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.     

Schistosoma japonicum and Paragonimus ohirai: antagonism between S. japonicum and P. ohirai in Oncomelania nosophora

Antagonistic interactions between Schistosoma japonicum and Paragonimus ohirai were examined in the snail host, Oncomelania nosophora. When P. ohirai-infected snails were exposed to S. japonicum miracidia at intervals of 4 to 18 weeks post-first exposure, only a few snails (0-7%) were found to be superinfected with S. japonicum sporocysts. Sporocysts were fewer in number than those of single infected controls. Mature S. japonicum cercariae were not observed. Furthermore, when the snails were examined at intervals of 14 to 18 weeks post-second exposure, neither sporocysts nor cercariae of S. japonicum were found. On the other hand, when the snails were exposed to miracidia of S. japonicum and P. ohirai simultaneously, they were easily infected with both parasites. At 26 weeks after simultaneous exposure, however, the infection rate of S. japonicum was significantly lower than that of controls. In contrast, when S. japonicum-infected snails were exposed to P. ohirai miracidia, they were superinfected with P. ohirai, although the infection rate was somewhat lower than that of controls. These results indicate the existence of antagonism between S. japonicum and P. ohirai in O. nosophora. Furthermore, P. ohirai was dominant over S. japonicum in the antagonistic interactions in this snail host.     

Miracidia of an Egyptian strain of Schistosoma mansoni differentiate between sympatric snail species

The host-finding behavior of miracidia of 2 strains of Schistosoma mansoni from Egypt and Brazil was studied by recording their responses to snail-conditioned water (SCW) from the Egyptian sympatric snails, Biomphalaria alexandrina, Physa acuta, Lymnaea cailliudi, and Balinus truncatus, as well as from Biomphalaria arabica and Biomphalaria glabrata. Miracidia of the Egyptian strain significantly preferred SCW from their compatible hosts B. alexandrina and B. arabica and showed no or a weak response to SCW from the other sympatric species, whereas miracidia of the Brazilian strain did not differentiate between SCW from different snail species.     

日本血吸虫毛蚴对钉螺的钻穿及在螺体内的分布和移行

采自安徽省池的钉螺每粒感染５０只湖南株日本血吸虫毛后的组织学观察说明：毛蚴钻穿钉螺有从螺鳃部、头足总后有皮以及实质组织（外套膜、触角和阴茎）等三方面途径,其中以前二者尤为重要;毛蚴进入螺鳃丝后直接进入血液循环系统,从头足表皮进入的毛蚴,除了少数在钻穿部位附近滞留外,多数继续向头足部深层的肌肉和窦状组织间隙移行,以前头足窦、直肠和消化道外的组织间隙以及肾脏为主要的移行部位;从外套膜、触角、阴茎等部位     

洞庭湖外睾吸虫新种及其生活史

本文报告洞庭湖区鲶鱼肠道寄生的洞庭湖外睾吸虫Exorchis dongtinghuensis sp.nov(新种)及其全程生活史,其第一中间宿主为湖北钉螺Oncomelania hupensis;第二中间宿主为鲤鱼、鲫鱼和金鱼;终宿主为鲶鱼Parasilurus asotus。作者对各期宿主作了人工感染试验和现场自然感染调查。对其发育过程作了观察比较。     

Incompatibility between miracidia of Schistosoma mansoni and Helisoma duryi occurs at two stages: penetration and intramolluscan establishment

Helisoma spp. snails are not susceptible to infection with miracidia of Schistosoma mansoni because the miracidia do not penetrate them. However, in view of the phylogenetic proximity and histocompatibility between Helisoma spp. and the normal intermediate host, Biomphalaria glabrata , schistosome miracidia conceivably could survive if experimentally introduced into the hemocoel of Helisoma spp. To test this hypothesis, schistosome-susceptible NIH albino B. glabrata, schistosome-resistant Salvador B. glabrata, and Helisoma duryi were injected with miracidia of S. mansoni, and the outcome was followed both by monitoring snails for infection for several weeks and by histological examination at 24 and 48 hr post-injection (PI). Patent infections developed in most NIH albino snails but in none of the Salvador B. glabrata or H. duryi individuals. Histological analysis showed a higher proportion of normal sporocysts in various tissues of NIH albino snails at both time periods relative to Salvador snails, which contained mostly sporocysts undergoing hemocytic encapsulation. In H. duryi , nearly all sporocysts were dead by 48 hr PI.     

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.     

Influence of saccharose on the development of cercariae from Schistosoma mansoni strains BH and SJ.

The development of cercariae from Schistosoma mansoni strains BH and SJ in Biomphalaria glabrata and Biomphalaria tenagophila treated with saccharose was studied. The molluscs were maintained in dechlorinated tap water containing 0.01% saccharose. After one week of treatment with saccharose, B. glabrata and B. tenagophila were exposed to ten S. mansoni miracidia, from BH and SJ strains respectively. Control snails of both species were maintained in dechlorinated tap water without saccharose and exposed to the same number of miracidia. There was no significant difference between the infection rates of snails treated or not with saccharose. However, the two groups of B. glabrata had significantly greater infection rates than the corresponding B. tenagophila groups. Molluscs treated with saccharose had a lower survival rate, with the greatest mortality occurring immediately before and at the beginning of cercariae release. Treatment with saccharose did not result in the release of more cercariae, but larvae from molluscs so treated showed a greater capacity to penetrate mouse skin, which was attributed to the greater energy supply during larval development in the mollusc.     

Introduced Schistosomiasis: Evaluation as a Public Health Hazard

Schistosomiasis was found in many agricultural workers from Yemen who are residing in the San Joaquin Valley, and a study was done to evaluate the public health hazard of this imported disease. If the necessary intermediate hosts are present, a local focus of infection could be established.Numerous Biomphalaria obstructa snails collected in the vicinity of the Avenue 82 irrigation canal near Oasis, Riverside County, showed no evidence of natural schistosome infection. Laboratory-reared offspring of these snails were exposed to miracidia of Schistosoma mansoni originating from Yemen immigrants and to miracidia from a standard laboratory strain of Puerto Rican origin obtained from the National Institutes of Health. All exposures of California B. obstructa were made with a laboratory stock of highly susceptible B. glabrata snails also obtained from NIH as controls. Although miracidia penetrated California snails no evidence of infection was detected whereas the B. glabrata controls showed normal, mature infections with numerous cercariae.There appears little likelihood that B. obstructa can serve as intermediate host for schistosomiasis.     

Resistance of Biomphalaria schrammi of Arcos, Minas Gerais, Brazil, to infection with 2 strains of Schistosoma mansoni

The descendants of planorbid snail Biomphalaria schrammi Crosse, 1864, collected in the region of Arcos, State of Minas Gerais, Brazil, were exposed to miracidia of two strains of Schistosoma mansoni: the "LE" strain from Belo Horizonte, Minas Gerais State and the "SJ" strain from S?o José dos Campos, State of S?o Paulo. Of the 172 snails exposed to miracidia of both strains, none were infected. On the other hand, 100 Biomphalaria glabrata snails of the control group showed infection rates of 88% ("LE" strain) and 40% ("SJ" strain). The mortality rates of B. schrammi and B. glabrata were 40% and 10%, respectively.     

Resistance to desiccation of Biomphalaria glabrata adults infested by various miracidia of Schistosoma mansoni

1200 adult Biomphalaria glabrata were submitted during 6 weeks to anhydrobiosis condition. Some snails were healthy, some were previously infected 3 days or 12 days ago with 8 +/- 2 miracidia of Schistosoma mansoni, others were shedding cercariae. The snails were put on soil or buried into hermetically closed, or ventilated, plastic boxes. There was no survival of snails kept in sealed boxes, or among positive snails, but 44% of control healthy snails and 40.6% of infected (for 3 or 12 days) snails in ventilated boxes were living at the term of the desiccation stage. Survival was better for "on soil" snails than for "buried" snails, but no difference was shown between 3-days and 12-days infection. The surviving desiccated B. glabrata had a lesser death rate and a lesser cercarial production than infected snails kept in water. An inferior production of male cercariae comparatively to female and to "mixed" cercariae was demonstrated by statistical analysis of the cercarial sheddings. In all positive snails, periodic variations of cercarial production was shown, whatever the sex of those cercariae. In addition many pauses of the sheddings were established by the authors.     

The effects of miracidal aging and dilution of snail-conditioned water on responses of miracidia of Megalodiscus temperatus.

Miracidia of Megalodiscus temperatus from newly hatched until 10 hr old were tested for their ability to react to Helisoma trivolvis snail-conditioned water (SCW) by contact with return (CR) to agar blocks and by percentage of miracidia reacting to a point inoculation of SCW as determined by a photographic time exposure method. CR to agar blocks containing 1:50 SCW was greatest during the first 6 hr after hatching but declined thereafter. The reaction during the first hour to a point inoculation was lower than during the 2nd and 3rd hr. Results were variable from 4 to 10 hr after hatching with the lowest response recorded from 9 to 10 hr. Miracidial responses to dilutions of SCW were assessed by the same two methods. CR to agar blocks containing decreasing concentrations of SCW declined until at a dilution of 1:500 CR was only slightly above the controls. On the other hand, miracidial reactions to point inoculations of SCW as determined by the photographic method were still apparent at a dilution of 1:25,000, when 12% of the miracidia tested reacted. Thus, the photographic time exposure method gives a sensitive means for detecting altered miracidial behavior to various intrinsic and extrinsic factors.     

Effect of miracidial dose on adoptively transferred resistance to Schistosoma mansoni in the snail intermediate host, Biomphalaria glabrata

Adoptively transferred resistance to Schistosoma mansoni in the snail intermediate host Biomphalaria glabrata was measured as a function of miracidial challenge dose. Schistosome-susceptible snails implanted with the amebocyte-producing organ (APO) from resistant donors showed 29 and 39% prevalences of infection after challenge with 5 and 10 miracidia, respectively, but 68-83% prevalences when exposed to 25-200 miracidia. Prevalences in control (untampered) susceptible snails ranged from 97 to 100% at the different miracidial doses. Higher infection prevalences at elevated doses suggest that a range of transferred resistance occurs and possibly that low levels of APO-derived plasma factors or hemocytes in some recipients can be overwhelmed by larger numbers of parasites.     

Effect of floods on the transmission of schistosomiasis in the Yangtze River valley, People's Republic of China

The aim of the present study was to assess the effect of floods on the transmission of schistosomiasis in the Yangtze River valley, People's Republic of China. Retrospective analyses of malacologic, clinical and epidemiologic data, covering a 22-year period, were carried out to elucidate the dispersal patterns of intermediate host snails (Oncomelania hupensis), and acute and chronic infections with Schistosoma japonicum in humans in relation to floods. Potential O. hupensis habitats in years with floods were 2.6-2.7 times larger than in years when water levels were normal. Both the density and infection rate of O. hupensis dropped in the first two years after a flood, but significantly increased in the third year. The number of acute cases with schistosomiasis japonica was markedly higher in years characterized by floods; on average, 2.8 times more cases were observed when compared to years that the Yangtze River had normal water levels. In view of our findings, emergency responses are warranted as soon as possible after the occurrence of a flood in order to avoid or mitigate the reemergence and spread of human schistosomiasis in the People's Republic of China.     

Schistosoma mansoni modulation of phagocytosis in Biomphalaria glabrata

Both short-term (3 hr) exposure of Biomphalaria glabrata snails (M-line and 13-16-R1) to Schistosoma mansoni (PR1) miracidia and in vitro incubation of parasite sporocysts with host hemolymph components altered host phagocytic ability. Hemocytes obtained from susceptible (M-line) snails that had been exposed to parasite miracidia for 3 hr showed reduced levels of phagocytosis of yeast cells in vitro compared to hemocytes from unexposed individuals. Incubation of whole hemolymph with sporocysts in vitro also reduced yeast phagocytosis in this susceptible strain. In contrast, resistant (13-16-R1) hemocytes showed increased levels of yeast phagocytosis after in vitro incubation with the parasite, and the opsonic properties of 13-16-R1 plasma were greater after exposure of snails to miracidia. These strain-specific effects of S. mansoni on host hemocyte phagocytosis and plasma opsonization were seen only when both plasma and hemocytes were present at the time of exposure to the parasite.     

Resistance of Biomphalaria peregrina of Santa Rita do Sapucaí, Minas Gerais, Brazil to infection with 3 strains of Schistosoma mansoni

The descendants of the planorbid snail Biomphalaria peregrina, collected in the region of Santa Rita do Sapucaí, Minas Gerais, Brazil, were exposed to miracidia of three strains of Schistosoma mansoni: "LE" strain from Belo Horizonte, State of Minas Gerais; "SJ", strain from S?o José dos Campos, State of S?o Paulo and "AL" strain from State of Alagoas. Of 300 snails exposed to miracidia of the three strains, none was infected. On the other hand, 300 Biomphalaria glabrata of the control groups showed infection rates of 61.1 to 95.3% with the three strains. The mortality rates of B. peregrina and B. glabrata were 20% and 28%, respectively.     

Rescue of sporocysts of Schistosoma mansoni in nonsusceptible Biomphalaria by head-foot transplantation into susceptible snails

To measure the longevity of sporocysts of Schistosoma mansoni in nonsusceptible snails (13-16-R1 and Salvador strains of Biomphalaria glabrata, and Biomphalaria obstructa), the head-foot (HF) of miracidia-exposed snails was transplanted into the hemocoel of a susceptible NIH albino recipient at 1-36 days postexposure (DPE). Recipient snails which were not exposed to miracidia then were monitored for infection transferred by the implant, and infection prevalences in recipients of HF transplants from nonsusceptible donors were compared to those in snails implanted with an HF from NIH albino donors. Transplants from NIH albino snails between 1 to 15 DPE infected 98% of recipients. Similarly, at 1 DPE, 69-85% of transplants from nonsusceptible snails contained viable sporocysts, as shown by resulting patent infections in the recipients. Recipient infection prevalence, and presumably numbers of transplants containing viable sporocysts, declined as a function of DPE, and by 5-9 DPE this decrease was significant for all 3 types of nonsusceptible donors. However, viable sporocysts still occurred in B. obstructa and 13-16-R1 B. glabrata as late as 19 and 20 DPE, respectively, and in Salvador B. glabrata as late as 33 DPE. Thus, sporocysts persist in nonsusceptible snails considerably longer than suggested by results of previous histological studies.     

Comparative studies of the defense mechanism against Schistosoma japonicum of schistosome-susceptible and -resistant Oncomelania nosophora

The amphibious snail Oncomelania nosophora is an intermediate host of Schistosoma japonicum. Previously we reported that there are two strains of the snail, one resistant and one susceptible to a Mindoro, the Philippines, strain of S. japonicum. The resistant snails were collected from Nirasaki and susceptible snails from Kisarazu, Japan. To determine early cellular responses in the two snail strains, we examined histologic alterations in the snails for up to 18 h after the initial exposure to miracidia. In both strains, the penetrating miracidia were distributed in the foot, mantle, gills, heart, stomach, and kidney, and the mean number of penetrating miracidia was similar in both strains. After penetration, snail hemocytes migrated toward the larvae, and by 12 h after exposure, substantial numbers of penetrated larvae were surrounded and encapsulated by hemocytes. The percentage of larvae encapsulated by hemocytes during 12-18 h after the exposure was significantly higher in the resistant Nirasaki strain (60.9+/-19.8%) than in the susceptible Kisarazu strain (42.3+/-15.0%). In a few snails of the Nirasaki strain, all the larvae found were encapsulated by hemocytes. The differences in hemocyte responses between the two strains may explain the susceptibility of the snails to schistosome larvae.     

Transplantation of Schistosoma japonicum daughter sporocysts in Oncomelania hupensis

Schistosoma japonicum daughter sporocysts obtained from infected Oncomelania hupensis hupensis were successfully transplanted to parasite-free O. hupensis hupensis. Survival and infection rates of recipient snails were 80% and 75% respectively. Intramolluscan development of transplanted daughter sporocysts in recipient snails appears to proceed in a similar manner as those reported for transplanted S. mansoni and S. haematobium in their respective snail intermediate hosts. Complete colonization of the digestive gland of recipient snails by sporocysts was observed 80 days after transplantation. Cercarial production during a 10-day observation from recipient snails was characterized by periods of high and low and irregular daily emissions. The average daily cercarial production was 150 per snail. Cercariae produced by recipient snails were infective to mice. Of those cercariae exposed to mice, approximately 30% developed to adult schistosomes. These results have definitive utility in the maintenance of S. japonicum in the laboratory.     

Factors affecting adoptive transfer of resistance to Schistosoma mansoni in the snail intermediate host, Biomphalaria glabrata

We examined potential variables affecting adoptive transfer of resistance to Schistosoma mansoni in Biomphalaria glabrata implanted with amebocyte-producing organs (APOs) from resistant snails. Transplants of 7 tissues other than the APO (heart, kidney, mantle, albumin gland, brain, digestive gland, and gonad) did not transfer resistance, suggesting a unique property of this structure. Only APOs from donors previously exposed to miracidia transferred resistance, although whether this is evidence for a priming effect or merely the elimination of susceptible donors is not known. Variability in the donor and in the implant itself apparently was unimportant, inasmuch as implants from small or large snails or from 2 separate donors all conferred similar levels of resistance. Recipients of APOs from 2 additional resistant strains of B. glabrata, 10-R2 and Salvador, also displayed resistance. However, no resistance was transferred by APOs from schistosome-refractory B. obstructa. Histological examination of implants removed from recipients that either did or did not show transferred resistance revealed no differences in mitotic activity. Furthermore, implanted APOs from B. obstructa displayed no mitotic activity. Finally, reexposure of snails with transferred resistance to a large dose of miracidia caused infection in 70%, suggesting that either transferred resistance is transitory or it can be overwhelmed.