Masaio Ishizuka, a senior epidemiologist at the Sao Paulo University, said evidence suggests migratory birds have now infected local Brazilian species, making the bird flu virus endemic in the world's largest chicken exporter, which accounts for 39% of global trade.

SAO PAULO - Brazil's vast and diverse geography, with the Amazon to the north, mountain ranges along the Atlantic coast and the Andes to its west, may have helped it avoid the U.S. fate of widespread bird flu among commercial poultry flocks by keeping migratory birds away from farms in the country's interior.

The Brazilian Agriculture Ministry has updated on Wednesday the list of countries that have placed restrictions on chicken trade with Brazil, the world's largest exporter, after it confirmed its first case of bird flu on a commercial farm in May.