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This is the VOA Special English Development Report.

Scientists say they have made more progress in developing malaria-resistant mosquitoes. The idea is to release genetically engineered insects like these into mosquito populations as a way to control the disease.


Malaria is spread by mosquitoes

Each year more than three million people become infected with malaria. At least one million die, mostly young children and pregnant women in Africa. Malaria is also a problem in Asia and South America.

The parasites that cause malaria enter people's blood when they are bitten by the mosquitoes that carry the organisms. The parasites travel to the liver where they divide and grow. After a week or two, they invade red blood cells and reproduce thousands of times. They can destroy major organs.

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

Their advice could change in the future with the help of mosquitoes genetically engineered to block development of the parasite. In other words, they would not be able to spread the disease. Computer studies show that if malaria control is to succeed, insects like these are needed to replace mosquitoes in the wild.

Researchers at Johns Hopkins University in the United States reported on their work in the Proceedings of the National Academy of Sciences. They put equal numbers of malaria-resistant mosquitoes in a box with other mosquitoes. The insects mated, and all of them fed on mice infected with the malaria parasite.

The researchers took eggs produced by the mosquitoes and kept them until they became adult mosquitoes. These insects 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.

Earlier studies showed that disease-resistant mosquitoes would die early and not be able to replace wild ones. But in the new research, the scientists say they developed stronger mosquitoes. In any case, malaria-resistant mosquitoes might still need to be used in combination with drugs and insect poisons to control the disease.

And that's the VOA Special English Development Report, written by Nancy Steinbach. To learn more about malaria, use the search box at www.unsv.com and then click on Archive.
  原文地址：http://www.tingroom.com/voa/2007/7/41932.html