问答题 Recently, the news has been filled with reports of the "bird flu". 46． Asia is on a region- wide health alert, with governments slaughtering millions of chickens to contain outbreaks of the bird flu in Thailand, Vietnam, Cambodia, South Korea, Japan and China.
Influenza-commonly called "flu"-is one of the oldest and most common diseases known to man. It can also be one of the deadliest. 47．The great "Spanish flu" pandemic of 1918-1919 was considered the worst plague in history, killing up to 40 million people with half of the world's population infected in only a few months.
48．Influenza can also infect many different warm-blooded animals, such as birds. However, the "flu" virus usually develops different variants that are specialized for each species of animals that they infect. Cross species infections are rare.
A flu strain called influenza A (H5N1) appears to have made a successful jump from birds to humans. The viral strain was first isolated from South African birds in 1961．49．The first known human infection occurred in a Hong Kong toddler in May of 1997．By the end of 1997, there were 13 confirmed cases and four deaths, all in Hong Kong. In an attempt to stop the spread of the disease, the government of Hong Kong ordered the slaughter of all chickens, ducks, geese, quail and domestic pigeons.
Humans infected with H5N1 so far are thought to have caught the disease from fowl and no person-to-person transmissions have been reported. 50．The WHO, however, fears that the bird flu is highly adaptable and might leap the species barrier. It says anyone exposed to the disease should be quarantined to avoid contact with sufferers of regular human influenza.