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In the Kandalaksha Bay (White Sea), the experiments have been carried out to study the life cycle of the larval trematodes of the genus Himasthla (Dietz, 1909) from the intertidal whelk Littorina saxatilis. It has been established that the blue mussel, Mytilus edulis, is the second intermediate host for this species. The seagull Larus canus is the final host. The species has been identified as Himasthla elongata.
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Mature sperm of Rugogaster hydrolagi exhibit the structure typical of Trematoda, with 2 axonemes of the 9+ "1" pattern being incorporated into the sperm body, dorsal and ventral microtubules occurring in the principal region that contains the nucleus and mitochondrion, and a complete row of peripheral microtubules lying in the proximal region surrounding the two axonemes. During spermiogenesis, a zone of differentiation develops that comprises a row of microtubules along the cell membrane and an adjacent dense region along the nuclear membrane. The intercentriolar body and centrioles appear between the microtubules and the nucleus. Free flagella with striated rootlets grow out in opposite directions, the cell membrane protrudes and lengthens into a median cytoplasmic process (MCP), the nucleus and mitochondrion move into the MCP and the flagella rotate and eventually fuse with the process. A dense region develops in the spermatid shaft some distance from the proximal end, but it is not present in the mature sperm. The spermatid elongates and is eventually pinched off from the residual body at the level of the arching membranes after the rootlets and intercentriolar body have disappeared. Thus, spermatogenesis and sperm in the aspidogastrean Rugogaster hydrolagi correspond to those in digenean Trematoda.
The life cycle of Brachylaima ruminae n.sp. (Trematoda: Brachylaimidae), a duodenal parasite of rodents on the Mediterranean island of Formentera (Spain) is elucidated. The new species follows a terrestrial triheteroxenous life cycle. Eggs passed in the faeces of the definitive host must be ingested by a specific first intermediate host, the land snail Rumina decollata. Branched cercariogenous sporocysts develop in the digestive gland. Microcercous cercariae come out through the terminal birth pores of the branches. Cercariae shed by the snail are terrestrial, crawling on humid substratum. They contact the second intermediate host, another land snail, principally the species R. decollata and less frequently slugs and Helicids. Cercariae enter via the excretory pore and kidney duct to their specific final location, the kidney. Unencysted metacercariae develop in the kidney (also, less frequently, in the pedal glands) to the mature, infective stage. Infective metacercariae infest the definitive host when ingested together with the snail.
The fully developed flame bulb of Philopthalmus exhibits the structure characteristic of Trematoda and Monogenea: external and internal ribs forming a weir, external and internal leptotriches, and two longitudinal cytoplasmic cords connected by a septate junction. The proximal canal has a septate junction and surface lamellae. In developing cercariae, perikarya of terminal and proximal canal cells are close together, and sheet-like outgrowths of the terminal cell are externally surrounded by cytoplasm of the proximal canal cell containing a septate junction. Internal outgrowths and external cytoplasm are connected by many "membranes", i.e. desmosome-like structures. Internal sheets break up into internal ribs, and the external cytoplasm breaks up into external ribs, external and internal ribs connected by the filtration "membrane". The developing distal excretory duct possesses a septate junction and many branching and looping lamellae. A comparison of Philopthalmus with the cestode Austramphilina elongata, the only other platyhelminth species in which the development of the protonephridia has been studied at the ultra-structural level, revealed that the two species differ in the presence and absence, respectively, of a septate junction in the flame bulb at an early stage of development.
The presence of snake's blood inside the alimentary canal of the species Opisthogonimus lecithonotus (Trematoda, Digenea, Plagiorchiidae) collected from the mouth of Bothrops moojeni (Serpentes, Viperidae) is reported. The implications of this observation to the host snake are discussed.
In searching for species-specific DNA sequences of microphallid species (Digenea, Trematoda) we examined the ribosomal internal transcribed spacer regions (ITS) of three closely related species (Levinseniella group) hosted by mud snails (first intermediate host) and marine crustaceans (second intermediate host). In the ITS1 region we found consistent patterns of repeating sequences of 130 bp. Within each main repeat there was a varying number of subrepeats specific for each of the species. All repeats including subrepeats were identified by a similar starting sequence: 5'-CCTGTGG-3'. As this sequence has close resemblance to the chi sequence 5'-GCTGGTGG-3' found in phage lambda we speculate if it serves the same function as a recombination hotspot. Alternatively but less likely, it could be an inactive, mutational relic of a sequence that once served this purpose.
Chemical communication among freshwater organisms is an adaptation to improve their coexistence. Here,we focus on the chemical cues secreted by the freshwater gastropod Lymnaea stagnalis, which are known to stimulate behavioural responses of Trichobilharzia ocellata (Plathelminthes, Digenea, Trematoda) miracidia. Such responses are commonly claimed to influence transmission positively, but in response to chemical cues miracidia randomly change their swimming direction. This kind of response does not necessarily increase transmission, because miracidia may be trapped at the periphery of very large snail odour-clouds, which may prevent them from approaching the snail. On the other hand, the odour clouds may be too small to improve host-localisation. To shed light on these scenarios, the spreading of molecules released around L. stagnalis (active space) was visualised by recording host-finding responses of T. ocellata miracidia when they approached snails. Behavioural responses of miracidia indicated the spreading of compounds forming an attractive active space only around the host-snail L. stagnalis, but not around sympatric non-host-snail species. The active space increased approximately linearly with the time the snail rested at the same spot and within 5 min it reached a volume of more than 30 times that of the snail. We also demonstrated in a large-scale experiment, that the active space of L. stagnalis significantly increases the transmission success of T. ocellata miracidia. Additionally, the microhabitat selection of T. ocellata miracidia was studied, demonstrating that peripheral locations near the water surface were preferred, which are also preferred sites of L. stagnalis. Improved chemoperception and microhabitat selection may have been a consequence of coevolution with snails and benefited miracidia, which became efficient transmissive stages.
Survival of the cystophorous cercariae of Halipegus occidualis (Trematoda: Hemiuridae) from naturally infected Helisoma anceps (Gastropoda: Planorbidae) was determined following constant temperature storage at 4, 16, 22, 26 and 30 degrees C. At 4 degrees C, 90% of cercariae survived for 14 weeks and 50% survived for 30 weeks. Survival varied inversely with temperature, and at 30 degrees, 90% survived for 1.5 weeks and 50% survived for 2.5 weeks. At the time of release from snails, cercariae excysted within 0.5 s of stimulation. Excystment times ultimately increased to 1-3 s at all temperatures as length of storage increased, but no connection was detected between excystment time and the activity of the cercaria. Excystment times began increasing while survival was still above 90%. Temperature specific mortality rates of cercariae were estimated, and used to simulate the survival of cercariae released naturally at various times of the year. The results of these simulations suggest that cercariae of H. occidualis are present in the environment at all times of the year, but that cercariae present in late winter (January to mid-March) may have an impaired excystment mechanism that reduces their infectivity.
We encountered two cases of human intraocular infection with mesocercariae of Alaria (Trematoda), involving unrelated Asian men who had unilateral decreased vision. Both patients had pigmentary tracks in the retina, areas of active or healed retinitis, or both, and other signs of diffuse unilateral subacute neuroretinitis. Similar, nonnematode worms were seen in the patients' retinas and vitreous, respectively, several years after apparent infection. The worm in Case 1 was analyzed from projected fundus photographs and diagnosed as an Alaria mesocercaria on the basis of its shape, size (500 x 150 microns), and movement; it was successfully killed with laser. The worm in Case 2 was removed surgically from the vitreous and identified as A. mesocercaria, 555 x 190 microns, most likely A. americana. The probable source of infection in the patients was ingestion, in local restaurants, of undercooked frogs' legs containing A. mesocercaria. In addition to causing prolonged intraocular infection, A. mesocercaria was found to be a cause of diffuse unilateral subacute neuroretinitis, a condition previously attributed only to intraocular nematode larvae.
Analysis of 18S rDNA sequences isolated from Cyathura carinata (Crustacea: Isopoda) indicate that two different species of the Digenea (Platyhelminthes: Trematoda) parasitize this isopod species for which parasitic associations have previously been unknown. Phylogenetic analysis, based on the largest data set of digenetic 18S rDNA sequences published to date, also suggests that 18S rDNA is unsuitable for the reconstruction of phylogenetic relationships of the major digenetic lineages either due to rapid radiation of these lineages or the presence of homoplasy at this level.
A simple in vitro technique was devised to culture chick embryos in Petri dishes from the 4th to the 21st day of incubation. Leucochloridiomorpha constantiae (Trematoda) metacercariae were placed either singly or multiply (5/embryo) on the chorio-allantois of in vitro grown embryos on day 7 and were removed on day 14. Growth and development studies were also made on worms grown singly or multiply (5/chick) in the bursa of Fabricius of the domestic chick. Worms grown singly or multiply in embryos were sexually mature, although eggs from these worms were abnormal when compared with eggs from worms recovered from chicks. The mean body area of worms from chicks was 2-3 times greater than that of worms from embryos. The mean body area of single worms from embryos was significantly larger than that of worms grown multiply in this site. However, the mean body area of multiple worms from the chick was significantly larger than that of single worms from this site. Worm pairs or clusters were seen in all embryos with the multiple infections.
Allocreadium pichi n. sp. (Trematoda: Allocreadiidae) is described from the intestine of Galaxias maculatus (Osteichthyes: Galaxiidae) from Moreno Lake in Patagonia, Argentina. This species is distinguished from A. patagonicum Shimazu, Urawa & Coria, 2000, the other species recorded in the area, by its smaller body size, the diagonal position of the testes and different ratios of the suckers, testes and cirrus-sac in relation to body size. In addition, the synonymy of A. patagonicum with Polylekithum percai Ostrowski de Núñez, Brugni & Viozzi, 2000 is proposed herein.
Description of Oschmarinella mascomai n. sp. (Trematoda : Campulidae) a bile duct parasite of the striped dolphin, Stenella coeruleoalba (Meyen, 1833) (Cetacea : Delphinidae), from the Mediterranean Sea. Differential characters from the other species of this genus is described.