Bluetongue disease: what it is and how does it spread?

Bluetongue is a virus that affects cattle, sheep and deer and is primarily spread by infected midges, which bite on susceptible animals.

Although bluetongue is not a new disease, new variants of the disease known as serotype 3 or BTV-3 emerged in 2024 which is spreading faster than previous variants and so poses a greater risk to Ireland.

There is a huge range in the severity of the disease, with some infected animals showing little or no symptoms of disease while other infected animals are severely affected.

There is a long list of symptoms associated with bluetongue disease, with the UK Department of Environment, Food and Rural Affairs (DEFRA) outlining the following as the main symptoms in cattle:

Dutch farmers have reported that lameness is a big problem with infected cows losing their hoofs, milk yield dropping by 15% and only recovering three months after infection.

Infertility in cows and bulls as well as embryo loss and abortions have also been widely reported on Dutch dairy farms.

Where is the disease present?

Last year, the disease was widespread in northern France, the Netherlands, Belgium, Luxemburg and Germany. Many of the outbreaks have been severe with significant impacts on cow health and milk yield.

It is also present in England, but so far the impact has been low. The impacted zone is in the south east of England, closest to the continent.

While this zone covers over 24% of Great Britain, it contains only 11% of the susceptible animals that are in Britain so the rate of infection and spread of the bluetongue disease has been low there when compared to the higher livestock density regions such as the Netherlands.

There are no reported cases in Ireland and there never has been.

How can bluetongue enter Ireland?

The Department of Agriculture says that the most likely spread of bluetongue to Ireland would be through the importation of infected animals.

While movement restrictions are in place in regions where outbreaks are known, the main risk is of importing animals from regions where infections are unknown at the time.

The other big risk is of bluetongue entering Ireland from infected midges blown across the sea from Britain or the continent.

This risk is heightened during the summer months and is dependent on high temperatures and strong easterly winds.

While midges are active in early summer they are more likely to be spreading disease in late summer/autumn.

How can bluetongue be spread?

The main vector for bluetongue is midges that spread the disease by biting infected animals and then spreading the disease to uninfected animals that they subsequently bite.

Midges are most active during the summer months when average temperatures are high with transmission most likely in late summer.

The other recognised source of transmission is through semen, embryos and pregnancy.

Bluetongue infected animals cannot easily spread the disease to other animals and it cannot be spread to humans or affect food safety.

What if cases are found in Ireland?

In the event of an outbreak in Ireland the Department of Agriculture would impose control measures to try to eradicate the disease.

These measures would include introducing a restricted zone within a minimum of 150km from the source of the outbreak, or the whole country.

Animal movements within this zone would be restricted, particularly during the active spread period and exposed animals would have to be culled.

In Britain, pre-movement testing and authorisation is required before animals can be moved within and from the restricted zone.

In Britain, the cost of bluetongue testing is covered by the government but the cost of sampling by the vet is paid for by the farmer.

If bluetongue was discovered in Ireland, the live export trade of cattle and calves would be suspended.

A severe outbreak would have huge implications for farm output, with sheep flocks and dairy herds most at risk from the implications of bluetongue.

Are bluetongue vaccines available?

Vaccines for bluetongue are available and are now widely used in Europe and in the restricted zone in the UK.

A bit like the COVID-19 vaccine, the bluetongue vaccine does not prevent infection but reduces the impact of infection.

It is not yet clear by how much if at all the vaccines will help to reduce onward spread of the disease. The cost of the vaccine varies but a recent AHDB webinar put the cost for cattle at £8/head (€9.50/head) for two doses.

What to do if you suspect and animal has bluetongue?

The Department of Agriculture guideline is to isolate and house suspected animals and immediately contact the local regional veterinary lab to report the suspected case.

Comment

If the experience from Europe is anything to go by, the loss of Ireland’s ability to export live animals due to bluetongue would probably prove to be a small cost compared to the impact on production.

Bluetongue has been a disaster for farmers right across Netherlands, northern France and Germany.

Part of the reason for high milk prices today is that milk production took a big hit in this region last autumn and farmers are still counting the cost of that.

Keeping the disease out of Ireland will depend on plenty of good luck, but also the prevention of silly action such as importing infected livestock.

TB is a big enough challenge for the sector to be dealing with, we don’t need bluetongue on top of it.