Bluetongue risk could run into January, Pirbright scientists warn

Pirbright researchers urge vets and farmers to use the winter months to plan BTV-3 vaccination, as midge activity extends later into the year and confirmed cases in Britain pass 3,400.

Vets and livestock keepers are being urged not to mistake falling temperatures for the end of the bluetongue season, after scientists at The Pirbright Institute warned that new infections could still occur into early January.

The warning comes as Defra figures published on 19 October confirmed 12 new incidents in Great Britain, bringing the total since the beginning of July to 3,424. Bluetongue virus serotype 3 (BTV-3) continues to drive the outbreak, and no BTV-8 cases have been recorded this season.

The 2026–27 season began when the first English cases were confirmed on 10 July, followed by Scotland on 8 August. Since then, the virus has spread from its stronghold in Cornwall, Devon and Somerset across large parts of England, Wales and southern Scotland.

Why cooler weather is not the end

Speaking ahead of an AHDB webinar on the fertility impacts of the virus, Pirbright vector ecology fellow Dr Marion England explained that infected Culicoides midges could continue to transmit the virus potentially until the start of January.

The distinction matters. BTV is thought to need average daily temperatures above roughly 12°C to replicate within the midge. Once temperatures fall below that threshold, newly feeding midges are less likely to become infectious, but those already carrying the virus remain capable of transmission for as long as they survive.

Dr England noted that midges historically disappeared around November, but in recent years activity has persisted until the end of December or early January, leaving what she described as “a shorter window of reduced disease transmission”. She added that midge populations have remained at normal levels this year, with no evident impact from the ongoing drought.

Recent history supports the concern. Following the 2025–26 vector season, new BTV-3 cases were still being confirmed in Great Britain in the first weeks of 2026, including a Devon case confirmed on 9 January.

Fertility and production impacts

Fertility was the focus of the AHDB webinar held on 21 October, and it is an area where the effects of BTV-3 can outlast the clinical phase. Fever associated with infection can temporarily reduce semen quality in rams and bulls, while infection during pregnancy has been linked to abortion, stillbirth and congenital abnormalities in lambs and calves.

With tupping under way on many sheep farms, vets may want to discuss breeding soundness checks for rams that have shown signs of illness or are on holdings with confirmed cases, and to prepare clients for the possibility of reduced conception rates or poorer outcomes at lambing and calving next spring.

Clinical vigilance

Practitioners should continue to act promptly on suspicion. Signs recorded in recent English cases include crusting of the muzzle, nasal discharge, ulceration of the dental pad, lameness and lethargy in sheep, and lameness, muzzle reddening and oral ulcers in cattle. Goats, deer and camelids are also susceptible. There is no specific treatment, and the disease can be fatal.

Bluetongue remains a notifiable disease. Defra funds diagnostic testing for up to three animals where disease is suspected and reported, and vets in England can now confirm clear-cut cases on clinical examination alone, removing the wait for laboratory results.

Plan vaccination now

Pirbright’s central message is that the winter lull, short as it may be, should be used for planning. UK chief veterinary officer Christine Middlemiss has described vaccination as the only way to deal with BTV-3, and AHDB has consistently pointed to it as the most effective tool currently available.

Vaccine supply came under significant pressure during this year’s peak, with manufacturers bringing in additional doses as demand rose. Discussing requirements with clients over the coming months, rather than when midges re-emerge in spring, gives practices and suppliers time to secure stock, and gives animals time to complete primary courses and develop immunity before the next high-risk period.

Practical points for herd and flock health planning include:

• identifying priority groups, such as breeding stock, replacements and animals due to calve or lamb in spring
• checking each product’s authorised species, dosing schedule and onset of immunity
• reviewing the bluetongue status of replacement stock before purchase
• reminding clients that live ruminant trade from Great Britain to the EU is currently not possible

Looking ahead

With cases also confirmed in Ireland this season and the vector season stretching later into the year, BTV-3 looks set to remain a recurring feature of UK livestock practice. For vets, the months between now and spring offer the best opportunity to put vaccination plans in place.