In vitro excystation of metacercarial cysts of Echinostoma trivolvis from Rana species tadpoles

In vitro excystation studies were done on the metacercarial cysts of Echinostoma trivolvis obtained from the kidneys of naturally infected Rana species tadpoles. Cysts were excysted in an alkaline trypsin-bile salts medium and the percentage of excystation was compared with that from previous studies done on cysts obtained from the kidneys of snails. The percentage of excystation of E. trivolvis metacercariae from tadpole kidneys was similar to that reported for previous studies on cysts obtained from experimentally infected gastropod hosts. The possible role of tadpoles as an agent for the transmission of Echinostoma and echinostomiasis to humans is discussed.

In vivo and ectopic encystment of Echinostoma revolutum and chemical excystation of the metacercariae

In vivo and ectopic encystment of the cercariae of Echinostoma revolutum from Lymnaea elodes snails in Indiana and chemical excystation of the metacercariae were studied. In vivo encystment occurred in adults of Biomphalaria glabrata and Helisoma trivolvis (Colorado strain) snails and in neonatal and juvenile L. elodes snails. These results were expected because 37-collar-spined Echinostoma species show broad specificity in their second intermediate gastropod hosts. Encysted metacercariae of E. revolutum and Echinostoma trivolvis removed from experimentally infected snails and treated in a trypsin-bile salts excystation medium at 39 C showed 30.3% excystation for the former and 55.7% for the latter at 4 hr. The ducts and openings of the paraesophageal glands of excysted metacercariae of E. revolutum from cysts formed in snails did not stain with neutral red. Abnormal ectopic cysts with distorted outer walls and granular inner walls were obtained within 48 hr of placing E. revolutum cercariae in Locke's 1:1 plus 1% dextrose. These metacercariae excysted rapidly in the excystation medium and their paraesophageal gland ducts and openings stained with neutral red. Differences in ectopic encystment and chemical excystation in vitro can be used to distinguish these closely related species in the E. revolutum complex.

Low molecular weight hydrophilic chemicals that attract Echinostoma trivolvis and E. caproni cercariae

A Petri dish bioassay was used to study chemoattraction of the cercariae of Echinostoma trivolvis and E. caproni in the presence of various bench chemicals prepared as 5 mM solutions in agar. The design compared the attraction of cercariae migrating toward the plugs impregnated with chemicals compared to unimpregnated plugs (controls). Cercariae of both species were significantly attracted to an array of amino acids and to some carbohydrates. Cercariae of E. trivolvis but not E. caproni were attracted to the peptide glutathione. Cercariae of E. trivolvis and E. caproni were repelled from valeric and butyric acids, respectively. Cercariae of E. caproni but not E. trivolvis were repelled from dextrose. Although broad specificity exists for echinostome cercarial penetration in snail intermediate hosts, results of these studies suggest that there are specific differences in cercarial chemoattractants between E. trivolvis and E. caproni.

The occurrence and identification of Echinostoma revolutum from North American Lymnaea elodes snails

Lymnaea elodes snails collected in northern Indiana, U.S.A., were infected with larval stages of an echinostome bearing 37 collar spines and resembling members of the Echinostoma group. The taxonomic status of this digenean was determined through experimental infections of various definitive and first-intermediate hosts. In addition, characteristics of the penetration and paraesophageal glands in cercariae from this echinostomatid were compared with those from E. revolutum and E. trivolvis. Results indicate that this recently discovered 37-collar-spined echinostome parasitizing lymnaeid snails is E. revolutum, making this the first clear report of this trematode in North America.

Infectivity and growth of Echinostoma revolutum (Froelich, 1802) in the domestic chick

Infectivity and growth studies in domestic chicks were carried out on a strain of Echinostoma revolutum isolated from Lymnaea elodes snails in Indiana, U.S.A. Of 21 chicks, each fed 40 +/- 10 cysts of Echinostoma revolutum, 16 (64%) were infected with a total of 269 (32%) worms from approximately 840 cysts. Worms were found only in the ceca and rectum at 2-14 days p.i. In vivo excysted metacercariae were obtained in the lower ileum and ceca at 4 h p.i. Excysted metacercariae averaged 0.2 mm in length and 0.02 mm2 in body area. Worm length averaged 1.3 mm on day 6, 2.3 mm on day 8 and 3.6 mm on day 14. Mean body area averaged 0.29 mm2 on day 6, 0.62 mm2 on day 8 and 1.93 mm2 on day 14. Worms first became ovigerous on day 12. Growth of E. revolutum in the chick was delayed compared to previous findings on E. trivolvis, a closely related species of 37-collar-spined echinostome in the E. revolutum complex.

Effects of diet on the lipid composition of Echinostoma caproni (Trematoda) in ICR mice

High-performance thin-layer chromatography (HPTLC) was used to determine neutral lipids and phospholipids in the intestinal trematode Echinostoma caproni from experimentally infected ICR mice fed a high-fat diet (hen's egg yolk) as compared with worms from mice fed a standard laboratory diet. Worms were removed from the hosts at 2, 3, and 4 weeks postinfection (p.i.). Analysis by TLC-densitometry showed significantly greater amounts of triacylglycerols and free sterols at 2, 3, and 4 weeks p.i. in worms from mice on the high-fat diet as compared with worms from mice on the standard laboratory diet. Significantly greater amounts of phosphatidylcholine and phosphatidylethanolamine were found in worms from mice on the high-fat diet as compared with worms from those on the standard diet at 2 weeks p.i. but not at 3 and 4 weeks p.i. The results of this study suggest that the host diet influences the lipid content of E. caproni adults.

Experimental infection of Rana pipiens tadpoles with Echinostoma trivolvis cercariae

Studies were done on laboratory-raised Rana pipiens tadpoles experimentally infected with Echinostoma trivolvis cercariae. Tadpoles exposed individually to 250 cercariae died within 24 h. They were edematous at death and their kidneys were heavily infected with metacercarial cysts. Of 20 tadpoles exposed to 100 cercariae each, 9 survived the infection, and their growth was compared for 4 weeks postinfection (p.i.) with that of 20 control tadpoles that had not been exposed to cercariae. There was a significant weekly decline in the total length and body weight of the infected versus control tadpoles. Surviving tadpoles retained their metacercarial infections in the kidneys following metamorphosis to frogs. Following exposure of tadpoles to cercariae, cercarial bodies were first seen in the kidneys by 0.5 h p.i. Metacercariae that were molding their inner and outer cyst walls were first seen at 2.3 h, and by 8.5 h the inner and outer cyst walls were clearly defined. Domestic chicks exposed to cysts aged 2.5 and 4.0 h did not become infected, whereas ovigerous adults of E. trivolvis were recovered from chicks fed 12-h-old cysts. Cercariae aged 6 to 8 h were more infective to tadpoles than were either 1- or 20-h-old cercariae. The E. trivolvis-R pipiens tadpole model is suitable for the study of host-parasite relationships of echinostome larvae in a cold-blooded vertebrate host.

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.

Effects of high fat diets on worm recovery, growth and distribution of Echinostoma caproni in ICR mice

The effects of high fat diets (HFDs) on the host-parasite relationship of Echinostoma caproni in ICR mice were studied. Two HFDs were used, one consisting of a customized high fat diet (CHFD) with 45% lipid in the form of cottonseed oil, and the second consisting of an egg yolk diet (EYD) from domestic hens' eggs, with 31% lipid. Controls for both diets consisted of mice fed a standard laboratory diet with 5% lipid. Mice were each fed 25 cysts of E. caproni by stomach tube and necropsied 2, 3 and 4 weeks postinfection (PI). The weight of mice on the CHFD declined significantly compared to mice on the control diet, but there was no significant decline in weight of mice fed EYD compared to the controls. Worm recoveries from mice on both HFDs were significantly less than those from control hosts. There was a significant decline in worm dry weight, body area and uterine egg counts in worms on HFD compared to those on the control diet. Worms from hosts on HFD were located more anteriad in the gut than those recovered from mice on the control diet.

Maintenance of the life cycle of Echinostoma trivolvis (Trematoda) in dexamethasone-treated ICR mice and laboratory-raised Helisoma trivolvis (Gastropoda)

Echinostoma trivolvis is a ubiquitous 37-collar-spined echinostome found in aquatic birds and mammals and in the planorbid snail Helisoma trivolvis. This echinostome has not been cycled continuously in the laboratory. The present report provides details on the continuous life cycle of E. trivolvis in dexamethasone-treated ICR mice and laboratory-raised H. trivolvis snails. Previous attempts to obtain patent adult of E. trivolvis in mice hosts failed because of worm injection within 2 weeks of infection. ICR mice infected with encysted metacercariae and injected with 2 mg/kg dexamethasone daily for 28 days yielded gravid worms that produced 250-500 eggs/worms at 21 and 28 days postinfection (p.i.). Miracidia derived from these eggs or eggs containing fully developed miracidia were capable of infecting 3- to 5-mm shell-diameter, laboratory-reared H. trivolvis snails. These snails released cercariae by 35 days p.i. Cercariae encysted in the kidney-pericardium of the snails. Encysted metacercariae could be excysted in vitro in an alkaline trypsin-bile salts medium or in vivo when fed to domestic chicks.

In vitro studies on intraspecific and interspecific chemical attraction in daughter rediae of Echinostoma trivolvis and E. caproni

In vitro pairing and aggregation studies on daughter rediae of Echinostoma trivolvis and E. caproni were done at 22 degrees C in a Petri dish bioassay containing an agar substratum and a Locke's solution overlay. Pairing or aggregation was considered positive when rediae were in contact or within 1 mm of each other. Intraspecific and interspecific pairing or aggregation occurred in the bioassay when rediae were initially placed 5 or 10 mm apart. Movement of a single redia in the bioassay to a dialysis sac containing 1-10 rediae showed that intraspecific and interspecific pairing occurred in the absence of redial tactile stimulation. Movements of single rediae in the bioassay to agar plugs impregnated with redial excretory/secretory (ES) products occurred. The lipophilic fraction of the ES products was significantly more attractive than the hydrophilic fraction. The significance of redial chemical communication is not clear.

The expulsion of Echinostoma trivolvis: suppressive effects of dexamethasone on goblet cell hyperplasia and worm rejection in C3H/HeN mice

C3H/HeN mice were infected with Echinostoma trivolvis metacercariae on day 0, given intramuscular injections of dexamethasone daily for 5 or 7 days, and necropsied on days 5, 8, 12, 15, 20 and 30 p. i. Controls consisted of mice that were infected with echinostomes, but were not treated with dexamethasone. Dexamethasone treatment caused a delay in worm expulsion from the small intestine of the hosts, and the increase in goblet cell numbers that occurred in untreated mice was markedly delayed in the treated mice. Mast cell number in the small intestine increased rapidly from just after day 5 p. i. and reached a peak on day 15 p. i. in both dexamethasone-treated and control mice, although the increase in cell numbers was delayed slightly in the dexamethasone-treated mice. The eosinophil number in the small intestine of dexamethasone-treated mice was suppressed until 8 days p. i. and then increased reaching a peak on day 12 p. i., although the number was about one half that of the control. As determined on day 12 p. i., the mean body area of worms from dexamethasone-treated animals was significantly greater than that of the controls. Histological examination of the small intestine showed that the goblet and Paneth cell hyperplasia seen in mice infected with E. trivolvis was suppressed by dexamethasone treatment. Transmission electron microscopy revealed no marked ultrastructural differences in the small intestine of the dexamethasone-treated and control mice except that the former had an increased number of intracristal granules in mitochondria, an increase in vesicles in the apical epithelial cells and an increase in amorphous bodies and autophagic vacuoles in the Paneth cells. These results indicate that dexamethasone treatment delayed the expulsion of E. trivolvis from the small intestine of the host mouse in association with the suppression of goblet cell hyperplasia and increase in the number of mast cells and eosinophils.

Rapid expulsion of the intestinal trematodes Echinostoma trivolvis and E. caproni from C3H/HeN mice after infection with Nippostrongylus brasiliensis

The number of goblet cells in the small intestines of C3H/HeN mice increased rapidly following their infection with about 500 third-stage larvae (L3) of the intestinal nematode Nippostrongylus brasiliensis. The number of goblet cells reached its peak on day 9 postinfection (p.i.). Worm burdens in the hosts' small intestines were determined following a challenge infection with encysted metacercariae of the intestinal trematodes Echinostoma trivolvis or E. caproni on days 8 and 16 after primary infections with N. brasiliensis. All metacercariae of E. trivolvis or E. caproni used to challenge the hosts on day 8 p.i. were expelled. Considerable numbers of E. trivolvis (48.6%) and E. caproni (67.1%) remained in the intestines of hosts challenged with these echinostomes on day 16 p.i. All the controls used for E. trivolvis and E. caproni infections without primary infections with N. brasiliensis showed recovery rates greater than 70%. An enzyme-linked immunosorbent assay (ELISA) showed that the IgM titer rose remarkably and plateaued on day 11 p.i. No marked rise in the IgG or IgA titer occurred during the experiment. These results indicate that mucins increased by hyperplastic goblet cells associated with primary infections with N. brasiliensis are responsible for a rapid expulsion of the worms of the challenge infection with E. trivolvis or E. caproni from the mouse host.

Emergence of cercariae of Echinostoma trivolvis from Helisoma trivolvis under different conditions

Release of Echinostoma trivolvis cercariae from naturally infected Helisoma trivolvis snails maintained under different laboratory conditions was studied. Infected snails were isolated for 1 hr in Stender dishes containing 5 ml of artificial spring water and the number of cercariae released during this time was recorded. Of the conditions tested, i.e., light versus dark, day versus night, volume of water, snail maintenance temperature prior to isolation, temperature during isolation, food versus no food, aeration of water, disturbance of water, and isolation in snail conditioned water, the only significant factors in the emergence of E. trivolvis cercariae were temperature related. Observations on cercariae released in vitro from isolated rediae maintained in Locke's solutions were in accord with the in vivo results.

Effects of restricted food intake on neutral lipid and free fatty acid levels in the digestive gland-gonad complex and faeces of Biomphalaria glabrata (Gastropoda)

High-performance thin-layer chromatography (HPTLC) was used to determine neutral lipids and free fatty acids in the digestive gland-gonad complex (DGG) and faeces of Biomphalaria glabrata. Three populations of B. glabrata were given varying food intakes for one week. They were either unrestricted (lettuce ad libitum plus a weekly feeding of Tetramin), restricted (15-17 mg of lettuce every two days), or starved (no food). Samples were prepared by extraction in chloroform:methanol (2:1), followed by a Folch wash (0.88% aqueous KCl). The major lipids detected in the DGG were triacylglycerols, free fatty acids and free sterols. Free fatty acids and free sterols were the major lipids detected in the snail faeces. Analysis by TLC-densitometry showed a statistically significant difference in the DGG levels of triacylglycerols and free sterols between the unrestricted and restricted groups, as well as between unrestricted and starved groups. Analysis of faecal samples revealed a significant difference in free fatty acids between unrestricted and starved groups on the seventh day.

The expulsion of Echinostoma trivolvis from C3H mice: differences in glycoconjugates in mouse versus hamster small intestinal mucosa during infection

Mucosal glycoconjugates were examined in C3H mice and in hamster small intestines infected with Echinostoma trivolvis and in uninfected rodents, using periodic-acid Schiff (PAS) and high-iron diamine-alcian blue (HID-AB) staining and three different fluorescein-conjugated lectins: Triticum vulgaris agglutinin (WGA), Helix pomatia agglutinin (HPA) and Griffonia simplicifolia agglutinin (GSA-II). Lectin-labelling by electron microscopy was also undertaken with WGA and HPA lectin-gold probes. HID-AB stain demonstrated that the most mature goblet cells of the mouse villi contain sulfomucins, whereas those of hamsters contain sialomucins. The expression of lectin-binding sites and the intensity of the lectin binding in the small intestines were changed by echinostome infection. Specific differences in the reaction to mucin glycoproteins were clearly observed between the mouse and hamster intestines infected with E. trivolvis; lectin-binding to hyperplastic goblet cells and crypts in the infected mice increased, while no marked increase in the number of goblet cells and reaction to the glycoconjugates were observed in the infected hamsters. These findings indicate that the expression of terminal N-acetyl-D-galactosamine, sialic acid and N-acetyl-D-glucosamine increased in mucins secreted from hyperplastic goblet cells associated with E. trivolvis infection in mice. No marked increase in these glycoconjugates occurred in hamster infections. These findings reflect clear differences in infectivity of E. trivolvis in C3H mice versus hamsters.

Egg laying in vitro of Echinostoma caproni (Trematoda) in nutritive and nonnutritive media

Egg laying in vitro was studied in Echinostoma caproni adults placed in 10 ml of nutritive or nonnutritive media for 48 h in petri-dish cultures maintained at 37 degrees C in an atmosphere containing 7.6% CO2. Maximal egg laying occurred within 24 h in the defined medium RPMI 1640. Egg laying was significantly greater in this medium than in McCoy's or Locke's solution. Eggs released into the RPMI medium were capable of producing miracidia that were infective to Biomphalaria glabrata snails. Fried and Huffman (1996) referred to a technique used to obtain eggs of Echinostoma caproni in the defined medium RPMI 1640, but details of the study were not given. No information is available on egg laying of echinostomes in vitro. Such information could contribute to a better understanding of egg release in digeneans and would also be helpful in the acquisition of eggs for biology and chemistry studies. Current techniques used to obtain echinostome eggs involve worm homogenization, teasing of eggs from the worms' uteri, or recovery of eggs from feces (see Idris and Fried 1996 for details). The purpose of this communication is to report on an efficient procedure for the acquisition of eggs of E. caproni after the placement of adult worms in the defined medium RPMI 1640. E. caproni adults were grown in ICR mice for either 17 (young worms) or 112 days (old worms) as described previously (Ursone and Fried 1995a). Worms were removed from the small intestines and rinsed rapidly in three changes of sterile Locke's solution containing penicillin (200 IU/ml) and streptomycin (200 micrograms/ml; Fried and Contos 1973). Worms were placed in culture media within 30 min of their removal from hosts. Nutritive media consisted of RPMI 1640 and McCoy's medium (Sigma, St. Louis, Mo.). Non-nutritive media consisted of Locke's or Locke's 1:1 (Ursone and Fried 1995b). All media contained antibiotics as described above.

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.

Rapid expulsion of the intestinal trematodes Echinostoma trivolvis and E. caproni from C3H mice by trapping with increased goblet cell mucins

Echinostoma trivolvis (Cort, 1914) adults were rejected from C3H mice by 15 days post-exposure, corresponding to the increase in the number of goblet cells. Homologous and heterologous infections with the allopatric species E. caproni (Richard, 1964) were used to confirm the effect of increased secretion of goblet cell mucins in rejecting metacercariae of challenge infections of E. trivolvis or E. caproni on days 10, 16 and 20 p.i. after primary infections of E. trivolvis metacercariae. Five-day-old juveniles of E. trivolvis and E. caproni, which were recovered from C3H mice or hamsters, were also used for challenge infections on day 10 p.i. The metacercariae and juveniles, which were challenged homologously and heterologously on day 10 p.i., were almost all expelled. The metacercariae of E. trivolvis, which were challenged homologously on day 16, were completely rejected, but only a few challenged metacercariae of E. caproni in heterologous infection were recovered. Considerable numbers of E. caproni were recovered when challenge infections with the metacercariae were done on day 20 p.i., while only a small number of E. trivolvis was recovered. All controls without primary infections showed a recovery rate of over 50% of the worms. These results indicate that increased secretion of mucins by hyperplastic goblet cells associated with primary infections of E. trivolvis may be responsible for the expulsion of worms challenged homologously with E. trivolvis and heterologously with E. caproni from the mouse host.

Effects of the anthelmintics clorsulon, rafoxanide, mebendazole and arprinocid on Echinostoma caproni in ICR mice

Female ICR mice, 5 to 6 weeks old, were exposed by stomach tube to 25 metacercarial cysts of Echinostoma caproni per mouse. At 14 days post-exposure, mice were fed by stomach tube clorsulon (1000 mg/kg, 500 mg/kg and 100 mg/ kg) or rafoxanide (50 mg/kg, 25 mg/kg and 5 mg/kg) dissolved in dimethylsulphoxide (DMSO) carrier and mebendazole (1000 mg/kg and 500 mg/ kg) or arprinocid (100 mg/kg and 50 mg/kg) suspended in a 2:1 polyethylene glycol (PEG)/DMSO carrier. All drugs were obtained from Merck Inc. (Rahway, New Jersey, USA) and only single dose regimes were used. Experimentally infected mice that served as controls received either DMSO or 2:1 PEG/DMSO carriers or were not given the carrier. Mice were necropsied 15, 16, 18 and 20 days postexposure to worms. Doses of 100 mg/kg of clorsulon and 50 mg/kg of rafoxanide were 100% effective in eliminating the echinostomes on day 1 post-administration of the anthelmintics. Mebendazole and arprinocid were ineffective in eliminating worms at 1 or 2 days post drug administration.

Development, hatching, and infectivity of Echinostoma caproni (Trematoda) eggs, and histologic and histochemical observations on the miracidia

Light microscopy studies were done on the eggs and miracidia of the intestinal trematode Echinostoma caproni. Eggs were obtained by homogenizing adult worms derived from ICR mice in artificial spring water (ASW). To study egg development and to obtain miracidia, eggs were incubated in ASW in either a light or a dark environment for 10 days at 28 degrees C. Egg development was characterized and staged at 2-day intervals from day 0 to day 10 postembryonation. No significant difference in development was seen in eggs maintained under conditions of light or darkness. Eggs maintained in darkness for 10 days and exposed to incandescent light produced a large synchronous hatch of miracidia within 3 h of exposure to light. As expected, miracidia used to expose Biomphalaria glabrata snails produced patent infections at 5-7 weeks postinfection (p.i.). Embryonated eggs aged from 0 to 10 days that had been fed to B. glabrata snails also produced infections within 4 weeks of infection. Miracidial longevity studies showed that 50 newly hatched miracidia maintained at either 4 degrees, 12 degrees, 22 degrees, or 38 degrees C lived for 6, 28, 14, and 5 h, respectively. Histology studies were done on whole miracidia stained in 0.01% neutral red and in Schneider's acetocarmine. Histochemistry studies of miracidia stained with alcian blue (pH 2.5) showed the presence of acid mucopolysaccharides in the epidermal plates; miracidia treated with periodic acid-Schiff plus 0.5% malt diastase showed the presence of glycogen in the body and in the epidermal/subepidermal region. Miracidia stained with Lillie's Oil Red O showed the presence of sparse neutral fat droplets in the body.

Effects of Echinostoma trivolvis (trematoda) infection on metallic ions in the host snail Helisoma trivolvis (gastropoda)

Flame and graphite-furnace atomic absorption spectrometry and inductively coupled plasma atomic emission spectrometry were used to study the metallic ions in the digestive gland-gonad complex (DGG) of Helisoma trivolvis snails infected with the daughter rediae of Echinostoma trivolvis and in uninfected DGG. Seven metals were found to be present in infected and uninfected DGG at concentrations above the detection limits of the analytical methods. Of these, sodium was present in significantly higher amounts (Student's t-test, confidence level of 95%) in the infected versus uninfected DGG; magnesium and manganese occurred in significantly lower amounts in the infected DGG. Our results were compared with those from a Bulgarian study in which neutron activation analysis was used to determine elements in Lymnaea stagnalis snails infected with the intramolluscan stages of the 37-collar-spined echinostome E. revolutum. The Bulgarian study also reported a significant elevation of sodium but reduction of zinc in the hepatopancreas (i.e., digestive gland) of infected snails. Other differences between the two studies are discussed.