By Ana Mano and Roberto Samora SAO PAULO (Reuters) -Brazil began a 28-day bird flu observation period on Thursday which it hopes will show the country's chicken farms are free of the disease after local authorities said a farm where its first outbreak was detected had been fully disinfected. The outbreak in the world's largest chicken exporter, detected in the town of Montenegro in the state of Rio Grande do Sul, triggered trade bans from multiple countries. "It is under control, we have no evidence of new notifications," said Rosane Collares, a director at the state's agriculture secretariat. She said authorities will remain on watch because the incubation period of the bird flu virus is two weeks and they don't want to be caught off guard. The report from state authorities late on Wednesday that the farm was cleared means that if no other cases of bird flu are detected on Brazilian commercial chicken farms over the next 28 days, the country may be considered free of the disease. The count starts on Thursday, authorities said. "We need to ensure that the 28 days of observation occur without new outbreaks," Agriculture Minister Carlos Favaro said after a meeting with Rio Grande do Sul Governor Eduardo Leite this week. "We are reinforcing actions to ensure that everything is perfectly safe," he said. Eleven active investigations into potential bird flu cases in Brazil are ongoing, including two on commercial chicken farms in Santa Catarina and Tocantins states. On Wednesday, Tocantins state authorities ruled out an outbreak of bird flu in the farm where the investigation was being conducted, citing preliminary test results. However, the federal government is conducting additional tests, according to the agriculture ministry's website. Wagner Yanaguizawa, an analyst at Rabobank, said the next few days will be decisive in determining whether the outbreak has been contained. "After 28 days, if there are no new cases from then on, Brazil can declare itself free of the disease," he said, adding that it will then be up to the importers to lift existing trade bans. "But then trade flows will most likely return to normal," Yanaguizawa said. (Reporting by Ana Mano and Roberto Samora in São Paulo; Additional reporting by Débora Ely in Porto AlegreEditing by Philippa Fletcher)
