The dangerous bluetongue virus has been confirmed in five more animals on Norfolk cattle farms - bringing the county's total to 10 cases in the past month.
Since Friday night, animal health officials have identified the potentially-deadly animal disease in cattle on three new premises in the county, following "active surveillance" efforts.
All are within the 10km temporary control zone (TCZ) established on December 8 around a farm near Cantley - which became East Anglia's first case since 2007.
Defra says all the infected animals "will be humanely culled to minimise the risk of onward transmission".
Defra says the midge-borne disease does not affect people or food safety, but outbreaks "can result in prolonged animal movement and trade restrictions" - so it is a major worry for East Anglia's livestock farmers.
Although 44 infected animals have now been identified on 24 premises in Norfolk and Kent, government officials say there is "still no evidence that bluetongue virus is currently circulating in midges in Great Britain" - but surveillance is ongoing.
The virus is transmitted by biting midges which are usually most active between April and November, and it has been spreading rapidly in continental Europe.
Bluetongue affects ruminants including sheep, cattle, deer and goats as well as camelids such as llamas.
The Norfolk TCZ is not being extended, and movement restrictions continue to apply to cattle, sheep and other ruminants within the zone.
Livestock producers within the TCZ can only move animals out of the zone with a specific licence, which will only be granted if there is an "urgent and genuine welfare need to move the animals" - or if they need to move animals to another premises or abattoir within the TCZ; from outside the zone to permanently within the TCZ; or to go directly to slaughter at a designated abattoir.
Norfolk farmers have been warned to "remain vigilant" and report any suspicions of the virus immediately to the APHA (Animal and Plant Health Agency) on 03000 200 301. For more guidance on symptoms and prevention measures, see www.gov.uk/guidance/bluetongue.
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