Outbreaks of avian influenza, especially the highly pathogenic form, can be devastating for the poultry industry and for farmers. For example, an outbreak of highly pathogenic avian influenza in the USA in 1983-1984, largely confined to the state of Pennsylvania, resulted in the destruction of more than 17 million birds at a cost of nearly US$ 65 million. Economic consequences can be especially devastating in developing countries where 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. For example, an outbreak that began in Mexico in 1992 was not completely controlled until 1995.

    For these reasons, government authorities usually undertake aggressive emergency control measures as soon as an outbreak is detected.

(World Health Organization's Official Site January 28, 2004)