The government has announced a 'restricted zone' across Norfolk and Suffolk due to a surge in the number of bluetongue cases.
Farmers in both counties have been told to 'urgently act now' to prevent the disease spreading in their herds.
There have been several confirmed cases of bluetongue virus 'BTV3' at premises across East Anglia, with the total number now standing at 27 individual cases.
It follows confirmation of the disease in a single sheep on a farm in Norfolk earlier this week, which made it the first UK bluetongue case this summer.
The new restriction zone replaces the original temporary control zone (TCZ), which was set up earlier this week following the first case.
It means livestock keepers must now follow stricter restrictions on animal and germinal product movements.
All infected premises - which total ten - have been placed under restriction and susceptible animals can only be moved under licence from infected premises.
Essential moves of susceptible animals can take place without a licence within the restricted zone but cannot be moved out of the zone without a specific licence.
A general licence to move animals to designated abattoirs is also available.
UK Chief Veterinary Officer, Christine Middlemiss urged farmers not to move animals within the zone "unless it is absolutely necessary".
“Following an increased number of bluetongue cases, we have declared a restricted zone across Suffolk and Norfolk," she said.
"This means all keepers in these regions must urgently act now to both prevent the disease spreading to their herds and any further.
“We have not taken this action lightly and we are clear that farmers and their vets must remain vigilant and report any suspicions to APHA immediately.”
Bluetongue virus is primarily transmitted by midge bites and affects cattle, goats, sheep and camelids such as llamas.
The impacts on susceptible animals can vary greatly – some show no clinical signs or effects at all while for others it can cause productivity issues such as reduced milk yield, while in the most severe cases can be fatal for infected animals.
The virus can also be spread through germplasm (semen, ova, and embryos) as well as transmitted from mother to unborn offspring.
Farms close to the coast in counties along the east coast of England from Norfolk to Kent and along the south coast from Kent to Devon have been classed as the highest risk of incursion.
Last November, government vets identified the first case of the disease in Britain since 2007.
The government recently set out its plans to minimise the impact of a likely outbreak of bluetongue as experts feared a surge in cases during the summer months.
There is currently no BTV-3 vaccine authorised or approved for use in the UK, however free testing is now available for animal keepers.
BTV is a notifiable disease. Suspicion of it in animals in England must be reported to the Animal and Plant Health Agency on 03000 200 301.
