A plain-language guide to bluetongue: what it is, how it spreads, who it affects and why it matters — even though it cannot make a single person ill.
What is bluetongue?
A viral disease of ruminants.
Bluetongue is caused by bluetongue virus (BTV), a member of the Orbivirus genus. It affects domestic and wild ruminants — principally sheep and cattle, but also goats, deer, llamas and alpacas. There are more than two dozen recognised serotypes of the virus worldwide, and immunity to one serotype does not necessarily protect against another.
How does it spread?
Through the bite of an infected midge — not through contact between animals.
Bluetongue is transmitted by biting midges of the Culicoides genus. A midge that feeds on an infected animal can acquire the virus and pass it on when it later feeds on a susceptible one. Because the disease depends on an insect vector, its spread is shaped by things farmers cannot directly control: temperature, season, weather and midge activity, alongside the movement of livestock between areas.
Can I catch it from my animals, or from meat and milk?
No.
Bluetongue is not a public-health concern. It is not transmitted through contact with animals or their wool, and it is not transmitted through consuming meat or milk from an infected animal. Its significance is entirely in animal health, welfare, agricultural production and trade — not human infection risk.
What does it actually do to an animal?
It varies a lot by species.
Sheep tend to show the most obvious and severe clinical signs: fever, swelling of the face, lips or tongue, mouth ulcers, excessive salivation, lameness, and — in animals that recover — breaks in the wool. Cattle typically show milder signs, or none at all, depending on the strain involved, yet an apparently healthy infected animal can still be a source of virus for midges. Goats generally show minimal symptoms. This asymmetry matters for surveillance: cattle can act as a hidden reservoir even while sheep are visibly suffering.
Why is everyone talking about BTV-3 specifically?
Because it has spread further and faster than earlier strains.
Serotype 3 (BTV-3) was first detected in the Netherlands in September 2023, after the country had been free of bluetongue for over a decade. It spread through more than 5,000 Dutch farms that year alone, and by October 2024 had affected over 8,000. In 2024 it re-emerged and moved rapidly across Germany, Belgium, France, Portugal, Spain, Scandinavia, Switzerland, Austria, Greece — and the United Kingdom. In the Netherlands, BTV-3 caused sheep mortality of up to 75 per cent on affected holdings, roughly ten times worse than the previous major strain, BTV-8. Estimates of the resulting economic losses across Europe run into the hundreds of millions of euros, once reduced milk yield, lost fertility, abortion and trade restrictions are factored in alongside animal deaths.
Is it notifiable? What do I have to do if I suspect it?
Yes — and reporting is a legal requirement, not just good practice.
Bluetongue is a notifiable disease in the UK. A keeper who suspects it must report it, after which the Animal and Plant Health Agency assesses the report and arranges sampling and testing where needed. We cover what that reporting process looks like in practice, and why it matters as much as the laboratory result, in Bluetongue Is Moving Again: What Happens When Farmers Become Part of the Surveillance System?
Are there vaccines?
Yes, and they are now central to managing BTV-3.
Three BTV-3 vaccines are currently authorised for use in the UK. A vet must prescribe them, but keepers can administer them themselves. Vaccination does not eliminate the need for surveillance — products differ in what they claim to reduce, whether viraemia, mortality, clinical signs or lesions — so it should be discussed with a vet rather than treated as a guarantee against infection.
Why can’t affected areas just cull their way out of it?
Because once a vector-borne disease is established in the local insect population, culling stops working.
Targeted culling can be considered when infection first appears in a new area, on the logic that removing the first positive animals might prevent the virus establishing locally. Once BTV-3 is circulating within local midge populations, however, that logic breaks down: the virus is no longer confined to identifiable infected animals, so mass culling becomes both disproportionate and ineffective. That is precisely why vaccination, movement controls and rapid reporting — rather than large-scale slaughter — are the tools being used against the current outbreak.
Questions & Answers
What kind of animals does bluetongue affect?
Ruminants: principally sheep and cattle, but also goats, deer, llamas and alpacas. Wild ruminant species can be affected too.
Is bluetongue a risk to human health?
No. It is not transmitted through contact with animals or wool, or through consuming meat or milk. It has no public-health significance.
How is bluetongue transmitted?
By the bite of infected Culicoides midges, not by direct contact between animals. Its spread depends on midge activity, which is affected by temperature, season and weather, as well as by livestock movement.
Why is BTV-3 considered particularly severe?
In the Netherlands, BTV-3 caused sheep mortality of up to 75 per cent on affected holdings — roughly ten times worse than the previous major strain, BTV-8 — and it has spread across more of Europe, faster, than earlier serotypes.
Do vaccinated animals still need to be reported if they show signs of disease?
Yes. Vaccination reduces risk but is not a guarantee against infection, and bluetongue remains a notifiable disease regardless of vaccination status.
Why doesn’t culling stop the disease once it has spread?
Because bluetongue is spread by midges, not by contact between animals. Once a serotype is circulating in the local midge population, the virus is no longer confined to identifiable infected animals, making mass culling disproportionate and ineffective compared with vaccination and movement control.
Go deeper
This is the short version. For the full picture — UK case numbers, the reporting gap, compensation and what better surveillance design would look like — read the analysis Bluetongue Is Moving Again: What Happens When Farmers Become Part of the Surveillance System? For another live example of surveillance catching an emerging vector-borne threat early, see Aedes aegypti Is Breeding in Britain: This Is What Prevention Looks Like Before the Emergency.
References
- World Organisation for Animal Health (WOAH). Bluetongue. Disease factsheet.
- Animal and Plant Health Agency (2026). Bluetongue: how to spot and report it. GOV.UK.
- Department for Environment, Food & Rural Affairs and Veterinary Medicines Directorate (2026). Bluetongue serotype 3 (BTV-3) vaccination. GOV.UK.
- Department for Environment, Food & Rural Affairs and Animal and Plant Health Agency (2026). Bluetongue virus in Europe. GOV.UK.
Key Takeaways
- Bluetongue is a viral disease of ruminants — sheep, cattle, goats, deer and camelids — spread by biting Culicoides midges rather than by contact between animals.
- It poses no risk to human health: it cannot be caught from meat, milk or handling affected animals.
- Sheep tend to show the most severe clinical signs, while cattle are often infected with mild or no symptoms yet can still carry and spread the virus to midges.
- Serotype BTV-3 has spread rapidly across the UK and northern Europe since 2023, at times causing mortality far higher than earlier bluetongue strains.
- Vaccination and prompt reporting of suspected cases are the main tools available, because once a serotype is established in local midge populations, culling stops being an effective control option.