VOA慢速英语 2007 0515b

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This is SCIENCE IN THE NEWS in VOA Special English. I'm Steve Ember.

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And I'm Barbara Klein. On our program this week, we will tell about a possible way to control the disease malaria 1. Researchers have reported a decrease in the rate of male births in the United States and Japan for the past thirty years. We will tell about their findings. We also will tell about a study on the effects of vitamins in pregnant women.

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If malaria control efforts are to succeed, experts say mosquitoes in the wild must be replaced with parasite 2-resistant 3 ones



Researchers in the United States are exploring a possible way to control malaria. They are developing insects resistant to the disease.

More than three million people become infected with malaria each year. The disease kills at least one million people every year. Malaria is found in Africa, Asia, the Middle East and South America.

Malaria parasites 4 enter a person’s blood through the bite of a very small insect -- the mosquito. The malaria parasites travel to the liver. The organisms grow and divide there. After a week or two, the parasites invade red blood cells and reproduce thousands of times. They cause a 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.

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People die from malaria because they are not treated or treatment is delayed. Different drugs can prevent the parasites from developing in the body. But experts still say the best way to prevent the disease is not to be bitten by a mosquito.

That could change in the future. Research scientists at The Johns Hopkins University have created mosquitoes that cannot spread the malaria parasite. Computer studies show that such insects are needed to replace mosquitoes in the wild if malaria control is to succeed. The researchers reported their findings in the Proceedings 5 of the National Academy of Sciences.

Earlier studies showed that disease resistant mosquitoes might not be as healthy as wild ones. Those with resistance would die early and not be able to replace the others.

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The Johns Hopkins researchers put equal numbers of malaria resistant mosquitoes in a box with other mosquitoes. All the insects fed on mice that had been infected with the malaria parasite. The researchers took eggs made by the insects and kept them until they became adult mosquitoes. These new mosquitoes were then permitted to feed on infected mice. The researchers did this again and again. After nine generations, seventy percent of the mosquitoes were malaria resistant.

The researchers say they changed the genetic 7 structure of the mosquitoes to produce a protein called S.M. One. The S.M. One gene 6 blocks the development of the malaria parasite inside the insect. The genetically 8 engineered mosquitoes mated with mosquitoes lacking this gene. So their young had a single copy of the gene -- not two. This is thought to be the reason the genetically engineered mosquitoes did not die early as the others.

Other researchers say the Johns Hopkins work confirms earlier studies concerning disease resistant insects. But they say more work needs to be done, especially with human malaria parasites. The researchers say creation of the new insects alone will probably not be able to control the disease. They say malaria resistant mosquitoes could be used in combination with drugs and insect poisons to stop malaria in the future.

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A new report says the number of boys born in the United States and Japan has decreased every year since nineteen seventy. The report says the reason for the decrease is unclear. But it says environmental and other influences might be involved.

American and Japanese researchers studied thirty years of birth records from the two nations. The researchers say they found fewer boys were born in comparison to girls. They say the decrease in births was equal to one hundred thirty-five thousand white males in the United States. In Japan, the decrease was equal to one hundred twenty-seven thousand fewer males.

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The study found a decrease of seventeen males for every ten thousand births in the United States since nineteen seventy. And it found an even greater decline in Japan -- thirty-seven males for every ten thousand births. It also found a continued rise in deaths of male fetuses 10. The fetuses died before they were fully 11 developed.

The researchers examined birth records of African-Americans as a separate group from white Americans. They found that the number of male births among African-Americans increased a little. But the rate of male births to female births for African-Americans was lower than that of whites.

The study found that all races experienced a decrease in the number of fetal deaths, probably because of improved medical care.

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Devra Lee Davis of the University of Pittsburgh Center Institute led the study. She says scientists do not know the reason for the decline in male births, but suspect environmental poisons.

Earlier reports show that researchers suspected a similar decrease in male births in other industrial nations.

Scientists already know that men who work with some chemicals and metals have fewer baby boys. Scientists also know that some things influence both a woman’s ability to have a child and the health of her children. These include her physical health, the foods she eats and the chemicals in the air around her.

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Professor Davis says other things can affect the health of a male fetus 9. They include the weight and age of the parents, and their use of alcohol drinks and drugs.

The report says one in every four to five married adults today report difficulty having children. It says evidence shows that chemicals in the air can affect the health of male reproductive fluid. This increases the chances of men producing a physically 12 disabled child.

Professor Davis says more research is needed to examine these questions in greater detail among small groups. Experts say such research could lead to environmental changes that will protect young people and their children in the future.

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The World Health Organization estimates twenty million babies are born too small each year. It says a baby weighing less than two thousand five hundred grams at birth has a less than desirable weight for good health. Ninety-five percent of such children are born in developing countries.

One recent study shows that pregnant women in developing countries have healthier babies if the women are given vitamins. Researchers from the United States and Tanzania found that vitamins could help reduce low birth weight. Their findings were reported last month in The New England Journal of Medicine.

Wafaie Fawzi of the Harvard University School of Public Health led the study. Professor Fawzi says low birth weight can cause serious health problems in babies. He says low birth weight has been linked to poor growth and mental development, and even early death.

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There are fourteen kinds of vitamins. People who do not get enough of these chemicals in their food, or want more, often take multivitamins.

In the study, multivitamin pills were given to four thousand two hundred pregnant Tanzanian women. The pills contained all the B vitamins, as well as vitamins C and E. They also included iron and folate in levels several times higher than advised for women in industrial nations.

Four thousand other women received a harmless substance. None of the women had the virus that causes the disease AIDS.

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The researchers found a twenty percent decrease in health risks for babies when mothers took the vitamins every day. There were no major differences between the two groups in the rate of early births or deaths of babies.

The researchers say the vitamins helped improve the growth of fetuses probably by improving the mother's natural defenses against disease and hemoglobin levels. Hemoglobin is the coloring in red blood cells that carries oxygen.

Professor Fawzi says multivitamin pills should be considered for all pregnant women in developing countries. He says the pills improve health and are not costly 13.

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This SCIENCE IN THE NEWS was written by Nancy Steinbach and Lawan Davis. Brianna Blake was our producer. I'm Steve Ember.

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