Circadian Pattern of Cercarial Emergence in Schistosoma Mansoni(Platyhelminthes: Digenea) from Isolated Biomphalaria Glabrata

The present work aimed to compare the acrophases (peak hours) of emergence of Schistosoma mansoni cercariae among isolated individuals of the snail Biomphalaria glabrata. Laboratory stocks of melanic B. glabrata from the same biotope as the S. mansoni strain (Belo Horizonte, Minas Ger-ais) were used. Twenty-two snails individually exposed to five miracidia were tested. Chronobiological trials were performed outdoors after an acclimation period of at least a week. Three groups of snails were tested between November 1989 and April 1991. Cercarial emergence from individual isolated snails was quantified every 3 h for 3 consecutive days. In all trials, most cercariae were found to emerge during daytime (94.9%). Time series and chronograms showed recurrent peaks during the daytime. The periodogram suggested that 24 h was the period that best fitted cercarial emergence data in 90.9% of the snails. The single cosinor analysis confirmed 24-h rhythms in 95.5% of the snails. Acrophases of cercarial emergence among individual snails occurred between 14:15 and 17:02. They did not differ significantly. The population cosinor analysis indicated greater homogeneity in the 24-h rhythms of cercarial emergence than in the snail groups of each chronobiological trial. Acrophases of cercarial emergence occurred between 14:53 and 15:27 and did not differ significantly among all trials. Data from the three trials were pooled and analyzed using the population cosinor. This statistical method indicated a homogeneity in the 24-h rhythms of cercarial emergence from all snails, with acrophase occurring around 15:00. Results showed that the acrophases of cercarial emergence of S. mansoni are similar among isolated B. glubrura specimens. Data support the hypothesis of a “gate” rhythm in the dynamics of cercarial production and emergence. It is suggested that the adaptive importance of the “gate” mechanism is associated with the concentration of cercariae in the water at times when the vertebrate is present, optimizing the contact between the parasite and the host. The emergence of some cercariae at night (5.1% of the total number of emerged cercariae) suggests a flexible “gate” that could be associated with a residual light effect or with experimental procedures in the laboratory.     

Schistosoma bovis: Variability of cercarial production as related to the snail hosts: Bulinus truncatus, B. wrighti and Planorbarius metidjensis

Development of Schistosoma bovis from Spain in different species or genus of intermediate hosts (Bulinus truncatus, B. wrighti and Planorbarius metidjensis) modifies cercarial productivity and its dynamics. From B. truncatus to B. wrighti and to P. metidjensis, cercarial productivity decreases while the length of the production period is increased. Variations in the dynamics are less obvious between the two species of Bulinus than between Bulinus spp. and P. metidjensis. In the latter the emission pattern is characterized by a 45–48-day production rhythm. These differences are explained in terms of larval demographic strategies and biotic capacities of the hosts. The validity of employing cercarial production as an indicator of host-parasite compatibility is discussed.     

Enzymes in Schistosoma intercalatum and the relative status of the Lower Guinea and Zaire strains of the parasite

Seven enzyme systems [phosphoglucomutases (PGM), glucose phosphate isomerases (GPI), glucose-6-phosphate dehydrogenases (G6PD), malate dehydrogenases (MDH), laetate dehydrogenases (LDH), acid phosphatases (AcP) and hexokinases] in extracts of adult worms from two isolates of Schistosoma intercalatum, one from Zaire and one from Cameroun, were compared by isoelectric focusing. Two systems (GPI and PGM) were also compared in extracts of cercariae. Distinctive differences between the strains were found in the LDH system and even more marked differences in the G6PD and PGM systems (the latter were apparent in both adult worm and cercarial extracts). These observations are discussed in conjunction with existing evidence on the results of intermediate host infection experiments and of experimental hybridization between the two strains of S. intercalatum. In turn these aspects are discussed in the light of what is known about other species of African Schistosoma. It is concluded that any definite decision on the relative status of the two strains of S. intercalatum is still premature.     

ITS2 ribosomal RNA indicates Schistosoma hippopotami is a distinct species

The internal transcribed spacer region of the ribosomal RNA, ITS2, was sequenced from a singlé specimen of S. hippopotami collected from a pulmonary artery of the hippopotamus, Hippopotamus amphibius in South Africa. The nucleotide sequence was aligned with those of S. mansoni, S. rodhaini, S. haematobium, S. intercalatum, S. curassoni. S bovis and S. japonicum. Both maximum parsimony and genetic distance analyses were performed on these data sets. Using S. japonicum as outgroup to the African schistosomes, a single most-parsimonious tree was obtained of length 64 steps with a consistency index of 1. S. hippopotami was the sister-group to the remaining African species. This species has lateral-spined eggs and its basal position in the tree suggests that this condition is primitive and that terminal-spined eggs developed secondarily. Molecular data clearly show that S. hippopotami cannot be considered synonymous with S. mansoni. Assuming the hippopotamus is the normal host of S. hippopotami, phylogenetic analysis is consistent with an ancient association between schistosomes and ungulates.     

Identification des cercaires de Schistosoma africains émises par Bulinus umbilicatus,B. truncatus et B. forskalii

Résumé Trois indices chétotaxiques AD, AL et U, des cercaires de quatre espèces pré-identifiées de Schistosoma africains, émises par des Mollusques infestés naturellement ou expérimentalement, ont été calculés. AD et AL correspondant respectivement à la distance relative entre les papilles dorsales et les papilles latérales. U correspond au nombre total des papilles du tronc caudal. La simple comparaison des moyennes arithmétiques d'un ou deux de ces trois indices permet de distinguer les cercaires de Schistosoma haematobium et de S. curassoni émises par Bulinus umbilicatus; les cercaires de S. haematobium et S. bovis émises par B. truncatus; les cercaires de S. bovis et S. intercalatum émises par B. forskalii.

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Identification des cercaires de Schistosoma africains émises par Bulinus umbilicatus, B. truncatus et B. forskalii

Three chaetotaxic indices, AD, AL and U, of cercariae of four pre-identified African Schistosoma species, obtained from natural or experimental infections, were established. AD and AL correspond respectively to the relative distance between the dorsal and lateral papillae. U corresponds to the total number of tail stem papillae. The simple comparison of average values of one or two of these three indices facilitated identification of the cercariae of Schistosoma haematobium and S. curassoni emitted by Bulinus umbilicatus, cercariae of S. haematobium and S. bovis shed by B. truncatus, and cercariae of S. bovis and S. intercalatum emitted by B. forskalii.

     

Adherence of blood platelets and leucocytes to hybrid schistosomes

The bovine parasite, Schistosoma mattheei was crossed with the human schistosome,S. haematobium. The Fl hybrids resulting from this cross were viable in both snails and rodents. However, F1 × F1 (F2) crosses were less viable in snails and a proportion of them seemed to be changed structurally when viewed by scanning electron microscopy. Certain of the schistosomes were covered with a dense mass of interconnected blood platelets resembling a temporary haemostatic plug but not a blood clot. Interspersed between the platelets were a small number of leucocytes. We suggest that the platelets may have responded to the presence of an antigen which is masked in normal schistosomes but which is exposed in certain F2 hybrids.     

Schistosoma mansoni and Schistosoma japonicum: Utilization of amino acids

, , and 1972. Schistosoma mansoni and Schistosoma japonicum: utilization of amino acids. International Journal for Parasitology 2: 425–430. The production of ¹⁴CO₂ from 12 labeled amino acids by S. mansoni and S. japonicum was studied. No ¹⁴CO₂ was detected from incubations with glycine, isoleucine, leucine, lysine or phenylalanine. Differences were found between sexes and/or species for the other amino acids studied. Species related differences included a greater rate of metabolism of glutamic and aspartic acid by S. mansoni than by S. japonicum. Proline and histidine were utilized by S. mansoni males and females, respectively. S. japonicum male worms did not utilize proline, while histidine was not utilized by the female of this species. Major sex related differences included greater ¹⁴CO₂ production from glutamic acid, aspartic acid and arginine by S. mansoni males than by females, and the utilization of histidine by male S. japonicum but not by females. Incubation in tyrosine resulted in the release of only small amounts of ¹⁴CO₂ by female worms of both species but no ¹⁴CO₂ production by male worms.     

Schistosoma mansoni: silver ion (Ag +) stimulates and reversibly inhibits lipid-induced cercarial penetration.

Certain long-chain polyunsaturated fatty acids (FA) found on mammalian skin trigger cercariae to penetrate and transform into schistosomules; however, the mechanism by which FAs stimulate cercariae is unknown. In order to determine whether argentophilic papillae concentrated at the apical region of the cercariae are the chemoreceptors that may mediate cercarial response to FAs, an assay assessed the proportion of cercariae that penetrated a 0.25% agar matrix in the presence (61%) and the absence (2.3%) of linolenic acid at 0.22 mM. Silver nitrate (Ag+) which selectively binds to cercarial papillae (Short and Cartrett, J. Parasitol. 59, 1041, 1973) is nontoxic (at 0.09 mM used in this study) as demonstrated by the ability of Ag+ treated cercariae to mature successfully into adult worms (8.8% maturation compared to 10.2% of untreated controls, n = 5) after subcutaneous injection. When Ag+ was added to cercarial suspensions, penetration into linolenic-impregnated agar was significantly inhibited (80.8%). Washing cercariae free of Ag+ reversed this inhibition. These data, as well as observations that both argentophilic papillae and cercarial response to FAs disappeared within 3 to 4 hr after mechanical conversion to schistosomules, implicate argentophilic papillae on cercariae as chemoreceptors for lipid stimulation.     

Imaging diagnosis of schistosomiasis japonica--the use in Japan and application for field study in the present endemic area

For detecting lesions-related schistosomiasis japonica, X-rays, scintillation scanning, ultrasonography (US), computed tomography (CT), magnetic resonance (MR) and endoscopic examinations with biopsies have been used in Japan. Liver fibrosis and calcified changes are detected by US and CT. Most of the lesions that are detected by endoscopic examinations are due to deposited ova of Schistosoma japonicum. Portal hypertension is detected by US, CT and gastroscopic examination. Because schistosome infection decreased rapidly in Japan, most of the studies on imaging diagnosis were performed on chronic lesions or sequelae of schistosomiasis. Most of the techniques were used on admitted patients in well-equipped hospitals. US was introduced in the 1970s as a safe, rapid, non-invasive and inexpensive technique and has been used for diagnosis in hospitals and screening in the fields. As a typical US image of the liver, septal formation by high echogenic bands like mosaic was described, and this network pattern was reported in the other endemic countries; China and Philippines. As an appropriate technique, US has been broadly used in developing countries. Not only for diagnosis in a hospital, but also for monitoring changes of morbidity, US is used in the community level. Network pattern related to the severity of S. japonicum infection, has not been described in S. mansoni or S. haematobium infection. Appearance of network pattern depends on pathological changes such as periportal fibrosis, postnecrotic fibrosis and calcified ova. For advanced studies on morbidity of schistosomiasis japonica, further research on pathological basis of network pattern and standardization of US diagnosis are necessary.     

Further studies on the carbohydrate metabolism of immature Schistosoma mansoni

Further studies on the carbohydrate metabolism of immature Schistosoma mansoni. International Journal for Parasitology 3: 783–787. Analysis of whole cercariae, cercarial bodies and tails and schistosomula shows the tail contains 26 per cent of the cercarial nitrogen, 46 per cent of the glycogen and 59 per cent of the cytochrome oxidase. 32 per cent of the total nitrogen and 22 per cent of the glycogen of the cercarial body is lost during penetration. Oxygen uptake of adult worms but not of cercariae increases between 30 and 37°C. A temperature of 41°C partly inhibits cercarial oxygen uptake but not that of adult worms. Incubation of schistosomula, 21-day-old and adult worms in nitrogen increases the rate of glycolysis.