Farmers have been warned of a “very high” probability of a new strain of bluetongue being brought in through midges blown over from Europe.

Affecting livestock such as cattle and sheep, symptoms include a blue and swollen tongue, fever, reduced milk yield and in the most severe cases, death.

It does not affect humans or food safety.

It is spread through biting midges, and while there is no evidence bluetongue is currently circulating in midges in Britain, the Government warns the insects can be blown long distances on the wind and bring the virus over from mainland Europe.

A new strain of bluetongue known as BTV-3, which emerged in the Netherlands in September 2023, was first identified in November in England.

Since then there have been 126 cases in the outbreak, seven sheep and 119 cattle, across four counties, Kent, Norfolk, Suffolk and Surrey.

A risk assessment published by the Animal and Plant Health Agency (APHA) following the outbreak last year, warns there is a very high probability of a new introduction of bluetongue virus of the new BTV-3 strain into Britain during 2024 through infected biting midges being blown over from northern Europe.

There is also a medium risk of another strain, BTV-8, being carried in by midges blown from northern France.

Biting midges are most active between April and November, and the timing of any potential incursion of the disease will depend on temperatures and wind patterns, officials said.

Farmers are being urged to remain vigilant and monitor their animals frequently, while making sure their livestock and land and up-to-date contact details are registered with the APHA in case of an outbreak.

There is currently no vaccine in the UK for the BTV-3 strain of the virus, although a new vaccine has been approved for emergency use from the start of May in the Netherlands and Belgium.

Chief veterinary officer Dr Christine Middlemiss said: “Our robust surveillance systems show we have now entered the period where biting midges are more active, and we know that the likelihood of bluetongue virus entering Great Britain is increasing.

“Despite the increase in midge activity, the current risk of transmission has not changed, but I would urge farmers to remain vigilant and report any suspicions to the Animal Plant Health Agency.”

She added: “Bluetongue virus does not pose a threat to human health or food safety.”

Biosecurity minister Lord Douglas Miller said that once the risk of transmission increased, free bluetongue tests would be offered to livestock owners in high-risk counties.

He added: “We are actively engaging with vaccine manufacturers on the development of a BTV-3 vaccine for use in the UK.”