Some 4.7 million chickens and turkeys have been slaughtered in Virginia following an outbreak of avian influenza (bird flu).

The outbreak prompted culls at 194 farms, the state agriculture department said.

Bird flu is a virus that reduces the growth of birds and slows their egg production. Although it is not dangerous to humans, it can very quickly be spread to neighbouring farms and flocks.

Various countries and other US states have imposed a ban on poultry and derived products from Virginia following the outbreak. In April, for example, the Japanese subsidiary of McDonald's pulled chicken products from its menu, including the popular Chicken McNuggets, as supplies dwindled.

The agriculture department in Virginia has stressed that it is winning the battle against the disease, with the number of new cases falling in recent days.