填空题

The World Health (36) says avian influenza could become a worldwide threat unless governments act now to stop it. Officials at the United Nations (37) warn that bird flu could kill as many as seven million people. They say the number of deaths would depend on the (38) of the virus once it entered the general population. So far, avian influenza has mostly (39) people who have been around infected birds and their waste. The W.H.O. said at the end of September that it had reports of 60 deaths. These were among 160 (40) cases since December, 2003. The deaths were (41) in Vietnam. Fifteen flu viruses infect birds. Officials are most (42) about the h-five-n-one virus. It could spread easily from person to person if it mixes with human flu virus. That might happen if a person or an animal, such as a pig, becomes infected with both human and avian flu. The body has no (43) against bird flu. Anti-viral medicine has been used with some success to treat bird flu. Scientists have a vaccine that might protect against the virus. (44) . Also last week, scientists in the United States announced that they have remade the so-called Spanish flu virus. (45) . The scientists say they found that the Spanish flu came from birds. (46) . They also hope to find ways to protect against any big outbreak.