An initial protection zone was put in place after infected birds were found at Whim Poultry Farm in West Linton last Thursday, while a second outbreak was discovered at Halls Farm near Penicuik on Monday.
Other cases were recorded at Whitelees Poultry Farm, in Cleghorn, near Lanark in South Lanarkshire on 12 November.
Bird keepers have been warned not to release game birds at the current time to stop the spread of infection.
They have also been asked to keep records of people visiting their premises and will have to apply for a special licence to move mammals such as cows, goats and sheep which provide milk for human consumption.