Pathophysiologic alterations in Biomphalaria glabrata infected with Angiostrongylus costaricensis

Hemolymph glucose, alkaline phosphatase, lactic dehydrogenase, and creatine phosphokinase in Biomphalaria glabrata infected with Angiostrongylus costaricensis were significantly higher on day 27 postinfection (PI) than in uninfected snails. Hemolymph total calcium from infected snails was less on days 6, 12, and 27 PI than that from controls. Total hemolymph protein was similar for controls and infected animals during the entire study. Throughout the study the mean number of amoebocytes/mm³ hemolymph from infected snails was significantly less than that for controls. Mean total wet weights of digestive gland and foot muscle from infected and uninfected snails was similar throughout the study. Mean μg glycogen/mg wet weight of digestive gland from infected snails was significantly greater on days 24, 27, and 28 PI than that from controls. Mean μg glycogen/mg wet weight of foot muscle from infected snails was significantly reduced between days 12 and 28 PI from that of uninfected snails. It is suggested that hemolymph glucose and digestive gland glycogen in infected snails are augmented by glycogen breakdown in the foot muscle of parasitized animals. Elevations in hemolymph enzymes are due to tissue destruction by larvae emerging from the foot muscle of infected snails. Parasite-induced derangements in shell metabolism underlie observed changes in hemolymph calcium in infected snails.     

Physiology and lipid metabolism of Littorina saxatilis infected with trematodes

Physiological and biochemical alterations in Littorina saxatilis infected with larval trematodes were investigated and compared with the metabolism of non-parasitized snails. Oxygen consumption rates of infected snails differed from those of non-infected controls in medium sized individuals (30 to 130 mg) but not in very large infected individuals (> 200 mg). Small snails (0.5 to 8.5 mg) were seldom infected by parasites, and this size-class consisted only of non-infected specimens. The specific oxygen consumption rate of infected snails was not dependent on their mass and remained constant over the size ranges investigated. Alterations in the snail metabolism appeared to be connected to injuries to digestive gland tissues caused by the parasites. The glycogen concentration and fatty acids of neutral lipids and phospholipids in the digestive gland were determined. Infected snails differed from uninfected snails in the complete absence of glycogen in digestive gland and had proportionally higher quantities of eicosenoic (20:1) acid in the total phospholipids. It remains unclear whether infection by trematodes activates enzymes in the snail's digestive gland to synthesize eicosenoic (20:1) acid, or whether the sporocysts themselves possess these enzymes. The role of phospholipid fatty acids in the regulation and maintenance of the parasite's metabolism is briefly considered. Biochemical alterations observed in the fatty acid composition may have an adaptive significance, by helping to stabilize the host-parasite system.     

Activation of anaerobic metabolism in Biomphalaria glabrata (Mollusca: Gastropoda) experimentally infected by Angiostrongylus cantonensis (Nematoda,Metastrongylidae) by high-performance liquid chromatography

The activity of lactate dehydrogenase and the concentrations of glucose in the hemolymph and of glycogen in the digestive gland and cephalopedal mass of Biomphalaria glabrata experimentally infected with Angiostrongylus cantonensis were evaluated. Additionally, high performance liquid chromatography (HPLC) was used to determine the hemolymph concentrations of some carboxylic acids (oxalic, piruvic, lactic and succinic). After one, two and three weeks of infection, the snails were dissected to collect the hemolymph and separate the tissues. A significant reduction of the levels of glucose in the hemolymph was observed as of the first week of infection in relation to the control group. The lactate dehydrogenase activity of the infected group was significantly higher than the average of the control group. This increase was accompanied by a reduction of the levels of piruvic acid and an increase in the levels of lactic acid in the hemolymph of the parasited snails, confirming the acceleration of the anaerobic metabolism, necessary for the host to obtain energy and maintain its redox balance. In parallel, there was a decrease in the glycogen content of the storage tissues, with that reduction being significantly greater in the cephalopedal mass than the digestive gland, demonstrating that in this interaction system, the mobilization of glycogen was not sufficient to maintain and reestablish the normal glycemia of the infected snails.     

Trichobilharzia ocellata: physiological characterization of giant growth, glycogen depletion, and absence of reproductive activity in the intermediate snail host, Lymnaea stagnalis

Giant growth, depletion of energy stores, and inhibition of reproductive activity are striking effects of many trematode parasites on their intermediate snail hosts. Two hypotheses have been put forward to explain these phenomena: (1) host and parasite compete for energy rich and other essential nutrients, with the parasite as the winner, and (2) the parasite intervenes in the endocrine control of reproduction of the snail. These hypotheses were tested in the present study with the Trichobilharzia ocellata/Lymnaea stagnalis association. The snails were infected at a juvenile stage, and release of cercariae started on Day 55 after exposure. It was shown that enhanced growth of infected snails is not paralleled by a greater increase in dry weight, but hemolymph volume does increase, being 35% greater than in the noninfected controls. Control snails, on the other hand, showed an increase in the percentage body dry weight during sexual maturation. The conclusion is that infected snails retain an essentially juvenile body structure. In control snails, glycogen was depleted from the mantle store at the start of egg laying but the onset of cercariae production marked a severe glycogen depletion from the headfoot and the mantle in infected snails, being nearly complete on Day 68 after exposure. The hemolymph glucose concentration was only slightly lower in infected than in control snails and it did not change (in both groups) during glycogen mobilization. This suggests that glycogen mobilization does not result from the snail and the parasite competing directly for metabolites within the hemolymph. Infection inhibited the maturation of the accessory sex organs: there was no increase in the relative wet weights nor in the amounts of DNA and secretion products in the albumin and prostate glands. Infected snails did not lay eggs. It is presumed that the parasite produces one or more agents which intervene in the action of the gonadotrophic hormones. The release of these agents commences at an early stage of infection.     

Parasite influences on host life history: Echinostoma revolutum parasitism of Lymnaea elodes snails

Using field surveys and experimental infections, we investigated the influence of a trematode parasite on life history traits of adult Lymnaea elodes snails. We found that parasitism significantly affected the growth, fecundity, and survival of host snails. Within five of the six natural L. elodes populations we sampled, shell length of echinostome-infected hosts was significantly greater than for uninfected conspecifics. Furthermore, we show that gigantism occurs among experimentally infected snails due to an accelerated growth rate and size-selective mortality following an Echinostoma revolutum infection. The fecundity of infected snails sharply decreased beginning at 3 weeks post exposure (PE) and all egg production eventually ceased for most hosts by 5–6 weeks PE. Energy constraints, imposed by parasite development, alter the host energy budget. Early in the infection, parasite depletion of host energy reserves reduces host reproduction, but sufficient resources remain to allow accelerated host growth. Mortality was increased among host snails at two distinct stages: shortly after exposure and several weeks after cercariae were first released. We did not observe tissue degradation in snails during the first 4 weeks after exposure to the parasite, but destruction of host tissues was noted among snails dying later in the infection. Received: 5 September 1997 / Accepted: 19 November 1997     

Changes in chemical components in the freshwater apple snail, Pomacea canaliculata (Gastropoda: Ampullariidae), in relation to the development of its cold hardiness

The apple snail, Pomacea canaliculata, is an invasive freshwater snail. It increases its cold hardiness before winter. However, the physiological mechanism of cold hardiness in molluscs is poorly understood, especially in freshwater molluscs. In this study, we examined the changes in low molecular weight compounds, glycogen and lipids, in the body of P. canaliculata in association with the development of cold hardiness. When snails without cold hardiness were experimentally cold-acclimated, the amount of glycerol, glutamine, and carnosine increased, while glycogen and phenylalanine decreased. Overwintering cold-tolerant snails collected from a drained paddy field in November also showed increased glycerol in their bodies with decreasing glycogen concentration, compared to summer snails collected from a submerged field. Water content also decreased during the cold acclimation, although the water loss was minimal. These results indicate that the freshwater snail, P. canaliculata enhances cold hardiness by accumulation of some kinds of low molecular weight compounds in its body as some insects do. However, the actual function of each low molecular compound is still unknown.     

Tissue responses exhibited by Biomphalaria alexandrina snails from different Egyptian localities following Schistosoma mansoni exposure

Snails’ susceptibilities to infection with Schistosoma mansoni were determined through observation of infection rates, total cercarial production and tissue responses of the first generation (F1) of Biomphalaria alexandrina snails, originally collected from different Egyptian governorates (Giza, Fayoum, Kafr El-Sheikh, Ismailia and Damietta) and responses were compared between groups. The emergence of cercariae for a 3-month period and the calculation of survival and infection rates, in control (Schistosome Biological Supply Center; SBSC) and infected snails were evaluated. SBSC and Giza snails showed greater susceptibilities to infection and lower mortality rates. In addition, at 6 and 72 h post-exposure to miracidia all the snail groups showed no difference in the anatomical locations of sporocysts. The larvae were found in the head-foot, the mantle collar and the tentacles of the snails. Sporocysts showed normal development with low tissue reactions in SBSC and Giza snail groups infected with S. mansoni miracidia (SBSC). However, in Fayoum, Kafr El-Sheikh, Ismailia and Damietta snail groups, variable tissue responses were observed in which numerous hemocytes made direct contact with S. mansoni larvae forming capsules. The results suggested that, different responses of B. alexandrina snail’s hemocytes towards S. mansoni are related to the degree of susceptibility of these snails. So this is important in planning the strategy of schistosomiasis control.     

Proteomic,metabolic and immunological changes in Biomphalaria glabrata infected with Schistosoma mansoni

Mansonic schistosomiasis is a neglected disease transmitted by Biomphalaria spp. snails. Understanding what happens inside the intermediate host is important to develop more efficient ways of reducing schistosomiasis prevalence. Our purpose was to characterize metabolic and immunological changes in Biomphalaria glabrata 24 h after exposure to Schistosoma mansoni. For this purpose, proteins were extracted from snails’ whole tissue with Tris-Urea buffer and digested with tripsin. Mass spectrometry was performed and analyzed with MaxQuant and Perseus software. Also, the hemolymph of five snails 24 h post exposure was collected, and the numbers of hemocytes, levels of urea, uric acid, nitric oxide, calcium, glycogen and alanine and aspartate aminotransferases activities were assessed. Snails were also dissected for measurement of glycogen content in the cephalopodal region and gonoda-digestive gland complex. Globin domain proteins were found to be up-regulated; also the number of circulating hemocytes was significantly higher after 24 h of exposure to the parasite. NO levels were higher 24 h post exposure. Several proteins associated with energy metabolism were found to be up-regulated. Glycogen analysis showed a significant decrease in the gonad-digestive gland complex glycogen content. We found several proteins which seem to be associated with the host immune response, most of which were up-regulated, however some were down-regulated, which may represent an important clue in understanding B. glabrata – S. mansoni compatibility.     

Effects of experimental stress on the glycogen content of Cepaea hortensis (Mollusca)

A method for measuring the glycogen content of the hepatopancreas of Cepaea hortensis is described. Glycogen content was determined for snails from field population cages and from a nearby natural population. Results showed that caged snails possessed lower levels of glycogen than did the natural population, while the lowest levels of glycogen were associated with higher snail densities in the cages. There is evidence for an increase in glycogen content of C. hortensis during the late summer in nature and in experimental populations. The results are discussed with regard to the selective effect that glycogen may have on Cepaea and to the interpretation of events occurring in populations of Cepaea that glycogen assay could provide.     

Quantification of parasite development in the host-parasite system Biomphalaria glabrata and Schistosoma mansoni

The visceral mass of Biomphalaria glabrata uninfected or infected with Schistosoma mansoni was serially sectioned. The amount of hepatopancreas tissue and of parasite tissue was quantified. In pool-infected snails the volume of the whole visceral mass increased very significantly until week 6 and then decreased. Due to the growing parasites the volume of the visceral mass in infected snails was at most times higher when compared with uninfected snails of the same dimensions. Two weeks p.i. there was a permanent and significant increase of parasite tissue until week 6. During this time the amount of hepatopancreas tissue still increased. From this time onwards till week 12 the proportion of parasite tissue remained rather constant, indicating a kind of regulation, whereas the hepatopancreas tissue decreased to about one-third of the volume found in uninfected snails of the same shell diameter. Compared with infections by a single miracidium there was a significant increase in parasite tissue after infection with two miracidia. Infections with more miracidia (5, 10, and 20) gave no significant further increase. This also demonstrates a kind of regulation. Mortality rate, growth rate and egg production were studied during an infection period of 12 weeks.     

Altered feeding response as a cause for the altered heartbeat rate and locomotor activity of Schistosoma mansoni-infected biomphalaria glabrata

Biomphalaria glabrata infected with Schistosoma mansoni for 33 days fed more often than uninfected snails. Whereas uninfected snails had nocturnal increases in feeding, snails with a 33-day-old infection of S. mansoni fed as often during the day as in the night. Using direct observation and film analysis, we found that feeding increased the heartbeat rate and locomotor activity of B. glabrata. When snails were allowed to feed ad lib., infected snails had higher heartbeat rates than uninfected snails both during the day (P less than 0.01) and the night (P less than 0.001). However, when the snails were deprived of food for 24 hr, infected snails had slightly higher heartbeat rates than uninfected snails only during the day (P less than 0.05). There was no difference between the heartbeat rates of feeding, infected snails and the heartbeat rates of uninfected snails that were starved for 8 hr, and then allowed to feed. Uninfected snails had nocturnal increases in heartbeat rate regardless of feeding schedule, but infected snails had greater nighttime heartbeat rate than daytime heartbeat rate only when they were not allowed to feed. Infected snails had less nocturnal locomotor activity than uninfected snails when feeding, but there was no difference between the locomotor activity of infected and uninfected snails when the snails were deprived of food for 24 hr. Absence of food also resulted in an increased nighttime to daytime ratio of locomotor activity of infected snails. These results suggest that the increased heartbeat rate and altered rhythms of heartbeat rate and locomotor activity in B. glabrata infected with S. mansoni for 33 days were caused by the altered feeding response of these snails.     

Population dynamics of two snail species,Planaxis sulcatus and Cerithium moniliferum,and their trematode species at Heron Island,Great Barrier Reef

Summary The population dynamics of the prosobranch snail Planaxis sulcatus and its trematode parasites on 600 m of beachrock on the southern side of Heron Island, Great Barrier Reef, were studied. Populations of Planaxis show little mixing, due to lack of long-distance movements. From March 1973 to June 1975, an increase in the numbers of small and medium-sized snails occurred, but the biomass (dry tissue weight) of the snail population did not change. Snails were infected with one species of Aspidogastrea and six species of cerariae. Infections with cercariae did not significantly affect the relative weight of the snails. Multiple infections were random, i.e. neither negative nor positive interactions between trematode species could be demonstrated. Proportions of uninfected snails and snails infected with various trematode species remained more or less constant from July 1973 to February 1975.The population dynamics of the prosobranch snail Cerithium moniliferum and its 11 species of cercariae and one species of Aspidogastrea in a small area at Heron Island were studied. Numbers of large snails decreased and numbers of small snails increased from August 1973 to June 1975. The biomass of the Cerithium population increased only slightly. Prevalence of infection changed significantly only in large snails.Infections of Cerithium moniliferum and Peristernia australiensis with an aspidogastrid species decreased strongly from January 1971 to March/April 1972 and had not recovered by mid 1975.Seasonal fluctuations could not be demonstrated for any of the snails or parasites.The data for Planaxis suggest equilibrium conditions and saturation of the habitat.     

Total protein and carbohydrate content and protease and disaccharidase activities in the hemolymph of Lymnaea stagnalis naturally infected with digenean larvae

Lymnaea stagnalis is an intermediate host of many Digenea. The infestation affects host metabolism. The aim of the work was to investigate hemolymph biochemical indicators of L. stagnalis infected with four species of trematodes: Diplostomum pseudospathaceum, Paryphostomum radiatum, Plagiorchis elegans or Opisthioglyphe ranae. The protein profiles and proteinase activity in the hemolymph of sexually mature individuals of Lymnaea stagnalis maintained at 19°C were tested. As the carbohydrates are main substrates for energetic metabolism of the great pond snail their content and disaccharidase activity were also studied. Hemolymph samples were collected during weeks 3 and 4 of rearing. No significant differences in the total protein content between uninfected individuals and snails infected with the first three trematode species were detected. In the snails infected with O. ranae the quantity of total proteins was near twice higher than in those uninfected. A higher share of 70 kDa proteins in infected than in uninfected snails as well as reduction of the low molecular weight fractions of proteins for snails infected with D. pseudospathaceum and P. radiatum were detected. During week 3, carbohydrate content in the infected snails did not differ from that in the controls while during week 4 it was significantly lower in snails infected with P. elegans or O. ranae. The content of the major soluble carbohydrate in the hemolymph - saccharose — changed in a similar way. No activity of trypsin or pepsin in the hemolymph sample was detected while the activity of chymotrypsin was lower in infected snails vs. controls. On the other hand, saccharase and maltase activities were higher in infected than in uninfected snails. The biochemical hemolymph indicators in naturally infected host-snails show some differences depending on the parasite species but they are not sufficiently species-specific to offer the basis for establishing the model unique for a particular parasitosis. Our results from the field did not always coincide with those from the laboratory.     

Parasite and host elemental content and parasite effects on host nutrient excretion and metabolic rate

Ecological stoichiometry uses the mass balance of elements to predict energy and elemental fluxes across different levels of ecological organization. A specific prediction of ecological stoichiometry is the growth rate hypothesis (GRH), which states that organisms with faster growth or reproductive rates will require higher phosphorus content for nucleic acid and protein synthesis. Although parasites are found ubiquitously throughout ecosystems, little is understood about how they affect nutrient imbalances in ecosystems. We (1) tested the GRH by determining the carbon (C), nitrogen (N), and phosphorus (P) content of parasitic trematodes and their intermediate host, the freshwater snail Elimia livescens, and (2) used this framework to determine the trematode effects on host nutrient excretion and metabolism. Snail and parasite tissues were analyzed for elemental content using a CHN analyzer and soluble reactive phosphorus (SRP) methods. Ammonium and SRP assays were used to estimate N and P excretion rates. A respirometer was used to calculate individual snail metabolism. Trematode tissues contained lower C:P and N:P (more P per unit C and N) than the snail tissues. Snail gonadal tissues more closely resembled the elemental content of parasite tissues, although P content was 13% higher in the gonad than the trematode tissues. Despite differences in elemental content, N and P excretion rates of snails were not affected by the presence of parasites. Parasitized snails maintained faster metabolic rates than nonparasitized snails. However, the species of parasite did not affect metabolic rate. Together, this elemental imbalance between parasite and host, and the altered metabolic rate of infected snails may lead to broader parasite effects in stream ecosystems.     

Phenology of the rhodomelarian algae Neorhodomela aculeata and Ceramium kondoi and their survival strategies against herbivorous snails

The seasonal growth and reproductive phenology of Neorhodomela aculeata (Perestenko) Masuda and Ceramium kondoi Yendo, and the food preferences of herbivorous snails were examined to elucidate (i) why snails select the fronds of N. aculeata for their habitat; and (ii) the survival strategies of the two red algae under grazing pressures. The maximal lengths and weights of both algal species were recorded for each season over a 12‐month period beginning with the spring of 2003. C. kondoi grew in length at a faster rate than N. aculeate, whereas the turf alga N. aculeata produced new branches from the tips of broken branches. The reproductive period of C. kondoi was between the spring and summer but the reproductive organs of N. aculeata were observed throughout the year. The algal loss rate of fresh N. aculeata to snails was low but snails had a food preference for N. aculeata when compared to C. kondoi in an artificial food experiment. These results indicate that snails may adapt to chemical compounds characteristic of N. aculeata and that the alga further reduces predation damage by its structural resistance. In conclusion, the survival strategies of C. kondoi appear to be rapid growth, seasonal sexual reproduction, and a delicately branched frond morphology that reduces stable feeding patterns of its predators plus high tissue nitrogen content, whereas the survival strategy of N. aculeata includes regenerative growth responses, structural toughness and chemical defenses while under the grazing pressure of herbivorous snails.     

Influence of Echinostoma paraensei (Lie and Basch, 1967) infection on the calcium content in Biomphalaria glabrata (Say, 1818)

The calcium content in the hemolymph and shell of Biomphalaria glabrata (Say, 1818) was determined after exposure to different parasite burdens (5 and 50 miracidia) of Echinostoma paraensei (Lie and Basch, 1967). The snails were dissected 1, 2, 3, and 4 weeks after infection to collect the hemolymph and shell. An increase in calcemia was observed in snails infected with both miracidial doses. A significant decrease in the calcium ions in the shell was observed, coinciding with the calcemia peak in the hemolymph. This indicates greater mobilization of calcium between the shell and hemolymph to regulate the calcium content in the body when the snail is exposed to stress conditions, as has also been observed in some other infected snail species. The results obtained indicate that in this model, the calcium metabolism depends on the miracidial dose used.     

Comparative glucose tolerance studies in the freshwater snail Biomphalaria glabrata: influence of starvation and infection with the trematode Schistosoma mansoni

Summary The dynamic reactions of B. glabrata on intravasal loads of 20–1000 g glucose·g live fresh wt^-1 were studied in standard fed snails (SFS). Starved snails (SS) and snails infected with S. mansoni (IS) were given 100–500 g glucose·g fresh live wt^-1. Mean hemolymph glucose level was 12.1 mg·100 ml^-1 in SFS. It was not significantly lower in SS (10.7 mg·100 ml^-1), but significantly reduced in IS (8.5 mg·100 ml^-1). Since hemolymph volumes were significantly increased in SS, the amount of circulating glucose (pool) did not change (75 g·g body weight^-1) compared to SFS (62 g·g^-1). It was, however, reduced to 41 g·g^-1 in IS. In SFS the circulating glucose pool had to be doubled to induce significantly elimination of the injected glucose. Tripled pools were eliminated with half-times of 45 min, whereas lower and higher glucose loads were eliminated significantly slower (half-times: 80–105 min). Glucose tolerance of SS was reduced: half-times were doubled, and metabolization of injected glucose was reduced. Since tissue fresh weights were lowered by 40%, absolute incorporation of ¹⁴C from labeled glucose was lowered, but specific incorporation (per mg) was higher than in SFS and IS. Glucose tolerance of IS was increased: metabolic clearance rates rose by 70% and half-times were shortened by 30%, though absolute and specific rates of ¹⁴C incorporation were lowered. However, IS lost 25% of the label to the water, whereas SFS lost 12% and SS only lost 8%. Using the antimetabolite 2-deoxyglucose, 80% of the losses proved to be glucose in IS, and 50% in SFS. The present results suggest the existence of a glucostatic regulation in B. glabrata with lower sensitivity and capacity than in mammals. As to glucose tolerance, the often reported parallelism in metabolic shifts induced by starvation and parasitic infection was not confirmed.Abbreviations SFS standard fed snails - SS starved snails - IS infected snails - MGG midgut-gland-gonad - RB rest of the bodymass - MCR metabolic clearance rate     

Effects of aestivation and starvation on the neutral lipid and phospholipid content of Biomphalaria glabrata infected with Schistosoma mansoni

The effects of aestivation or starvation on the neutral lipid and phospholipid content of Biomphalaria glabrata patently infected with Schistosoma mansoni were determined by high-performance thin-layer chromatography-densitometry. Infected-aestivated snails were maintained in a moist chamber at 24 +/- 1 C and a relative humidity of 98 +/- 1%. Infected-starved snails were maintained in artificial spring water (ASW) at 23 +/- 1 C without exogenous food. Infected snails (the controls) were maintained in ASW at 23 +/- 1 C and fed lettuce ad libitum. The 3 groups were maintained in the laboratory for 7 days, and then the lipids from the digestive gland-gonad complex (DGG) were extracted and analyzed by class. Infected-aestivated snails exhibited greater mortality rate and weight loss after 7 days than did the infected-starved snails. The steryl ester concentration in the infected-starved snails was significantly increased (P = 0.010) compared with the controls but not compared with infected-aestivated snails; the concentration of phosphatidylcholine in infected-aestivated snails was significantly decreased (P = 0.007) compared with the controls but not when compared with the infected-starved snails. Aestivation or starvation had a significant effect on the concentration of certain lipid classes in the DGG of B. glabrata infected with S. mansoni.     

Studies on the prolonged storage of Metarhizium anisopliae conidia: effect of temperature and relative humidity on conidial viability and virulence against mosquitoes

The shell lengths, dried shell weights, soft tissue wet weights, and soft tissue dry weights were ascertained for noninfected Ilyanassa obsoleta and for the same snail species naturally infected with the following digeneans: Himasthla quissetensis, Zoogonus lasius, Cercaria dipterocerca, Lepocreadium setiferoides, Microphalloides nassicola, Stephanostomum tenue, and Microbilharzia variglandis. Analyses of the data obtained indicate that infection with all of the trematodes listed above causes neither enhanced growth of soft tissues nor accelerated lengthening of the shell. However, snails infected with sporocysts of Z. lasius have significantly heavier shells than do noninfected snails. These data suggest that infection with Z. lasius may have caused enhanced growth in the form of increased calcium deposition in the shell of I. obsoleta, possibly as a result of parasitic castration. In addition, the mean dry weight of the soft tissues of snails infected with M. variglandis, when normalized for shell length, is significantly lower than that of noninfected snails, possibly as a result of parasite-induced pathology. Finally, comparisons among infected snails indicate a trend toward increased soft tissue dry weight in snails infected with L. setiferoides, although the mean dry weight of these snails does not differ significantly from the mean dry weight of noninfected snails.     

Schistosomatium douthitti: biochemical and morphological effects of an experimental infection in mice

The pathophysiological changes that occur in mice experimentally infected with Schistosomatium douthitti were studied. Male ICR mice, 6-8 weeks in age, were exposed to 100 cercariae of S. douthitti from infected snails (Lymnaea catascopium) and sacrificed weekly for a total of 13 weeks. Liver homogenates, serum samples, and histological sections of liver tissue were examined. Results showed that body weights of animals with prepatent infections were higher than those of corresponding controls. After patency, which occurred at 5 weeks, body weights were lower and liver weights were higher resulting in significantly increased liver weight/body weight ratios. Hematocrit values declined progressively in patent infections. Total cholesterol in liver was generally higher in the parasitized groups reaching significance during patency. Values rose with age in both control and parasitized groups, but sooner in the latter. Free cholesterol was increased in the liver of animals with patent infections. Total lipid content of the liver was reduced in the infected animals throughout the study. Both liver glycogen and serum glucose levels in the infected animals rose over the control values. The activity of alkaline phosphatase (E.C.3.1.3.1) was elevated in liver tissue of infected mice. Glutamic-pyruvic transaminase (E.C.2.6.1.2) activity was higher in serum but lower in the livers of animals harboring patent infections. Total bile salt concentration in parasitized animals did not differ appreciably from control values; however, gallbladders were enlarged five times in the infected animals. Histologically, liver sections from infected mice showed granulomas in various stages of formation and degeneration. Granulomas contained from 1 to 40 schistosome eggs. After 6 weeks of infection, granulomas were characterized by many neutrophils and monocytes. Few lymphocytes and eosinophils were present. As the granulomas developed, fibroblasts and connective tissue became more prominent. Glycogen deposits were observed surrounding granulomas and were increased in older infections. Adult worms contained abundant amounts of glycogen and cholesterol in their parenchymal tissues.