25 November 2024

Bluetongue: What are the risks for Irish cattle farmers and what can we do about it?

At the recent National Beef Conference, Dr. Eoin Ryan, Department of Agriculture, Food and the Marine (DAFM) presented on ‘Bluetongue: What are the risks for Irish cattle farmers and what can we do about it?’

Bluetongue is a notifiable exotic disease, caused by bluetongue virus (BTV), that infects ruminant animals (such as sheep, cattle, goats and deer) and camelids (such as llama and alpaca).

Although Ireland is currently bluetongue free, the virus could spread to Ireland through import of infected animals, infected foetuses, germinal products (ova, semen, embryos) or wind dispersal of infected midges from infected areas. Several different serotypes (variations) of bluetongue virus are currently circulating in Europe.

As bluetongue is a notifiable disease, any suspect case of bluetongue must be reported to the Department of Agriculture, Food and the Marine (DAFM) without delay. Farmers, veterinary practitioners and other relevant stakeholders should remain vigilant for bluetongue. It is important that bluetongue is considered as a possible differential diagnosis if suggestive clinical signs are present, as quick detection is key for successful management and control. The quicker we detect the first case, the better our chances of stopping it spreading widely. This could mean a huge difference to cattle and sheep farmers across Ireland.

There are no public health risks associated with bluetongue. Bluetongue does not affect human health or food safety. However, it does have a huge impact on farmers whose animals become infected, due to the financial and emotional stresses involved.

Watch a video recording of Dr. Eoin Ryan’s presentation below

What do infected animals look like? The clinical signs of bluetongue

Cattle or sheep infected with bluetongue can develop a range of clinical signs. These may include some or all of the following: fever, inappetence (loss or lack of appetite), drop in milk yield, reddening of the mucus membranes, sores on the nose, gum and dental pads, swelling of the face, lips and tongue (i.e. “blue tongue”), breathing difficulties if the tongue swells, drooling, discharge from the eyes and/or nose, lameness due to coronitis (inflammation and swelling at the top of the hoof) and abortion or deformities in offspring/ foetuses. In severe cases, death can result.

Sheep are more likely to show obvious and more severe clinical signs of bluetongue than cattle if they become infected, and mortality rates can reach 30 to 70%. Some animals may not show any clinical signs; however, and these animals can pose a risk for spreading the disease to new areas or countries.

The clinical signs of bluetongue can resemble other conditions commonly seen in sheep and cattle such as infectious bovine rhinotracheitis (IBR), photosensitization, malignant catarrhal fever (MCF), or anaphylaxis. Cases of bluetongue serotype-3 in the Netherlands in autumn 2023 and into 2024 resulted in huge production losses, significant welfare issues and high mortality (up to 60%) in some outbreaks.

Due to the similarities between the deformities caused by Schmallenberg virus and bluetongue virus in offspring/ aborted foetuses, foetal carcasses submitted for post-mortem to Regional Veterinary Laboratories are routinely tested for bluetongue and Schmallenberg viruses. Similarly, because bluetongue is only one of a number of conditions which can cause severe milk drop in dairy cattle, samples from such disease investigations are routinely tested for bluetongue as part of the overall diagnostic testing.

How do midges spread bluetongue?

Bluetongue is a vector borne disease; it is carried and spread by infected biting midges (Culicoides species). These midges are present in Ireland and are generally most active between April and November. Bluetongue is non-contagious; this means it does not transfer directly from an infected animal to another animal, which might be in the same pen via direct contact. Infection is spread when a biting midge bites an infected animals and subsequently transmits the virus by biting another susceptible ruminant host. A single bite from a bluetongue infected midge can cause a new bluetongue infection.

Temperature plays a key role in bluetongue transmission and gives rise to the seasonality associated with the virus. Warmer temperatures throughout the summer and into the autumn months, increase the risk of bluetongue transmission during this time. Warmer temperatures are needed for both bluetongue virus replication within the midge (referred to as the ‘extrinsic incubation period’ or EIP) and for an increase in midge activity. In the late summer-to-autumn period, midge numbers are at their highest and temperatures are still high enough for the virus to replicate in infected midges. Bluetongue virus replication within a midge can take between 4 to 20 days, and requires an average temperature above 12°C. The speed of replication increases as temperatures increase, which shortens the bluetongue replication cycle. This means that, when temperatures are higher, the virus replicates faster within infected midges, shortening the time required for the infection cycle and thus aiding the rapid spread of the disease. Although midges will remain active above temperatures of 4°C, during colder winter temperatures, midges are unable to spread the virus during these colder periods, and so the transmission risks reduce.

Once bluetongue virus enters the midge population, eradication becomes very difficult requiring high vaccination uptake levels maintained over a period of several years. If a vaccine is not available for a given serotype, eradication is not usually feasible.

How could bluetongue come to Ireland?

There are several potential ways in which bluetongue virus could be introduction into Ireland.

During the warmer months when midges are more active and the virus can replicate in them (roughly April to November), infected midges could be blown on the wind from Britain or France across the sea and onto counties along the southeast and eastern coast. Once there, these infected midges could bite susceptible animals, establishing infection. If the outbreak is not reported and tackled promptly, or if animals are moved to other areas before the disease becomes obvious, bluetongue could spread across the area and more widely in Ireland.

The virus could spread to Ireland through the import of infected animals. Imports from Great Britain have been suspended since November 2023. For the movement of cattle and sheep to Ireland from other EU Member States, there are complex certification requirements in place to prevent infected livestock entering Ireland. Despite these controls, the risk is still present as they cannot eliminate all risk. For this reason, the Department strongly recommends against importing any susceptible livestock into Ireland at all.

Bluetongue can also be spread by germinal products (ova, semen, embryos) collected from infected animals. This can happen in cases where the animal is not showing obvious clinical signs at the time of collection. For this reason, the import of germinal products poses a danger of importing bluetongue virus, as appropriately certified germinal products from bluetongue affected countries are not without risk of introducing bluetongue into Ireland. This is why the Department strongly recommends against importing bovine or ovine germinal products into Ireland at all currently.

Pregnant cattle which become infected can pass the infection to their unborn calf. When these calves are then born weeks or months later, they are infectious. Midges which feed on them can then spread a new wave of infection in that area.

The epidemiological situation in Europe has changed rapidly during 2024, with disease spreading quickly into new, previously unaffected, regions and countries. This is why it is risky to import livestock; although the area may be thought to be free of bluetongue at the time the stock are purchased, by the time they are to be shipped to Ireland, the virus may have spread locally and not yet have been detected.

A summary of the current restrictions on the movements of live animals and germinal products into Ireland

Great Britain (GB) to Ireland (IE)

The import of live ruminants from Great Britain (GB) to the island of Ireland (IE & NI) remains suspended.
Germinal products (semen, ova, embryos) may be imported from GB into Ireland once the relevant animal health requirements for bluetongue virus can be certified.

Other EU Member States to Ireland (IE)

The introduction of livestock or germinal products from other EU member states is permitted only where detailed certification requirements to safeguard against bluetongue can be satisfied.
The Department will not pay compensation for animals infected by imported germinal products, nor for imported animals which subsequently test positive for bluetongue in the post-entry sampling.
There is currently a chance that animals in certain EU Member States may not meet certification requirements for entry into Ireland, if there are bluetongue outbreaks in the area.

Vaccination against bluetongue virus

Vaccination against bluetongue virus is a key control measures and is necessary for disease eradication.

Licensed bluetongue vaccines are commercially available for bluetongue serotypes 1, 4 and 8 which can help to facilitate intra-EU movement. Animals from certain countries require vaccination against bluetongue to meet certification requirements, prior to movement. Proof of vaccination status for the BTV strains recently circulating in those countries or regions should be obtained.

The recent emergency use of BTV3 vaccines in EU Member States and in Great Britain have been authorised under emergency circumstances as a disease control measure, where BTV3 is circulating. These BTV3 vaccines do not guarantee that animals will not become infected; however, they do reduce the severity of the disease and the amount of the virus in the blood of infected animals, and so they are of great benefit to livestock farmers in reducing the impact of an outbreak of bluetongue. BTV3 vaccines have not yet obtained European Marketing Authorisation, nor have they determined an immunity period guaranteed in the specifications of the vaccine. It is important to note that, for this reason, animals vaccinated using these BTV3 vaccines do not meet the certification requirements for intra-community trade. This means that livestock vaccinated using BTV3 vaccines cannot enter Ireland.

In autumn 2024, an outbreak of serotype 12 (BTV12) was detected in the Netherlands. BTV12 had not previously ever been detected in Europe. No vaccine is available at all for this new strain. This means that if it spreads widely in spring 2025, control will be very challenging. This poses an additional risk for Ireland, in addition to the existing risk of BTV3.

Challenges regarding bluetongue control

Bluetongue is a challenging disease to manage, as several characteristics of bluetongue virus and the disease progression make control difficult. Bluetongue infected animals present with potentially severe clinical signs (in sheep) alongside a potentially high percentage of subclinical or undetected infections (adult cattle). Several bluetongue serotypes exist which may have differences in their clinical presentations.

Bluetongue infected animals have a persistent viraemia (i.e. a period during which virus remains present in the blood), during which the virus could be passed onto a biting midge, resulting in onward transmission. Bluetongue vaccinations do not provide cross protection between bluetongue serotypes. Challenges with vector control, including the potentially huge quantities of vectors in the environment, make this avenue of disease control difficult. Traditional disease control and eradication methods including movement controls, stamping out and vector controls have not always been successful in bluetongue control.

Bluetongue virus entry into Ireland would have significant implications for trade and would likely result in considerable losses at farm level through cattle and sheep becoming sick and in some cases dying. In other European countries, concerning levels of mortality have been seen, and sick animals have taken a long time to recover.

What can Irish cattle farmers do to reduce the risk of bluetongue?

Ireland is the last country in our region of Europe which is not infected with bluetongue. Although the risk is considerable, we do have a chance of remaining BTV-free and of successfully tackling any incursion if we identify it quickly and respond in time, before it spreads.

There are three things Irish cattle farmers can do to reduce the risk to their herds:

Do not import cattle into If you choose to do so despite this advice, take every precaution and fully comply with the strict rules in place to address this risk.
Do not import semen or embryos into Ireland. If you choose to do so despite this advice, take every precaution and fully comply with the strict rules in place to address this risk.
Report any suspect cases of bluetongue to your Regional Veterinary Office promptly, so that (if the suspect case is confirmed) onward spread to other farms across Ireland can be halted before it is too

View the full National Beef Conference proceedings here