Schistosomatium douthitti: Exposure of Lymnaea catascopium to irradiated miracidia

Irradiation of Schistosomatium douthitti miracidia (4000, 5000, or 6000 rad) did not substantially alter their behavior or ability to penetrate their snail host. Treatment with 4000 rad was not sufficient to prevent all miracidia from establishing patent infections in Lymnaea catascopium, although significantly fewer snails exposed to these miracidia shed cercariae than did controls exposed to normal miracidia. Irradiation of miracidia with either 5000 or 6000 rad totally prevented cercarial production. Although destruction of irradiated mother sporocysts by encapsulating amebocytes was occasionally observed, most expanded without concomitant multiplication of germinal cells and embryo production and then collapsed. They generally persisted in this state throughout the period of observation (32 days). Snails sensitized by exposure to irradiated miracidia and challenged 2 or 10 days later with normal miracidia were as likely to develop patent infections as were snails exposed only to normal miracidia. Double sensitization of snails with irradiated miracidia also failed to confer protection upon challenge with normal miracidia. Most challenge sporocysts developed normally, often in close proximity to collapsed irradiated sporocysts.     

Leucocytosis in Biomphalaria glabrata sensitized and resensitized to Echinostoma lindoense

Leucocytosis was shown to occur in the pulmonate gastropod Biomphalaria glabrata exposed to the trematode Echinostoma lindoense. In these sensitized snails, the leukocyte count in the hemolymph was elevated 3 to 5 days postexposure to miracidia, and prior to complete encapsulation of sporocysts. This increase continued 1 to 5 days after destruction of sensitizing, irradiated E. lindoense sporocysts. Counts returned to normal levels after this period. A significant and more rapid increase in numbers of circulating leukocytes occurred 1 to 6 hr after reexposure of snails to a sensitizing dose of nonirradiated E. lindoense sporocysts. The leukocyte counts usually returned to normal levels after this period, except in snails in which some resensitizing sporocysts remained alive.     

Effects of UVB on interactions between Schistosoma mansoni and Biomphalaria glabrata

Ultraviolet B (UVB, 280-315 nm) radiation is detrimental to both of larvae of the digenetic trematode Schistosoma mansoni and its snail intermediate host, Biomphalaria glabrata. We explored effects of UVB on three aspects of the interaction between host and parasite: survival of infected snails, innate susceptibility and resistance of snails to infection, and acquired resistance induced by irradiated miracidia. Snails infected for 1 week showed significantly lower survival than uninfected snails following irradiation with a range of UVB intensities. In contrast to known immunomodulatory effects in vertebrates, an effect of UVB on susceptibility or resistance of snails to infection could not be conclusively demonstrated. Finally, exposure of susceptible snails to UVB-irradiated miracidia failed to induce resistance to a subsequent challenge with nonirradiated miracidia, a result similar to that reported previously with ionizing radiation.     

Studies on resistance in snails. 3. Tissue reactions to Echinostoma lindoense sporocysts in sensitized and resensitized Biomphalaria glabrata.

The resistance of Biomphalaria glabrata snails that have been sensitized by various levels of irradiated or nonirradiated Echinostoma lindoense miracidia increased after a second challenge infection with nonirradiated miracidia of the same species. This was demonstrated by increased suppression of migrating capacity of invading sporocysts, an accelerated host tissue reaction, and a greater tendency of snail amebocytes to flatten while attacking the parasite. Three methods of elimination of invading sporocysts were observed: (1) encapsulation by amebocytes followed by destruction of the sporocysts; (2) expulsion of the sporocyst through the host epithelium after its encapsulation in the subepithelial tissues; (3) blockade of the parasite's entry into subepithelial tissues by a localized amebocyte aggregation. The basic mechanism of host snail response to a single or a repeated challenge infection appears to be similar, though an anamnestic reaction is evident in the accelerated response following a second challenge exposure.     

Studies on resistance in snails: Specific resistance induced by irradiated miracidia of Echinostoma lindoense in Biomphalaria glabrata snails

In juvenile Biomphalaria glabrata snails exposed to irradiated Echinostoma lindoense miracidia, the sporocysts migrated to the heart at the same speed as did nonirradiated sporocysts in control snails. However, in each snail so exposed to irradiated miracidia, amebocyte clumps in the snail's heart destroyed the sporocysts within 2–9 days post-exposure. This process induced a strong, highly specific resistance to homologous reinfection in these previously susceptible snails. The snails remained susceptible to Schistosoma mansoni and Paryphostomum segregatum (Echinostomatidae), but were partially resistant to Echinostoma paraensei and E. liei, two echinostome species closely related to E. lindoense.     

Location of Biomphalaria glabrata (Say) by miracidia of Schistosoma mansoni Sambon in natural standing and running waters on the West Indian Island of St. Lucia

Upatham E. S. 1973. Location of Biomphalaria glabrata (Say) by miracidia of Schistosoma mansoni Sambon in natural standing and running waters on the West Indian Island of St. Lucia. International Journal of Parasitology3: 289–297. The ability of S. mansoni miracidia to locate B. glabrata in natural ditches and streams was investigated. Miracidia located and infected snails at distances of 9–14 and 97-54 in horizontally in standing and running waters respectively. In running water, no infection occurred above a velocity of 13.11 $\text{cm}\text{sec}$. In both types of habitat, infection rates in snails increased with increasing levels of miracidia but decreased as the location of caged snails moved away from the miracidial point of entry. Laboratory experi- ments showed that the number of daughter sporocysts was proportional to the number of miracidia. Judging by the number of daughter sporocysts recovered only a small percentage of miracidia succeeded in locating and penetrating snails (6.8–13-7 % and 1.4–6.2 % in standing and running waters respectively). In standing water, infection may be inhibited by the limited ability of miracidia to move horizontally. In running water, the flow extends significantly the effective scanning capacity of the miracidia, giving them a better chance of coming into contact with snails, which is of importance in the epidemiology of schistosomiasis. Owing to a con- siderable wastage of miracidia and the higher relative efficiency of miracidia at lower densities in detecting snails, control measures such as chemotherapy or provision of safe water supplies designed to lower egg output and reduce contamination may not seriously influence transmission unless S. mansoni egg production or contamination is massively reduced.     

Induction of resistance in Oncomelania hupensis nosophora against Schistosoma japonicum, but not against Paragonimus ohirai, using irradiated miracidia

Oncomelania hupensis nosophora snails sensitized with X-irradiated Schistosoma japonicum miracidia demonstrated resistance against a following challenge infection with non-irradiated homologous miracidia. The resistance in O. h. nosophora against S. japonicum was acquired within 1 day of sensitization, and it was strongest in a group challenged at an interval of 3 days. The resistance persisted for at least 4 weeks. Histological examinations revealed amoebocyte accumulation around the challenged S. japonicum sporocysts. On the other hand, when O. h. nosophora sensitized by exposure to X-irradiated P. ohirai or S. japonicum miracidia were subsequently challenged with normal P. ohirai miracidia, no resistance was observed, although they expressed the resistance against heterologous S. japonicum infection.     

Ribeiroia marini: pathogenesis and larval trematode antagonism in the snail, Biomphalaria glabrata

Larval trematode antagonism between Ribeiroia marini and Schistosoma mansoni was studied in the snail Biomphalaria glabrata. A laboratory-raised Puerto Rican strain of B. glabrata was exposed to single and double infections with given numbers of: (1) embryonated eggs of R. marini from laboratory rats, and (2) miracidia of S. mansoni from mice. Snails were maintained in outside environmental tanks in San Juan, Puerto Rico and larval trematode interactions were examined in a series of five experiments. Snails of all sizes were highly susceptible to single infections with R. marini. Rediae and cercariae caused extensive damage to the digestive gland and ovotestis resulting in premature death of snails. Heavily infected snails were castrated and stopped laying eggs. Snails infected first with S. mansoni were only partly susceptible to superinfection with R. marini given on Day 23. In a reverse experiment, snails infected first with R. marini were only partly susceptible to a second infection with S. mansoni given on Day 23. In simultaneous exposures, snails developed double infections (22%) with R. marini dominant and S. mansoni sporocyst and cercaria production reduced. While R. marini is not a strong direct antagonist against established S. mansoni infections, it has several attributes as a possible biological control agent: hardy eggs easily produced in rats; high infectivity to snails of all ages; and ability to castrate and prematurely kill B. glabrata. The R. marini-rat system described here provides a convenient laboratory and field model for the study of intrasnail trematode antagonism and biological control.     

Response to the amoebocyte-producing organ of sensitized Biomphalaria glabrata after exposure to Echinostoma caproni miracidia

Stimulation by exposure to Echinostoma caproni miracidia triggered the activity of the amoebocyte-producing organ (APO) of sensitized Biomphalaria glabrata snails. This organ is the site of formation of cells which subsequently migrate to all parts of the body. Amoebocyte production started very soon after exposure, and was maximal at 3 or 4 days; it then declined very fast and, at 6–7 days, the organ had almost returned to its initial state.     

Sublethal effects of ultraviolet b radiation on miracidia and sporocysts of Schistosoma mansoni: intramolluscan development, infectivity, and photoreactivation

Schistosoma mansoni occurs in tropical regions where levels of ultraviolet B (UVB; 290-320 nm) light are elevated. However, the effects of UVB on parasite transmission are unknown. This study examines effects of UVB on the miracidia and sporocysts of S. mansoni, focusing specifically on intramolluscan development, infectivity, and the ability to photoreactivate (repair DNA damage using visible light). Histology revealed that miracidia irradiated with 861 J x m(-2) underwent abnormal development after penetrating Biomphalaria glabrata snails. Total number of sporocysts in snail tissues decreased as a function of time postinfection (PI), among both nonirradiated and irradiated parasites; however, this decrease was greater in the latter. Moreover, whereas the proportion alive of nonirradiated sporocysts increased PI, that of irradiated sporocysts, i.e., derived from irradiated miracidia, decreased. Irradiation of miracidia with UVB resulted in decreased prevalence of patent infection (defined by presence of daughter sporocysts) in a dose-dependent manner, and no infections occurred at a dose of 861 J x m(-2). Like many aquatic organisms, including the snail host, parasites were able to photoreactivate if exposed to visible light following UVB irradiation, even subsequent to penetrating snails. These photoreactivation results suggest cyclobutane-pyrimidine dimers in DNA as the primary mechanism of UVB damage, and implicate photoreactivation, rather than nucleotide excision, as the main repair process in S. mansoni.     

Host reactions in Biomphalaria glabrata to Schistosoma mansoni miracidia, involving variations in parasite strains, numbers and sequence of exposures

M-line Biomphalaria glabrata snails are susceptible to Puerto Rican (PR-1) strain of Schistosoma mansoni, but are resistant to a St. Lucian (LC-1) strain. 10-R2 B. glabrata snails are resistant to both strains of S. mansoni. When 10-R2 snails were exposed repeatedly to PR-1 S. mansoni miracidia for 5 consecutive days, all of the sporocysts were encapsulated and destroyed by the snails. Thirty-four per cent of sporocysts examined in M-line snails with similar exposures were also degraded. In double concurrent infections of M-line B. glabrata with [³H]leucine-labeled and unlabeled PR-1 and Lc-1 S. mansoni, the incompatible Lc-1 miracidia were selectively attacked and destroyed. This destruction occurred irrespective of the sequence of exposure of the 2 strains of miracidia, and whether or not the miracidia were labeled. Successful superinfection of M-line B. glabrata with homologous S. mansoni miracidia was obtained at least 4 days after the primary exposure to the miracidia.     

Studies on resistance in snails. 5. Tissue reactions to Echinostoma lincloense in naturally resistant Biomphalaria glabrata.

Laboratory-raised juvenile albino Biomphalaria glabrata snails show a wide range of natural resistance to a single infection with 50 or 100 miracidia of Echinostoma lindoense. In the most resistant snails all sporocysts are destroyed in peripheral tissues soon after miracidial penetration. In less resistant snails some sporocysts reach the heart where they are encapsulated. In fully susceptible snails, all sporocysts rapidly migrate to the heart, where they mature and continue to develop. The greater part of our B. glabrata colony consists of snails in which sporocysts reaching the heart will survive, but in which a varying number of sporocysts will be destroyed in the tissues. These snails are usually considered susceptible, as they do become infected. Tissue reactions induced by sporocysts following a single infection in naturally resistant snails are similar to reactions in snails with an acquired resistance. In fully susceptible snails, the amebocyte-producing organ remains small and inactive. It is slightly to moderately stimulated in partially resistant snails in which destruction of sporocysts occurs in the tissues and surviving larvae are found in the ventricle. In snails in which amebocyte aggregates or capsules develop in the ventricle, the organ becomes markedly enlarged. Migration of sporocysts in the snail appears not to be continuous, as periodic rests seem to occur. Migration follows intrusion of the sporocyst through the tissues, induced by bodily distension and contraction, and then proceeds within the arteries against the blood flow, passing from one endothelial attachment site to another, possibly aided by negative pressure during ventricular diastole.     

Pathology and host responses induced by Schistosomatium douthitti in the freshwater snail Lymnaea catascopium.

Most Schitosomatium douthitti miracidia penetrated the esophageal wall of Lymnaea catascopium without provoking amoebocyte encapsulation responses or extensive pathological changes. Amoebocytes frequently attached to developing mother and daughter sporocysts, but did not encapsulate or destroy them. Pressure resulting from extensive growth of mother sporocysts ruptured the transverse membrane of some snails. After releasing daughter sporocysts, mother sporocysts in some snails were destroyed by amoebocytes. Many migrating cercariae became trapped in the tissues of L. catascopium, particularly in the posterior portion of the foot, and were encapsulated and destroyed. Large increases in numbers of amoebocytes in the anterior portion of the lung roof of infected snails were noted, even before cercarial production had been initiated. Atrophy of the digestive gland occurred in infected snails.     

Studies on resistance in snails: A specific tissue reaction to Echinostoma lindoense in Biomphalaria glabrata snails

In juvenile albino Biomphalaria glabrata snails exposed for the first time to Echinostoma lindoense miracidia, and observed to be resistant, the sporocysts migrated to the heart at the same speed as they did in susceptible snails. However, in resistant snails the sporocysts were soon destroyed in the heart by amebocyte clumps. When these snails were then re-exposed to miracidia of the same species of trematode, the sporocysts were quickly destroyed soon after miracidial penetration, chiefly in the head-foot region. This strongly accelerated tissue reaction appears to have been induced by the previous contact with the same parasite. The sensitization of the snail tissues was highly specific: the hosts remained susceptible to Schistosoma mansoni and Paryphostomum segregation (Echinostomatidae), although partial resistance was observed against Echinostoma paraensei and E. liei, which are closely related to E. lindoense.     

Acquired resistance in snails. Induction of resistance to Schistosoma mansoni in Biomphalaria glabrata

Acquired resistance to Schistosoma mansoni PR-I strain has been induced in Biomphalaria glabrata 442132 strain by infecting the snails with irradiated homologous miracidia. Present and previous results support the hypothesis that acquired resistance to trematodes in snails is an enhancement of the host's natural resistance to the parasite.     

Schistosoma mansoni: Splenic lymphocyte responses of mice after initial exposure to highly irradiated cercariae

Inbred $\text{C}\text{57}\text{B}\text{1}\text{6}$ and CBA mice were immunized with ⁶⁰Co-irradiated (50 kR) Schistosoma mansoni cercariae. Based on the percentage reduction from controls in the numbers of adult parasites developing from a challenge cercarial exposure, the level of protection among immunized $\text{C}\text{57}\text{B}\text{1}\text{6}$ mice ranged from 56 to 74%, and among immunized CBA mice from 10 to 27%. In a longitudinal study, parallel in vitro comparisons of mitogen- and antigen-stimulated lymphocyte proliferative responses were performed with spleen cells from immunized and control mice of both strains. In contrast to decreased mitogen reactivity during a chronic, patent infection, immunization with irradiated cercariae resulted in no alteration in PHA and LPS responses in the reactivity of either strain. A vigorous antigen-specific reactivity was noted in the responses of immunized CBA mice. Additionally, a biphasic pattern of responsiveness characterized the CBA responses to antigens of cercarial, adult worm, or schistosomal egg origin. In comparison, there was a greatly diminished reactivity in immunized $\text{C}\text{57}\text{B}\text{1}\text{6}$ mice to the same antigens. Therefore, no obvious correlation existed in this model between the relative magnitude of antigen-specific responses between the two strains and the level of anti-schistosome immunity induced.     

Schistosoma mansoni: Cytotoxicity of hemocytes from susceptible snail hosts for sporocysts in plasma from resistant Biomphalaria glabrata

Sporocysts of Schistosoma mansoni (PR1 strain) survive and grow in Biomphalaria glabrata PR albino strain snails, whereas they are encapsulated and die in B. glabrata 10R2 strain snails. These processes also occur in an in vitro system in which the only living cells are those of sporocysts and snail hemolymph. Hemocytes of the susceptible snail are normally not effective in damaging sporocysts. However, when the encounter occurred in the presence of cell-free plasma from resistant snails, previously impotent hemocytes severely damaged sporocysts in 24 hr. The cytotoxic capacity of resistant strain hemocytes was not altered by plasma from susceptible snails. Furthermore, it was retained even when plasma was replaced by culture medium free of snail components. The nature of the plasma factor(s) which facilitated damage by otherwise impotent hemocytes is discussed, and evidence is evaluated for the hypothesis that snail resistance is dependent upon the specificity of cytophilic factors present both in the plasma and on the hemocyte plasma membranes.     

Schistosoma mansoni: Infectivity and immunizing effects of in vitro derived schistosomula attenuated by X irradiation

Irradiated and nonirradiated in vitro derived schistosomula of Schistosoma mansoni were injected intraperitoneally into mice. Sixteen percent of nonirradiated schistosomula, 8% of those irradiated with 1000 R, and virtually none of those irradiated with 3000 R and above survived in mice for 5 weeks. However, those irradiated with 3000 R survived in small numbers for shorter periods of time. Schistosomula irradiated with 3000 or 6000 R were used to immunize mice against subsequent infection with cercariae. Prior ip injections of schistosomula irradiated with 3000 R resulted in reductions in worm burden after challenge from 5 to 91%; the observed protection was related to the number of inoculations. The subcutaneous route appeared to be less effective. Schistosomula irradiated with 6000 R produced less protection than those irradiated with 3000 R.     

The life history of Sanguinicola klamathensis

The life history of the trematode blood fluke, $\text{Sanguinicola klamathensis}$ was studied using experimentally infected cutthroat trout ($\text{Salmo clarki}$) and by examining wild salmonid populations. This study was carried out at the Hagerman National Fish Hatchery, Idaho, during 1971–1973. Ova, miracidia, sporocysts, cercariae, immature flukes, and adult flukes were measured, described, and photographed. A life cycle for the blood fluke is presented.     

Further characterization of passively transferred resistance to Schistosoma mansoni in the snail intermediate host Biomphalaria glabrata.

A heat-labile plasma factor from genetically resistant 10-R2 Biomphalaria glabrata snails confers passively transferred resistance (PTR) to Schistosoma mansoni when injected into susceptible snails within 24-hr of exposure to miracidia. However, no additional details on PTR have emerged since the initial 1984 report, nor has the plasma resistance factor been characterized. In the present study, new information is provided on the occurrence of resistance factor in plasma of additional types of snails, effect of "priming" resistant plasma donors by prior exposure to miracidia, duration of PTR, molecular weight of resistance factor, and fate of sporocysts in snails with PTR. Susceptible NIH albino snails injected 24 hr prior to exposure to miracidia with individual samples of plasma from a different strain (Salvador B. glabrata) or a different species (B. obstructa) of nonsusceptible snail displayed infection prevalences of 49% or 59% of control levels, respectively, whereas injections of homologous plasma had no effect. PTR was not enhanced by prior exposure of resistant Salvador plasma donors to miracidia. Unexpectedly, PTR induced by injections of Salvador plasma persisted for at least 21 days. The molecular weight of the resistance factor(s) was between 10 and 30 kDa, based on results of centrifugal ultrafiltration. A significantly higher proportion of dead sporocysts occurred in histological sections of tentacles from snails injected with Salvador plasma than in tentacles of snails injected with NIH albino plasma at 7 days postexposure to miracidia. Most dead sporocysts in Salvador plasma-injected snails were undergoing gradual degeneration, rather than rapid, hemocyte-mediated destruction, as occurred in Salvador snails.