SCIENCE IN THE NEWS - Diseases Spread by Mosquitos

SCIENCE IN THE NEWS - Diseases Spread by Mosquitos
By Nancy Steinbach

Broadcast: Tuesday, January 25, 2005

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VOICE ONE:

This is SCIENCE IN THE NEWS, in VOA Special English. I'm Barbara Klein.

VOICE TWO:

 
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And I'm Bob Doughty². On our program this week, we tell about diseases spread by mosquitoes -- the most widely hated insects in the world.

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VOICE ONE:

Mosquitoes are very small insects. There are more than two thousand different kinds of mosquitoes. Female mosquitoes bite people to drink their blood. Male mosquitoes do not drink blood. They drink fluids from plants.

The female mosquito uses its long thin sucking tube to break the skin and find blood. The insect injects the victim with a substance that keeps blood flowing.

The female mosquito drinks the blood and uses it to produce eggs. One meal gives her enough blood to produce as many as two hundred fifty eggs. The mosquito lays them in any standing³ water.

VOICE TWO:

The eggs produce worm-like creatures in two days to a few months. However, some eggs can stay in water for years until conditions are right for development. The worm-like creatures feed on organisms in the water. After four to ten days, they change again, into creatures called pupas. The pupas rise to the surface of the water. Adult mosquitoes pull themselves out of the pupas and fly away.

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VOICE ONE:

The World Health Organization says mosquitoes cause disease and death for millions of people throughout the world. That is because mosquitoes can carry organisms that cause disease. However, the disease does not affect mosquitoes.

 
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W.H.O. officials expressed concern about the possible spread of disease after the major earthquake in the Indian Ocean last month. The earthquake produced huge waves that killed thousands of people. The waves destroyed many villages and left floodwaters in coastal⁴ areas. The officials have warned that the floodwaters could increase the risk of diseases spread by mosquitoes.

VOICE TWO:

The most important disease spread by mosquitoes is malaria⁵. More than three hundred million people become infected with malaria each year. At least one million die from it every year. The disease is found in Africa, Asia, the Middle East and South America.

Malaria parasites⁶ enter a person's blood through a mosquito bite. These organisms travel to the liver. They grow and divide there. After a week or two, the parasites invade red blood cells and reproduce⁷ thousands of times. They cause the person's body temperature to rise. They also may destroy major organs. People with malaria may suffer kidney⁸ failure or loss of red blood cells.

VOICE ONE:

Some drugs are generally effective in preventing and treating malaria. They are designed to prevent the parasites from developing in the body. The most commonly used malaria prevention drugs are chloroquine, mefloquine and doxycycline.

People die from malaria because they are not treated for the disease or the treatment is delayed. Health officials are increasing efforts to reduce the number of deaths from malaria.

VOICE TWO:

Dengue fever is another disease that is carried by mosquitoes. The insects can survive in new and different environments. They can spread diseases to new areas. For example, experts say only nine countries had dengue fever before Nineteen-Seventy. Since then, the disease has spread to more than one hundred countries around the world.

The World Health Organization says about fifty million people suffer from dengue fever each year. There is no cure. Children may develop a kind of the disease that is not serious. They may have a high body temperature and some areas of skin may turn red.

VOICE ONE:

Older people suffer from dengue fever much more. They may develop reddish skin and lose their sense of taste. They also may have terrible pain in the head or behind their eyes. And they may experience pain in joints¹⁰ such as the elbow or knee. This kind of joint⁹ pain is the reason why dengue fever is sometimes known as breakbone fever.

The most severe kind of the disease is called dengue hemorrhagic fever. People who have this disease bleed from the nose or other openings in the body. Dengue hemorrhagic fever kills about five percent of all people it infects. The only treatment involves controlling the bleeding and replacing lost body fluids.

VOICE TWO:

Yellow fever is another disease carried by mosquitoes. There are no effective drugs against yellow fever. Doctors can only hope that a person's defense¹¹ system is strong enough to fight the disease. The World Health Organization says there are an estimated two hundred thousand cases of yellow fever each year. It is found mainly in Africa, northern South America and the islands of the Caribbean Sea.

A virus causes yellow fever. A few days after a mosquito bite, the victim experiences high body temperature and pain in the head or muscles. Victims also may expel¹² food they ate. Most patients improve after three to four days.

VOICE ONE:

However, fifteen percent of patients develop a more serious condition. High body temperatures re-appear and the body turns yellow in color. The victim bleeds from the nose, mouth, eyes or stomach. Half the people with this condition die within ten to fourteen days.

A vaccine¹³ can prevent yellow fever. The vaccine strengthens the body's defense system against the disease. Medical experts say the vaccine is safe and very effective. The protection continues for at least ten years and possibly for life.

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VOICE TWO:

Mosquitoes also carry lymphatic filariasis, a disease commonly known as elephantiasis. The disease has already affected¹⁴ more than one hundred twenty million people. One third of those infected live in India. Another one third are in Africa. The others live in South Asia, the Pacific Ocean, or the western half of the world.

Mosquito bites spread the worms that cause elephantiasis. People usually begin to develop the disease as children. Many children never experience signs of the disease. But it may cause hidden damage to the body's lymphatic system and kidneys¹⁵.

The worst signs of elephantiasis appear in adults. The signs are more common in men than in women. These include damage to the arms, legs, and reproductive organs. Two drugs are effective in treating the disease. Experts say that keeping the affected areas clean can decrease the damage and reduce the number of times that it takes place.

VOICE ONE:

Still another disease carried by mosquitoes is encephalitis. It causes an infection or swelling¹⁶ of the brain. Many different viruses cause different kinds of the disease. One virus lives naturally in birds and horses. Mosquitoes spread it to people. Mosquitoes in several Asian countries spread a kind of encephalitis known as Japanese encephalitis. A vaccine can prevent this sickness.

Other kinds include West Nile encephalitis, Saint¹⁷ Louis encephalitis and Eastern Equine encephalitis. Most healthy people infected with the virus show no signs. Or they become sick for only a day or two. But those with weak natural defenses may develop a severe infection. They may suffer from high body temperature, headache, shaking and even death.

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VOICE TWO:

Experts have learned many things about mosquitoes. For example, the insects can smell carbon dioxide in the breath of a person or animal from as far away as sixty meters. Mosquitoes often like the blood of animals better than the blood of people.

Mosquitoes like dark colors. They do not bite women who are bleeding during their fertility period. But they do bite pregnant¹⁸ women. Many kinds of mosquitoes are most active in the early morning and early at night. They eat mostly at night.

VOICE ONE:

Experts say the best way to prevent the diseases carried by mosquitoes is not to be bitten by one. There are several ways to prevent mosquito bites. Do not keep standing water anywhere near your home.

Remove all containers that could provide a place for mosquitoes to live. Stay in an enclosed area when mosquitoes are most active. Wear clothes that cover most of the body. Other ways to prevent mosquito bites are to put anti-insect chemicals on the skin, clothing and sleeping areas. Also, place special nets treated with insect poison on windows and over the bed at night.

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VOICE TWO:

This SCIENCE IN THE NEWS program was written by Nancy Steinbach. Cynthia Kirk was our producer. The engineer was Eva Nenicka. I'm Bob Doughty.

VOICE ONE:

And I'm Barbara Klein. Join us again next week for more news about science in Special English on the Voice of America.

1 graphic   

adj.生动的，形象的，绘画的，文字的，图表的

参考例句：

• The book gave a graphic description of the war.这本书生动地描述了战争的情况。
• Distinguish important text items in lists with graphic icons.用图标来区分重要的文本项。

2 doughty   

adj.勇猛的，坚强的

参考例句：

• Most of successful men have the characteristics of contumacy and doughty.绝大多数成功人士都有共同的特质：脾气倔强，性格刚强。
• The doughty old man battled his illness with fierce determination.坚强的老人用巨大毅力与疾病作斗争。

3 standing   

n.持续，地位；adj.永久的，不动的，直立的，不流动的

参考例句：

• After the earthquake only a few houses were left standing.地震过后只有几幢房屋还立着。
• They're standing out against any change in the law.他们坚决反对对法律做任何修改。

4 coastal   

adj.海岸的，沿海的，沿岸的

参考例句：

• The ocean waves are slowly eating away the coastal rocks.大海的波浪慢慢地侵蚀着岸边的岩石。
• This country will fortify the coastal areas.该国将加强沿海地区的防御。

5 malaria   

n.疟疾

参考例句：

• He had frequent attacks of malaria.他常患疟疾。
• Malaria is a kind of serious malady.疟疾是一种严重的疾病。

6 parasites   

寄生物( parasite的名词复数 )； 靠他人为生的人； 诸虫

参考例句：

• These symptoms may be referable to virus infection rather than parasites. 这些症状也许是由病毒感染引起的，而与寄生虫无关。
• Kangaroos harbor a vast range of parasites. 袋鼠身上有各种各样的寄生虫。

7 reproduce   

v.生育，繁殖，复制，重做

参考例句：

• The machine can reproduce a key in two minutes.这机器能在两分钟内复制一把钥匙。
• The picture will reproduce well.这照片会印得很清楚。

8 kidney   

n.肾，腰子，类型

参考例句：

• Several of the patients had received kidney transplant.病人中有几位已接受了肾移植手术。
• The operation to transplant a kidney is now fairly routine.肾脏移植手术如今已相当常见。

9 joint   

adj.联合的，共同的；n.关节，接合处；v.连接，贴合

参考例句：

• I had a bad fall,which put my shoulder out of joint.我重重地摔了一跤，肩膀脫臼了。
• We wrote a letter in joint names.我们联名写了封信。

10 joints   

接头( joint的名词复数 )； 关节； 公共场所（尤指价格低廉的饮食和娱乐场所） （非正式）； 一块烤肉 （英式英语）

参考例句：

• Expansion joints of various kinds are fitted on gas mains. 各种各样的伸缩接头被安装在煤气的总管道上了。
• Expansion joints of various kinds are fitted on steam pipes. 各种各样的伸缩接头被安装在蒸气管道上了。

11 defense   

n.防御，保卫；[pl.]防务工事；辩护，答辩

参考例句：

• The accused has the right to defense.被告人有权获得辩护。
• The war has impacted the area with military and defense workers.战争使那个地区挤满了军队和防御工程人员。

12 expel   

vt.把...开除，驱逐，放逐，排出，喷出

参考例句：

• They were told at first that they should simply expel the refugees.一开始有人告诉他们应该直接将那些难民驱逐出境。
• The headmaster may expel the boy from the school.校长可能要把那个男孩从学校开除。

13 vaccine   

n.牛痘苗，疫苗；adj.牛痘的，疫苗的

参考例句：

• The polio vaccine has saved millions of lives.脊髓灰质炎疫苗挽救了数以百万计的生命。
• She takes a vaccine against influenza every fall.她每年秋季接种流感疫苗。

14 affected   

adj.不自然的，假装的

参考例句：

• She showed an affected interest in our subject.她假装对我们的课题感到兴趣。
• His manners are affected.他的态度不自然。

15 kidneys   

肾形矿脉； 肾，肾脏( kidney的名词复数 )； （可食用的动物的）腰子

参考例句：

• The function of the kidneys is to excrete wastes from the body. 肾的功能是排泄人体里的废物。
• She got a very dangerous disease of kidneys. 她得了一种很危险的肾病。

16 swelling   

n.肿胀

参考例句：

• Use ice to reduce the swelling. 用冰敷消肿。
• There is a marked swelling of the lymph nodes. 淋巴结处有明显的肿块。

17 saint   

n.圣徒；基督教徒；vt.成为圣徒，把...视为圣徒

参考例句：

• He was made a saint.他被封为圣人。
• The saint had a lowly heart.圣人有谦诚之心。

18 pregnant   

adj.怀孕的，怀胎的

参考例句：

• She is a pregnant woman.她是一名孕妇。
• She is pregnant with her first child.她怀了第一胎。