Table of Contents lev h microscopic.… · pathogens(path•uh•juhnz) —disease carriers diphtheria (dif•theer•ee•uh)—a disease that causes difficulty in breath-ing, high

Phoenix Graphix ___ 1R ___ Final _x_ PDF

Introduction to the Reading Partners and the Strategies . . . . . . . 6

Unit 1: Unsolved Mysteries in MedicineUnit 1 Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Learn the Strategies: Viruses: The Tiniest Killers . . . . . . . . . . . . . . . . . . . . . 11

Organizing Information: Network Tree . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Writing for Comprehension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Vocabulary: Multiple Meanings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Fluency: Readers’ Theater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Practice the Strategies: Medical Detectives: In Search of MicroscopicSuspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25Vocabulary: Synonyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34Fluency: Journal Entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Apply the Strategies: Curing the Common Cold . . . . . . . . . . . . . . . . . . . . 37 Vocabulary: The Prefix anti- . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44Fluency: Limericks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45Reading in the Real World: Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46Connecting to the Real World: Explore More . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Unit 2: The Olympics—Then and NowUnit 2 Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50Learn the Strategies: The Ancient and Modern Games . . . . . . . . . . . . . . . 53

Organizing Information: Time Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62Writing for Comprehension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63Vocabulary: Greek Words . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64Fluency: Interview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

Practice the Strategies: Olympic Traditions . . . . . . . . . . . . . . . . . . . . . . . . 67Vocabulary: Idioms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76Fluency: Journal Entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

Apply the Strategies: “Swifter, Higher, Stronger” . . . . 79Vocabulary: Roots and Affixes . . . . . . . . . . . . . . . . . . . . . . 86Fluency: Poetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87Reading in the Real World: Schedule . . . . . . . . . . . . . . . . . 88Connecting to the Real World: Explore More . . . . . . . . . . . . 90

Table of Contents

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Table of Contents (continued)

Unit 3: Rediscovering People in America’s PastUnit 3 Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92Learn the Strategies: Mystery of the Mound Builders . . 94

Organizing Information: Outline . . . . . . . . . . . . . . . . . . . . . . . . 106Writing for Comprehension . . . . . . . . . . . . . . . . . . . . . . . . . . 107Vocabulary: Algonquian Words . . . . . . . . . . . . . . . . . . . . . . . . . 108Fluency: Poetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109

Practice the Strategies: In Search of Jamestown . . . . . . . . . . . . . . . . . . . 110Vocabulary: The Root nat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120Fluency: Readers’ Theater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121

Apply the Strategies: Urban Archaeology: Peeling the Big Apple . . . . . . 122Vocabulary: Synonyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132Fluency: Poetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133Reading in the Real World: Events Calendar . . . . . . . . . . . . . . . . . . . . . . . . . . . 134Connecting to the Real World: Explore More . . . . . . . . . . . . . . . . . . . . . . . . . . . 136

Unit 4: Endangered or Extinct?Unit 4 Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138Learn the Strategies: Going, Going, Gone . . . . . . . . . . . . . . . . . . . . . . . . 140

Organizing Information: Cause-and-Effect Chart . . . . . . . . . . . . . . . . . . . . . . . . 152Writing for Comprehension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153Vocabulary: Word Origins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154Fluency: Poetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155

Practice the Strategies: Valuing “Varmints” . . . . . . . . . . . . . . . . . . . . . . . . 156Vocabulary: Analogies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166Fluency: Biography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167

Apply the Strategies: DDT and the Peregrine Falcon . . . . . . . . . . . . . . . 168Vocabulary: Eponyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176Fluency: Interview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177Reading in the Real World: Time Scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178Connecting to the Real World: Explore More . . . . . . . . . . . . . . . . . . . . . . . . . . . 180

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Unit 5: They Came Across the WaterUnit 5 Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182Learn the Strategies: Dan Thuy’s New Life in America . . . . . . . . . . . . . . 184

Organizing Information: Sequence Chain . . . . . . . . . . . . . . . . . . . . . . . . . 194Writing for Comprehension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195Vocabulary: French Words . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196Fluency: Poetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197

Practice the Strategies: The Acosta Family . . . . . . . . . . . . . . . 198Vocabulary: Context Clues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208Fluency: Folktale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209

Apply the Strategies: One More Border: The True Story of OneFamily’s Escape From War-Torn Europe . . . . . . . . . 210

Vocabulary: Multiple Meanings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222Fluency: Readers’ Theater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223Reading in the Real World: Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224Connecting to the Real World: Explore More . . . . . . . . . . . . . . . . . . . . . . . . . . . 226

Unit 6: The FutureUnit 6 Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228Learn the Strategies: From the Horse to the Skycar . . . . . . . . . . . . . . . . 230

Organizing Information: Series of Events Chain . . . . . . . . . . . . . . . . . . . . . . . . . 240Writing for Comprehension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241Vocabulary: Prefixes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242Fluency: Song Lyrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243

Practice the Strategies: Medicine in the New Millennium . . . . . . . . . . . 244Vocabulary: Root Words and Affixes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254Fluency: Readers’ Theater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255

Apply the Strategies: Space Colonies: Our Future Home? . . . . . . . . . . . . 256Vocabulary: Words From Roman Mythology . . . . . . . . . . . . . . . . . . . . . . . . . . . 266Fluency: Speech . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267Reading in the Real World: Time Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268Connecting to the Real World: Explore More . . . . . . . . . . . . . . . . . . . . . . . . . . . 270

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Hi! We’re your

Reading Team Partners!FOR

In each unit, you’ll learn three strategies—one to use Before you read,one to use During your reading, and one to use After you read. You’llwork with these strategies in all three reading selections in each unit.

In the first selection, you’llLearn the unit strategies.When you see a red button likethis , read “My Thinking”notes to see how one of usmodeled the strategy.


In the second selection in eachunit, you’ll Practice the strategiesby jotting down your own notesabout how you used the same unitstrategies. The red button willtell you where to stop and thinkabout the strategies.

Have you noticed that the reading you do in science and social studies isdifferent from reading stories and novels? Reading nonfiction is different.When you read nonfiction, you learn new information. We’ll introduce youto some strategies that will help you read and understand nonfiction.

When you read the last selection in eachunit, you’ll Apply the strategies. You’ll decidewhen to stop and take notes as you read.

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Preview the Selectionby looking at the title andheadings to predict whatthe selection will be about.

Make Connectionsby relating information thatI already know about thesubject to what I’m reading.

Recallby summarizing theselection in writing orout loud.

Activate PriorKnowledgeby looking at the title,headings, pictures, andgraphics to decide what Iknow about this topic.

Interact With Textby identifying the mainidea and supporting details.

Evaluateby searching theselection to determinehow the author usedevidence to reachconclusions.

Set a Purposeby using the title and headings to write questionsthat I can answer while Iam reading.

Clarify Understanding by using photographs,charts, and other graphicsto help me understandwhat I’m reading.

Respond by drawing logicalconclusions aboutthe topic.

Preview the Selectionby looking at the photo-graphs, illustrations, captions, and graphics topredict what the selectionwill be about.

Make Connectionsby comparing my experiences with what I’m reading.

Recallby using the headingsto question myselfabout what I read.

Activate PriorKnowledgeby reading the introductionand/or summary to decidewhat I know about thistopic.

Interact With Textby identifying how thetext is organized.

Evaluate by forming a judgmentabout whether theselection was objectiveor biased.

Set a Purposeby skimming the selectionto decide what I want toknow about this subject.

Clarify Understandingby deciding whether theinformation I’m reading isfact or opinion.

Respond by forming my ownopinion about whatI’ve read.

UNIT6

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Here they are—the Before, During,and After Reading Strategies.

DURING READING AFTER READINGBEFORE READING

Now that you’vemet the team,it’s time to getstarted.

UNIT5

UNIT4

UNIT3

UNIT2

UNIT1

Use these strategies with all your nonfiction reading—social studies andscience textbooks, magazine and newspaper articles, Web sites, and more.

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DURING READING

AFTER READING

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Recall by summarizing theselection in writingor out loud.

Make Connections by relating information thatI already know about the subjectto what I’m reading.

LEARNthe strategiesin the selectionViruses: The Tiniest Killerspage 11

BEFORE READING

Preview the Selection by looking at the title and headings to predict what theselection will be about.

Unit1

Unit1


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PRACTICEthe strategiesin the selectionMedical Detectives: In Search ofMicroscopic Suspectspage 25

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APPLYthe strategiesin the selectionCuring the Common Coldpage 37

Unsolved Mysteriesin Medicine



Think Aboutthe

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Preview the Selection by looking at the title and headings to predictwhat the selection will be about.

My ThinkingThe strategy says to preview the selection to predict what the selection will be about. The titlesays that viruses kill. The headings mention cells,viruses, the past, and a battleground. I predict theselection will explain viruses, our history, and ourfuture challenges in relation to viruses. Now I’mready to read and find out if my prediction is right.

BEFORE READING


DURING READING

Make Connections by relating information that I already know aboutthe subject to what I’m reading.

My ThinkingThe strategy says to make connections by relatinginformation I already know about the subject towhat I’m reading. I will stop and think about thisstrategy every time I come to a red button like this .


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In 1519, a Spanish explorer named Hernando Cortezlanded in an area that is now part of Mexico. A year later,in 1520, thousands of Aztec Indians began fighting againstCortez and his 400 men. What happened next changed thecourse of history. The Aztecs had built a strong civilization.They were experienced warriors. The Aztecs should havebeen able to kill all the Spaniards. But they didn’t. In fact,the Aztecs hardly fought the Spaniards at all. Cortez’stroops were able to defeat the mighty Aztec nation. Cortezdestroyed the Aztecs’ capital city. He built Mexico City onits ruins.

How could this have happened? How could a few hundred soldiers defeat an entire empire?

LearnLearnthe strategiesthe strategies


The Aztecs greet HernandoCortez. This drawing isfrom a manuscript byFriar Diego Duran.

Viruses:The Tiniest

Killers


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A Virus Destroys an ArmyThe Aztecs were not really defeated by the Spanish

army, but by a disease—smallpox. On the night of theirdefeat, smallpox had broken out in the city. It quicklykilled the nephew of Montezuma, the Aztec emperor, andmany other Aztecs.

The Spanish had grown up with smallpox. Most of thesoldiers probably had it as children. If you survive small-pox, you won’t get it again. This is called building up animmunity.

In the New World, however, smallpox was unknown.The Spanish first brought it across the Atlantic Ocean. Thelocal population had no immunity against it. The diseasehad a disastrous effect on the Aztecs. Their warriors fellvictim to the virus, and the nation was defeated. Over thecourse of many years, smallpox killed millions of thenative population.

Vo • cab • u • lar • ysmallpox—a serious, highlycontagious disease marked bychills, fever, and pimples onthe skin

immunity (i•myoo•ni•tee)—the ability to resist a disease


germs

cells cells

How Some Germs Are Spread

When someone coughsand sneezes, germsare forced out intothe air.

The germs enteryour body whenyou breathe.

The germs attackyour cells, makingyou sick.

Diagram Why are theretwo arrows leading fromthe blue circle? How is thescale of the pictures in theblue circle different fromthe pictures in the blackcircles?

Answer: One blue arrowindicates what happenswhen a person sneezes.The other blue arrow indi-cates what happens to theperson who is exposed tothe sneeze. The scale inthe black circles is magni-fied to show the germsclose up.


Make Connectionsby relating informationthat I already know aboutthe subject to whatI’m reading.

My ThinkingI knew thatpeople commonlycatch colds. But Idid not know coldswere viruses.

Vo • cab • u • lar • yorganism(or•guh•niz•uhm)—anyliving thing

pathogens (path•uh•juhnz)—disease carriers

diphtheria(dif•theer•ee•uh)—a diseasethat causes difficulty in breath-ing, high fever, and weakness

antibiotics(an•ti•by•ot•iks)—a group ofmedicines that destroy bacteria

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What Is a Virus?Until about 100 years ago, almost any disease-causing

organism in humans was called a virus. But as scientistslearned what caused illnesses, they discovered thatdifferent types of pathogens, or disease carriers, causedifferent illnesses. Some, such as poisons, were easilyidentified. These included carbon monoxide, lead,mercury, arsenic, and potassium cyanide. Such chemicalsdestroy the body’s tissues if they are breathed in or eaten.

Bacteria—microscopic living organisms—also werefound to cause many diseases. These include strep throat,staph infections, and diphtheria. Much of our earlyknowledge about bacteria was gained through the work ofbrilliant and courageous scientists. People such as LouisPasteur, country doctor Robert Koch, and others learnedhow to combat bacteria with antibiotics. At first, itseemed that antibiotics could conquer all forms of disease.

Unfortunately, there was another, more resistantpathogen—the virus. So far, scientists have named morethan 3,000 viruses. Of those, several hundred affecthumans.

Fortunately, most viruses cause only a mild illness, orno illness at all. The most common type of virus producesthe most common disease—the cold.

Some viruses are very dangerous, however. Virusescause HIV, rabies, influenza, measles, smallpox, and manyother illnesses. In fact, diseases caused by viruses areresponsible for many deaths worldwide.

The Edge of LifeWhile bacteria are small—about four one-hundred

thousandths of an inch (that’s 4/100,000)—viruses are evensmaller. In fact, the largest known virus is only one-thirdas large as an average bacterium. Viruses are so small thatthousands of them can live inside a single cell!

Perhaps the oddest thing about viruses is that they existon the edge of life. They are not quite alive. Yet they arenot quite dead, either. Bacteria are definitely living things.They reproduce by dividing their cells. They need food,water, and oxygen to survive. Some can move around ontheir own.

the strategiesthe strategiesLearnLearn



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Viruses can’t do anything until they invade a livingcell. Then they take over the cell. Viruses are completelyparasitic. They are “living” in only one sense: They controltheir own reproduction. Outside a host cell, however, avirus is inert. It just sits and waits for a host to come along.

How Cells FunctionIn order to understand why viruses are dangerous, you

have to understand how they interact with cells. All cells—plant, animal, or bacteria—contain strands of chemicalscalled RNA and DNA. Roughly speaking,DNA is the cell’s master recipe, andRNA is its chef. RNA “cooks”the DNA, eventually makingthe organism called for inthe DNA recipe. WheneverRNA and DNA reproduce,their goal is to turn outperfect, unchangingcopies of themselves.

Viruses are strands ofRNA or DNA without acell to do all the cookingthat the complete reciperequires. That’s why theyneed to invade cells. Onceinside, the trouble begins.

My ThinkingI already knewthat cellscontained DNA.Now I understandhow DNA works.

Virus• not-quite living

particle

• must invade acell to survive

• reproduces quicklyinside a cell

• difficult to kill

• sometimeskilled by vaccines

• living organism

• can survive onits own

• reproduces bydividing its cells

• killed by antibiotics

Mic

roor

gani

sm

Bacterium

Viruses inside a cell


Vo • cab • u • lar • yparasitic (par•uh•sit•ik)—growing, feeding, and livingon or in another organism

host—a living thing on whichanother living thing lives

inert (in•urt)—having nopower to move or act


Vo • cab • u • lar • ymembranes—thin layers oftissue that cover or line certainorgans

nutrients (noo•tree•uhnts)—foods

evolution(ev•uh•loo•shuhn)—a processin which change takes place

mutation(myoo•tay•shuhn)—a changein a living thing that can beinherited by its offspring

[ 15 ]

Invading a CellIt might sound odd, but a virus uses its shape as a

weapon to invade a cell. If a virus wants to invade aparticular cell, it grows into a particular shape. Forexample, some viruses are thin rods. Some look like six-sided bullets. Others bristle with spikes. One even lookslike a spider with a doll’s head!

Cells defend themselves by trying to stay cut off fromthe outside world. But cells still need entryways throughtheir membranes so that nutrients, salts, and other need-ed materials can enter. Cells also need openings to throwout waste products. These areas are called receptor sites,and they are shaped differently on different cells. Virusestry to find receptor sites through which they can fit.

If a virus finds an opening in a cell that is a good fit, itcan trick the cell into letting it in. Once inside, the virus’sDNA interferes with the cell’s DNA “cooking” process,although no one knows exactly how.

A Master MultiplierThe DNA in a virus uses a cell’s DNA to produce copies

of itself. This can happen very quickly. One doll’s headvirus can create about 100 new viruses per cell in about30 minutes.

Those 100 viruses thenleave that cell and invade 100new cells. Once they repro-duce, there can be 10,000viruses. Then those 10,000invade 10,000 more cells.Within a couple of hours, onevirus can become 100 millionviruses.

One thing that helpsviruses stay ahead of thebody’s defenses and ahead ofmodern medicine is theirrapid evolution. They canchange their shape frequentlyin a process called mutation.Whenever a virus copies its


Model of DNA

Doll’s head virus



[ 16 ]


DNA inside a cell, pieces of the DNA often get copied inthe wrong order—just as you may sometimes mix up theposition of the letters on your computer keyboard and typea word incorrectly. Because viruses change almost con-stantly, it is easy for them to find new ways to invade hostcells and spread themselves around.

Deadly Outbreaks of the PastThe changing nature of viruses is best shown by one of

the most common viral diseases, influenza, or simply “theflu.” The flu has probably been attacking humans for atleast 2,000 years. A deadly epidemic in Athens, Greece, inthe year 430 B.C. may have been influenza.

Some writers in the Middle Ages clearly describeinfluenza epidemics. More recently, an outbreak ofSpanish flu, which occurred between 1918 and 1919,killed about 22 million people worldwide. That’s more thantwice as many as the death toll from World War I. Therewere major flu epidemics in 1957 (Asian flu), in 1968(Hong Kong flu), and in 1977 (Russian flu). In fact, a flupandemic—a worldwide spreading of the disease—seemsto occur about every ten years.

An influenza virus often breeds first in ducks or pigssomewhere in Asia. Then it sweeps across Africa andEurope, finally ending up in America. Why this patternoccurs is unclear. It might be because contact amonghumans, ducks, and pigs is more frequent in Asia.

How to Fight a VirusIt is difficult to kill a virus once it takes hold.

Antibiotics can stop diseases caused by bacteria. Becauseviruses work from inside cells, medicines can’t attackviruses without attacking and killing the cells, too. Adifferent plan is needed.

When viruses first move from one kind of animal toanother, some of the more dangerous strains are weakened.Scientists use these weakened viruses to make vaccines.Vaccination allows the body to build up an immunityto the virus. If the virus tries to infect a body that hasbeen vaccinated, the body’s own defenses can kill it.

My ThinkingI knew that theflu is short forinfluenza. But I didnot know how deadlythe virus can be.

Vo • cab • u • lar • ypandemic (pan•dem•ik)—a worldwide spread of adisease

vaccines (vak•seenz)—substances used for theprevention of diseases




My ThinkingMy grandmothergets the influenzavaccine each year.But I did not knowthat she still might beable to get the flu.

Vo • cab • u • lar • yvector (vek•tuhr)—an organism that carries adisease from one host toanother

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Smallpox has been completely eliminated in humans,thanks to vaccination. The last known cases of smallpoxwere seen in 1977.

Viruses and VectorsVaccination doesn’t work as well with influenza, howev-

er. The first year a person gets a flu shot, he or she proba-bly won’t get sick. But the next year, the same vaccinemight not work as well. By the third year, there’s a chancethe vaccine won’t work at all. The reason: The flu viruschanges its form all the time.


Viruses use another tool, called a vector, to keepinfecting new host animals. Vectors are organisms thatcarry a virus from one host to another. In the case of themost deadly viruses, vectors allow the virus to spreadbefore the host animal dies. This is important for thevirus’s survival. If the host dies before the virus is spread,the virus dies with it.

In 1918, people wore masks. They mistakenly thought theywould be protected from the flu.



Vectors spread diseasein two ways. The first is aset of symptoms causedby the virus. Symptomsin the host help it spreadeasily to other hostsbefore the original onedies.

In the case of rabies,symptoms include froth-ing at the mouth andbiting. The virus is spreadby the infected animal’ssaliva. The same processis used by the cold virusin humans, which isspread by coughing andsneezing.

The second type ofvector is an animal thatcarries the virus without getting sick from it. This is howmosquitoes spread viral diseases such as yellow fever.

[ 18 ][ 18 ]

Vo • cab • u • lar • ysymptoms (sim•tuhmz)—signs of a disease


I knew thatmosquitoes couldspread diseases,but I did not real-ize that they carrythe virus without gettingsick themselves.


Mosquitoes like this one (shown in amagnified view) spread yellow feverand other diseases.

HIV virus


Think Aboutthe

Recall by summarizing the selection in writing or out loud.

My ThinkingThe strategy says to summarize the selection.Viruses live in host cells by invading them. There havebeen major outbreaks of viruses in the past. Peopleget vaccines to help prevent them from catching avirus. Research is being done to find treatments forviruses.

AFTER READING

[ 19 ]

Vo • cab • u • lar • yleukemia(loo•kee•mee•uh)—a cancerof the blood

predators (pred•uh•tuhrz)—living things that hunt otherliving things for food

prey (pray)—any animalhunted by other animalsfor food

A Changing BattlegroundBecause there are so many viruses, and because they

change rapidly, our fight against them takes place on aconstantly changing battleground. New vaccines are need-ed all the time because new viruses appear frequently. HIV,West Nile virus, and SARS are a few of the newest. So far,no cures have been found for them.

Research has shown that viruses can even cause certainforms of cancer, such as adult T-cell leukemia. But little isknown about this so far.

You might be familiar with the phrase “survival of thefittest.” This means that the strongest creatures and plantssurvive. Most people see this fight for survival as a strug-gle among enemies: predators and prey, or one humanbattling another. Many biologists now believe, however,that one of the most important factors in how life hasdeveloped on Earth has been how organisms respond toviral infections. Fitness in the microscopic world may bemore important than fitness in the visible world. Viruseshave never given up the struggle. They continue to be oneof our most dangerous enemies. And in many ways theyremain an unsolved medical mystery.




Graphic organizers help us organize information. I think this articlecan be organized by using a network tree. Here is how I organized theinformation. I put my central idea at the top. I used supportingideas on the next level, and details relating to the supporting ideason the bottom levels.

Vectors carrythe virus from host

to host.

Organizing InformationOrganizing Information

Network Tree

[ 20 ]


Viruses:The Tiniest Killers

What is a virus?

What does avirus do?

Some of the newest recognized

viruses are HIV,SARS, West Nile.

It is a microorganism.

It invades cellsto live and multiply.

There are no curesfor viruses,

only vaccines.

It is made of RNAor DNA without

a cell.


A Summary ofViruses: The Tiniest Killers

Viruses are microorganisms. They are so small that thousands ofthem can live inside one tiny cell in our bodies. A virus is only aboutone-third the size of an average bacterium. Viruses are made ofstrands of RNA or DNA. However, they cannot function outside a cell.The cell’s outer membrane tries to keep viruses out, but the virusesseek out receptor sites on the membrane. These receptor sites areopenings that are the correct shape to allow certain viruses to slipinto the cell. After invading a cell, a virus quickly multiplies, makingmillions of copies of itself.

Medicine cannot cure a disease caused by a virus. Still, vaccinescan help people build up immunity to certain viruses. Unfortunately,viruses often change shape, or mutate. Then the old vaccine cannotkeep them out of the body’s cells. A new vaccine must be developed.

Some viruses can be spread by saliva or blood. Other viruses arespread by vectors. A vector is an organism, such as a mosquito, thatcarries the virus to other animals without getting sick itself.

Smallpox is an old virus, but vaccines keep this virus under control.Newer viruses include AIDS, West Nile virus, and SARS. So far, scien-tists have not found a cure for these.

I used my graphic organizer to write a summary of the article.Can you find the information in my summary that came frommy network tree?

Writing for ComprehensionWriting for Comprehension

[ 21 ]

Introduction Here is how I developedmy introductory para-graph. It gives readersan idea of what theyare about to read.

Body I used information fromthe network tree toconstruct the paragraphsin the body of my paper.

Conclusion I summarized my paperby explaining the mostrecent findingsregarding viruses.



[ 22 ]

Many words have more than one meaning. When words are usedin different subjects, they can mean different things. Knowing thedifferent meanings of words prevents confusion when you read.

The word host is a good example. You are probably familiar withthe following meanings of the word host:

• a person who entertains guests• a television or radio personality who leads a talk show

Read the passage that contains the word host from “Viruses: TheTiniest Killers.”

They are “living” in only one sense: They contr ol their ownreproduction. Outside a host cell, however, a virus is inert.It just sits and waits for a host to come along.

From the serious subject of the sentence you can tell that hostmust have another meaning. The word host in the passage means“a living thing on which another living thing lives.” When yousee the word host in a passage, you can look for clues in the sen-tence to help you choose the correct meaning.

Multiple Meanings

The words below appear in “V iruses: The Tiniest Killers,” andthey deal with the subject of biology. You may know othermeanings for the words. On a separate sheet of paper , writetwo sentences that show two different meanings for eachword. If you need help, use a dictionar y.

1. immunity 3. evolution2. inert 4. predator


DevelopingDeveloping


[ 23 ]

When you perform this script for your class, besure to speak slowly, loudly, and expressively soall will understand and appreciate the stor y.

TIPFluency

➢

Readers’ TheaterRead the play out loud and practice the parts as if youwere part of an ancient people.



Narrator: Aztecs had never seen anything like smallpoxbefore. When so many became infected, they thought it wasa punishment from the gods. The medicine man per formedhealing rituals and advised the people on how to use herbs.Apothecaries sold herbal medicines in the marketplace.Aztec soldier: Healer, help us!Medicine man: Why have you come to me?Aztec soldier: We are sick and dying. Hundreds of us lie suf-fering. We are on fire with fever. We ache in our heads andbacks. These sores come first to our faces and hands. Thenthey spread to our arms and our bodies. What is this tor-ment? Can you help us?Medicine man: The Sun god is not pleased with us. He hassent this mysterious sickness to destroy us. Aztec soldier: What can we do?Medicine man: Go to the apothecary and bring back copal,agave, and black beetles.Aztec soldier: What will we do with these?Medicine man: We will burn the copal and let its smokepurify the rooms of the sick. I will make an ointment ofagave and black beetles to spread on the burning sores. Insteam baths, you will sweat out the evil spirits.Aztec soldier: I will run to the apothecar y now.



DURING READING

Think Aboutthe

BEFORE READING


When you come to a red button like this ,write notes on your own paper to tell how youused this strategy.

[ 24 ]


Write notes on your own paper to tell how youused this strategy.

rfr.H.se.u1.P.p024-035_73416 2/3/10 3:44 PM Page 24


the strategiesthe strategiesPracticePractice

Vo • cab • u • lar • yfatal (fayt•l)—deadly

[ 25 ]

One of the First Medical DetectivesDuring the early 1880s in France, Louis Pasteur

[pas•toor], a chemist, was trying to find a cure for rabies.At the time, rabies was a dangerous disease and alwaysfatal in humans. Because people were so afraid of gettingrabies, mobs sometimes hunted down and killed peopleinfected with the disease.

The symptoms of rabies are scary. First, you feel asthough your skin is crawling. Then you become so excitedthat you can’t calm down. You begin to feel very afraid,and for some reason you become afraid of water. Next,your body begins to shake wildly and you can’t control it.In the next stage, you can’t move at all. Then, death hap-pens quickly.

Pasteur in his laboratory

In Search of MicroscopicSuspects

In Search of MicroscopicSuspects

Medical DetectivesMedical Detectives


[ 26 ]

Vo • cab • u • lar • ytransmitted (trans•mi•tid)—passed from one to another

isolate (eye•suh•layt)—to separate from others

deliberately(di•lib•uhr•it•lee)—on purpose

euthanized(yoo•thuh•nyzd)—put todeath in a painless way

Rabies most often infects dogs and their relatives, suchas wolves and foxes. It is also found in bats and raccoons.No matter which animal catches rabies, this terrible dis-ease always produces the same results. Rabid animals diea painful death—so painful that it usually drives themmad. They attack and bite anything that comes near them.In fact, that is how rabies usually is transmitted—throughthe bite of an infected animal. The virus that causes thedisease lives in the animal’s saliva. Pasteur tried intently toisolate the virus that causes the disease.

Finding the VirusWhenever his friends heard of a rabid

dog, they would send a telegram toPasteur. The scientist then would sendsome of his assistants to catch the dog.

Once, two of Pasteur’s assistants tiedup a mad bulldog with a rope and heldhim down on a table. Pasteur put a glassstraw in his own mouth. He moved closeto the bulldog and sucked the dog’sfoaming saliva from its lips. Pasteur’saction was either brave or foolhardy.One slip would have meant a fatal dogbite to his face.

Despite his efforts, Pasteur never found the virus thatcauses rabies. That’s because viruses are extremely tinyorganisms. They could not be seen by the best micro-scopes Pasteur had in his lifetime. The rabies virus wasn’tfound until 1903, nearly 20 years later.

Fighting the Unseen OrganismEven though Pasteur couldn’t find the rabies virus, he

developed a vaccine that would cure the disease. He did itby using a clever plan. He deliberately infected rabbitswith saliva from mad dogs. He used rabbits because theyusually don’t carry rabies. Any animal that doesn’t carry adisease probably has a way of killing it within its body.

First, Pasteur euthanized the rabbits. Then he cut outand crushed parts of their spinal cords—the thick cord ofnerve tissue inside the backbone. The crushed rabbit

Pasteur with his rabbits in hislaboratory, around 1884




Write notes on yourown paper to tell howyou used this strategy.

[ 27 ]

spinal cords were aged, which weakened the virus. Theaging took from one day to two weeks. The longer theaging period, the weaker the virus.

Pasteur then vaccinated a healthy dog with the rabbittissue. That is, he injected the tissue into the animal’sbrain. He did this once a day for 14 days in a row. He usedthe oldest spinal tissue first. Each day, the virus that heused had been aged a little less. Finally, he put the vacci-nated dog into a cage with a rabid dog. After a few days,he removed the “healthy” dog from the cage. It had beenattacked and bitten by the rabid dog, but it showed nosign of rabies. Pasteur continued to test the dog for a year.When it failed to develop rabies, he knew he had found aneffective vaccine against the disease.

The First Human TestOne healthy dog

was no guarantee thatPasteur’s rabies vaccinewould work on humans.He needed to test hismedicine on a person.That happened on July4, 1885, the day thatnine-year-old JosephMeister was bitten bya rabid dog.

Meister was walkingto school when the dogknocked him downand bit him again andagain. The boy coveredhis face with his hands.A bricklayer who waswalking by saw theattack and beat the dog off him using an iron bar. Anotherneighbor brought out his gun and shot the dog.

Meister’s parents took the boy to Pasteur in Paris.The youngster was so stiff from his many wounds thathe could hardly walk. Meister would certainly die if hewent untreated. Pasteur decided to try his vaccine onthe boy.


Louis Pasteur watched asnine-year-old JosephMeister received the rabiesvaccine in his stomach.



[ 28 ]

Vo • cab • u • lar • yanxious (angk•shuhs)—worried

Monsieur (muh•syur)—the French word for “Mister”

eventually(i•ven•choo•uh•lee)—aftersome time

An “Old Softy”Because Pasteur used and often killed animals in

his experiments, a lot of people thought he must be acruel man. In reality, however, he was an “old softy.”Although he knew his work was necessary, he hated whathe had to do to the test animals. He couldn’t even assistin many of the operations that were required to performthe experiments.

Likewise, when Pasteur began trying his vaccine onJoseph Meister, he grew very anxious. He was unable towork and he couldn’t sleep. He even had a nightmare inwhich he saw young Joseph suffocating in his own saliva.

Joseph Meister received 12 shots in 11 days. The lastone contained rabies vaccine that had been aged for onlyone day. The virus in it was still strong enough to kill. Butyoung Joseph trusted Pasteur. That night, he said, “DearMonsieur Pasteur, kiss me good night.” The sick boy sleptvery well. Pasteur hardly slept at all.

Joseph Meister’s doctor kept him under observation forten more days. Eventually, he sent him home, completelycured. The news brought many people to Pasteur’s labora-tory. They were seeking cures to other diseases. But LouisPasteur was a chemist, not a physician. His assistants hadto explain, “He does not cure individuals. He only tries tocure humanity.”

The Work of the CDCLouis Pasteur was one of the first modern medical

detectives who tracked down invisible killers, such asrabies. Today, many of these detectives work in Atlanta,Georgia, at America’s “FBI of diseases”—the Centers forDisease Control and Prevention (CDC). The agency worksboth in the United States and around the world.

Over the past two decades, the CDC has become impor-tant in the education about and prevention of HIV. Likerabies, HIV is a deadly virus. It weakens the body’simmune system, which defends the body against illness.HIV can be spread in several ways. Most often, however,the virus is spread from infected people through sexualcontact and drug use.






[ 29 ]

Vo • cab • u • lar • yDengue fever(deng•gee)—an infectiousdisease marked by high fever,rash, headache, and severemuscle and joint pain

epidemic (ep•i•dem•ik)—rapid spreading of disease tomany people at the sametime

Today, HIV is probablythe best-known virus for

which the CDC is seek-ing a cure. But thereare others as well.Hantavirus is adeadly virus spreadby mice. Hantavirusis found mostly inthe southwesternUnited States.Dengue fever is also

caused by viruses. Itis known as “break-

bone fever” because itcauses severe pain in the

joints. The disease is reach-ing epidemic proportions in

South and Central America. TheCDC also tracks outbreaks of rabies

and influenza, as well as diseases caused by bacteria.

Searching for CluesWhen an outbreak

of a disease occurs,CDC investigators firsttry to find out whatthe victims have beendoing and what theymight have in com-mon. They collectinformation from thedoctors who treatedthe victims. If possi-ble, they also collectblood and tissue sam-ples. Then, like detec-tives, they try to find apattern: Did all thesepeople eat at the same pizza parlor?


Hantavirus

Gather information from victims:Ask victims where they have been,

what they have had to eat and drink.

Collect blood and tissue samplesfrom victims (if possible).

Look for and identifypatterns among victims.

Determine cause of disease.

How the CDC Investigates a Disease

Chart Review thesequence of steps in thechart. Could the CDCchange the order of thesteps in their investiga-tion? Why or why not?




[ 30 ]

Vo • cab • u • lar • yculprit—a person or thingthat is guilty

strain—a particular type

Did they go to the same dog show? Did they buy groundbeef from the same supermarket?

An Unusual OutbreakCDC scientists tracked down a

new disease in a hotel inPhiladelphia, Pennsylvania, in1976. There, at a meeting of agroup called the American Legion,more than 150 people had becomeill. Twenty-nine of them died.

Stories began appearing aboutpossible causes of the disease, whichis now known as “Legionnaires’disease.” For example, some peoplethought that the victims had beenpoisoned. Others believed that the people had caught theflu. One person even said that the illnesses were caused byvisitors from outer space!

The real answer was pretty dull, but very dangerous.The culprit was a strain of bacteria. It eventuallywas given the scientific name Legionellapneumophila [noo•moh•feel•uh]. Thebacteria were found to be growing inthe hotel’s air conditioning system.Once the bacteria had beenidentified, the disease could becontrolled by antibiotics.

A Deadly StrainIn 1995, a laboratory

worker died in the town ofKikwit, Zaire [zeye•eer], incentral Africa. (Today Zaire isknown as the DemocraticRepublic of the Congo.) He hadundergone two operations, butdoctors believed his death wascaused by a virus. Many of thepeople who had assisted at theoperations also became ill.


Ebola virus

Lung infected withLegionella pneumophila


[ 31 ]

Vo • cab • u • lar • yincubation(in•kyuh•bay•shuhn)—aperiod of time betweeninfection and onset ofsymptoms

encephalitis(en•sef•uh•leye•tis)—a virusthat causes swelling of thebrain

pathologist(pa•thol•uh•jist)—a doctorwho determines a cause ofdeath

Blood samples of 14 of the sickest people were sent tothe CDC. The agency discovered that they all were infectedwith the Ebola virus. The Ebola strain acts very quickly. Itkills by turning the internal organs into liquid. This causessevere bleeding. Victims of Ebola can die within a fewdays.

Cities in QuarantineBack in Zaire, the government completely closed off

Kikwit, a city of half a million people. Armed guards werestationed at checkpoints around the city to turn awayvisitors. Kinshasa, Zaire’s capital, a city of 5 millionpeople, also was closed. When the outbreak in Kikwitwas over, about 250 people had died from Ebola.

Even though there is no cure for Ebola, there are waysto fight it. The virus has a very short incubation period—about 4 to 16 days. The disease is most easily transmittedduring this period. So, someone who has it cannot infectother people for very long. The way to fight Ebola is toisolate its victims until the incubation period is over. Also,Ebola is not easy to transmit. Usually a person has tocome into direct contact with infected blood or body fluidsin order to catch the virus.

Manhattan MysteryIn the summer of 1999, the CDC investigated two

strange disease outbreaks in New York City. One outbreakaffected people; the other involved animals.

Outside the city, on Long Island, 23 horses had adisease that was unknown to local veterinarians. Nine ofthe horses died. Mysteriously, hundreds of wild crowswere dying as well.

Meanwhile, back in Manhattan, 60 people became illwith encephalitis, a virus that causes swelling of thebrain. Seven eventually died. Could there be a connectionamong all the animal and human victims?

After Labor Day weekend, Dr. Tracey McNamara, theBronx Zoo’s pathologist, started getting calls about thedead crows around the city. Dead crows also were turningup on the zoo grounds. At the same time, McNamaranoticed that some of the zoo’s birds were ill. One bald






[ 32 ]

eagle was shaking. A cormorant spent his last hoursbefore he died swimming in circles. A Chilean[chil•ay•uhn] flamingo and a snowy owl also died. Dr.McNamara wondered if the illnesses affecting the birdsand the people were the same. At first, no one believedher. “If I had a nickel for every person who told me I wasnuts, I’d retire,” she said later.

Some scientists thought the disease affecting peoplemight be St. Louis encephalitis, a disease usually seen inmore southern areas. This dangerous illness is spread bymosquitoes. But it had never affected birds before. Themystery deepened.

Two special laboratories, one in Ames,Iowa, and one in Fort Collins, Colorado,examined samples of dead bird tissue andsamples of human tissue. Both labs con-firmed what McNamara thought—the samedisease was affecting the animals and the people. But it wasn’t St. Louis encephalitis.The mysterious illness turned out to be WestNile virus. This virus had caused encephalitisin people and in horses in Africa, Australia,the Middle East, and Europe. Further testsshowed that the people, horses, crows, andzoo birds in New York that had become sickin this outbreak had all caught the West Nilevirus. That information solved the mystery,but not the problem.

Blame It on the MosquitoOther recent virus outbreaks that the CDC

has dealt with are SARS and the H1N1 virus,popularly called “swine flu.” SARS is believedto be caused by coronaviruses. This type isassociated with respiratory illnesses. It is

spread from person to person and has been found in over20 countries, primarily China.

Entomologists (scientists who study insects) havediscovered that the West Nile virus comes from the biteof an infected mosquito. Mosquitoes get it when they feed

Disease

Rabies

Ebola

AIDS

Legionnaires’disease

West Nilevirus

Cause

Virus spreadthrough thesaliva ofinfectedanimals

Virus spreadthroughinfected bloodor body fluids

Virus spreadthroughinfected bloodor body fluids

Bacteria

Virus spreadthroughinfectedmosquitoes

Treatment/Cure

Pasteur’svaccine

No treatments;No cure

Antiviral drugsslow virusgrowth;No cure

Antibioticdrugs

No treatments;No cure

Cause and Cure of Some Diseases


Vo • cab • u • lar • ycormorant (kor•muhr•uhnt)—a large sea bird





Think Aboutthe

Recall by summarizing the selection in writing or out loud.

Write notes on your own paper to tell how you used this strategy.

AFTER READING

[ 33 ]

on infected birds. If pesticides aresprayed in areas that are commonbreeding grounds to mosquitoes,they die, which can slow theoutbreak of the virus.

Is the threat ofthese disease-carryingmosquitoes gone?Unfortunately, no. The WestNile epidemic of 2002 hasmade this apparent. Butresearchers have developed avaccine that prevents thespread of the virus in mice,which is a step in the right direction towardhaving a vaccine for humans. Testing will begin onhumans in the immediate future.

The drama of the West Nile virus continues. So dosimilar stories around the globe. Luckily for us, most ofthese microscopic “suspects” are no match for the medicaldetectives at the CDC. Like Pasteur before them, thesescientists and doctors will continue to track down theclues they need to solve medical mysteries.



[ 34 ][ 34 ]

Synonyms are words that have the same or similar meaning. In“Medical Detectives: In Search of Microscopic Suspects,” the wordanxious is defined as “worried.” Anxious and worried are synonyms.

Writers use synonyms either when they do not want to repeat aparticular word, or when they want to use the best word toexpress their idea. Although anxious and worried are synonyms,they have different degrees of meaning. Someone who is anxiousis, in fact, very worried. Anxious can be used to describe animals,but worried usually describes people. When you use a newsynonym, it is a good practice to look it up in a dictionar y tomake sure you use the word correctly.

Synonyms

Below are five synonyms for anxious. On a separate sheet ofpaper, complete the sentences that follow with the words inthe list. Remember to use a dictionar y if you need help.

terrified alarmeduneasy apprehensive

agitated

1. I was _____ about going to camp this year because myfriends from last summer were not returning.

2. The evening news showed people who were _____ by thefalling buildings during an earthquake.

3. The principal was _____ when he heard that the fugitivewas only blocks away from the school.

4. My mother becomes _____ if I don’ t get home fromschool on time.

5. When I was hiking, I saw a deer become _____ by a smallairplane passing overhead.

Phoenix Graphix ___ 1R _x_ Final ___ PDF



[ 35 ]

As you practice reading and per forming thisentry, try to read it from the pont of view ofa serious scientist who is worried about asick child.

TIPFluency

➢

Journal EntryLouis Pasteur probably took notes to record his experimentsand investigations. Imagine you are reading from his journal.Practice reading the entry out loud, then perform it foryour class.



Notebooks From Medical DetectivesEditor’s Note: July 6, 1885 8:00 PM

It is 60 hours since Joseph Meister , a boy of 9 years, wasattacked and bitten by a rabid dog. (Large amounts of grass,straw, and wood chips in the dog’s stomach assure me that itwas indeed mad.)

The boy has not less than 14 bites. His condition is severe.Without treatment, he has no chance of sur vival. However, itis not without great unease that I have agreed to inoculatethe boy with the rabies vaccine.

Drs. Vulpian and Granter will assist. The first treatment willbe one-half syringe of spinal cord of a rabbit. The rabbit diedof rabies on June 21, and the spinal cord has been conser vedin a flask of dry air for 15 days. It will be injected under afold of skin in the right hypochondrium.


[ 36 ]


BEFORE READING


DURING READING

Recall by summarizing the selection in writing orout loud.

Use your own paper to jot notes to apply theseBefore, During, and After Reading Strategies.In this selection, you will choose when to stop,think, and respond.

AFTER READING

Think Aboutthe


rfr.H.se.u1.A.p036-049_73416 2/3/10 3:49 PM Page 36

Vo • cab • u • lar • yinfection (in•fek•shuhn)—a disease caused by germs

pneumonia(noo•mohn•yuh)—a diseasethat causes the lungs tobecome inflamed

bronchitis (bron•keye•tis)—an illness caused by infectionand swelling of the bronchialtubes

Have you ever “caught” a cold? Most of us get atleast 2 colds a year, and many of us get 4. It’s not unusualfor young children to get as many as 12 colds every year!You may have wondered why there is no cure for thecommon cold; after all, medical researchers have foundcures for more serious diseases. So why haven’t theyfigured out the cold? It’s because the common cold maybe common, but it’s certainly not simple.

What Is a Common Cold?Common colds cause sneezes, sore throats, and runny,

stopped-up noses. Sometimes you get a cough; sometimesyou have a slight fever. You feel tired, and your musclesusually ache. You might get a more serious infection,such as pneumonia or bronchitis, after a cold becauseyour body’s resistance to infection is weak.

[ 37 ]

the strategiesthe strategies



[ 38 ]

Although colds are mild illnesses, they have a bigimpact on human lives. Millions of days of school andwork are lost every year because of colds. Students who go

to school with a cold are probablynot able to learn as much as theywould if they were well.

We can catch a cold any timeof the year, but we are more likelyto catch a cold in the winter. Thisisn’t exactly because of the coldtemperatures. It’s because the air isdrier when it is cold outside, andmoisture in the air that usuallyhelps protect the lining of ournoses is absent. Being cold doesn’tgive us a cold. In fact, trying to staywarm may help make us sick. We

are more likely to stay indoors when it is cold outside, andwe are exposed to more cold germs in the enclosed spaces.

What Causes a Cold?Colds are caused by viruses, which are tiny organisms

that can’t live on their own. They survive only in the livingcells of another living creature. We “catch” a cold byinhaling a cold virus that someone hascoughed or sneezed into the air orby getting a virus on our handsand then touching our eyes,nose, or mouth. A cold viruscan’t live long on its own—up to three hours outsidesomeone’s body. When acold virus enters a livingcell, it uses the cell’senergy to grow. The virusreproduces itself andenters other living cells,and then the host cell isdestroyed. This processeventually produces adisease, such as a cold.


July

Aug

ust

Sept

embe

r

Oct

ober

Nov

embe

r

Dec

embe

r

Janu

ary

Febr

uary

Mar

ch

Apr

il

May

June

The Cold “Season”

You can catch a cold anytime of year. The cold“season” lasts fromSeptember to May. Thischart shows the differenceamong the months.


the strategiesthe strategiesApplyApply

[ 39 ]

Vo • cab • u • lar • yefficient (i•fish•uhnt)—getting results with the leastpossible effort or waste

antibodies—disease-fightingorganisms

When you have a cold, your body maybe home to as many as 10,000 cold virus-es! You probably have about 1,000 viruseswhen you first start to feel a cold comingon. Unlike bacteria, viruses do notrespond to medicines such as penicillin,which can quickly eliminate a bacterialinfection. The medicines that many peo-ple take for a cold only help alleviate coldsymptoms—the stopped-up nose, achymuscles, and cough. They don’t kill theviruses.

Our Valuable Immune SystemOur bodies have an efficient system

for fighting diseases. That immune systemincludes cells, tissues, and organs thatwork together to fight the germs—bacte-ria or virus—that make us sick. Bloodvessels, skin, tears, and even the hairs inyour nose are all part of your immunesystem. Blood vessels carry antibodiesand white blood cells that combat disease. Skin preventsmany harmful germs from entering your body. Tears pre-vent germs from entering through your eyes. Throat cellscollect germs that sneak through your mouth. Yourimmune system is a powerful force. The aches and feverthat are part of a cold are signs that the immune systemis working.

The immune system is very specialized. Specific cellsdo specific jobs: Some cells recognize organisms or sub-stances that don’t belong in the body, others mark theinvaders, while still other kinds of cells prepare for theactual attack. The immune system attacks in two ways: Tofight some kinds of infections, it makes antibodies, whichare special proteins that are carried by the blood anddestroy invading germs; to fight viruses, the immune sys-tem sends out killer T cells, which attack and kill the cellsin which the viruses live. Remember, viruses cannot liveon their own; they live in other cells. By killing the hostcells, the T cells destroy the virus.


The parts of your immune system worktogether to help your body fight diseases.

Adenoids

Tonsils

Thymus

LymphVessels

Spleen

LymphGlands

BloodVessels

Appendix

BoneMarrow

The Immune System


[ 40 ]

Vo • cab • u • lar • yimmunization(im•yuh•ni•zay•shuhn)—a treatment to make a personresistant to a disease

side effects—unwanted reactions to drugs

As amazing as this is, the immune system is smart andeven has a memory. The immune system recognizesgerms it has met before, so when it meets these germsagain, it kicks into action more quickly, and you don’t getas sick. You may not get sick at all.

How do vaccines work? When you receive animmunization for a disease such as measles, you get aweak dose of the disease. Your immune system revs upto take care of the invading viruses. The dose is bigenough to teach your immune system what this disease’sviruses are like, but small enough so that you don’t getreally sick. If the immune system remembers diseases,why do we keep getting colds? If scientists can makevaccines, why haven’t they developed a cold vaccine?

Can We Cure the Common Cold? A scientist determined that a cold virus is complex

when he made an exact model of one. His creation lookedlike a miniature planet filled with mountain peaks anddeep canyons. There are more than 200 different coldviruses that belong to 5 viral families. The immunesystem must treat each virus as something new, becauselearning about one cold virus doesn’t help your bodydefend itself against another. To complicate matters, theseviruses keep changing, which makes it hard for theimmune system to recognize and fight them. That’s whywe keep catching colds.

Because a vaccine is developed to help the immunesystem fight a disease, these same conditions apply.One vaccine works only on one virus that is formed aparticular way. This has made it impossible for scientiststo develop a vaccine for the common cold.

Testing Cold-Cure DrugsTesting the effectiveness of new cold drugs is tricky.

With most drugs, scientists first run laboratory tests. Theytest the drug on animals, usually rats and mice. Theyinfect the animal with the disease, then give the drug tothe animal to see if it works. These animal tests also helpscientists observe the drug’s side effects.




[ 41 ]

Vo • cab • u • lar • yrespiratory(res•puhr•uh•tor•ee)—havingto do with breathing

However, the cold virusesthat bother humans do notgive rats and mice a cold.Scientists have been ableto infect chimpanzees withcold viruses, but the chimpsdon’t get sick. This meansthat after running laboratorytests, scientists must testnew drugs on humans.Because of the possibilityof side effects, they don’tusually test a drug on peoplewithout first testing it onanimals. The exceptionwould be a drug to treatan unusual or dangerousdisease—certainly not thecommon cold!

A Cold SprayIn the late 1990s,

scientists developed a spraythat helps ward off coldviruses. In test cases, people who were exposed to coldsand used the spray didn’t get as sick as people who didn’tuse the spray. Some people using the spray didn’t catch thecold at all. This spray isn’t something you spray in the airto kill cold viruses. It’s a spray to use in your nose.

To understand how the spray works, you need toknow two things. First, one family of cold viruses is therhinovirus. This is a big family and accounts for morethan 40 percent of the colds we get—more than any otherfamily. This group attacks your respiratory system. Mostrhinoviruses enter your body through your nose (rhinoactually means “nose”).

The second thing to understand is that the cells in ourbodies are coated with special molecules. These moleculessit on the outside of the cells and act as a sort of glue.They help substances stick to each other and also helpcells stick to each other. The cells in the lining of your


Mice do not get sick fromhuman cold viruses.


[ 42 ]

Vo • cab • u • lar • yattracted (uh•trak•tid)—drawn to

interferon (in•tuhr•feer•on)—a substance made by thebody to fight disease

preventative(pri•ven•tuh•tiv)—able tokeep from happening

nose are covered with a coatingcalled ICAM-1, so when you breathein a rhinovirus, it grabs onto a cellcoated with ICAM-1 and gets aneasy ride into a cell.

You probably remember that sci-entists have been frustrated by thechanging nature of cold viruses. Ifthe form of these viruses keepschanging, would the virus keepbeing attracted to an ICAM-1?Although the shape of cold viruseschanges, the point at which a coldvirus attaches to an ICAM-1 staysthe same. Discovering that helpedscientists develop the nasal spray.

Here’s how the spray works. Themist in the spray contains lots offake ICAM-1s. When you use thespray, you fill your nose with thesefakes. The cold viruses don’t seemto know the difference, so many of

them latch onto the fakes. The viruses that grab a fakeICAM-1 can’t get to a cell in your body. The virus dies, andthe cold goes away.

Developing Other Cold CuresThis spray is just one possible cold treatment. Even

though it seems to work, it will be a long time before itbecomes available. Drug companies need to figure outwhen people should begin to take the spray, how oftenthey can use it, and how much of it they should take at atime. In the meantime, scientists are experimenting withsubstances that will protect the ICAM-1s from the coldviruses. One substance they developed works by discon-necting cold viruses and ICAM-1s that have alreadybecome attached. Another is interferon, a substance thebody naturally makes to fight disease. Scientists can nowmake interferon in a laboratory.

Research for the cure of other diseases may help curethe common cold. Cures or preventative drugs for AIDSare very important in the medical research world. AIDS, a

Reconstruction of a human rhinovirus attached to ICAM-1receptors. The virus is the sphere, and the ICAM-1 receptorsare the cylinders.




[ 43 ]

severe disorder, is caused by a virus that weakens theimmune system. Scientists involved in AIDS research arelearning a great deal about the immune system. Theirwork helps scientists who are researching cures for otherviral diseases, including the common cold.

What Does All This Mean?Because there are five different cold virus families and

hundreds of different viruses, it will probably be a ratherlong time before there is a successful cure for the commoncold. So what do we do? We should try hard not to get acold in the first place. If we do get one, it is important thatwe take care of ourselves so we get better faster.

Avoiding a cold may be easier than you think. Washyour hands often and keep them away from your nose,mouth, and eyes. Eat a balanced diet that includes manyfruits and vegetables, and drink at least eight glasses ofwater a day. Try to get a good night’s sleep every night.Exercise regularly, and spend time with people you enjoy.All these things help keep your immune system strong.These tips are common sense, and you’ve heard them allbefore, but the key is to actually follow them!

Colds may be bothersome, but they aren’t necessarilydangerous. You’ll get a cold two or three days after you’vebeen exposed to the virus. Most colds last about a week,but the cough might last longer. When you do get a cold,use common sense. Get plenty of rest, and drink warm,soothing liquids. Cover your mouth with a tissue whenyou cough or sneeze. Throw away used tissues immediate-ly and wash your hands often, so that you don’t infectother people. If you spend time with young children whoare not yet in school, you may have a difficult time avoid-ing colds. Young children catch a lot of colds because theirimmune systems haven’t learned how to fight the coldviruses.

So, the next time you get a cold, sit back and relax.Take care of yourself and your cold. Just think: This isone cold you’ll never have again!



[ 44 ][ 44 ]

The prefix anti- is Greek. It means “against” or “opposite.” Whenyou see the prefix anti- at the beginning of a word, it suggests thatthe word probably means “against” or “opposing” something.

Anti- is often used in medical terms. Look at the example from“Curing the Common Cold.”

Blood vessels carry antibodies and white bloodcells that combat disease.

In this example, the meaning of the word part bodies is unclear.Look at the other words in the sentence for context clues. Thewords combat and disease suggest that bodies means “disease.”From the context clues and the prefix anti-, you know thatantibodies means “organisms that fight against disease.”

The Prefix anti-

Read the following sentences. Each sentence contains amedical term with the prefix anti-. Figure out the meaningof the boldface words from the prefix and context clues.Write your answers on a separate sheet of paper . Thencompare your answers to the definitions in a dictionar y.

1. Hydrogen peroxide and iodine are commonantiseptics.

2. She took an anti-inflammatory medicine to relievethe swelling in her knee.

3. Doctors give anticoagulants to stop blood clots.4. We’ll know in a few days if the antibiotic can stop

the spread of infection.5. After eating chili for breakfast, he needed an antacid.




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Try to read each limerick in a light and livelyway. Then read the limericks in different voicesthat reflect sadness, tiredness, silliness, andseriousness.

TIPFluency

➢

LimericksA limerick is a short, rhyming poem that is also funny .While we usually do not think of a cold as beingfunny, reading or writing about one in a limerick cansometimes ease the pain. Practice reading the followinglimericks out loud. Then read them to your class.



Home From SchoolThere once was a young girl named Rose,Who for days stayed at home in bedclothes.Her head, it was achy.Her voice low and shakyWhen she said, “I’ve a code in by dose.”

Runaway NoseA puzzled young man from BostonHad a nose more annoying than fun.It seemed to be swellingAnd was too clogged for smelling,And yet, it continued to run.


[ 46 ]

in the Real WorldMap

West Nile Virus in the United States in 2003

West Nile virus is spread by infected mosquitoes, which get the virus byfeeding on infected birds. You cannot get West Nile virus by just touchingor kissing someone who has it.

Four of every five people who get West Nile virus have no symptoms.One of every five people has mild symptoms, such as fever , headaches,and vomiting. One in every 150 infected people will become seriously ill.These people may suffer permanent effects or even die.

Indicates human disease case(s)

Avian, animal, or mosquito infections

#

222 617149

3

1

2

375

1

13

2947

209

720

79

91

1942

1039

147

17

54

64

25

124

87 37 50

26

47

19

108237

71

142 26

24

6

94 3

75

17

34

17

7

17

3

3



[ 47 ]

Discussion QuestionsAnswer these questions with a partner or on a separate sheet of paper .

1. Which three states had the highest number of cases of W est Nile virus at the timethis map was created?

2. What does the map tell you about the states with the most cases of this virus?

a. The states are all on the coast.b. The states all have very warm weather in the summer.c. The states are all in the middle of the nation.d. The states also have the largest population in the nation.

3. Which states below had no reported human cases when this map was made?

a. Utah, Nevada, Arizonab. Washington, Maine, Hawaiic. Massachusetts, Rhode Island, Delawared. All states had some reported human cases.

4. This map is updated each week. Why do you think that is necessar y?

5. Based on this map, which state is more likely to have the first human case of W estNile virus, Maine or Hawaii? Why?

6. Based on your knowledge of mosquitoes, what kind of weather helps spread thisvirus?

a. cold b. wet c. windy d. dry

7. How would the numbers on this map change if W est Nile virus were spread bytouching or coughing?

a. The most crowded states would have the most cases.b. The least crowded states would have the most cases.c. Most of the cases would be in the South.d. Most of the cases would be in the North.

8. What does the map tell you about the cases of W est Nile virus in California?

a. The cases are all around large cities.b. The cases are mostly on the coast.c. There are few cases in the desert areas.d. There are few cases compared to the state’ s population.



Mock InterviewWork with a partner to portray anews reporter and a doctor. Thereporter should ask the doctorquestions about the latest researchon the common cold.

“Cold Care Package”Assemble one for an imaginaryfriend who has a cold. Include all ofthe items you think are necessaryto make a friend feel better.

Song

Perform for the class. The song

should consist of tips to help your

fellow students remember how to

prevent catching a virus, such as

the flu.

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to the Real World

EXPLORE

MORE

Work With a PartnerResearch and write a report onone of the viruses mentioned inthe unit. Include a diagram or achart. Then present your reportto the class.

Imaginary DiseaseCreate a health informationpamphlet to describe an imaginarydisease’s symptoms, how it isspread, and its cure.

Flow ChartShow the process medical

investigators might use to

track down the cause of an

outbreak of an unknowndisease.



Related BooksAronson, Virginia. The Influenza

Pandemic of 1918. Chelsea HousePublishers, 2000.

Brynie, Faith Hickman. 101 QuestionsAbout Your Immune System You FeltDefenseless to Answer—Until Now.Twenty-First Century Books, 2000.

Cefrey, Holly. The Plague. RosenPublishing Group, 2001.

—Yellow Fever. Rosen Publishing Group,2002.

De Hahn, Tracee. The Black Death.Chelsea House Publishers, 2002.

Derkins, Susie. The Immune System.Rosen Publishing Group, 2001.

Donnellan, William Lorne. The Miracle ofImmunity. Benchmark Books, 2003.

Edelson, Edward. The Immune System.Chelsea House Publishers, 2000.

Getz, David. Purple Death: The MysteriousFlu of 1918. Henry Holt, 2000.

Isle, Mick. Everything You Need to KnowAbout Colds and Flu. Rosen PublishingGroup, 2000.

Kittredge, Mary. The Common Cold.Chelsea House Publishers, 2001.

Marrin, Albert. Dr. Jenner and theSpeckled Monster: The Search for theSmallpox Vaccine. Dutton Children’sBooks, 2002.

Monroe, Judy. Influenza and OtherViruses. LifeMatters, 2002.

Ridgway, Tom. Smallpox. RosenPublishing Group, 2001.

Walker, Pam, and Elaine Wood. TheImmune System. Lucent Books, 2003.

Yount, Lisa. Disease Detectives. LucentBooks, 2001.

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Web sites have been carefully researched for accuracy, content, and appropriateness. However,teachers and caregivers are reminded that Web sites are subject to change. Internet use shouldalways be monitored.

Interesting Web SitesTo learn more about the subjects you read about in this unit, visit:

http://www.commoncold.org

http://www.nlm.nih.gov/medlineplus/commoncold.html

http://www.amnh.org/exhibitions/epidemic/

http://www.pbs.org/wnet/secrets/previous_seasons/case_plague/index.html

http://www.cdc.gov

http://www.who.int/en



Documents

Table of Contents lev h microscopic.… · pathogens(path•uh•juhnz) —disease carriers diphtheria (dif•theer•ee•uh)—a disease that causes difficulty in breath-ing, high