PCR-based molecular discrimination between Maritrema eroliae and Probolocoryphe uca (Digenea: Microphallidae) in Kuwait Bay.

Microphallid trematodes are common parasites in marine snails and crustacean hosts at Kuwait Bay. The larval stages of two microphallids, Maritrema eroliae and Probolocoryphe uca, are difficult to differentiate morphologically. In this study, two PCR-based techniques were established for quick and accurate discrimination between the larval stages of the two microphallid species, employing restriction fragment length polymorphism (PCR-RFLP) and species-specific primers. Both techniques utilized nucleotide differences in the second internal transcribed region (ITS2) of the ribosomal DNA (rDNA) in the two species. For the PCR-RFLP technique, restriction enzyme AvaII was selected and it generated different restriction profiles among the two microphallids. In addition, species-specific primers were prepared for each microphallid species that amplified distinctive fragments. Both techniques showed that the larval stages of the two microphallid species can be identified accurately. However, direct PCR amplification using species-specific primers was more advantageous than the PCR-RFLP technique since it allowed rapid and specific discrimination between the two species. This technique provides a useful tool that can be used in future studies for the study of the distribution of microphallid species and their definitive hosts at different localities of Kuwait Bay.

Molecular identification of Austrobilharzia species parasitizing Cerithidea cingulata (Gastropoda: Potamididae) from Kuwait Bay.

Avian schistosomes belonging to the genus Austrobilharzia (Digenea: Schistosomatidae) are among the causative agents of cercarial dermatitis in humans. In this paper, ribosomal and mitochondrial DNA sequences were used to study schistosome cercariae from Kuwait Bay that have been identified morphologically as Austrobilharzia sp. Sequence comparison of the ribosomal DNA (rDNA) 28S and 18S regions of the collected schistosome cercariae with corresponding sequences of other schistosomes in GenBank revealed high sequence similarity. This confirmed the morphological identification of schistosome cercariae from Kuwait Bay as belonging to the genus Austrobilharzia. The finding was further supported by the phylogenetic tree that was constructed based on the combined data set 18S-28S-mitochondrial cytochrome oxidase I (mtCO1) sequences in which Austrobilharzia sp. clustered with A. terrigalensis and A. variglandis. Sequence comparison of the Austrobilharzia sp. from Kuwait Bay with A. variglandis and A. terrigalensis based on mtCO1 showed a variation of 10% and 11%, respectively. Since the sequence variation in the mtCO1 was within the interspecific range among trematodes, it seems that the Austrobilharzia species from Kuwait Bay is different from the two species reported in GenBank, A. terrigalensis and A. variglandis.

Temporal variations in the infection of a population of Cerithidea cingulata by larval trematodes in Kuwait Bay.

The prosobranch gastropod Cerithidea cingulata (Gastropoda: Potamididae) in Kuwait Bay was examined for larval trematode infections over a 17-month period. A total of 2537 snails were examined and 1265 (49.9%) found to be infected with one or more species of trematodes. The component community in the snail comprised 12 species representing the families Cyathocotylidae (2), Echinostomatidae (2), Haplosplanchnidae (1), Heterophyidae (2), Microphallidae (1), Philophthalmidae (2), Plagiorchiidae (1) and Schistosomatidae (1). Cyathocotylid II (41.6%) was by far the most prevalent species followed by the microphallid (3.9%), the two species comprised 90% of the total trematode fauna. The prevalence of infection increased with shell size and was significantly higher in male (47%) than female (33%) snails. Multiple infections were observed in only 15 (1.2%) of the infected snails; cyathocotylid I and cyathocotylid II combination occurred 14 times and heterophyid I and the microphallid occurred once. Trematode species were more diverse and prevalent in winter, and cercarial shedding peaked in summer. Behaviour of the definitive host and snail population dynamics were probably the major contributors to the detected temporal pattern in the infections.

Temporal variations in the infection of a population of Clypeomorus bifasciata (Gastropoda: Prosobranchia) by a digenean microphallid larva in Kuwait Bay.

The prosobranch snail Clypeomorus bifasciata in Kuwait Bay was examined for digenean infections over a one year period during 1994/1995. A total of 1500 snails was examined and 567 (37.8%) were found to harbour nine digenean species. The prevalence of a microphallid species was 33.9% while each of the others occurred in less than 1.2% of the snails. The prevalence of infection increased with shell size. Multiple infections were observed in only five of the infected snails and the microphallid was involved in all of them. Snails were infected with the microphallid throughout the year and there appeared to be two peaks in the proportion of infected snails shedding cercariae, a winter peak from November to January and a summer peak from June to August. The crab Xantho exaratus collected from snail sampling sites was heavily parasitized by microphallid metacercariae of the genera Longiductotrema and Microphallus. This is the first report on microphallid metacercariae in crabs in the Arabian Gulf region.