UCD Herd Health Group Statement on BTV-3 in Ireland
Evidence of BTV-3 infection was detected in Irish cattle for the first time on 22nd January 2026. In January 2026, the European Commission implemented a regulation re-categorising Bluetongue (serotypes 1-24), from a "Category C" to a "Category D+E" disease. This change is scheduled to take full effect on 15th July 2026. As a result, BTV will be treated as a disease under surveillance rather than a disease to be eradicated. No Member State will be able to achieve official freedom from the disease, and at a national level, emphasis will be placed on movement controls and surveillance rather than disease eradication1i (DAFM, 2026). At farm level, decisions regarding control measures should be based on discussions between farmers and Private Veterinary Practitioners. The following view is intended to support and inform these discussions at a time when there is significant uncertainty on appropriate courses of action, limited time available prior to the higher risk period for spring calving herds, and whilst more detailed formal reviews are ongoing.
Background and exposure risk
BTV-3 serotype emerged in the Netherlands in September 2023. The source of the emergence is not yet known. In November 2023, evidence of an incursion into England was detected. In 2024 and 2025, BTV-3 spread massively throughout the mainland of Europe. In England, cases steadily moved westward during this period with confirmations in Wales in September 2025. The first evidence of infection in Northern Ireland was discovered in November 2025.
There are two potential sources from which Irish herds and flocks could become infected in 2026: (i) “overwintering” of the current incursion and emergence of infection from this site(s), and (ii) transmission following a second introduction via windborne spread (or animal introduction) from the UK or mainland Europe.
Local epidemiological investigations are ongoing investigating the present incursion. On 29th January, DAFM confirmed the presence of infection on additional surrounding farms. The precise mechanism for overwintering of BTV is unclear; however, the chances of the infection successfully overwintering and acting as source(s) of infection for the 2026 season increases as further infected farms are identified. In addition, given the extent and geographical distribution of BTV-3 now in the UK, it seems likely that we will see subsequent windborne incursions seeding infection from England and Wales, as well as other potential sites.
For these reasons, the likelihood of Irish cattle being exposed to BTV-3 in the coming season is now much higher than it has been previously.
Potential impacts and mitigation
Deciding on the appropriate actions for Irish farmers is a key consideration for 2026. At present, vaccination is the only evidence-based control option available to farmers now at risk of exposure. In addition to assessing exposure risk, the decision as to whether to vaccinate or not in 2026 requires considering the likely impacts of infection should the herd become infected.
The characteristic clinical signs of BTV-3 are well documented and not the focus of this opinion. In terms of production, the reported impacts are potentially significant. For Irish farmers, the most important factors are likely to be potentially large fertility impacts (embryonic death, bull infertility and abortion); congenital defects (principally hydrancephaly) and perinatal mortality in calves infected in utero; increased mortality rates in all age groups; lameness; and decreased milk yield.
It is important to note that there is variation in the severity and duration of clinical signs reported by different countries that have already been affected, and between different farms in the same country. In the Netherlands, Belgium and France, mortality and fertility impacts have been dramatic in both cattle and sheep. In the UK however, although there have been fewer formal reports of disease impact, there are indications that the observed clinical and production impacts have been substantially less than those documented in other European countries.
How this apparent reduced impact in UK livestock might have occurred is not yet clear. As a result, the likely impact of the disease in Ireland, even in the case of the infection becoming established in 2026, is uncertain. However, in discussing the risk posed by BTV-3 with farmers, it is worth noting that our dairy herds and spring-calving suckler herds could be especially vulnerable to BTV-3 impacts. This is because the time of highest vector activity (June to September) aligns with the point at which much of the national cattle herd will be in early to mid-gestation. BTV-3 infection at this point of gestation is associated with embryonic death and congenital defects in calves (Delooz et al., 2025). Due to the substantial consequences of even minor reductions in reproductive performance to short- and long-term profitability of spring-calving systems, losses for individual herds could be substantial should the infection enter the herd during this time.
Discussions with farmers in advance of the 2026 breeding season is advised. Highlighting the high level of uncertainty in terms of impact, yet potential for substantial adverse impacts in naïve herds, is important so that farmers can make decisions in line with their priorities and risk appetite for 2026 and subsequent years.
UCD Herd Health Group
Reviewed by
Prof. Raphaël Guatteo, Oniris, France
Prof. Bart Pardon, University of Ghent, Belgium
Dr Inge Santman-Berends, Royal GD, Netherlands