TESTS have revealed the Schmallenberg sheep and cattle virus has spread to the Stroud valleys.
It was first detected in Germany and the Netherlands in 2011. Midges are suspected of carrying it across the English Channel.
Sixteen positive tests have been reported in the county during the past year and Leonard Stanley cheesemaker Liz Godsell fears there could be many more.
She said: "We have had it. The vet said up to 80% of all diary herds could have it.
"It is easy to test cattle for it, in their milk. It's just another thing we have to live with."
Mostly associated with sheep, the virus causes fatal birth defects. There is not believed to be a risk to people.
Vet Bryony Kendall from Tyndale Farm Veterinary Practice in Lower Wick, Dursley, said shw knew positive tests had come from milk samples as they were part of a wide network of practices.
Latest figures for Gloucest-ershire from the Animal Health and Veterinary Laboratories Agency, which carries out the tests for Defra, show 15 positive tests in cattle and one in sheep.