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.

Brazil has declared itself free from bird flu after no new cases emerged in commercial farms since the first outbreak in May, paving the way for a return to international markets for the world’s largest chicken supplier.

FileBrazil on Wednesday declared its commercial flocks free of the bird flu virus after observing a 28-day period without any new commercial farm outbreaks, the country's ministry of agriculture said.