Responses of the neurosecretory cells of the freshwater snail,Indoplanorbis exustus to hydrothermal stress

Changes in the neurosecretory cell cytology of I. exustus subjected to hypertonic saline (0.1 ml of 1.5%/snail) loading and thermal stress (35°C) for two hours, have been investigated. Of the two types of neurosecretory cells A and B that are present in the central nervous system (CNS) of I. exustus, striking changes were evident only in B cells. After both treatments, there was about 33% decline in NSM (Neurosecretory material) intensity. However, the nuclear diameter of B cells was significantly (P < 0.001) increased in the snails administrated with hypertonic saline unlike in those exposed to 35°C wherein significant (P < 0.005) decline was evident. The adaptive significance of the neuroendocrine system of I exustus is discussed in relation to hydrothermal stress.     

Laboratory studies on the direct effect of temperature on the freshwater vector snail,Indoplanorbis exustus (Deshyes)

The present study includes the effect of temperature on the survival of young and adult snails, embryonic development, embryonic growth and egg laying of Indoplanorbis exustus. In Indoplanorbis exustus the bottom lethal temperature was 7.0°C and 7.5°C for young and adults respectively. while the upper lethal temperature was 34.0°C and 32.0°C for young and adult snails respectively. Between the temperatures 12.5°C and 36.5°C the embryonic development was accelerated and the incubation period was shortened. The growth of embryos was found to be faster at 25.0°C. The optimum temperature for egg laying was observed at 25.0°C.     

Influence of temperature on survival, growth and fecundity of the freshwater snail Indoplanorbis exustus (Deshayes).

To note the effect of temperature on survival, growth and fecundity, newly hatched (zero day old) snails Indoplanorbis exustus were cultured at 10 degrees, 15 degrees, 20 degrees, 25 degrees, 30 degrees and 35 degrees C constant temperatures and room temperature (17.5 degrees-32.5 degrees C). Individuals exposed to 10 degrees C died within 3 days while those reared at 15 degrees, 20 degrees, 25 degrees, 30 degrees, 35 degrees C and room temperature survived for a period of 6, 27, 18, 16, 12 and 17 weeks respectively. An individual added on an average 0.21 mm and 0.45 mg, 0.35 mm and 7.94 mg, 0.63 mm and 15.5 mg, 0.81 mm and 27.18 mg, 1.07 mm and 41.48 mg and 0.78 mm and 31.2 mg to the shell diameter and body weight respectively at those temperatures per week. The snails cultured at 15 degrees C died prior to attainment of sexual maturity. On an average, an individual produced 31.9 and 582.77, 54.86 and 902.18, 56.01 and 968.45, 49.32 and 798.68 and 62.34 and 1143.97 capsules and eggs respectively at 20 degrees, 25 degrees, 30 degrees, 35 degrees C and room temperature (17.5 degrees-32.5 degrees C).     

Studies of the relationships between Schistosoma nasale and S. spindale and their snail host Indoplanorbis exustus

Infectivity and cercarial production of Indoplanorbis exustus related to variation of miracidial dose (1, 4, 10 or 20) with Schistosoma nasale and S. spindale from Sri Lanka were studied. The intermediate host-parasite relationships of the two schistosome species showed marked differences under the conditions of observation recorded in this study. Prepatent death rates (PDR) were on average higher for S. spindale (30%) than for S. nasale (10%). The size of the miracidial dose to which snails had been exposed had no effect on PDR. The infection rates (IR) were on average higher for S. nasale (41%) compared with S. spindale (27%). Highest IR occurred after exposure to 4 miracidia in S. nasale infections (79%) and after exposure to 10 miracidia in S. spindale infections (60%). The highest daily average cercarial production per snail was recorded for S. nasale at a level of 4 miracidia (1311), and for S. spindale at a level of 10 miracidia (1615). At low level (1 or 4 miracidia) of exposure, I. exustus showed a better compatibility with S. nasale than with S. spindale. An opposite tendency was observed at higher levels (10 or 20 miracidia) of exposure. Unsuccessful infections of Lymnaea luteola with either S. nasale or S. spindale indicate that this species is not involved in transmission.     

Two avian schistosome cercariae from Nepal,including a Macrobilharzia-like species from Indoplanorbis exustus

As part of a global survey of schistosomes, a total of 16,109 freshwater snails representing 14 species were collected from lakes, ponds, rivers, rice fields and swamps mostly in the Terai region of southern Nepal. Only two snails were found to harbor avian schistosome cercariae even though Nepal is well known for its rich avian diversity. One schistosome infection was from an individual of Radix luteola and on the basis of phylogenetic analyses using 28S rDNA and cox1 sequences, grouped as a distinctive and previously unknown lineage within Trichobilharzia. This genus is the most speciose within the family Schistosomatidae. It includes 40 described species worldwide, and its members mostly infect anseriform birds (ducks) and two families of freshwater snails (Lymnaeidae and Physidae). The second schistosome cercaria was recovered from an individual of Indoplanorbis exustus that was also actively emerging a Petasiger-like echinostome cercaria. Although I. exustus is commonly infected with mammalian schistosomes of the Schistosoma indicum species group on the Indian subcontinent, this is the first specifically documented avian schistosome reported in this snail. Both cercariae reported here are among the largest of all schistosome cercariae recovered to date. The I. exustus-derived schistosome clustered most closely with Macrobilharzia macrobilharzia, although it seems to represent a distinct lineage. Specimens of Macrobilharzia have thus far not been recovered from snails, being known only as adult worms from anhingas and cormorants. This study is the first to characterize by sequence data avian schistosomes recovered from Asian freshwater habitats. This approach can help unravel the complex of cryptic species causing cercarial dermatitis here and elsewhere in the world.     

Observations on the hatching process and salt and water regulation in the embryos of the freshwater snail Indoplanorbis exustus

The freshwater snail Indoplanorbis exustus laid its eggs in triple layers in a gelatinous, ribbon shaped matrix. Hatching was by mechanical means. The capsular membrane of the embryos was more permeable to water than to other organic and inorganic ions.     

Direct and delayed effects of low temperature on the freshwater snail Indoplanorbis exustus (Deshayes, 1934), intermediate host of schistosomias

The direct and delayed effect of short-term exposure to low temperature (17.5 °C) on growth, reproduction and longevity of adolescent and mature freshwater Indoplanorbis exustus Deshyaes (Mollusca: Gastropoda) was studied in the laboratory. We found that growth and reproduction were retarded, but were enhanced when later they were returned to ambient temperature.     

Cytochemical studies on the prostate glands of the trematodes, Paramphistomum epiclitum and Paradistomoides orientalis

Pear-shaped prostatic gland cells which surround the ejaculatory duct of Paramphistomum and Paradistomoides, secrete two types of products: (i) granules which are cytochemically complex containing lipids, proteins and polysaccharides (1:2, glycol groups) and (ii) globules which contain phospholipids only. The cytoplasm of these cells, in addition to high acid phosphatase activity, also contains RNA, proteins and polysaccharides.     

Ultrastructural and histochemical observations on the tegument of Gastrodiscoides hominis (Paramphistoma: Digenea).

The tegument of the paramphistome, Gastrodiscoides hominis, is basically similar to that of other digeneans. It is folded into concentrically arranged furrows and ridges bearing numerous tightly packed tubercules, and extends into the oral cavity. An area of specialized tegument is present on the ventral surface, anterior to the disc region. Mitochondria are absent from the tegumental syncytium and underlying tegumental cells, suggesting that the tegument may serve principally as a protective layer rather than in active uptake phenomena. However, extensions of the lymph and parenchyma systems are closely associated with the base of the tegumental syncytium and may provide ATP for active processes. Ciliated and non-ciliated sensory papillae are present, particularly around the oral opening. Numerous lymph channels are present in the sub-tegument and may be involved in osmoregulation.     

Comparison of the hemoglobins of the platyhelminths Gastrothylax crumenifer and Paramphistomum epiclitum (Trematoda: Paramphistomatidae).

1. Gastrothylax crumenifer and Paramphistomum epiclitum parasitize the water buffalo Bubalus bubalis. 2. Gastrothylas hemoglobin consisted of two fractions of ca 30,000 and ca 18,000 by gel filtration. SDS-electrophoresis showed both to be single, ca 15,000 chains. 3. Paramphistomum hemoglobin was ca 16,000 by both gel filtration and SDS-electrophoresis. 4. Reversed-phase chromatography of carboxymethylated trematode and buffalo globins gave single peaks and two peaks, respectively. Although Paramphistomum hemoglobin provided and N-terminal sequence, Gastrothylax hemoglobin did not, suggesting blocked N-terminals. The buffalo sequences were found to be identical to the sequences of the alpha and beta chains of bovine hemoglobin. 5. Although Paramphistomum hemoglobin consists of only one chain, Gastrothylax hemoglobin consists either of one chain which aggregates to a dimer or of two different chains, only one of which aggregates to a dimer.     

Genetic variation among laboratory strains of the planorbid snail Biomphalaria glabrata

Isozymes of laboratory strains of Biomphalaria glabrata have been studied by starch gel electrophoresis. Methods are outlined for adaptation of this technique to the genetic study of these snails. Twenty-eight presumptive gene loci have been identified. Twelve invariant enzymes were observed. Sixteen loci displayed some polymorphism within or among the strains. These polymorphisms were generally widespread among strains from Brazil, Puerto Rico, St. Lucia, and the Dominican Republic. A high degree of intrastrain polymorphism was noted even in some presumably inbred laboratory strains. Crosses between strains were used to demonstrate the genetic basis for the patterns observed at 9 of the 16 polymorphic loci.     

Influence of low temperatures on the cercarial shedding of Paramphistomum daubneyi from the snail Lymnaea truncatula

Lymnaeids in nature are subjected to temperature fluctuations that may have an influence on the shedding of cercariae. Thus, experimental infections of Lymnaea truncatula by Paramphistomum daubneyi were performed to determine whether a sudden fall in temperature--daily dipping of infected snails into spring water at 14-15 degrees C, or at 6-8 degrees C--followed by its increase at 20 degrees C in the subsequent hour, had an influence on the characteristics of snail infection and cercarial production. The immersion of infected snails in cold water during a short period delayed the first cercarial shedding, at day 66 on average, in the 6-8 degrees C group vs at day 57 in the 14-15 degrees C group, or at day 49 in the 20 degrees C group. The percentage of cercaria-shedding snails was greater in the 6-8 degrees C group than in the 14-15 degrees C and the 20 degrees C ones: 41.8% vs 17.3% and 7.1%, respectively. The total number of cercariae given by each infected snail was also higher in the 6-8 degrees C group. A fall in the temperature of water during daily change, followed by its increase at 20 degrees C within the subsequent hour, stimulated the cercarial shedding of P. daubneyi.     

Ultrastructural and histochemical observations on the tegument of Gastrodiscoides hominis (Paramphistoma: Digenea)

The tegument of the paramphistome, Gastrodiscoides hominis, is basically similar to that of other digeneans. It is folded into concentrically arranged furrows and ridges bearing numerous tightly packed tubercules, and extends into the oral cavity. An area of specialized tegument is present on the ventral surface, anterior to the disc region. Mitochondria are absent from the tegumental syncytium and underlying tegumental cells, suggesting that the tegument may serve principally as a protective layer rather than in active uptake phenomena. However, extensions of the lymph and parenchyma systems are closely associated with the base of the tegumental syncytium and may provide ATP for active processes. Ciliated and non-ciliated sensory papillae are present, particularly around the oral opening. Numerous lymph channels are present in the sub-tegument and may be involved in osmoregulation.     

Ultrastructural observations on the tegument and associated structures of the monogenean Cichlidogyrus halli typicus (Price & Kirk, 1967) Paperna, 1979.

The tegument of the ancyrocephaline monogenean gill parasite Cichlidogyrus halli typicus is basically similar to that of other monogeneans. However, there are some tegumental features shared with relatively few other monogeneans, namely the presence in the surface tegument of extensive regions of homogeneous granular cytoplasm, a close association between myofibres and the basal region of the tegument and the production of two different tegumental secretory bodies by the same cyton. It is suggested that the regions of homogeneous granular cytoplasm found in the troughs between the circular muscle fibres provide some kind of support for the tegument, perhaps related to contraction of the tegumental circular muscle fibres and body shape changes. Three kinds of transtegumental sensory structures are recognized, namely a uniciliated bulb, a bulb bearing a non-ciliary process and a non-ciliated bulb. The latter two kinds are reported for the first time in monogenans. Possible functions of these sensory structures are discussed.     

The hemoglobins of the trematodes Fasciola hepatica and Paramphistomum epiclitum: a molecular biological, physico-chemical, kinetic, and vaccination study

The trematode Fasciola hepatica (Fa.he.) is a common parasite of human and livestock. The hemoglobin (Hb) of Fa.he., a potential immunogen, was chosen for characterization in the search for an effective vaccine. Characterization of trematode Hbs show that they are intracellular single-domain globins with the following remarkable features: (1) Fa.he. expresses two Hb isoforms that differ at two amino acid sites (F1: 119Y/123Q; F2: 119F/123L). Both isoforms are monoacetylated at their N-termini; (2) the genes coding for Fa.he. and Paramphistomum epiclitum (Pa.ep.) Hbs are interrupted by two introns at the conserved positions B12.2 and G7.0.; (3) UV/VIS and resonance Raman spectroscopy identify the recombinant Fa.he. HbF2 as a pentacoordinated high-spin ferrous Hb; (4) electron paramagnetic resonance spectroscopy of cyano-met Fa.he. HbF2 proves that the endogenously bound imidazole has no imidazolate character; (5) the major structural determinants of the globin fold are present, they contain a TyrB10/TyrE7 residue pair on the distal side. Although such distal-site pair is a signature for high oxygen affinity, as shown for Pa.ep. Hb, the oxygen-binding rate parameters for Fa.he. Hb are intermediate between those of myoglobin and those of other trematode Hbs; (6) the three-dimensional structure of recombinant Fa.he. HbF2 from this study closely resembles the three-dimensional structure of Pa.ep. determined earlier. The set of distal-site polar interactions observed in Pa.ep. Hb is matched with small but significant structural adjustments; (7) despite the potential immunogenic character of the fluke Hb, vaccination of calves with recombinant Fa.he. HbF2 failed to promote protection against parasitic infection.     

Use of enzyme electrophoresis for differentiating Schistosoma nasale and S. spindale infections of Indoplanorbis exustus in Sri Lanka

Indoplanorbis exustus is the intermediate snail host of both Schistosoma nasale and S. spindale in Sri Lanka. Due to the similar morphology of the cercariae difficulties exist in identifying the species of schistosome infecting snails at transmission sites. Isoelectric focusing in polyacrylamide gels of malate dehydrogenase, glucose phosphate isomerase, phosphoglucomutase and acid phosphatase has been carried out on extracts of cercariae and potentially useful diagnostic markers have been identified. Cellulose acetate membrane electrophoresis has been used to separate two glucose phosphate isomerase phenotypes each of which appears to be diagnostic for one of the species. This simple electrophoretic technique has been used to identify schistosome infections in Indoplanorbis exustus collected at two transmission sites in Sri Lanka. Out of a total of 1,240 snails collected, 13 snails were shown to be infected with S. nasale, 19 with S. spindale and two snails were found to have mixed infections.