Bluetongue virus 'BTV-3' has been confirmed in Somerset and West Sussex, counties currently not under any restriction, the government has confirmed.
The two cases were linked to animals known to have moved to premises in these areas before bluetongue restrictions were put in place, Defra said.
The farms are now under restriction and the infected animals have been culled, with further testing to be undertaken to ensure there has been no local transmission.
In England, a total of 82 farms have now reported an outbreak of the disease since late August, which was this summer's first case.
Nine counties - East Yorkshire, East Sussex, West Sussex, Norfolk, Suffolk, Essex, Lincolnshire, Kent and Somerset - have recorded BTV-3, with numerous restricted zones and temporary control zones in place.
The disease, which is spread by midge bites, is damaging and can reduce milk yield, cause sickness, and reduce reproductive performance.
In the most severe cases, it can cause death with all of these outcomes impacting farmers’ incomes.
Animal and Plant Health Agency (APHA) chief executive, Jenny Stewart, urged farmers and livestock keepers to be vigilant.
“Since the first BTV-3 case for this season was detected last month, case numbers have continued to rise.
"I want to remind keepers of the importance of monitoring their livestock and taking up free testing where necessary.
“Scientists, vets and field teams from APHA are working hard to help tackle bluetongue virus and ensure farmers are kept up to date and supported.”
It follows confirmation of the disease in a single sheep on a farm in Norfolk in late August, which made it the first UK bluetongue case this summer.
Before this, in November 2023, government vets identified the first case of the disease in Britain since 2007.
The worsening situation follows the government's decision to permit the use of three bluetongue vaccines to curb infections.
The vaccines are suppressive, meaning they will reduce some of the clinical signs experienced by animals with the disease, but they do not prevent infection.
Bluetongue does not affect people or food safety, but outbreaks can result in prolonged animal movement and trade restrictions.
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.
