POLICY BRIEF: Characterising the climatic risk levels for bluetongue in Scotland

A model has been developed, which provides a risk reference of BTv transmission at any time and location based on historical climate records. The risk reference of BTv transmission is indicated as the percentage of days with potential for BTv transmission. The figure shows example outcomes from the model which mapped the percentage of days during 1993-2016 that had some potential for BTv transmission (aggregated by the fortnight). It illustrates that the risk of BTv transmission in Scotland increased in warmer seasons.

To characterize the general risk of onward transmission of bluetongue in GB at different times of year.

In the event of future introductions of bluetongue to Scotland through wind-borne midges or importation of infected animals these analyses will give an indication of whether there is any risk of onward transmission given the time of year and historical precedent. This will indicate whether further immediate actions are required. However, any conclusions from these models should be followed-up with analysis of observed weather from the time of introduction.

We used a model of the risk of bluetongue transmission that is being prepared for publication and was presented at the ISVEE conference in 2018. The model uses historical weather data from across Europe fitting risk for each day. Here we adapt the data using fine scale UKCIP weather data for the UK for 1993 – 2016 to fit temperatures on an hourly basis to give a higher (and more realistic measure) of risk. Parameters are not based on Northern European midge species or the BTv-8 serotype that is currently circulating in France because there is no current data for these. Instead the parameters are based on the serotypes and midge species most similar to those in Scotland, but neither is the same in either case. As current evidence suggests that bluetongue is cold-adapted we include parameters to include the most coldadapted serotypes that were described by a review by Carpenter (2011). The model can be quickly updated with revised parameters as they become available.

Example of the outputs from the model showing the percentage of days between 1993 and 2016 that were suitable for transmission. These outputs can be drilled into at greater spatial and temporal resolution as needed.

Bessell PR, Searle KR, Auty HK, Handel IG, Purse BV, Bronsvoort BM. Assessing the potential for Bluetongue virus 8 to spread and vaccination strategies in Scotland  Science Reports 2016 Dec 13;6:38940.  http://www.nature.com/articles/srep38940