Diseases Spread by Mosquitos

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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 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 standing water.

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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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 coastal areas. The officials have warned that the floodwaters could increase the risk of diseases spread by mosquitoes.

The most important disease spread by mosquitoes is malaria. 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.

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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.

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.

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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.

Yellow fever is another disease carried by mosquitoes. There are no effective drugs against yellow fever. Doctors can only hope that a person's defense 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.

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A vaccine 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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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 kidneys.

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Other kinds include West Nile encephalitis, Saint 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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Mosquitoes like dark colors. They do not bite women who are bleeding during their fertility period. But they do bite pregnant women. Many kinds of mosquitoes are most active in the early morning and early at night. They eat mostly at night.

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.

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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.

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