Teagasc has reiterated concerns around bluetongue virus (BTV) and the impact it would have on Irish farming, and what farmers can do to reduce the risk.
Bluetongue is a notifiable exotic disease that infects ruminant animals, including sheep, cattle, goats and deer.
Although Ireland is currently bluetongue free, the virus could spread to Ireland through imports of infected animals; imports of infected foetuses and 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.
Teagasc stresses that any suspected case of bluetongue must be reported to the Department of Agriculture, Food and the Marine without delay.
It is important that bluetongue is considered as a possible diagnosis if suggestive clinical signs are present, even if those signs might also suggest other diseases, as quick detection is key for successful management and control.
Teagasc said that quick detection of the first case could mean a “huge difference” to cattle and sheep farmers across Ireland.
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.
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.
Cattle or sheep infected with bluetongue can develop a range of clinical signs.
These may include some or all of the following:
- Fever;
- 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);
- Abortion or deformities in offspring/foetuses.
In severe cases, death can occur in infected animals.
Sheep are more likely to show obvious and more severe clinical signs of bluetongue than cattle, and mortality rates can reach 30% to 70%. Some animals may not show any clinical signs, and, according to Teagasc, these animals can pose a risk for spreading the disease to new areas or countries.
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.
Bluetongue is not contagious between animals, but 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.
Infection is spread when a 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, and for an increase in midge activity.
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.
These midges could enter Ireland by being blown on the wind from Britain or France to counties in the east and south of Ireland.
The disease could also enter Ireland by the importation of infected animals. Imports from Britain have been suspended since November 2023 since outbreaks started there, while movement of cattle and sheep from other EU countries are subject to complex certification requirements in place.
Despite these controls, the risk cannot be completely eliminated, and the department recommends against importing any susceptible livestock at all.
The same advice is in place for germinal products (ova, semen, embryos).
Although the disease is not contagious, infected pregnant animals can pass the disease to their offspring, which would then be born infected.
The epidemiological situation in Europe has changed rapidly during 2024, with the disease spreading quickly into new, previously unaffected, regions and countries.
This is why it is deemed a risk 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.
Licenced vaccines are available for bluetongue serotypes 1,4 and 8, while a vaccine for serotype 3 has been approved for emergency use in the EU and UK. However, receiving a serotype 3 vaccine does not allow an animal to enter Ireland, as it has not obtained full authorisation.
In autumn this year, an outbreak of serotype 12 was detected in the Netherlands, and no vaccine is available for that strain, meaning controlling a serotype 12 outbreak would be highly challenging.
Moreover, vaccines for one serotype do not provide protection for another.
Ireland is the last country in north-western Europe that is not infected with bluetongue. Teagasc says that, although the risk is considerable, there is chance of remaining bluetongue-free, and of successfully addressing an outbreak of the disease.
For that reason, farmers are advised as follows:
- Do not import cattle into Ireland, and, if you choose to do so despite that advice, take every precaution and comply with the rules in place to address the risk;
- Dot not import semen or embryos into Ireland, and, if you choose to do so despite that advice, remain compliant with all relevant rules;
- Report any suspected case of bluetongue to your regional veterinary office (RVO) promptly, so that, in the event of infection, onward spread to other farms across Ireland can be halted before it is too late.