First Expert Elicitation of Knowledge Conducted in 2023 on Possible Drivers of Observed Increasing Epizootic Haemorrhagic Disease Incidence in Europe.

Epizootic haemorrhagic disease (EHD) is a viral noncontagious arthropod-borne disease transmitted by blood-sucking midges of the genus Culicoides. Its causative agent, the EHD virus (EHDV), belongs to the genus Orbivirus and is responsible for domestic and wildlife ruminants' disease outbreaks, especially in North America, Asia, Africa and Oceania. These outbreaks not only cause significant morbidity and mortality but also have welfare, social and economic implications. Recently, EHD has become a real threat to the European Union, with outbreaks confirmed in October and November 2022 in Sardinia and Sicily. To better understand this phenomenon, we investigated the drivers of the observed increasing EHD incidence in Europe through expert knowledge elicitation. We listed 51 possible drivers grouped in eight domains and elicited 41 European experts to (i) allocate a score per driver, (ii) weight this score within each domain and (iii) weight the different domains and attribute an uncertainty level for each. An overall weighted score per driver was calculated, and drivers with comparable scores were grouped in four distinct terminal nodes using a regression tree analysis. The four drivers included in a terminal node with the highest scores were (i) the influence of temperature on the abundance or survival of vector populations; the legal or illegal movements of live animals from (ii) third countries or (iii) from neighbouring countries of Europe and the European Union; and (iv) the current unavailability of vaccines against Circulating Serotype 8. Our results support researchers in prioritizing studies targeting the most relevant drivers of the observed spread of EHD in animals in Europe. In addition, some strategic lines in terms of research and action are depicted.