bite of an infected insect

13. Disease caused by contact with a particular rash

14. Disease that causes swelling in glands under a person’s jaw

15. Disease that most often infects people in undeveloped countries


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18.3VIRAL DISEASES

Power Notes

Vaccine

1.

2.

3.

4.

Viral Disease Details

Definition:

Examples of diseasesthat have vaccines:

Examples of diseasesthat do not havevaccines:

Characteristics:


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18.3VIRAL DISEASES

Reinforcement

KEY CONCEPT Some viral diseases can be prevented with vaccines.

Many infectious viruses exist. Examples of illnesses caused by viruses include

• The common cold: More than 200 viruses are known to cause a cold. With somany viruses, it is not easy to find a cure. In fact, cold viruses can mutate asthey move from one person to another.

• Influenza: The flu spreads quickly and can result in frequent local epidemics. Anepidemic is a rapid outbreak of an infection that affects many people. The highmutation rate of flu viruses makes it necessary for a new influenza vaccine to bemade every year. A vaccine is a substance the stimulates the body’s own immuneresponse against invasion by infectious agents.

• SARS: Severe acute respiratory syndrome (SARS) has symptoms similar toinfluenza, such as fever and coughing or difficulty in breathing. SARS is arelatively recent concern, as it first appeared in late 2002.

• HIV: Human immunodeficiency virus, or HIV, is a retrovirus. Retro- means“backward,” which describes how retroviruses work. A retrovirus containsRNA and uses an enzyme called reverse transcriptase to make a DNA copy. Incomparison, most viruses use DNA to make an RNA copy in a cell. An active HIVinfection destroys white blood cells of the host’s immune system. The loss of whiteblood cells ultimately causes AIDS, acquired immune deficiency syndrome. Oncea person’s immune system is affected, he or she may be unable to fight off even thecommon microorganisms that humans encounter every day.

Vaccines can prevent some, but not all, viral diseases. A vaccine is made from the samepathogen—disease-causing agent—that it is supposed to protect against. Vaccinesconsist of weakened versions of the virus, or parts of the virus, that will cause thebody to produce a response. In the host’s body, the vaccine works by preparing thehost’s immune system for a future attack.

1. Why is it hard to find a cure for the common cold?

2. How does receiving a vaccine affect a person’s immune system?

3. Why is HIV called a retrovirus?

4. How might a mild infection act similarly to a vaccine?


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SECTION

18.4BACTERIA AND ARCHAEA

Study Guide

KEY CONCEPT

Bacteria and archaea are bothsingle-celled prokaryotes.

VOCABULARYobligate anaerobe plasmid endosporeobligate aerobe flagellumfacultative aerobe conjugation

MAIN IDEA: Prokaryotes are widespread on Earth.

1. What two groups of organisms include all prokaryotes on Earth?

2. Some prokaryotes don’t need oxygen to live. Where are three environments wheremethane-producing archaea have been found?

MAIN IDEA: Bacteria and archaea are structurally similar but have differentmolecular characteristics.In the top left of the Y shape, write the characteristics of bacteria. In the top right, write thecharacteristics of archaea. At the bottom, write the characteristics bacteria and archaea havein common. Then lightly cross out those characteristics at the top of the Y.

Bacter ia Archaea

Both


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MAIN IDEA: Bacteria have various strategies for survival.

3. What is binary fission?

4. Describe one way that prokaryotes exchange genetic material.

5. How do some bacteria survive unfavorable conditions?

6. How is an endospore formed?

Vocabulary Check

obligate anaerobe

obligate aerobe

facultative aerobe

plasmid

flagellum

conjugation

endospore

7. Can survive whether oxygen is present or not

8. Long whiplike structure used for movement

9. Needs oxygen to survive

10. Specialized prokaryotic cell that can withstand harsh conditions

11. Prokaryotic method of gene exchange

12. Cannot live in the presence of oxygen

13. Separate circular piece of a prokaryote’s genetic material


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Power Notes

1.

2.

3.

4. 5.

6.

BacteriaStructural characteristics

Obligateanaerobe:

Facultativeanaerobe:

Obligateanaerobe:

Molecular characteristics

Archaea


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Reinforcement

KEY CONCEPT Bacteria and archaea are both single-celled prokaryotes.

Prokaryotes, which include bacteria and archaea, are the most widespread and abundantorganisms on Earth. Prokaryotes can be grouped based upon their need for oxygen.

• Obligate anaerobes cannot live in the presence of oxygen. An obligate anaerobeis actually poisoned by oxygen.

• Obligate aerobes must have oxygen in their environment to survive.

• Facultative aerobes can survive whether oxygen is present in the environment ornot.

Prokaryotes do not have any membrane-bound organelles such as a nucleus containingdouble-stranded DNA. Instead, their DNA is surrounded by cytoplasm and is in theform of a circle. Prokaryotes may also have plasmids. A plasmid is a small piece ofgenetic material that can replicate separately from the prokaryote’s main chromosome.

Bacteria and archaea look very similar, but many of their structures are made of differentcompounds. This indicates that bacteria and archaea are not closely related. Molecularevidence suggests that archaea have at least as much in common with eukaryotes as theydo with bacteria. For instance, although they both often have flagella—long, whiplikestructures outside of a cell that are used for movement—the flagella of bacteria arestructurally different from those of archaea. The cell walls and membranes betweenthe two kingdoms of prokaryotes are also different. Bacteria have a polymer calledpeptidoglycan in their cell walls, whereas archaea do not. The amount of peptidoglycanthat bacteria have is an important characteristic of bacteria. Bacteria are often identifiedbased on this difference, by using a staining method called a Gram stain.

The strategies that prokaryotes use to survive and to transfer genes have made themvery successful at adapting quickly to almost any habitat. Some prokaryotes can surviveharsh conditions by forming endospores, a specialized cell with a thick protective wall.Prokaryotes can transfer genes to each other through conjugation, an exchange ofchromosomes through a hollow bridge formed to connect two or more cells.

1. Prokaryotes are not the only organisms that can be grouped based upon their need foroxygen. In which of the three groups listed would humans fall under?

2. What are two characteristics of a prokaryote’s genetic material?

3. To the untrained eye, bacteria and archaea can look identical. What type of evidence ledto these two groups being placed in separate kingdoms?


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SECTION

18.5BENEFICIAL ROLES OF PROKARYOTES

Study Guide

KEY CONCEPT

Prokaryotes perform important functions for organismsand ecosystems.

VOCABULARYbioremediation

MAIN IDEA: Prokaryotes provide nutrients to humans and other animals.

1. Some prokaryotes live in animal digestive systems. What are three ways theseprokaryotes are helpful to the animals they live inside?

2. What are two ways animals help the prokaryotes that live in their digestive tracts?

3. What are examples of types of food we eat that are fermented by bacteria?

MAIN IDEA: Prokaryotes play important roles in ecosystems.Write the details about some of the roles prokaryotes play in an ecosystem.

Role Details

4. Atmospherecomposition

5. Element cycling

6. Nitrogen fixation


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7. Peas, beans, and other legumes have a mutualistic relationship with bacteria. Where dothe bacteria associated with these plants live?

8. The bacteria associated with legumes provide nitrogen to the plant in a usable form.Describe how they do this.

9. Some bacteria can digest oil. How are these bacteria helpful?

10. What does the term biodegradable mean?

11. What is a type of human-made material that is not biodegradable?

Vocabulary Check12. The term bioremediation can be broken into parts. Bio- means “life, or living organism.”

Remediation, or remedy, means “the act or process of correcting a fault.” How do theseword parts relate to what you have learned about bioremediation?


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Power Notes

Provide nutrients: Fix nitrogen:

Benefit ecosystems: Bioremediation:

Prokaryotes perform importantfunctions for organisms and ecosystems.


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Reinforcement

KEY CONCEPT Prokaryotes perform important functions for organisms andecosystems.

Prokaryotes are a key part of animal digestive systems. Having a balanced communityof prokaryotes in our bodies is important for our health. Prokaryotes have a beneficialrelationship, or mutualistic symbiosis, with the host animal. They break down food andhelp the animal absorb nutrients from the food that it eats. In return, the prokaryotesget a place to live. Prokaryotes also make vitamins and other compounds, and occupyplaces that might otherwise be filled by disease-causing bacteria. Humans also enjoymany foods that have unique flavors due to fermentation by bacteria. Fermented foodsinclude yogurt, cheeses, pickles, soy sauce, sauerkraut, and vinegar.

Even though you can’t easily see them, prokaryotes play important roles in everyecosystem they occupy. Some prokaryotes, such as cyanobacteria, produce oxygenthrough photosynthesis. Others help recycle carbon, nitrogen, hydrogen, and sulfurthrough the ecosystem. Animals and plants also depend on prokaryotes to “fix”atmospheric nitrogen, converting it to a form that is usable by other organisms. Nitrogenis necessary to make amino acids and proteins.

Another important use of prokaryotes in the environment is to help relieve Earth’spollution. Bioremediation is a process that uses prokaryotes to help break downpollutants in the environment. For example, some types of bacteria can digest oil,which is helpful for cleaning up oil spills and other industrial accidents. Bacteria candigest other pollutants as well. When you hear the term biodegradable, it often refers tothe ability of bacteria to break down a material. Some of the only materials made byhumans that cannot be biodegraded are certain types of plastics.

1. What are three ways we benefit by having prokaryotes living in our digestive tracts?

2. Why do you think that we do not get sick from eating foods such as yogurt that oftencontain live bacteria cultures?

3. What are three important roles that prokaryotes play in an ecosystem?

4. What are two ways that prokaryotes help relieve pollution?


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SECTION

18.6BACTERIAL DISEASES AND ANTIBIOTICS

Study Guide

KEY CONCEPT

Understanding bacteria is necessary to prevent and treatdisease.

VOCABULARYtoxinantibiotic

MAIN IDEA: Some bacteria cause disease.

1. What are two ways that bacteria can cause illness?

2. Why are people often unaware of the presence of potentially disease-causing bacteria intheir bodies?

3. What are two ways that people can get food poisoning?

MAIN IDEA: Antibiotics are used to fight bacterial disease.

4. Why can’t antibiotics be used to cure infections caused by viruses?

5. What are two types of organisms that produce antibiotics naturally?

6. What can you do to help prevent getting a bacterial infection?


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MAIN IDEA: Bacteria can evolve resistance to antibiotics.In the chart below, use your own words to describe the factors that have led to widespreadantibiotic resistance.

Factor Resistance

7. Overuse

8. Underuse

9. Misuse

Vocabulary Check10. A poison released by a living thing

11. Medicine that helps you fight bacterial infection

Identify the InfectionUse Figure 18.18 to help you identify the infection when given the causes.

12. an open wound that gets dirty

13. breathing in this bacteria’s endospores

14. skin making excess oil

15. getting bitten by an infected wood tick

16. many bacteria on teeth and gums


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Power Notes

Cause

Result

Antibiotic resistance:

Overuse:

Underuse:

Misuse:

Antibioticresistance

1.

1. 2. 3.

2.

3.

4.

Bacterial Infection Details


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Reinforcement

KEY CONCEPT Understanding bacteria is necessary to prevent and treat disease.

Although the majority of bacteria are not pathogenic, some do cause disease. Bacteriacan cause illness to a host in two basic ways: by invading tissues and attacking cells orby making poisons, or toxins, that can be carried by blood to sites throughout the body.A toxin is a poison released by an organism.

Some bacteria make their hosts sick through food poisoning. Bacteria that normallylive in nasal passages, such as Staphylococcus aureus, can be transferred to food whenfood handlers don’t wash their hands after they blow their nose. This transfer can resultin serious food poisoning, known as staph poisoning. Even high temperatures cannotdestroy a toxin produced by S. aureus. The most common source of food poisoning byS. aureus, however, is from foods that were contaminated after they were cooked. Ifcontaminated food is not refrigerated, bacteria can multiply and produce a large amountof toxin. Another deadly type of bacteria that causes food poisoning is Clostridiumbotulinum. These bacteria produce a deadly toxin. Botulism is usually caused by theeating of improperly canned foods that were contaminated with endospores of C.botulinum before being sealed. Bulging cans are a sign that these disease-causingbacteria may be present.

Antibiotics, chemicals that slow the growth of bacteria, are used to fight bacterialinfection. They are produced naturally by some species of bacteria and fungi. Manyantibiotics work by stopping bacteria from forming cell walls. They can be used asmedicine for humans and other animals without damaging their cells, since animal cellsdo not have cell walls. However, through natural selection, many bacteria have becomeresistant to commonly used antibiotics. It is important not to use antibiotics whenbacteria are not causing an illness. It is also important to finish an entire prescription ofantibiotics if you have a bacterial infection—otherwise, you may not have destroyedall of the bacteria, only the weakest ones.

1. How is a toxin different from other poisons?

2. What are the two general ways that bacteria cause illness?

3. Why is keeping food refrigerated important for safety?

4. What is one way that antibiotics are effective against disease-causing bacteria?


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CHAPTER

18SELECTING DATA REPRESENTATION

Data Analysis Practice

An important step in a scientific investigation is to determine which type of graph accuratelyrepresents data collected in a study.

The table below contains data collected about the chemical composition of a bacterial cell.The second column shows the percentage of each substance in the cell. The third columnshows the number of types of each molecule.

CHEMICAL COMPOSITION OF A BACTERIAL CELL

Substance Percent of Total CellWeight

Number of Types of EachMolecule

Water 70 1

Inorganic Ions 1 20

Sugars 1 250

Amino Acids 0.4 100

Nucleotides 0.4 100

Fatty Acids 1 50

Other Small Molecules 0.2 300

Macromolecules 26 3000

1. Graph Data Determine which type of graph would best represent each of the twosets of data, then graph each set of data on separate graphs in the space below.

Unit 6 Resource Book Data Analysis Practice 51McDougal Littell Biology

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2. Explain Why did you choose each graph type to represent each set of data?

3. Conclude What can you conclude from each set of data?

52 Data Analysis Practice Unit 6 Resource BookMcDougal Littell Biology

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CHAPTER

18WEST NILE VIRUS: TRAIL OF A NEW EPIDEMIC

Pre-AP Activity

You have learned in Chapter 18 that viruses cause illness by invading a host’s tissues. Buthow are viruses actually transmitted to the host? If you’ve ever had a cold, you already knowthat pathogens can be transmitted through the air. Some viruses are transmitted throughcontact with another person or a contaminated object; others are transmitted when the hosteats contaminated food. Another mode of transmission is via a vector––an animal that carriesa pathogen from one host to another. The most common vectors are arthropods such as lice,fleas, ticks, and mosquitoes. These parasitic organisms can infect a host when they feed onits blood.

WEST NILE VIRUS: AN OVERVIEW

West Nile virus (WNV) is a vector-borne virus transmitted by infected mosquitoes to birds,humans, and a number of different mammals. Wild bird populations serve as a reservoir forthe virus. A reservoir is a host that harbors a pathogen, serving as a source from which thepathogen can infect others. WNV generally cycles between mosquitoes and birds; humansand other mammals are incidental hosts. Most infections occur in the summer and fall.

Most people infected with WNV show no clinical signs of illness. Among thoseindividuals who do become ill, symptoms include fever, headaches, fatigue, and a mild rashon their backs. More severe illnesses stemming from WNV involve the central nervoussystem. West Nile meningitis, which causes a high fever, headache, and a stiff neck, resultswhen the tissue covering the brain and spinal cord is infected. West Nile encephalitis involvesinflammation of the brain itself, and symptoms can include mental confusion, paralysisof limbs, and coma.

EPIDEMIOLOGY

The first documented case of West Nile virus was in Uganda in 1937. For several decades, thevirus was confined to Africa and the Middle East. It appeared in France in 1962 and Romaniain 1996. Its appearance in New York City in 1999 was the first in the Western Hemisphere.The virus was identified after a summer that featured an unusually high number of bird deaths.A public health alert to physicians around the state led to diagnoses of the disease in humans.By the end of that year, 62 human cases had been documented, of which seven proved fatal.

Epidemiologists began tracking the spread of the virus. By 2001 the geographicdistribution extended to the Gulf of Mexico and to states just west of the Mississippi River.By 2005, all of the lower 48 states reported cases of WNV in birds and wildlife, if not inhumans. The number of mosquito species that carried the virus increased each year of theepidemic, from four species in 1999 to 60 in 2005.

THE MOVING RESERVOIR

The reservoir for the virus also has increased: WNV has been isolated from more than 160species of wild birds. Among these are nonmigratory birds, such as crows and sparrows, andbirds that migrate south each fall for the winter.

Some birds undertake a migration that is elliptical. The Connecticut warbler, for example,flies south-southwest in the fall from its home range in the northeast. After spending thewinter in the Caribbean, it then flies north-northwest through the south and midwest states. It

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then spends the breeding season in the upper midwest and south central Canada, and headsthrough the northeast states again in the fall.

YOUR TURN

Now it’s your turn to investigate the WNV epidemic. Examine the map presented below. Themap shows in which year the various states and regions had West Nile virus present for thefirst time in birds, mosquitoes, or mammals. You will notice right away the large increase inaffected states between 2000 and 2001, and again between 2001 and 2002.

20002001200220032004

Answer the following questions on a separate piece of paper.

1. Notice that WNV reached California before it hit Nevada, Utah, and Arizona. Explainhow the climates and environments of these states may have been involved with howquickly WNV reached them.

2. Formulate an explanation of WNV’s spread across the U.S. How might you relate themigratory patterns of birds to the pattern of WNV’s distribution? Feel free to draw onthe map above to model the migratory pattern of birds such as the Connecticut warbler.

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CHAPTER

18THE CASE OF TYPHOID MARY

Pre-AP Activity

You have learned in Chapter 18 that infection with certain strains or types of bacteria cancause serious disease. Some people can carry and transmit infectious diseases withoutrealizing it because they don’t exhibit any symptoms. Such individuals are called carriers.

TYPHOID FEVER: AN URBAN SCOURGE

Typhoid fever is caused by infection with Salmonella typhi, a bacterial pathogen of humans.Typhoid bacteria are transmitted when people ingest contaminated food or water, or whencontaminated sewage gets into water used for drinking or washing food. In the body, S. typhiinhabits the intestines and is shed in the feces. If the shedder doesn’t practice good hygiene,such as washing the hands after using the toilet and before handling food, he or she can spreadthe bacteria to others. Once S. typhi is ingested, it quickly spreads to the blood, producingheadaches, upset stomach, and very high fever that can lead to death.

THE CASE BEGINS

At the turn of the 20th century, infectious diseases such as cholera and typhoid fever werethe leading cause of death in the United States, particularly among the urban poor. This waslargely due to poor sanitation: clean water was at a premium in the crowded tenementsof poor city neighborhoods. Guidelines on hygiene—washing hands, especially beforehandling food—were slow to reach poor people. However, public health officials had begunto understand the importance of proper sanitation, and were focused on improving the watersupply and educating the public on personal hygiene.

In 1906, an outbreak of typhoid fever among six members of a wealthy family wasreported to authorities. The Warren family had spent the summer visiting friends on LongIsland. Cases of typhoid among the wealthy were unusual, particularly in affluent summercommunities. Investigators made a thorough search of the home and grounds but failed tofind a source of contamination. Further questioning revealed that the family had becomeill several weeks after hiring a new cook—and that the cook had left their employ shortlyafter the outbreak began. The cook was described as a healthy Irish woman around 40 yearsold by the name of Mary Mallon.

Mary Mallon was born in 1869 in Ireland, and immigrated to the United States whenshe was 14 or 15. Like many Irish immigrant girls of that time, Mary first found work as amaid. She had a gift for cooking and, noting that a cook’s wages were higher than a maid’s,she became a cook. Between 1900 and 1906 she worked as a cook for eight families. Asinvestigators later learned, members of six of the eight families became ill with typhoid feverafter Mary came to work for them; one of them, a young girl, had died.

THE INVESTIGATION

George Soper, the epidemiologist investigating the Warren household outbreak, wasconvinced that Mary Mallon was an otherwise healthy carrier of typhoid. In the springof 1907, he located Mary, who now was cooking for another family. Soper approachedMary without warning and somewhat abruptly: he showed up at the kitchen door where sheworked, briefly explained that she was spreading disease through her cooking, and informedher that she had to furnish blood and stool samples immediately. Mary, understandablyshocked and probably frightened, chased him out of the house with a carving fork. A similarscenario ensued when the next city health official arrived at Mary’s kitchen door. The

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official then returned with five police officers. Armed with her carving fork, Mary ranout of the house and hid nearby. After a search of several hours they found Mary hidingunder a stairway. Cornered, she became even more violent, and it took all five policemento restrain her. She was then transported to an isolated quarantine facility. A large part ofMary’s reaction resulted from her firm belief that they had the wrong person. She maintainedthat she had never had typhoid, so she could not be a carrier, refusing to accept the possibilitythat she had probably once had a very mild case and had not realized it. However, weeklytests conducted over several months on her blood and stools showed that she harbored alarge population of S. typhi. Soper later recalled how the results supported his hypothesisof how Mary had transmitted the disease:

From October 16, 1907, to February 5, 1908, weekly examinations of the stoolsgave . . . from 25 to 50 per cent typhoid-like colonies on the culture plates . . . Thecook was virtually a living culture tube in which the germs of typhoid multipliedand from which they escaped in the movements from her bowels. When at toilether hands became soiled, perhaps unconsciously and invisibly so. When sheprepared a meal, the germs were washed and rubbed from her fingers into the food.No housekeeper ever gave me to understand that Mary was a particularly cleancook . . . the infectious matter is believed to have been carried from the cook’shands to the people who were later taken sick by means of ice cream containingcut-up peaches. Mary prepared this herself. In this instance no heat sterilizedthe washings from her hands.

From: The Military Surgeon, July 1919, Vol. XLV No. 1

QUARANTINED FOR LIFE

Nicknamed “Typhoid Mary” by the newspapers, Mary remained in quarantine for three years.She was released in 1910 on condition that she never work again handling food. At first sheadhered to this, but in 1915, using a false name, she took a cooking job at a hospital. Heridentity was discovered when 25 people became ill and two died in a typhoid outbreak there.Seized again by authorities, Mary was returned to quarantine, where she remained untilher death in 1937 from complications of a stroke. Throughout her life, Mary adamantlymaintained that she had never had typhoid fever.

Answer the following questions on a separate piece of paper.

1. Describe the investigation of the Long Island outbreak in the language used to outlinethe steps of the scientific method.

2. Do you think that carriers are a greater public health threat than people who are ill?Why or why not?

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CHAPTER

18VIRUSES AND PROKARYOTES

Vocabulary Practice

virus prophage flagellum

pathogen epidemic conjugation

viroid vaccine endospore

prion retrovirus bioremediation

capsid obligate anaerobe toxin

bacteriophage obligate aerobe antibiotic

lytic infection facultative aerobe

lysogenic infection plasmid

A. Choose the Right Word Choose the term that corresponds to each definition below,then briefly explain the relationship that the group of terms all share:

virus viroid bacteriophage

prion pathogen

1. Infects plants

2. Only made of protein

3. Infects prokaryotes

4. Made of protein capsid and genetic material

5. General term for anything disease-causing

6. RELATIONSHIP:

lytic infection prophage lysogenicinfection

retrovirus

7. Made by viral DNA inserted into host DNA

8. Makes a DNA copy from RNA

9. Infection in which virus combines with the host and may lie undetected

10. Infection in which the virus causes the host cells to burst

11. RELATIONSHIP:

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VOCABULARY PRACTICE, CONTINUED

obligate anaerobe obligate aerobe facultative aerobe

12. Cannot survive in the presence of oxygen

13. Does not need oxygen but uses it if it is available

14. Must have oxygen to survive

15. RELATIONSHIP:

plasmid conjugation flagellum endospore

16. Resistant, dormant cell

17. Extra genetic material

18. Whiplike structure that aids movement

19. Way to transfer genetic material

20. RELATIONSHIP:

B. Do-It Yourself Matching In a random order, write short definitions for each term onthe blank lines to the right. Then give your paper to a classmate who should write the numberof the term next to the correct definition.

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1. antibiotic

2. vaccine

3. epidemic

4. pathogen

5. virus

6. prion

7. bioremediation

8. toxin

9. retrovirus

10. viroid


C. Synonyms or Antonyms Identify the words in each pair as synonyms, which arewords that mean roughly the same thing, or antonyms, which are words that mean roughly theopposite.

1. virus/bacteriophage

2. obligate anaerobe/obligate aerobe

3. pathogen/viroid

4. bioremediation/toxin

D. Situational Vocabulary Circle the letter of the situation that most closely relatesto each vocabulary word.

1. prion: a) infectious protein; b) infectious carbohydrate

2. capsid: a) protein covering of a virus; b) lipid covering of a virus

3. lytic infection: a) bursts host cells; b) bursts viral cells

4. lysogenic infection: a) forms a plasmid; b) forms a prophage

5. prophage: a) host DNA and viral DNA; b) host DNA and bacterial DNA

6. epidemic: a) outer layer of skin; b) widespread infection

7. vaccine: a) protects against all viral infections; b) protects against some viral andbacterial infections

8. retrovirus : a) makes an RNA copy of viral DNA; b) makes a DNA copy of viral RNA

9. facultative aerobe: a) can use oxygen if available; b) must have oxygen to survive

10. plasmid: a) extra genetic material in bacteria; b) essential genetic material in bacteria

11. conjugation: a) method of genetic material transfer; b) method of survival in harshconditions

12. endospore: a) bacterial DNA in tough outer coat; b) extra DNA that transfers betweencells

13. antibiotic: a) kills or slows growth of virus and bacteria; b) kills or slows growth ofbacteria only

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E. Analogies Read each analogy. Decide which term is most like it.

capsid vaccine bioremediation

epidemic flagellum toxin

1. Preparing the football team by practicing defensive plays before the big game

2. A football helmet covering and protecting the brain of the player

3. The legs of the players, moving them down the field

4. Insults being yelled from the stands and making the players feel bad

5. The catchy cheerleader’s chant spreading to everyone throughout the stands

6. The cleaning crew picking up all the litter after the game

F. Word Triangle Write the definition of each term in the bottom section of the triangles.In the middle section, write a sentence in which the term is used correctly. In the top section,draw a small picture to illustrate the term.

1. BACTERIOPHAGE:

2.

3.

4. PROPHAGE:

5.

6.

7. PLASMID:

8.

10. FLAGELLUM:

11.

9. 12.

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