Migratory birds may be spreading viruses that cause bird flu around the world, say scientists.

Outbreaks in poultry may become more common in the future, especially in ill-prepared countries, they warn.

A severe strain found at a duck farm in the UK last year may have been carried by wild birds out of Russia, according to Dutch researchers.

The virus is a low human health risk, but wild birds on long migratory routes should be monitored, they say.

H5N8 is a strain of bird flu that appeared late last year in Russia, East Asia, North America and four European countries, including the UK.