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VOICE ONE:

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

VOICE TWO:

And I'm Bob Doughty. On ourprogram 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 twothousand different kinds of mosquitoes. Female mosquitoes bitepeople 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 theskin and find blood. The insect injects the victim with a substancethat 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 hundredfifty eggs. The mosquito lays them in any standing water.

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

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

W.H.O. officials expressed concernabout the possible spread of disease after the major earthquake inthe Indian Ocean last month. The earthquake produced huge waves thatkilled thousands of people. The waves destroyed many villages andleft floodwaters in coastal areas. The officials have warned thatthe floodwaters could increase the risk of diseases spread bymosquitoes.

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

Malaria parasites 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 andreproduce thousands of times. They cause the person's bodytemperature to rise. They also may destroy major organs. People withmalaria may suffer kidney failure or loss of red blood cells.

VOICE ONE:

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

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

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

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

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Older people suffer from dengue fever much more. They may developreddish skin and lose their sense of taste. They also may haveterrible pain in the head or behind their eyes. And they mayexperience pain in joints such as the elbow or knee. This kind ofjoint pain is the reason why dengue fever is sometimes known asbreakbone fever.

The most severe kind of the disease is called dengue hemorrhagicfever. People who have this disease bleed from the nose or otheropenings in the body. Dengue hemorrhagic fever kills about fivepercent of all people it infects. The only treatment involvescontrolling the bleeding and replacing lost body fluids.

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Yellow fever is another disease carried by mosquitoes. There areno effective drugs against yellow fever. Doctors can only hope thata person's defense system is strong enough to fight the disease. TheWorld Health Organization says there are an estimated two hundredthousand cases of yellow fever each year. It is found mainly inAfrica, 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 ormuscles. Victims also may expel food they ate. Most patients improveafter three to four days.

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However, fifteen percent of patients develop a more seriouscondition. High body temperatures re-appear and the body turnsyellow in color. The victim bleeds from the nose, mouth, eyes orstomach. Half the people with this condition die within ten tofourteen days.

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

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Mosquitoes also carry lymphatic filariasis, a disease commonlyknown as elephantiasis. The disease has already affected more thanone hundred twenty million people. One third of those infected livein India. Another one third are in Africa. The others live in SouthAsia, the Pacific Ocean, or the western half of the world.

Mosquito bites spread the worms that cause elephantiasis. Peopleusually begin to develop the disease as children. Many childrennever experience signs of the disease. But it may cause hiddendamage to the body's lymphatic system and kidneys.

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

VOICE ONE:

Still another disease carried by mosquitoes is encephalitis. Itcauses an infection or swelling of the brain. Many different virusescause different kinds of the disease. One virus lives naturally inbirds and horses. Mosquitoes spread it to people. Mosquitoes inseveral Asian countries spread a kind of encephalitis known asJapanese encephalitis. A vaccine can prevent this sickness.

Other kinds include West Nile encephalitis, Saint Louisencephalitis and Eastern Equine encephalitis. Most healthy peopleinfected with the virus show no signs. Or they become sick for onlya day or two. But those with weak natural defenses may develop asevere infection. They may suffer from high body temperature,headache, shaking and even death.

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

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

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

Remove all containers that could provide a place for mosquitoesto live. Stay in an enclosed area when mosquitoes are most active.Wear clothes that cover most of the body. Other ways to preventmosquito bites are to put anti-insect chemicals on the skin,clothing and sleeping areas. Also, place special nets treated withinsect 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 BobDoughty.

VOICE ONE:

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