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1、Visit www.readinga- for thousands of books and materials.www.readinga-InFLUenzaInFLUenzaA Reading AZ Level Z Leveled BookWord Count:2,286LEVELED BOOK ZTWZWritten by Ned JensenInFLUenzaWritten by Ned JensenInFLUenzaLevel Z Leveled Book Learning AZWritten by Ned JensenIllustrated by Cende Hill All rig
2、hts reserved.www.readinga-CorrelationLEVEL ZUVN/A50Fountas&PinnellReading RecoveryDRAPhoto Credits:Front cover:iS Perkins;back cover:Santos06/D;title page:iS Wilson;pages 3,8,16:courtesy of James Gathany/CDC;page 4:Photodisc/C Squared Studios/Getty Images;page 5:courtesy of Cynthia Goldsmith/CDC;pag
3、es 7,10(top left,top right,bottom right),13,14,22:Jupiterimages Corporation;page 9(top):iS Martin;page 9(bottom):iS Campbell;page 10(left):iS Davis;page 12:Sebastian Kaulitzki/D;page 18:courtesy of Library of Congress,Prints&Photographs Div LC-USF34-039530-D;page 19:courtesy of Knowland Collection/O
4、akland,CA Public Library/Edward A Rogers;page 21:REUTERS/Beawiharta EN/RCSwww.readinga-InFLUenza Level Z Table of ContentsIntroduction .4What Is the Flu?.5Changing Viruses .9The Body Fights Back .11Preventing the Virus from Taking Over .14Treating the Flu .17History of the Flu .18Conclusion .22Gloss
5、ary .233IntroductionHave you ever shivered with chills or burned up with a fever?Have you ever had a sore throat,a stuffy nose,a pounding headache,and muscle aches?Have you ever felt really fatigued even though youve just woken up in the morning?If you feel symptoms such as these,flu germs may have
6、invaded your body.By learning about the fluwhat it is,what causes it,what its symptoms are,and how to treat ityou can fight back against this illness and stay healthy.4A water bottle and a blanket can help when you have the flu.InFLUenza Level Z What Is the Flu?The flu is also called influenza(in-fl
7、oo-EN-zah).Its caused by a virus that has the ability to quickly spread between people.A virus is a tiny microorganisma microbe,or germthat is invisible to the naked eye.A virus is composed of a little bit of genetic material surrounded by a hard protein shell that protects it.Viruses are submicrosc
8、opicso small that scientists must use extremely powerful microscopes to see them.Even when viewed through a microscope,a virus can only be seen after its image has been magnified to one thousand times its original size.In fact,viruses are so small that hundreds of thousands of them can live on the h
9、ead of a pin.Viruses are everywhere.Some wont bother you at all,but some can be dangerous,even deadly,to people and other animals.And during flu season,which lasts from October through May in the northern hemisphere,viruses are widespread.Like many other organisms,viruses need a particular type of h
10、ome in order to survive and reproduce.Unfortunately for humans and other animals,that home is inside us!5Viruses act as intracellular parasites.Although they can live on their own for a period of timesometimes for yearseventually they must find organisms to serve as hosts and get inside their cells
11、in order to reproduce.Once a virus infects a human being,it uses its hard protein shell to make a hole in a cell,which it then invades.Once inside the host cell,the virus inserts its own genetic information into the cell and begins to rapidly make copies of itself.One to four days after infection,th
12、e host may begin to experience symptoms and feel sick.6Avian influenza virusA virus invades a cell in a human body.The virus takes over the cell and makes copies of itself.Copies of the virus break out of the cell and start invading other cells.How a virus spreads in the body123InFLUenza Level Z The
13、re are many kinds of flu,and each is caused by a specific virus.But even though there are different types of flu,their symptoms are very similar.Flu is an infection of the respiratory tract that usually causes you to feel achy,feverish,congested,fatigued,and sick to your stomach.7Influenza has three
14、 basic types:Influenza A,Influenza B,and Influenza C.Influenza A can cause serious illness in humans and other animals and is usually responsible for large outbreaks.Influenza B is milder,causes smaller outbreaks,and affects only humans(mostly children).Influenza C usually causes only mild illness i
15、n humans.All types of influenza can be passed from an infected person to a healthy person through the air or through contact with objects such as eating and drinking utensils.The influenza virus is often transmitted in saliva from an infected persons mouth and on droplets of mucus sneezed or coughed
16、 into the air.For this reason,it is always important to cover your mouth and nose when you cough or sneeze.Its also important to wash your hands after going to the bathroom and before eating or preparing food.If you are infected,the very best thing you can do is to stay home and away from other peop
17、le so you dont spread your germs.8Tiny drops of saliva and mucus fill the air when you sneeze.Flu viruses attack the respiratory tract.lungsmouthnosepharynxwindpipe(trachea)larynxInFLUenza Level Z Changing VirusesViruses are capable of changing,or mutating.Flu viruses are among the most changeable o
18、f all viruses.Each type of virus that mutates from another virus is called a strain of that virus.Many influenza viruses start in wild animals,most often in birds.These viruses can easily mutate into strains that infect ducks and chickens on farms.Once a virus has infected birds on farms,it can furt
19、her mutate into strains that can infect animals such as pigs,and even humans.9Since chickens,pigs,and humans come in close contact on farms,the spreading and mixing of viruses can be deadly.The chain of animals infected as the infection moves from wild animals to humans varies from virus to virus.A
20、single virus chain may include animals as different as dogs and whales.Sometimes a virus takes a shortcut in the chain,such as the avian virus of 1997,which jumped directly from birds to humans.10Wild birds(above)often pass viruses to farm chickens(right),which come into more contact with people.A s
21、ample virus chainwild duckpigchickenhumanInFLUenza Level Z The Body Fights BackThe human body has ways of fighting back against the invasion of flu viruses.The immune system protects against the invasion of harmful microbes by producing chemicals called antibodies,which travel in the blood and patro
22、l the body in search of invaders.Antibodies are programmed to destroy a specific type of microbe.When they find an invasive microbe,antibodies attack and destroy any cells that contain the virus.Because viruses have the ability to mutate,influenza can be a terrible enemy.Even if your body successful
23、ly fights the virus,the virus can change into a different strain from which your body has no protection,or immunity.Then your body has to start all over again,learning how to fight the new strain at the cellular level.Scientists always worry that the next new strain will be even more deadly than pre
24、vious ones.11Your body produces white blood cells to protect you against infectious diseases.Your body can detect invading microbes in your bloodstream because these diseases carry antigens in their proteins.Special cells in your immune system,such as T helper cells,can sense antigens in small porti
25、ons of viruses poking out of your cells.When your body finds an antigen,it has many different ways to attack.The T helper cells produce more antibodies.T helper cells also call in cells called phagocytes(FAY-goh-sites),which eat microbes.Or,they call killer T cells,which can destroy cells that are i
26、nfected with a virus.12antibodiesviruseswhite blood cellwhite blood cellcell infected with flu virusArtists image of killer T cells attacking a virusviruskiller T cellInFLUenza Level Z One of the best things about the immune system is that it will always remember a microbe it has fought before.It wi
27、ll always know just how to fight it again in the future.You may even develop an immunity to a particular microbe;your body can learn to fight so well that your immune system can completely destroy a virus before you feel sick at all.These are just some of the amazing ways your body defends itself ag
28、ainst invaders.Depending on the kind of microbe it finds,your body produces many different kinds of cells.Most of the time,your body knows exactly how to fight an invading microbe.However,if the immune system of a human body invaded by a virus is weak,viruses can get a stronghold and begin reproduci
29、ng faster than the immune system is able to destroy them.When this happens,the body comes down with flu symptoms that quickly get worse without medical care.13Preventing the Virus from Taking OverYou can take some commonsense actions to prevent a flu virus from entering your body.Two of the best way
30、s to stay healthy are by getting plenty of rest and eating well.Avoid contact with objects used by infected people for eating and drinking.Wash your hands frequently and keep your fingers out of your mouth.These precautions are important because an infected person can be contagious before showing an
31、y symptoms.The person may not know that he or she has been exposed and is about to get sick.Avoiding people who have flu symptoms,such as sneezing and coughing,will also help protect you from the virus.14Scientists study ways to help your body fight the flu.Washing your hands often will help keep yo
32、u from getting the flu.InFLUenza Level Z However,even the most cautious people can become infected.Fortunately,medical scientists have found a way to keep the flu virus from taking over your body.They have developed vaccines.Vaccines are weakened or dead flu viruses that are injected into a persons
33、body before the person gets sick.These weakened viruses cause the body to produce antibodies that attack and destroy the weakened or dead germs.Once the body has“rallied the troops”and produced antibodies to destroy the viruses injected into the body,it is on alert and prepared to attack stronger vi
34、ruses that may invade during flu season.Each strain of a virus requires a different vaccine.Some flu vaccines contain several strains.When these strains are injected into the body,each one causes the body to produce a particular antibody to destroy it.Exposing the immune system to multiple strains p
35、repares the body to defend against many forms of viruses that doctors think might be present during a particular flu season.1516Vaccines for most viral strains have an eighty-percent prevention rate,which means that eighty percent of the time,youll be immune and wont get sick from a strain you have
36、been vaccinated against.Thats pretty high,but its not perfect,so you might still get the flu even if youve received a vaccine.But if youve had the vaccine,your symptoms will be milderyou wont ache so much,and you wont feel so hot.However,if you become infected with a strain that is different from th
37、ose in your flu shot,you can still get sick.Scientists must be good detectives to predict which strains to put into the shot each year.Not everyone has the same risk of catching the flu,and some people get more seriously ill than others.People who are very young or very old,or who already have healt
38、h conditions such as diabetes and heart disease,are at greater risk of catching the flu than others.Do You Know?British physician Edward Jenner developed the first vaccine in 1796 when he injected patients with cowpox virus to protect them from the similar but much more dangerous smallpox virus.InFL
39、Uenza Level Z 1718A doctor gives children shots of vaccine in 1941.Treating the Flu Preventing the flu is not always possible.However,once viruses infect your body,you still can do several things to fight back.Pharmacies offer many over-the-counter medicines that can help relieve the symptoms of the
40、 flu.These medicines can eliminate the achy feeling in your head and muscles.They can also help reduce a fever.Drinking plenty of fluids,such as water or fruit juices,can also help.You should get plenty of rest so your body can better fight the viruses that have invaded your cells.Think about all th
41、e work your immune system has to do when its fighting an infection.Its no wonder you feel pain and exhaustiontheres a war going on inside your bloodstream!Give your body plenty of water and rest so it can do its job.Most people recover from the flu without receiving any special medical treatment.For
42、 very serious cases of the flu,however,doctors do have some medicines that they can use.Although antibiotic drugs have no effect on viruses,some antiviral drugs do target flu viruses.However,antiviral drugs and medicines that work well against one strain of virus might be useless against another str
43、ain.Viruses can also develop resistance and even immunity to drugs over time.History of the FluThroughout history,there have been many outbreaks of influenza.Some of them have been mild and not very widespread.Other outbreaks have been severe,spreading throughout the world and killing millions of pe
44、ople.Once a flu virus develops and infects a few people,it can spread rapidly to become an epidemic.Scientists have evidence suggesting that flu epidemics date back hundreds and possibly even thousands of years.Each epidemic has killed thousands of people or more.InFLUenza Level Z 1920The history of
45、 any influenza outbreak begins with a single person.On March 11,1918,a young man in the U.S.Army reported to a hospital with a fever,sore throat,and a headache.Shortly after,many other soldiers at his base developed the same symptoms.In one week,the Army hospital was treating more than five hundred
46、sick soldiers.By the end of spring,forty-eight of those people had died.At first,no one knew why,not even the doctors and scientists.Doctors later learned that the illness was caused by a particular strain of the influenza virus.In total,this strain of influenza,known as the Spanish flu,killed more
47、than 600,000 Americans and 25 to 40 million people worldwide.When an outbreak reaches this size,it is known as a pandemica disease that spreads rapidly around the world.But the pandemic of 1918 was not the only major influenza outbreak in history.The Asian flu,which appeared in 1957,caused about 70,
48、000 deaths in the United States.It got its name because it first appeared in China before coming to the United States in June 1957.Another strain of flu,the Hong Kong flu,was first detected in Hong Kong,China.In 1968,this virus caused another pandemic,resulting in 34,000 deaths in just the United St
49、atesas many people as live in a small city.And in 2009,the H1N1 swine flu became the first pandemic in 41 years,infecting people in over 70 countries.This map shows an example of how pandemics,such as the Asian flu of 19571958,might spread from one area to many others.1918 Spanish flu patientsChinaJ
50、apanPACIFIC OCEANIndiaRussiaMongoliaInFLUenza Level Z 2122Masks that fit around the nose and mouth are sometimes worn to help prevent the spread of viruses.However,the masks do not work all the time.Other outbreaks have caused widespread concern without developing into actual pandemics.These include