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This is SCIENCE IN THE NEWS, in VOA Special English. I'm Sarah Long.

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And I'm Bob Doughty. In February, the World Health Organization will hold a series of meetings in Geneva, Switzerland. Health experts and representatives of drug makers will discuss the newest developments in the continual fight against influenza.

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The flu -- in humans and birds -- is our subject this week.

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Influenza is a common infection of the nose and throat, and sometimes the lungs. It is caused by a virus which passes from one person to another.

The flu causes muscle pain, sudden high body temperature, breathing problems and weakness. It is most common in the winter months.

Generally, people feel better after a week or two. But the flu can kill. It is especially dangerous to the very young, the very old and those with a weak defense system against disease.

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Historical records have described sicknesses believed to be influenza for more than two-thousand years. The Roman historian Livy described such a disease attacking the Roman army. People in fifteenth century Italy thought the sickness was caused by the influence of the stars. So they named it "influenza."

In seventeen-eighty-one, influenza went from Europe to North America to the West Indies and Latin America. It spread in Asia in eighteen-twenty-nine, then again in eighteen-thirty-six. It also traveled to Indonesia, Russia and the United States.

In eighteen-eighty-nine, the flu began in Central Asia, spread north into Russia, east to China and west to Europe. Later, it affected people in North America and Africa. Experts say two-hundred-fifty-thousand people died in Europe in that flu pandemic. Worldwide, the number was at least one-million.

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But the deadliest outbreak of influenza on record involved a flu that first appeared in Spain. The so-called Spanish flu killed between twenty-million and fifty-million people around the world in nineteen-eighteen and nineteen-nineteen. Even young, healthy people became sick and died in just a few days.

Times when diseases spread throughout the world are called pandemics. The W-H-O says the next flu pandemic is likely to kill as many as six-hundred-fifty-thousand people in industrial countries. But it says the greatest effect will likely be in developing countries. The agency notes that health care resources in those countries are limited, and populations are weakened by poor health and diet.

Researchers say the new kind of flu will appear unexpectedly. They will not have enough time to identify it and produce a vaccine. That is why they are developing faster ways to produce vaccines.

Eighty years ago, the flu virus took months to spread around the world. Today, airplane travel means a virus can spread around the world within days. Experts say another virus like the one that appeared in nineteen-eighteen could be as dangerous as any disease ever known.

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Medical experts have identified three major kinds of flu. They call them type A, B and C. Type C is the least serious. People may get it and not even know it. But researchers study the other two kinds very closely. Viruses change to survive. This can make it difficult for the body to recognize and fight an infection.

A person who has suffered one kind of flu usually cannot develop that same kind again. The defense system produces antibodies. These substances stay in the blood and destroy the virus if it appears again. But the body may not recognize a flu virus that has even a small change.

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There are some antiviral drugs that doctors may use to treat influenza. But health officials say the best thing is to get a yearly vaccine to prevent the flu.

Each year, medical researchers work to develop vaccines to prevent the flu from infecting people. They meet in February to discuss which kinds of flu viruses to include in the next formulation. They try to decide which vaccines will be most useful in fighting against the kinds of flu they think will appear months later.

For this flu season, the vaccine chosen a year ago did not include the virus known as the Fujian strain. It came from Fujian province in China. It appeared late. To avoid a delay, it was not included in the vaccine.

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No one knows yet exactly how much protection the vaccine provided people this flu season. The northern flu season usually does not begin until December. This season, however, people started to get the flu in October. The World Health Organization says the majority of cases identified so far have involved the Fujian strain.

As of last week, the W-H-O reported that influenza remained widespread in many countries in central and eastern Europe. Cases also increased in Italy and Japan. And the flu remained widespread in some parts of Canada and the United States.

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Humans are not alone. Chickens and some other animals also get the flu. Since December, parts of Asia have had high levels of bird flu. Avian influenza virus has jumped to some people. But direct contact with chickens or their waste has been suspected. The World Health Organization says there has been no evidence that the virus has spread person-to-person.

Researchers are concerned about what could happen if the virus mixes genetic material with human flu virus. The new virus might then spread from person to person. People would become infected with proteins their bodies have never seen before. So they would have no defense.

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Scientists are especially concerned about Asia, where many human influenza viruses first appear.

In nineteen-ninety-seven, an outbreak of bird flu in Hong Kong infected eighteen people and killed six. Workers killed more than one-million chickens to control the threat.

Last year in Hong Kong, bird flu infected two people and killed one. Also last year, a different flu virus infected some agricultural workers and killed one person in the Netherlands.

In the current outbreak, the W-H-O says Vietnam and South Korea have the first epidemics ever documented in those countries. Japan has its first epidemic since nineteen-twenty-five.

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But Vietnam and Thailand had the only human cases confirmed as of Monday. At least seven people in Vietnam have developed bird flu. Six of them died. Of those, five were children. In Thailand a six-year-old boy became the first death in that country. Thailand is the fourth largest exporter of chicken in the world.

Announcements of flu outbreaks in chickens expanded in recent days to also include Indonesia and Cambodia. Pakistan and Taiwan have both reported outbreaks of less serious forms.

Health officials say chicken and eggs that have been well cooked should be safe to eat. The W-H-O says poultry should be cooked to seventy degrees Celsius. And the agency advise people to wash their hands after touching poultry products.

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Millions of chickens have died of bird flu, or been killed in an effort to contain the spread. The World Health Organization says it is also working to develop a vaccine to protect people from the bird virus.

The agency, part of the United Nations, says the effort requires the use of a new technology. This is called "reverse genetics." Scientists collect the virus from human victims. Then they mix genetic information from that virus with a virus grown in a laboratory.

The resulting virus is recognized by the defense system in the body and causes a protective reaction. Drug companies could then use this virus to produce large amounts of vaccine. But the W-H-O says a vaccine may not be ready for several months to several years.

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The World Health Organization says influenza is thought to result in two-hundred-fifty-thousand to five-hundred-thousand deaths a year. As many as five-million people get severe cases of the flu. Lost productivity adds up to great economic costs. So medical and agricultural officials say stopping the spread of influenza is one of their most important jobs year after year.

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SCIENCE IN THE NEWS was written by Nancy Steinbach. Caty Weaver was our producer. This is Bob Doughty.

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And this is Sarah Long. Join us again next week for more news about science in Special English on the Voice of America.