Using Mosquitoes to Help Fight Malaria / Can Aspirin Reduce Colon-Cancer Risk? / Tsetse Flies a Threat to Agriculture

This is Sarah Long. And this is Bob Doughty with SCIENCE IN THE NEWS, a VOA Special English program about recent developments in science. Today, we tell about mosquitoes that were genetically changed to reduce the spread of malaria. We tell about a possible use of aspirin to reduce the risk of colon cancer. And we tell about the threat of the tsetse (TSET-see) fly to agriculture.

Scientists have reported progress in efforts to disarm mosquitoes that carry the disease malaria. The scientists say they changed the genes of some mosquitoes so that the insects are less effective in spreading malaria.

The study is said to be the first to suggest that genetic engineering could be used to fight the deadly disease. Genetic engineering is the technology of changing the genes of living things.

Malaria is caused by an organism carried by some kinds of mosquitoes. Mosquitoes take in the organism when they feed on the blood of an infected person or animal. The malaria parasite then moves from the insect's stomach into the salivary glands near its mouth. When the mosquito bites its next victim, the parasite enters the victim's blood.

As many as five-hundred-million people around the world are infected with malaria each year. The disease kills as many as three-million people each year. Most of the victims are children in Africa, south of the Sahara Desert.

Experts say traditional methods are failing to control the mosquitoes that carry malaria. Chemical sprays can be harmful to both human health and the environment. Also, the malaria parasite is becoming increasingly resistant to many drugs.

In the new study, an international team of scientists changed the genes of a version of mosquitoes that infects mice with malaria. Marcelo Jacobs-Lorena (mahr-SELL-oh JAY-cubs-luh-REHN-ah) of Case Western Reserve University in Cleveland, Ohio, directed the study.

Last year, his team identified a molecule called S-M-One. S-M-One stops the malaria parasite from passing from a mosquito's stomach to its salivary gland. The team put the gene for the molecule into the mosquitoes. The gene was added to a molecular system that produces the enzymes the insects need to feed on blood.

The scientists carried out two kinds of experiments with the genetically-engineered mosquitoes. In the first, they studied what happened to the mosquitoes when they bit malaria-infected mice. The scientists found that only half of the insects became infected with malaria parasites.

The results of the second experiment were even more successful. The scientists wanted to see if the genetically-engineered mosquitoes could pass malaria to uninfected mice. In two of three tests, none of the mice bitten by the mosquitoes became infected with the disease. In the other test, the number of mice that became infected was greatly reduced.

Scientists say genetically engineered mosquitoes could possibly be mated with wild mosquitoes to produce insects that could not spread the malaria parasite.

Nature magazine published the findings. The magazine also published comments by other scientists. Fotis Kafatos (FOH-tis kah-FAH-toes) of the European Molecular Biology Laboratory in Germany praised the study.

He said this is the first time that humans have reduced the ability of mosquitoes to spread malaria. However, he said it is not known if the research would work with malaria in humans. A different form of the parasite causes the disease in humans.

Aspirin is one of the world's oldest, least costly and most widely used drugs. Aspirin is a common treatment for headaches, colds and flu. It reduces other kinds of pain, such as pain caused by arthritis in the areas where bones are joined.

Aspirin also may help prevent some forms of cancer. One recent study showed that it can slow the development of unusual growths, or adenomas, in the colon. Adenomas are early signs of changes that can lead to colon cancer.

Colon cancer is the second leading cause of death from cancer in the United States, after lung cancer. The National Cancer Institute estimates fifty-six-thousand Americans will die from the disease this year. The group says that about one-third of those deaths could be avoided by testing to find and remove adenomas.

John Baron of Dartmouth Medical School in Lebanon, New Hampshire, directed the new study. He reported his team's findings at a meeting of the American Association for Cancer Research.

The study involved more than one-thousand patients in nine American cities. All the patients had had at least one adenoma removed within the past three months. The patients had no known heart disease or other conditions sometimes treated with aspirin. They also had no history of cancer in their families.

The patients were divided into three groups. Some patients took one common three-hundred-twenty-five milligram aspirin each day. Another group of patients took one low-strength aspirin that was only eighty milligrams. The other patients took an inactive substance.

Doctors examined the patients for new adenomas a year or more after the study started. The study found that the people who took one low-strength aspirin each day reduced their risk of developing new adenomas by nineteen percent.

Among patients who had a more aggressive kind of adenoma, the low-strength aspirin reduced the risk by forty percent. Doctor Baron believes aspirin may block the action of an enzyme needed for the growth of cancer tumors. However, the normal strength aspirin did not have this same preventive effect.

Millions of Americans take a low-strength aspirin every day to prevent heart attacks. The results of the study suggest that aspirin may be helping these people in other ways. The results confirm increasing amounts of evidence that aspirin can reduce the risk of some cancers.

However, doctors do not believe aspirin is safe for everyone. The drug often causes problems in the stomach or intestines, especially if taken in large amounts. These problems can include life-threatening bleeding.

The tsetse fly is a serious problem in many parts of Africa. Tsetse flies cause problems in an area of almost ten-million square kilometers. The United Nations Food and Agriculture Organization says some of this area is fertile land that could be used for agriculture. F-A-O officials say stopping the insect would help African farmers reclaim land and increase food production.

Tsetse flies feed on the blood of humans and animals. The fly carries a parasite that attacks the blood and nervous system of its victims. This organism causes Trypanosomiasis (trih-PAN-oh-so-MY-ah-sis), a disease known as nagana (nah-GAH-nah) in farm animals. In humans, the disease is called sleeping sickness.

Trypanosomiasis kills eighty percent of infected victims. The disease affects an estimated five-hundred-thousand people. It kills three-million farm animals each year. Thirty-seven countries in Africa are affected by tsetse flies.

Jorge Hendrichs is an insect control expert with the F-A-O. He says the tsetse fly keeps people poor by preventing them from producing the food they need to survive. The tsetse fly and trypanosimiasis have slowed the development of agriculture in Africa.

One-hundred-fifty-five-million cattle are being raised in tsetse-free areas south of the Sahara Desert. The area of land that is tsetse-free is small. It is being overused by both cattle and people.

One method that has proved successful in fighting the tsetse is the sterile insect treatment. Male flies treated with radiation become sterile, or unable to reproduce. The insects then are released into areas with other flies. After mating, the eggs of the wild females do not develop.

The F-A-O says the sterile insect treatment has been used with traps and other methods to end the tsetse fly problem on the Tanzanian island of Zanzibar. Mr. Hendrichs says these efforts have no long-lasting side effects on the environment.

This SCIENCE IN THE NEWS program was written and produced by George Grow. This is Bob Doughty. And this is Sarah Long. Join us again next week for more news about science in Special English on the Voice of America.