Discussion

Male fruitflies of the species Phortica variegata (Drosophilidae, Steganinae) are the intermediate host and vector of the zoonotic nematode Thelazia callipaeda (Spirurida, Thelaziidae). Whilst not currently endemic, recent evidence suggests a growing threat of T. callipaeda to UK animal and public health through infection of animals and humans whilst travelling abroad. Furthermore, presence of P. variegata in the UK has been confirmed on multiple occasions suggesting introduction of T. callipaeda is possible, although the current geographic distribution of P. variegata in the UK is unclear.

Ecological niche models have been used previously to predict the distribution of P. variegata in Europe and Italy. These results have been largely validated by the subsequent geographic spread of T. callipaeda across mainland Europe. We re-visited this analysis using up-to-date information to predict the current UK distribution of P. variegata and determine the likelihood of introducing autochthonous transmission of T. callipaeda. Our results suggest P. variegata presence in the south of England, including regions where this species has not previously been documented. Subsequent field sampling resulted in recovery of P. variegata at two locations, with suitable habitat identified at four others. Our results indicate a risk to the UK of T. callipaeda introduction. Surveillance of sylvatic definitive host species in locations with confirmed P. variegata presence is advised to monitor for evidence of autochthonous T. callipaeda transmission. Further work is planned to validate and improve the accuracy of this UK model through collection of additional field data.