Diseases Spread by Mosquitoes1
This is SCIENCE IN THE NEWS in VOA Special English. I'm Shirley Griffith. And I'm Steve Ember. Today, we tell about diseases spread by mosquitoes -- the most widely hated insects in the world.
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 thin sucking tube to break the skin, find blood and inject the victim with a substance that keeps blood flowing.
The female mosquito drinks the blood and uses it to produce as many as two hundred fifty eggs. The insect leaves the eggs in any standing water.
The eggs produce worm-like creatures called larvae in two days to a few months. However, some eggs can stay in water for years until conditions are right for development. The larvae 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.
The World Health Organization says mosquitoes carry organisms that cause disease and death for millions of people throughout the world. The most important disease spread by mosquitoes is malaria. The W.H.O. says two hundred forty-seven million people became infected with malaria in two thousand six. Malaria caused almost one million deaths, mostly among children in Africa. The disease is found in more than one hundred countries in Africa, Asia, the western Pacific Ocean, the Middle East and Central 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 and reproduce thousands of times. They cause the person's body temperature to rise. They also may destroy major organs. People with malaria may suffer kidney failure or loss of red blood cells.
Some medicines are generally effective in preventing and treating malaria. They are designed to prevent the parasites from developing in the body. People die from malaria because they are not treated for the disease or the treatment is delayed.
The World Health Organization says mosquito control efforts are improving in many areas. But it warns that mosquitoes are becoming increasingly resistant to pesticides, the products used to kill insects.
This month, the W.H.O. joined with other groups to announce a new effort against malaria. The goal is to reduce use of the pesticide known as DDT. The United States banned most uses of DDT in nineteen seventy-two.
The W.H.O. announced ten projects to test non-chemical methods for fighting mosquitoes. These include trees that repel mosquitoes and fish that eat the larvae. However, officials say any reduction in the use of pesticides must make sure that disease control efforts are not weakened.
Mosquitoes also carry dengue fever. 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.
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.
Older adults suffer from dengue fever much more. They may develop reddish skin and lose their sense of taste. They also may have pain in the head or behind their eyes. And they may experience pain in joints such as the elbow or knee. This kind of joint pain is the reason why dengue fever is sometimes known as breakbone fever.
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