Nematode biology and larval development of Thelazia callipaeda (Spirurida, Thelaziidae) in the drosophilid intermediate host in Europe and China

Abstract

Thelazia callipaeda, commonly known as the 'oriental eyeworm', has been recently reported in Italy and other European countries. The insect/s that act as intermediate hosts and details of larval development inside the vector remain unclear. In order to (1) demonstrate the species of fly that may act as vector/s for T. callipaeda in southern Italy (Site A) and China (Site B) and (2) describe the larval development of the nematode in the body of flies, 847 Phortica (Drosophilidae) flies were collected from the above two sites, each with a history of human and/or canine thelaziosis. Flies were identified as Phortica variegata (245 - site A) and Phortica okadai (602 - site B), experimentally infected by 1st-stage larvae (L1), kept at different temperatures and dissected daily until day 180 post-infection (p.i.). Dead flies from site A were subjected to specific polymerase chain reaction (PCR) assay to detect T. callipaeda. To demonstrate the role of Phortica as vectors of T. callipaeda, 3rd-stage larvae (L3) recovered from the proboscis of flies were deposited onto the cornea of the eyes of dogs and rabbits. Following dissection, 3 (2.9%) of P. variegata in site A were found to be infected by L3 in the proboscis on days +14, +21 and +53 p.i., compared with 26 (18.4%) of Phortica flies recorded as being positive by PCR. Sequences from positive PCR products were 99% identical to sequences of the corresponding species available in GenBank (AY207464). At site B, 106 (17.6%) of 602 dissected P. okadai were found to be infected by T. callipaeda larvae (different stages) and in total 62 L3 were recovered from the proboscis of 34 (5.6%) flies. The shortest time in which L3 were found was at day +14, +17, +19, and +50 p.i. respectively, depending on the environmental temperatures. Of 30 flies overwintered for 6 months, 6 L3 were detected at day +180 p.i. in 3 flies (10%). The biology of larval development was reconstructed on the basis of the dissection of 602 P. okadai-infected flies and the morphology of larval stages in the insect body described. The present work provides evidence that P. variegata and P. okadai act as vectors for T. callipaeda in southern Europe and in China, respectively. The phenomenon of overwintering is described here for the first time for T. callipaeda and discussed. Finally, the relationship between T. callipaeda and its fly vector is considered in light of disease prophylaxis and to model its dissemination into habitats and environments favourable to Phortica flies.

Local transmission of the eye worm Thelazia callipaeda in southern Germany

“…Adult whitish nematodes of about 0.5-2 cm and the first larval stages (L1) can be found particularly under the third eye lid provoking lacrimation, conjunctivitis or even keratitis and corneal ulcer (Otranto and Traversa 2005). In Europe, T. callipaeda is transmitted by Phortica variegata, as shown in Italy under natural and experimental conditions (Otranto et al 2005a). …”

Emergence of canine ocular thelaziosis caused by Thelazia callipaeda in southern Switzerland

“…Recent investigations identified Phortica variegata (Diptera, Drosophilidae) as a potential vector and intermediate host of T. callipaeda under experimental and natural conditions (Otranto et al, 2005a;2006b). An ecological niche model suggested that the climate of large areas of Europe could be suitable habitats for this vector (Otranto et al, 2006a) and thus are potentially endemic for T.…”

Canine and Feline Thelaziosis Caused by Thelazia Callipaeda in Serbia

“…However, P. variegata, the already proven intermediate host and vector for the eyeworm in Europe [18,19], had never been described in Serbia. Knowing this vector is the prerequisite for autochthonous thelaziosis in any area, as well as the fact that Serbia is part of areas in Europe expected as suitable for P. variegata [27], further investigations concerning this issue are necessary.…”

“…Human ocular infections caused by T. callipaeda detected in endemic areas of Italy, France and Spain implicated the epidemiological importance of this parasite and the need for control measures [16,17]. The intermediate host and vector for T. callipaeda in Europe is the fruit fl y Phortica variegata (Drosophilidae, Steganinae), which is confi rmed under both experimental and natural conditions [18,19].…”