Tingroom Radio—流感--传播增速和人类的抗体（在线收听）

 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. The greatest effect will likely be in developing countries. Health care resources in those countries are limited, and populations are weakened by poor health and diet. 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. Medical experts have identified three major kinds of flu. They call them type A, B and C. 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.