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

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And I'm Doug Johnson. This week, we will tell about a drug treatment for stroke victims. We also will tell about a possible explanation for the mysterious disappearance of bees. And, we will tell about a lot of plastic waste in the Pacific Ocean.

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Strokes are a major cause of death and disability. A stroke is a loss of blood flow in the brain. There are two kinds of strokes. An ischemic stroke happens when a blood vessel in the brain gets blocked. A bleeding, or hemorrhagic, stroke happens when a blood vessel breaks.

People are more likely to die from a hemorrhagic stroke. But ischemic strokes are more common, and doctors may be able to treat them.

A drug called tissue plasminogen activator, or tPA, can break up blood clots. But experts generally advise against using the drug if more than three hours have passed after the first signs of a stroke.

There is a risk that giving a patient a strong blood thinner during a stroke can cause bleeding inside the brain. The longer the wait, experts say, the more likely that the risks of treatment will be too great.

But recent findings suggested that tPA may be effective in saving brain tissue even if three to four and a half hours have passed.

Some studies have failed to produce clear evidence to support treatment after three hours. But researchers reported recently that the evidence was stronger when they combined the results of the four major studies already done.

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The findings were published in the journal Stroke. The researchers said tPA improved the chances of a successful result by thirty-one percent and produced no change in the death rate.

Scientists from Belgium and Germany worked with Maarten Lansberg of the Stanford University School of Medicine in California. One of the scientists worked for a company that makes tPA for use in Europe. America's National Institutes of Health paid for the study.

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If you think someone is having a stroke, you should seek help immediately. The warning signs often appear suddenly. These include trouble walking, weakness especially on one side of the body, difficulty seeing and difficulty speaking.

Yet people who seem healthy can suffer a stroke without even knowing it. A study published last year involved about two thousand people with an average age of sixty-two. Brain imaging showed that nearly eleven percent of them had suffered what is known as a silent stroke.

The study found a link between silent strokes and a condition called atrial fibrillation. This is the most common cause of an unusual, or abnormal, heartbeat in older adults.

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Colony collapse disorder first struck honey bees in the United States in late two thousand six. Over the next two years, beekeepers lost more than one-third of their honey bees.

Scientists in the United States and other countries have been working to explain the mysterious disappearances of bees. Now, a new study suggests that several viruses may act together.

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The scientists found that the affected bees had a number of viruses from a group called picorna-like viruses. The infections observed in the bees included Israeli acute paralysis virus and deformed wing virus.

Extremely small insects are likely involved in spreading the viruses. Varroa mites have been causing serious problems in bee colonies in the United States since the late nineteen eighties. These mites carry picorna-like viruses.

The viruses appear to harm the bees' ability to use their genes to produce proteins needed to fight infections.

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University of Illinois Professor May Berenbaum says it appears that bees could deal with one or two viruses at the same time, but not three or four. She says the picorna-like viruses seize control of the ribosome in cells. Ribosomes are structures in which proteins are made.

The professor says ribosome is important to the survival of any organism. If it is compromised, then the bees could not defend themselves against pesticide products, fungal infections, bacteria or poor nutrition. These have all been identified as possible causes of the collapse disorder.

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Imagine a mass of floating waste two times the state of Texas. Texas has a land area of more than six hundred and seventy-eight thousand square kilometers. So it might be difficult to imagine anything twice as big.

The waste includes bags, bottles and containers. Plastic products of all kinds -- even shoes. There also are lots and lots of extremely small pieces of plastic.

All together, this mass of waste floating in the North Pacific Ocean is known as the Great Pacific Ocean Garbage Patch. It weighs about three million, five hundred thousand tons.

The eastern part of the Great Pacific Ocean Garbage Patch is about one thousand six hundred kilometers west of California. The western part is west of the Hawaiian Islands and east of Japan. The two patches of waste are connected together in the shape of a dog bone -- a really big bone about nine thousand kilometers long.

The waters surrounding the Great Pacific Ocean Garbage Patch are known as the North Pacific Gyre. The area has been described as a kind of oceanic desert, with light winds and slow moving water currents. Slow enough that garbage from all over the world collects there.

Experts say the garbage gets trapped in the currents for years before being pushed out. Some of the trash finds its way to coastal areas around the world.

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In recent years, there have been growing concerns about the floating garbage and its effect on sea creatures and human health. America's Environmental Protection Agency estimates that about one hundred thousand sea animals die each year as a result of the plastic waste. An estimated one million sea birds are also affected.

Scientists say thousands of the animals get trapped in the floating waste, resulting in death or injury. Even more die from a lack of food or water after swallowing pieces of plastic. The plastic can block air passages. The trash can also make the animal feel full, lessening its desire to eat or drink.

The floating garbage also can have harmful effects on people. There is an increased threat of infection and disease from polluted waste, and from eating fish that swallowed waste. Divers can also get trapped in the plastic, and it can get caught up in boating equipment. The plastic also releases chemicals into the water. Some of the chemicals are harmful to both humans and animals.

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The existence of the North Pacific Garbage Patch first gained public attention in nineteen ninety-seven. That was when racing boat captain and oceanographer Charles Moore and his crew sailed into the garbage while returning from a racing event.

Five years earlier, another oceanographer learned of the trash after a shipment of rubber duckies got lost at sea. Many of those toys are now part of the Great Pacific Ocean Garbage Patch.

Charles Moore and his team at the Algalita Marine Research Foundation have spent ten years studying plastic waste and testing water from the ocean. Their studies found up six times more plastic in the water than zooplankton, the small organisms normally found floating near the ocean's surface. They have also found small pieces of plastic inside the stomachs of fish like mahi-mahi.

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Last month, a team from the University of California at San Diego became the latest group to travel to the Great Pacific Ocean Garbage Patch. The team of students and research volunteers set off on a three-week boat trip to examine the area. 

They were shocked by the amount of waste they saw. They gathered hundreds of sea creatures and water samples to measure the garbage patch's effect on ocean environment. There were small pieces of plastic in every sample.

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