Climate change and the spread of vector‐borne diseases: using approximate B ayesian computation to compare invasion scenarios for the bluetongue virus vector C ulicoides imicola in I taly

Abstract

Bluetongue ( BT ) is a commonly cited example of a disease with a distribution believed to have recently expanded in response to global warming. The BT virus is transmitted to ruminants by biting midges of the genus C ulicoides , and it has been hypothesized that the emergence of BT in Mediterranean Europe during the last two decades is a consequence of the recent colonization of the region by C ulicoides imicola and linked to climate change. To better understand the mechanism responsible for the northward spread of BT , we tested the hypothesis of a recent colonization of Italy by C . imicola , by obtaining samples from more than 60 localities across I taly, C orsica, S outhern F rance, and N orthern A frica (the hypothesized source point for the recent invasion of C . imicola ), and by genotyping them with 10 newly identified microsatellite loci. The patterns of genetic variation within and among the sampled populations were characterized and used in a rigorous approximate B ayesian computation framework to compare three competing historical hypotheses related to the arrival and establishment of C . imicola in I taly. The hypothesis of an ancient presence of the insect vector was strongly favoured by this analysis, with an associated P ≥ 99%, suggesting that causes other than the northward range expansion of C . imicola may have supported the emergence of BT in southern Europe. Overall, this study illustrates the potential of molecular genetic markers for exploring the assumed link between climate change and the spread of diseases.

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