Text 3 [A] We try our best to develop a vaccine. [B] The cause of the flu epidemics arising so often in Asia. [C] The general introduction of "BIRD FLU". [D] The reason of the new strain of flu arising. [E] The diseases caused by viruses threat human-beings. [F] The connections between bird and viruses are complex. ______ Human beings have known the diseases caused by viruses since thousands of years ago; and were fearful of them. The diseases are infectious hepatitis, polio, rabies, and AIDS. Now we can find easily that why the late Sir Peter Medawar, Nobel laureate in physiology or medicine, wrote "A virus is a piece of bad news wrapped in protein." Perhaps the most lethal virus in human history has been the influenza virus. About 21 million Americans and Europeans died of flu within 18 months in 1918 and 1919. It was an astonishing number. The outbreak in Hong Kong in 2003 of a potentially deadly strain of flu has attracted the world’s attention once again on flu. Flu viruses we call are RNA animal viruses. An individual flu virus resembles a rod studded with spikes composed of two kinds of protein. There are three "types" of flu virus, distinguished by their capsid protein, which is different for each type: Type A flu virus causes most of the serious flu epidemics in humans, and also occurs in mammals and birds. Type B and Type C viruses are only in to humans and rarely cause serious health problems.