Sick birds pass the viruses to healthy birds through saliva, nasal secretions, and feces. Within a single region, bird flu is transmitted readily from farm to farm via (a) airborne feces-contaminated dust and soil; (b) by contaminated clothing, feed, and equipment; or (c) by wild animals carrying the virus on their bodies. The disease is spread from region to region by migratory birds and through international trade in live birds. Humans who are in close contact with sick birds, like chicken farmers and slaughterhouse workers, are at the greatest danger of becoming infected. Besides chicken, virus-contaminated surfaces and intermediate hosts such as pigs can be sources of infection for humans.
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