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PubMedDate not supplied

[Heat resistance of the cercariae of serveral species of trematodes].

Cercariae of Echinostoma sp., Cotylurus cornutus, Cercaria C Szidat, marites of which parasitize homeothermic hosts (birds), were found to have a high heat resistance at the effect of lethal temperature. There were established specific differences in the temperature level and its stability during a long period at a relatively constant environmental temperature. Thé heat resistance of cercariae of the same species does not change during their parasitism in different species of mollusks, hosts (e. g. C. C Szidat). Thermoresistance of mature cercariae of C. C Szidat and Cotylurus cornutus having entered the water is in agreement with the environmental temperature and changes with a temperature regime of the environment. Even an acclimation within 3 hours at 29 degrees results in a rise of the heat resistance of cercariae. Their stay at 4 degrees within 3 hours decreases two times the heat resistance.

Adaptation, Physiological↗
PubMedDate not supplied

[Cercaria chaetotaxy of 2 Venezuelan strains of Schistosoma mansoni].

By means of the silver impregnation of two lots of Schistosoma mansoni cercariae belonging to the strains: JR (32 cercariae) and C5 (45 cercariae), the number and pattern of disposition of the argentophillic papillae were determined with the following results: Average number of total dorsal papillae: 12.1 (JR strain) and 12.0 (C5 strain); the variation coefficients in this surface were less than 4% (JR strain) and bigger in JR than C5 strain. Average number of total ventral papillae: 12.15 (JR), 11.97 (C5); maximum value of the variation coefficient: 6.4% (JR), higher in JR than C5 strain. When the ventral surface was classified in four quadrants, the average number of papillae by quadrant was: quadrant A: 1.15 (JR) and 1.06 (C5): B: 1.06 (JR) and 1 (C5); C: 4.97 (JR) and 4.96 (C5); D: 5.03 (JR) and 4.98 (C5). The variation coefficients were higher in the A and B ventral quadrants, reaching maximum values of 31.9%, and 61.0% for the posterior quadrants C and D. When the ventral surface was divided in three equal parts for determining the position of the most variable papillae of this area, the greatest value of the variation coefficients obtained were for the 2nd thirds of the cercariae: 89.8% and 76.8% for C5 strain and 43.5% and 56.8% for JR strain. In relation to the total lateral papillae, the average numbers were: 17.0 (JR) and 16.6 (C5), with a maximum value of variation coefficient of (8.1% (C5). The average total number of papillae of the tail were: 25.6 (JR) and 26.1 (C5) for the ventral surface and 20.72 (JR) and 21.33 (C5) for the dorsal papillae. The comparison between the percents of the cercariae of two S. mansoni strains with more than 1 papillae on the anterior ventral quadrants A or B (94% JR and 34% C5), resulted with significant differences (P < 0.05).

Animals↗
PubMed1987

Intermediate host (Biomphalaria alexandrina) antigens partly protect against subcutaneous infections with cercariae of Schistosoma mansoni but are ineffective in infections by percutaneous invasion.

Mice were immunized against hepatopancreas homogenate of Biomphalaria alexandrina, using Al(OH)3 as adjuvant, and challenged by subcutaneous (s.c.) injection of Schistosoma mansoni cercariae, percutaneous invasion of cercariae and intravenous (i.v.) injection of mechanically prepared schistosomula of different ages. Significantly reduced (about 50%) numbers of adult S. mansoni were found 42 days after challenge in immunized animals infected by s.c. injection of cercariae. Protective effects were detectable as early as 4 days after infection when the numbers of schistosomules in the lungs were reduced in immunized animals. However, immunized animals lacked protective immunity against S. mansoni when infected via the percutaneous route with cercariae or by i.v. injection of schistosomules of different ages. Experiments show that immunization of hosts against intermediate host antigens does not protect against S. mansoni infection via the natural route.

Animals↗
PubMed1987

Scanning electron microscopy of rediae, cercariae, metacercariae and adults of Mesorchis denticulatus (Rudolphi, 1802) (Trematoda, Echinostomatidae).

A detailed study of the surface topography of the echinostome digenean Mesorchis denticulatus (Rudolphi 1802) Dietz 1909 was carried out using the scanning electron microscope. The surface area of the redia is increased by microvilli, and ciliate sensory structures are common around the mouth. The cannibalistic behaviour of the rediae is demonstrated by rediae which have the posterior end and tail of extraredial cercariae protruding from the mouth. The partly devoured cercariae had occasionally - apparently as a defence reaction - covered their bodies with a thick layer of cystogenous material, which, however, does not protect them from being eaten. The surface area of the tegument of the youngest extraredial cercariae is increased by small microvilli or knobs with a presumed function in nutrient absorption. The knobs disappear when the cercariae are fully developed. Flattened spines occur peripherally in the suckers. Different types of ciliate structures are especially common anteriorly. The infective metacercariae, which occur in the gill filaments of euryhaline fishes, have conspicuous collar spines and smaller pointed spines occur on most of the body surface. The spines continue to grow in the experimental final host, chickens. The flattened spines of the oral sucker remain, whereas those of the ventral sucker disappear. The ventral area between the suckers is spineless.

Animals↗
PubMed1995

A comparative study of the shedding of cercariae of Schistosoma haematobium in newborn Bulinus truncatus.

A comparative study of the shedding of cercariae of Schistosoma haematobium was performed in Bulinus truncatus and Planorbarius metidjensis individually exposed to 5 miracidia in their first 72 h of life. No significant difference was noted between the mean values of the two snail groups concerning the prepatent period duration (53-57 days at 24 degrees-26 degrees C), the patent period duration (41 days for B. truncatus, 70 days for P. metidjensis), or the total number of cercariae (1,499 per B. truncatus, 1,935 per P. metidjensis). Successive periods of heavy and low production were encountered in the shedding of cercariae; however, the periodicity was identical in the two snail species (25-27 days) and the emergence of cercariae peaked between 11 a.m. and 1 p.m.

Animals↗
PubMed2001

Influence of aqueous sediment extracts from the Oder River (Germany/Poland) on survival of Diplostomum sp. (Trematoda: Diplostomidae) cercariae.

Laboratory experiments were carried out to test whether the life span of Diplostomum sp. cercariae is affected by contamination of its aquatic environment. Freshly emerged cercariae therefore were exposed to either standardized water, Oder River (Germany/Poland) or Lake Odersee (Germany) extracts of aqueous sediments; mortality patterns and mean survival times (MSTs) were compared. Cercariae added to extracts of aqueous sediments from the Oder River and Lake Odersee exhibited impaired survival with significantly different mortality pattern and reduced MST compared to that of controls. A significant negative correlation (r = -0.843, p < 0.05) was found between MST and mercury content of sediments, indicating a potential impact of mercury on survival of Diplostomum sp. cercariae. The results indicate that contamination of freshwater habitats may influence the viability of free-living transmission stages of helminth parasites of fish and may thus be of epizootiological significance.

Animals↗
PubMed2006

An ultrastructural study of alimentary tract development in the cercariae of Diplostomum pseudospathaceum (Digenea: Diplostomidae).

Morphogenesis of the alimentary canal in developing Diplostomum pseudospathaceum cercariae has been studied using electron microscopy. The foregut primordium appears in early cercariae as a cellular cord. Later, the lumen develops within the foregut primordium, and its cells give rise to the cellular epithelium, limiting this lumen. During subsequent development, the lateral plasma membranes, separating the cells, disappear from the primary foregut epithelium as do nuclei and most of cellular organelles. These events seem to progress in several steps, and eventually, the foregut lining becomes the thin anucleate syncytial layer. In late cercariae, this layer becomes connected with nucleated cytons, producing secretory inclusions. Each of two caecal branches appears to arise from a row of large cuboid cells. The primordial gastrodermal cells are involved in synthetic and secretory activity and give rise to numerous secretory inclusions. These inclusions release their contents into the cavities which develop between adjacent primordial caecal cells. The intercellular cavities gradually increase in size and fuse to eventually form a single caecal lumen. In mature cercariae, the large caecal lumen packed with electron-dense secretory material is limited by a thin cellular gastrodermis, displaying no secretory features.

Animals↗
PubMed1997

Chemoattraction and penetration of Echinostoma trivolvis and E. caproni cercariae in the presence of Biomphalaria glabrata, Helisoma trivolvis, and Lymnaea elodes dialysate.

A petri-dish bioassay was used to study the chemoattraction and penetration of the cercariae of Echinostoma trivolvis and E. caproni in the presence of snail dialysates from Helisoma trivolvis (Pennsylvania and Colorado strains). Biomphalaria glabrata, and Lynmaea elodes. Significant chemoattraction was seen with E. trivolvis cercariae in the presence of all snail dialysates released from nonperforated dialysis sacs with a molecular-weight exclusion of 12,000. Under the same conditions, E. caproni was significantly attracted to B. glabrata and H. trivolvis (CO strain) but not to L. elodes or H. trivolvis (PA strain). Dialysis sacs were perforated with needles to allow the release of snail substances of all molecular weights into the bioassay. Cercariae of both species were significantly attracted to all snail dialysates released from perforated sacs. Moreover, cercariae entered these sacs and penetrated the snails, and 24 h later the percentage of cysts per snail species ranged from 70% to 83% for E. trivolvis and from 73% to 93% for E. caproni. Dialysates released from intact sacs were extracted in choloroform-methanol (2:1) to obtain hydrophilic and lipophilic fractions. When these extracts were placed on agar plugs in the bioassay, the lipophilic fraction, but not the hydrophilic fraction, was mainly chemoattractive.

Animals↗
PubMed1997

Fasciola hepatica: in vitro production of daughter rediae and cercariae from first- and second-generation rediae.

Fasciola hepatica mother rediae belonging to the first generation and the first cohort of the second generation were extracted from their snail intermediate host (Lymnaea truncatula) and maintained in vitro for 16 days to determine the quantity of daughter rediae and cercariae produced by each generation. L-15 Leibovitz medium with a saline fraction adjusted to that of the L. truncatula hemolymph was used for experiments. A total of 35 daughter rediae exited from the 21 mother rediae of the first and second generations, which were 14-32 days old at the onset of culture. Microscope examination of the mother rediae demonstrated the presence of numerous redial embryos and differentiating daughter rediae, whereas no cercaria was seen within their body. A total of 49 cercariae exited from the 17 mother rediae of the first and second generations, which were 29-50 days old at the onset of culture. No differentiating daughter redia was seen in these last mother rediae. The productivity of the first or second generation (first cohort) was nearly identical in terms of cercariae.

Animals↗
PubMed1985

Schistosoma mansoni: neurotransmitters and the mobility of cercariae and schistosomules.

The concentration-dependent action of alkyl-isothiouroniums on Schistosoma mansoni cercariae, ranging from partial to total abolition of locomotor and flame cell movements, and/or suppression of virulence, is due to H1-histamine receptor inhibition. Correspondingly, H1-receptor inhibitors of widely different chemical structure, such as clemizol, diphenhydramine, brompheniramine, and promethazine, in 0.03-0.06 nM concentrations, induced an analogous cercarial immobilization reversed by addition of excess histamine. In contrast, the H2-receptor inhibitors cimetidine and metiamide did not immobilize cercariae. Histamine, acetylcholine, and serotonin, added to cercarial suspensions, showed no direct activity. Their participation in the mechanism of cercarial mobility was shown by the dose-dependent effects of antagonists, such as the serotonin antagonist methysergide and the acetylcholinesterase inhibitor physostigmine. These effects were not reversible by addition of serotonin and acetylcholine, respectively. A histamine-irreversible cercarial immobilization induced by the H-liberator 48/80 suggested that, besides H1-receptor inhibition, H-liberation and/or depletion also participated in mobility and survival. The detection of histamine in the cercaria corroborated the participation of histaminergic mechanisms. S. mansoni schistosomules collected from the mouse lung reacted to H1 antihistamines like cercariae, with a dose-dependent reduction of mobility and somatic deformation, such as vacuolization, granulation, and caecal enlargement.

Acetylcholine↗
PubMed1993

Cercariae and metacercariae of Stephanostomum cloacum (Trematoda: Acanthocolpidae).

Cercariae and metacercariae of the acanthocolpid trematode, Stephanostomum cloacum (Srivastava, 1938) are described and illustrated, based on material collected from Chilka Lake, a brackish water lagoon. Natural infections with the cercariae were found in the snail, Nassarius orissaensis and with the metacercariae in the bivalve, Modiolus undulatus. Cercariae are distomate, ophthalmoxiphidiocercous, and possess a small stylet, simple tail, four pairs of penetration glands arranged in two groups and a large granular excretory bladder. Development of the cercaria into the metacercaria was followed in M. undulatus under laboratory conditions. Infections with adults of S. cloacum were identified in the fish Triacanthus biaculeatus, found in the lake.

Animals↗
PubMed1994

The glands of trematode cercariae of the family Microphallidae Travassos, 1920.

The ultrastructure of the glands of microphallid cercariae is described. The fully-formed cercariae possess only penetration glands opening onto the surface of the tegument. Cercarial embryos have tegumental glands transferring their secretion in the tegument. In all studied species two anterior pairs of penetration glands produce identical granules while two posterior pairs produce heterogeneous granules of various shapes and sizes. Tegument cells are divided into mucoid and two other types of tegument glands (TG1 and TG2). The mucoid glands of Microphallinae cercariae produce large fibrous granules, while those of Maritrematinae cercariae produce osmiophil ones. TG1 cells of Maritrema subdolum produce large rod-shaped granules and TG1 cells of Levinseniella brachysoma, Microphallus sp. and M. claviformis produce two types of osmiophil granules. TG2 produce small rod-shaped granules. The association of gland ultrastructure with their function and features of the microphallid life-history are discussed.

Animals↗
PubMed1996

Experimental infection of Helisoma trivolvis (Colorado strain) snails with cercariae of Echinostoma trivolvis.

A Colorado (CO) strain of Helisoma trivolvis resistant to miracidial infection, but susceptible to Echinostoma trivolvis cercarial penetration, was used to study encystment of cercariae released from naturally infected H.trivolvis (Pennsylvania strain). All 12 snails, 8-10 mm in shell diameter, each exposed to 25 cercariae and necropsied 1-4 days post-exposure were infected with between 9 and 19 cysts per snail (average 14). In all infectivity experiments, regardless of the size (age) of the Colorado strain snails used, encysted metacercariae were recovered from the kidney-pericardial region of experimentally infected snails within 24 h post-exposure. Snails exposed individually with 500 cercariae averaged 230 cysts per snail at 24 h p.i. Cercariae encysted at 6-8 h p.i., but not at 2 and 4 h p.i. Light microscopical observations of the cysts suggested that greater than 99% were viable. Metacercariae subjected to in vitro excystation in an alkaline trypsin-bile salts medium showed excystation rates of 60-85%. In conclusion, H. trivolvis (CO strain) is an excellent experimental second intermediate host for cercarial encystment of E. trivolvis.

Animals↗
PubMed1978

In vivo cercaria-schistosomulum transformation: inhibitory effect of oxamniquine.

High doses of oxamniquine (given intramuscularly) produced inhibition of cercaria-schistosomulum transformation following intraperitoneal injections of cercariae into mice. Cercariae, tail-less cercarial bodies, and schistosomula were recovered from the peritoneal cavity of drug-treated mice in numbers significantly different from those recovered from untreated mice. Since untreated animals induced transformation of almost all the injected cercariae, the data suggest the compound is active during the process of host-larvae adaptation.

Animals↗
PubMed1982

Schistosoma haematobium in the baboon (Papio anubis): effect of vaccination with irradiated larvae on the subsequent infection with percutaneously applied cercariae.

Groups of five baboons were vaccinated three times at approximately six-weekly intervals at a rate of 1,000 organisms per kg of gamma-irradiated Schistosoma haematobium larvae. Five vaccines were tested: 3 and 20 Krad cercariae applied percutaneously; fresh 3 and 20 Krad mechanically transformed schistosomula injected intramuscularly; and cryopreserved 20 Krad schistosomula injected intramuscularly. These five groups and an unvaccinated control group were challenged percutaneously with 7,500 S. haematobium cercariae three months after the last vaccination. The efficacy of the vaccines was judged by faecal egg excretion, and by adult worm and tissue egg recoveries at necropsy 4.5 months after challenge. Significant protection, with 64 to 89% reductions in worm burden and parallel reductions in egg production, was achieved by all but the cryopreserved vaccine, although egg production was not significantly reduced in those female worms which did mature. Cercariae tended to give more protection than schistosomula and 20 Krad more protection than 3 Krad. No significant pathology could be detected in an additional baboon vaccinated with 20 Krad schistosomula but not challenged with cercariae. This is an encouraging result for the development of a live vaccine against S. haematobium.

Animals↗
PubMed1984

Schistosoma mansoni: decay of resistance induced by gamma irradiated cercariae in the mouse.

The level of resistance induced by a single percutaneous infection of cercariae which had been previously exposed to 20 kr of gamma irradiation was compared in two strains of mice. Challenge cercariae were given at several time intervals after the preliminary immunization either to the same skin site as that used for immunization or to a previously unexposed skin site. No significant difference in resistance to infection was observed when a different skin site was used for the challenge. A higher degree of resistance to challenge was observed in CBA/Ca mice than in BALB/c mice. Immunity in both strains declined to about two thirds of the original level after six months and could not be detected when challenge cercariae were given 70 weeks after the single immunizing dose of irradiated cercariae.

Animals↗
PubMed1987

A cloned DNA probe identifies the sex of Schistosoma mansoni cercariae.

This report describes a method for the identification of the sex of Schistosoma mansoni cercariae using a cloned DNA probe which is female-specific. The probe is a 339 bp repeat; the sequence is presented. Cercariae from nine mono-miracidially infected snails were used in a double blind study. Mice were infected and the sex of adult worms observed. DNA was isolated from cercariae, digested with EcoRI, subjected to agarose gel electrophoresis, transferred to a matrix and hybridized with the cloned female-specific DNA probe. In all nine cases the sex of the cercariae as determined by DNA analysis agreed with the sex of the adult parasites.

Animals↗
PubMed1978

Oxygen uptake and lactate production by Schistosoma mansoni cercaria, cercarial body and tail, and schistosomule.

1. Oxygen consumption by Schistosoma mansoni cercarial bodies varies, with the batch of organisms, the incubation media and the temperature (27-37 degrees C), from 27.4 +/- 3.4 to 55.0 +/- 4.8 microliters O2/mg larval protein per hr. It is proportional to the concentration of organisms incubated, up to 25,000/ml, as calculated from whole protein. 2. Oxygen uptake by cercariae is inhibited by 5.6 mM glucose in the incubation media, a concentration that stimulates the respiration of cercarial bodies. 3. No significant differences in the oxygen uptake were presented by cercarial bodies with and without glycocalyx or glandular secretions, or devoid of all of them. 4. Inhibitors of the Krebs cycle and the respiratory chain, and uncoupling agents influence the oxygen uptake by cercariae, cercarial bodies and schistosomules to the same extent. 5. The permeability change presented by transformed larvae had no influence on the excretion of lactate by cercarial bodies, which is about 0.3 mumoles/mg protein per hr and remains constant for 5 hr; under nitrogen, this amount increased 70%. Cercariae in anaerobiosis, however, excreted as much as 15 times more lactate than under air. 6. Lactic dehydrogenases of cercariae, cercarial bodies and tails, and schistosomules are of the muscle type and do not change during the transformation.

Animals↗