Avian influenza, or “bird flu,” is a contagious disease caused by viruses that normally infect only birds and, less commonly, pigs. __26__ all bird species are thought to be susceptible to infection, domestic poultry flocks are especially vulnerable to infections that can rapidly reach epidemic proportions.
Outbreaks of avian influenza __27__ be devastating for the poultry industry and for farmers. For example, an outbreak of avian influenza in the USA in 1983–1984 resulted in the destruction of more than 17 million birds __28__ nearly US$ 65 million. Economic consequences are often most serious in developing countries __29__ poultry raising is an important source of income, and of food, for impoverished rural farmers and their families. When outbreaks become widespread within a country, control can be extremely difficult. __30__, government authorities usually undertake aggressive emergency control measures as soon as an outbreak is detected.
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