Morphology and molecular analysis of life-cycle stages of Proctoeces maculatus (Looss, 1901) (Digenea: Fellodistomidae) in the Bizerte Lagoon, Tunisia

Abstract

The life cycle of Proctoeces maculatus (Looss, 1901) (Digenea, Fellodistomidae) was studied in Bizerte Lagoon (Tunisia). Three sequential hosts appear to be involved: the Mediterranean mussel Mytilus galloprovincialis Lamarck, 1819 (Mytilidae) as the first intermediate host; the polychaete Sabella pavonina Savigny, 1822 (Sabellidae), as the second intermediate host; and fishes (Lithognathus mormyrus (Linnaeus, 1758) (Sparidae), Trachinotus ovatus (Linnaeus, 1758) (Carangidae) and Sparus aurata Linnaeus, 1758 (Sparidae) as the definitive hosts. It should be noted that S. pavonina was recorded as second intermediate host for P. maculatus for the first time. Molecular confirmation of the morphological identification of the life-cycle stages of this digenean was obtained using partial 28S rDNA sequences. Comparative sequences revealed that the sporocysts and the metacercariae are conspecific but they diverged by 0.3% from the adults. The present results raised the possibility of the existence of cryptic species within the different developmental stages. However, all the present isolates differed from material from Archosargus probatocephalus in the Gulf of Mexico identified as P. maculatus.

Development of quantitative PCR assay for detection of the trematode parasite Proctoeces maculatus in the blue mussel Mytilus edulis

“…These trematodes are predominately found in the mantle tissue of bivalves (see Fig. 1), where they cause partial or complete castration of the host (Uzmann 1953, Stunkard & Uzmann 1959, Machkevsky 1985, Feng 1988, Teia dos Santos & Coimbra 1995, Kim et al 2006, Antar & Gargouri 2015. High intensity infections can be seen macroscopically (Canzonier 1972) (see Fig.…”

“…maculatus does not display the typical trematode life cycle, which usually involves a gastropod intermediate host in which asexually reproducing larval forms (sporocysts) are found, a second intermediate host in which cercariae encyst as metacercariae (or encystment may occur on vegetation), and a definitive vertebrate host where sexual reproduction of adult trematodes occurs (e.g. Galaktionov & Dobrovolskij 2013, Antar & Gargouri 2015. Instead, P. maculatus can complete its entire life cycle within the mussel (Stunkard & Uzmann 1959, Lang & Dennis 1976, which likely becomes infected through accidental ingestion of trematode eggs (Lang & Dennis 1976).…”

“…Both end-point polymerase chain reaction (PCR) and quantitative real-time PCR (qPCR) provide superior reproducibility and efficiency compared to visual detection (Weiss 1995, Ndao 2009 and have proven effective for parasite characterization and identification (Polley & Thompson 2009). Antar & Gargouri (2015) recently used 28S rDNA to confirm P. maculatus in M. galloprovincialis and fish hosts from Tunisia. Such molecular methods can also be used to detect DNA from dead pathogens as long as the target nucleotide sequence is intact (Josephson et al 1993).…”

“…In some instances, P. maculatus elicits a hemocytic response in the host mussel (Sunila et al 2004) during which the parasites may be encapsulated and destroyed (Teia dos Santos & Coimbra 1995, Villalba et al 1997. The parasites are nearly impossible to identify in the fresh tissue of these mussels, as the elongated sporocysts become round and opaque, bearing little resemblance to living sporocysts.Molecular techniques offer greater sensitivity (Ndao 2009) and can detect the presence of trematodes at any life stage (Le et al 2012, Liu 2012, Antar & Gargouri 2015. Both end-point polymerase chain reaction (PCR) and quantitative real-time PCR (qPCR) provide superior reproducibility and efficiency compared to visual detection (Weiss 1995, Ndao 2009 and have proven effective for parasite characterization and identification (Polley & Thompson 2009).…”

“…Pondick (1983) proposed that this was because the colder water temperatures north of Cape Cod act as a barrier for P. maculatus. Although P. maculatus has been found in many other localities worldwide (Bray 1983), considerable taxonomic confusion exists surrounding the species, and it likely comprises a species complex (Valdivia et al 2010, Antar & Gargouri 2015.P. maculatus does not display the typical trematode life cycle, which usually involves a gastropod intermediate host in which asexually reproducing larval forms (sporocysts) are found, a second intermediate host in which cercariae encyst as metacercariae (or encystment may occur on vegetation), and a definitive vertebrate host where sexual reproduction of adult trematodes occurs (e.g.…”