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Nematode biology and larval development of Thelazia callipaeda (Spirurida, Thelaziidae) in the drosophilid intermediate host in Europe and China
- D. OTRANTO, R. P. LIA, C. CANTACESSI, G. TESTINI, A. TROCCOLI, J. L. SHEN, Z. X. WANG
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- Journal:
- Parasitology / Volume 131 / Issue 6 / December 2005
- Published online by Cambridge University Press:
- 22 July 2005, pp. 847-855
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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.
Biology of Thelazia callipaeda (Spirurida, Thelaziidae) eyeworms in naturally infected definitive hosts
- D. OTRANTO, R. P. LIA, V. BUONO, D. TRAVERSA, A. GIANGASPERO
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- Journal:
- Parasitology / Volume 129 / Issue 5 / November 2004
- Published online by Cambridge University Press:
- 05 October 2004, pp. 627-633
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Thelazia callipaeda (Spirurida, Thelaziidae) eyeworm causes ocular infection in carnivores and humans in the Far East; this infection has been recently reported also in Europe – northern and southern Italy – in dogs, cats and foxes. The natural vector/s of T. callipaeda is/are unknown and the development of the nematode in its definitive hosts is limited to an experimental trial on dogs. To contribute new insights into the development of T. callipaeda in the definitive host in field conditions, eyeworms were collected from naturally infected dogs from an area with a high prevalence of infection (up to 60·14%) in the Basilicata region of southern Italy, from January 2002 to December 2003. Conjunctival secretions were also collected and examined for the presence of immature stages. The presence of blastomerized eggs throughout the period – except for the months from May to November – indicates a seasonality in the reproductive activity of T. callipaeda, coinciding with the presence/absence of the vector. In fact, 1st-stage larvae were found in the lachrymal secretions of dogs in summer (June–July 2002 and 2003), ready to be ingested by flies feeding about the eyes. The evidence of 4th-stage larvae in March 2002 and April, July and October 2003 may be accounted for by the presence of flies that act as intermediate hosts of T. callipaeda from early spring to early autumn. The presence of immature stages in October indicates an overlapping generation of nematodes and a 2nd cycle of vector infection. This basic knowledge of the development of T. callipaeda will hopefully help future epidemiological studies to identify the intermediate hosts and define the likely risk for vectors in field conditions.