Mutated avian flu has been detected on five mink farms in Finland, said the Finnish Food Authority on Tuesday.
Three of the affected farms were detected on Monday, with another two announced on Tuesday.
Authorities are keeping a close eye on Finland's mink farms as a potential location for the infection to mutate into one transmissible between humans.
"The mutation is one that helps the virus spread between mammals, but not one that makes it more transmissable to humans," said Terhi Laaksonen of the food authority's animal welfare unit.
The virus could still mutate further, however.
Finland has around 400 mink farms, which are to be inspected for bird flu mutations in the coming days and weeks. Concerns have been raised about the risk of avian flu mutation on the farms, where mink are packed tightly in small cages with little room for exercise.
