Predicting the distribution of Phortica variegata and potential for Thelazia callipaeda transmission in Europe and the United Kingdom

Abstract

BackgroundMale fruitflies Phortica variegata (Drosophilidae, Steganinae) are the intermediate host of the zoonotic nematode Thelazia callipaeda (Spirurida, Thelaziidae). More than 10 years ago, when T. callipaeda was confined to remote regions of southern Italy, ecological niche models were used to predict the potential distribution of P. variegata across Europe and the likely risk of the nematode spreading through infected dogs travelling to/from endemic regions. As predicted, over the last 10 years T. callipaeda has spread rapidly across Europe. Recently, we identified the potential for its introduction to the UK through infected dogs travelling to/from endemic regions of mainland Europe.MethodsHere updated information is used to re-evaluate the model-predicted European, and specifically, UK distribution to determine the likelihood of T. callipaeda becoming established. Additionally, the UK distribution of P. variegata was further investigated through snapshot fly trapping at model-predicted locations.ResultsEcological niche modelling using Genetic Algorithm for Rule-set Prediction (GARP) analysis suggests a European range similar to that described previously, with some indication of potential spread further eastward. Finer scale UK mapping suggested that P. variegata presence was limited mostly to southern England, but highlighted regions where P. variegata has not been documented previously. The arbitrary fly trapping identified activity of P. variegata at two locations where the species has been found previously late in the season. No specimens were collected at model-predicted locations, although habitat suitable for the species was identified.ConclusionsGARP-model prediction of P. variegata distribution suggests presence of suitable conditions in previously undocumented regions of the UK and Europe and highlight the possibility for further spread of T. callipaeda across Europe, including the UK. Further work to validate the P. variegata UK model with field data will help improve its accuracy in predicting suitable areas, whilst surveillance of sylvatic definitive host species in such locations is advised to monitor for evidence of autochthonous T. callipaeda transmission.

Temperature is a common climatic descriptor of lachryphagous activity period in Phortica variegata (Diptera: Drosophilidae) from multiple geographical locations

“…The knowledge of the ecological niche of P. variegata is of major importance to understand if and how eyeworm infection can spread locally in different contexts, and what are the environmental drivers potentially favouring the establishment of the vector at a continental scale. A habitat suitability map of this species has been established, indicating a large potential of diffusion in Europe [8,9]. However, data at the origin of the development of the model are fragmentary and, more importantly, no information is available concerning environmental parameters affecting the population dynamics of P. variegata, except those obtained from a few sites [8,14].…”

“…The park is also home to a number of other sylvatic species common to british woodland habitats, including Meles meles and Vulpes vulpes. The trapping site used for this study was on a boundary between woodland and heath at a location where P. variegata has been documented on several occasions previously [9].…”

“…At the time when vector identity and biology were elucidated, the infection was known only in remote poor settings in southern Italy [4,6,7]. Nevertheless, ecological niche models predicted that large areas of Europe (including the UK) are suitable for the presence of P. variegata, thus highlighting the potential risk of T. callipaeda spreading to other European countries [8,9]. Indeed, whilst T. callipaeda had exclusively been reported from easternmost countries until two decades ago, it has now been described in both animals and humans from Austria, Belgium, Bosnia and Herzegovina, Bulgaria, Croatia, France, Germany, Greece, Hungary, Italy, Portugal, Romania, Serbia, Slovakia, Spain, Switzerland and Turkey [9][10][11][12].…”

“…Nevertheless, ecological niche models predicted that large areas of Europe (including the UK) are suitable for the presence of P. variegata, thus highlighting the potential risk of T. callipaeda spreading to other European countries [8,9]. Indeed, whilst T. callipaeda had exclusively been reported from easternmost countries until two decades ago, it has now been described in both animals and humans from Austria, Belgium, Bosnia and Herzegovina, Bulgaria, Croatia, France, Germany, Greece, Hungary, Italy, Portugal, Romania, Serbia, Slovakia, Spain, Switzerland and Turkey [9][10][11][12]. Thus, this parasite can be considered as an emergent vector-borne pathogen in Europe, and zoonotic infections have been diagnosed on several occasions.…”

Survival of Phortica variegata experimentally and naturally infected with Thelazia callipaeda

“…Although males of this zoophilic drosophilid feed on the lachrymal secretions of mammals, they may transmit T. callipaeda infective L3 to the definitive host (Otranto et al ., ). Subsequent to its first record of autochthonous transmission in Italy, 20 years ago (Otranto et al ., ), this eyeworm has rapidly expanded across Europe, now being considered endemic in many continental European countries (Colella et al ., ; Palfreyman et al ., ). In addition, this parasitosis is becoming established in domestic and wild carnivores in Europe (Otranto & Deplazes, ), with an increasing zoonotic potential.…”