The Schmallenberg virus causes lambs to be born dead or with serious deformities such as fused limbs and twisted necks, which mean they cannot survive.
Scientists are urgently trying to find out how the disease, which also affects cattle, spreads and how to fight it, as the number of farms affected increases by the day.
Infected ewes do not show any symptoms of the virus until they give birth, with horrific results. Farmers have described delivering the deformed and stillborn animals as heartbreaking.
The lambing season has only just begun, which means that the full impact of the disease will not be felt until the weather warms up and millions more animals are born.