New bluetongue control-and-protect zones came into place at midnight following the announcement that there are now 11 cases of the disease.
Bluetongue is spread to livestock by biting midges
The new zone comprises parts of Norfolk, Suffolk, Essex and Cambs.
It replaces a temporary area brought in on Tuesday. Vets have confirmed 11 cases of the virus - 10 in the Ipswich area and one near Lowestoft, Suffolk.
The zone also includes London and parts of Lincs, Leics, Northants, Beds, Kent, Bucks, Herts, Berks, Surrey and Sussex.
Rachel Carrington, of the National Farmers' Union in East Anglia, said there were "a number" of potential bluetongue cases being investigated.
There were "unconfirmed cases" in Norfolk, Essex and Cambridgeshire.
Professor Philip Mellor, from the Institute of Animal Health, said it was important to develop a vaccine against the strain of bluetongue affecting livestock.
Anthony Gibson, spokesman for the National Farmers' Union, said "When animals are off-colour, farmers are likely to report it as a possible case of bluetongue.
"But there's no sign yet that it has spread out from the Suffolk area where it was first identified. At the moment, bluetongue is less of a concern than foot-and-mouth disease."