The first suspected bluetongue outbreak in Northern Ireland is under investigation, after surveillance testing found the virus in two cows near Bangor in Co Down. 

The All Ireland Science Media Centre asked experts to comment.

Dr Gerald Barry, Assistant Professor of Virology & Deputy Director of the One Health Centre, University College Dublin, comments: 

  • How were these cases of bluetongue virus detected? 

“There is ongoing surveillance of bluetongue virus in animals. This is not based on whether or not they are sick, instead animals are sampled at slaughter and tested for the presence of antibodies against the virus. When an animal is infected with Bluetongue virus it will produce an immune response including antibodies, which help the body defend against infection. Lab tests can check to see if animals have antibodies against the virus, indicating a current or recent infection. Live imported animals, such as imported cattle from Europe are required to be tested too.

“There is minimal testing of midges in periods where there is no suspicion of Bluetongue virus circulation. This is because good surveillance of animals is much more effective – it is challenging to find positives in midges when there is little to no virus in animals. If, however, there is an outbreak of disease, then testing of midges in those regions could become important to monitor spread.”

  • Given current weather conditions, is midge activity still high enough to support transmission?

“Culicoides midge activity decreases a lot during colder periods, however, it may persist, particularly in enclosed barns where temperatures might be higher and they are protected from adverse weather conditions. Typically, ideal temperatures are in the region of 15 to 20 degrees Celsius but some midges will remain active down to 4 or 5 degrees Celsius. It is also important to note that not only is midge activity affected by colder temperatures, but virus activity is affected too. Bluetongue virus does not replicate well in midges at lower temperatures so when cold, even if a midge were to draw up some blood from an infected animal, the virus would struggle to replicate efficiently in the midge and therefore the likelihood of it passing onto another animal is reduced.”

  • Is vaccine coverage sufficient to control a potential outbreak? 

“There are multiple versions or serotypes of Bluetongue virus. The version that has been detected in Northern Ireland on this occasion is Bluetongue virus 3. There are vaccines available for this version but they aren’t particularly good. They don’t stop infection and they don’t block onward transmission. This means that vaccination alone is unlikely to be enough to rapidly stop an outbreak. Other measures such as the control of animal movement, a massive surveillance effort to detect infected animals and the removal of infected animals to slaughter are all necessary. Long term, we need improved vaccines that limit onward transmission or else it will become increasingly difficult to eliminate it from the country.”      

Declarations of interest: None declared 

Lucy Devlin, PhD Researcher, School of Biological Sciences, Queen’s University Belfast, comments: 

“We know that Culicoides midges—the species capable of transmitting viruses carried by livestock—occur naturally across the UK and Ireland, including Northern Ireland. Their presence is not unusual, but we don’t yet know whether any of these local midges may have been exposed to viruses last season, which is an important area for future research. Our laboratory work on midge cold tolerance, across multiple life stages, has shown that some species can survive lower temperatures than previously expected, including periods below freezing. This means that in mild winters, a small number of midges may persist for longer than usual, although this alone does not imply that any virus will survive over winter.

“Normally, the active midge season runs from around April to November, and activity drops to very low levels during winter. ‘Low’ doesn’t necessarily mean zero, because sheltered farm microclimates can sometimes support limited survival or sporadic activity, but the environmental conditions at this time of year make sustained transmission unlikely.

“We are currently halfway through a full-year study monitoring midge activity and whether the viruses they carry survive over winter, which will help improve understanding of seasonal patterns. There is still a great deal we do not know about how both midges and their viruses survive the winter or spread, and these remain urgent gaps to fill as weather patterns continue to change. While these viruses do not affect human health or food safety, proactive measures, including vaccination where appropriate can help protect livestock, and continued vigilance in monitoring animals remains important within the temporary control zone.”

Declarations of interest: “I’m a DAERA-funded PhD researcher at Queen’s University Belfast investigating how environmental change affects midge ecology and farm disease risk.”