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The sensory system of two species of cercariae of the genus Cryptocotyle, C. concavum and C. lingua, is described and differences are indicated in the location of sensillae of both species which make possible the clear differentiation of both species.
The sensory apparatus of cercariae of two species of trematodes (A. cobitidis and A. minor) is described. The species differ both morphologically and biologically. The only common feature in the sensory apparatus of the above species is the topography of sensillae in the posterior half of the lateral complex of the caudal trunk and of the furcal complex.
Though it is presently admitted that Schistosoma intercalatum is a well individualized species, detailed studies of superficial argentophilic structures of the miracidium and chaetotaxy of the cercaria do not allow these larval stages to be distinguished from those of S. bovis. Therefore this emphasizes the close relationship between the two parasites.
The AA. have studied in this research, the rôle explicated in vitro from the lipids contained in a man's skin, in a rat of the Wistar experimental group and in a mouse of the Swiss one. They have seen that some lipids fractions, as triglycerides, waxes and squalenes explicate an action that favours the penetration of the cercariae in vitro on a plate of agar and that such an action is due to the unsaturation in the above said fractions of sebaceous origin. On the contrary the lipids of skin origin as sterols and their esters inhibit the penetration.
Lethal effects of some washing powders, commonly used by local people in Cameroon, on Schistosoma mansoni cercariae have been investigated. Their specific toxicity and the influence of the water hardness on the toxicity of these compounds have been tested and standardized. The role of a local behaviour factor controlling schistosomiasis transmission in water contact sites is emphasized.
The effects of cercarial concentration and length of exposure on the infection of mice by Schistosoma japonicum and S. mekongi were studied under laboratory conditions. For all cercarial concentrations of 10, 20 and 30, mice exposed for 1 min acquired little or no infection. Total worm recovery tended to rise with an increase either in cercarial concentration or exposure time. The highest infection rate and worm burden were obtained in mice exposed for 64 min to 30 cercariae per mouse. The present investigation suggested that exposures of 1 min or less carried little risk of infection at low cercarial concentration. There was a greater risk of infection in prolonged exposure to low cercarial concentration. Prolonged exposures to high cercarial concentration carried the greatest risk of high infection rate and worm burden.
The antibody responses of patients infected with S. haematobium or S. mansoni were investigated in an indirect hemagglutination test (IHA) and an enzyme linked immunosorbent assay (ELISA) using crude extracts of cercariae and adult worms of S. haematobium and S. mansoni, and of adult worms of S. japonicum. Patients were Africans from endemic areas, as well as Europeans who had acquired their infection relatively recently. Although the IHA showed a similar pattern of antibody responses as the ELISA it was less sensitive to assess recently acquired infections. Of special interest, antibodies found in patients with schistosomiasis mansoni cross-reacted strongly with antigens extracted from adult S. haematobium and S. japonicum. In contrast, sera of patients with schistosomiasis haematobium reacted significantly better with the homologous antigen than with heterologous antigens. In the ELISA the ratio of the absorption values of anticercarial antibodies to antiworm antibodies could be used to discriminate chronic from recent infections.
Changes in the surface antigenicity and susceptibility to in vitro killing during development of schistosomula of Schistosoma mansoni were studied using serum from chronically infected mice (CIS) and from mice vaccinated with highly irradiated (20 krad) cercariae (VS). Binding of these sera was quantitated by counting the number of P388D1 cells (a transformed, macrophage-like cell of mouse origin, bearing Fc receptors for IgG) binding to the parasite surface. Compared with schistosomula derived in vitro by mechanical transformation (MS), schistosomula recovered 3 hr after skin penetration in vitro (SS) showed a significant loss in surface binding of CIS. Schistosomula recovered 3 hr after skin penetration in vivo (SRS) showed even less binding, and this trend continued such that parasites recovered from the lungs 5 days after infection (LS) showed only minimal binding, and 10-day-old worms from the portal system showed no significant binding. In contrast, VS, which bound significantly less well to MS than CIS, showed enhanced binding to SS, and in the face of their declining antigenicity with respect to CIS, 3- to 24-hr SRS maintained this raised level of antigenicity. Although there appeared to be a decline in binding of VS thereafter, LS remained antigenic, still binding as many cells as MS did despite the fact that they also expressed host antigens detected using antisera raised against mouse RBC. In spite of this persistence of VS binding up to the lung stage, resistance to eosinophil-mediated killing in vitro had developed by 48 hr post-infection, and LS were totally resistant to both eosinophil- and C-mediated killing.
The release of Schistosoma japonicum cercariae from Leytean Oncomelania quadrasi snails was observed under laboratory conditions. Two patterns of emergence were noted. The initial, nonperiodic emergence occurred immediately after submerging the snails in water and was followed by a periodic, diurnal emergence which peaked in the afternoon. The daily cercarial output of the periodic emergence appeared to be affected by exogenous light intensity. Furthermore, there was a cessation or reduction in cercarial output every 3rd or 4th day.
Infections with Himasthla quissentensis were obtained per cloaca in the domestic chick using cercariae. Worms showed a preference for the ileum where they grew and developed to maturity at a rate comparable to those raised in the gull (Stunkard, 1938). Those from the bursa of Fabricius showed relatively little growth and exhibited gonadal atrophy in some instances.
The life span and the pathogenicity of amphistomes developing from Cercariae indicae XXVI (Paramphistomum epicilitum) were considerably reduced when the metacercariae were gamma-irradiated at 2 krad or 3 krad. The higher irradiation dose resulted in the complete absence of the flukes in infected animals. Single vaccination of lambs and kids with 3000 metacercariae irradiated at 2 krad or 3 krad stimulated a significant degree of resistance against challenge with 5000 non-irradiated metacercariae. The resistance was more pronounced in the group vaccinated with metacercariae irradiated at 3 krad.
The "cercarian chaetotaxic index" from the human strain of Schistosoma mansoni from West Africa is conspicuously modified during the third transmission Biomphalaria pfeifferi-white mouse only. This might be the explanation why Planorbs collected in Guadeloupe discharge slightly different cercariae whether they come from stations where the infestation is predominantly from human origin or from stations where the infestation is predominantly from murine origin. On the contrary, the "Grand Etang" station is significatively different from all the others and seems to be exclusively murine transmitted.
The tegumental changes of Schistosoma japonicum cercaria were initiated when introduced into NCTC 109 containing antibiotics for axenizing. In some regions the tegument was covered with a penta- or heptalaminate membrane, and the surface coat changed into an electron-dense, amorphous material. Large vacuoles limited by a multilaminate membrane were evident in the tegumental cytoplasm, and some appeared to join or open to the tegument. After 4 h incubation in NCTC 109 containing 50% fresh rabbit serum, the outer tegumental membrane of schistosomulum became heptalaminate. The amorphous material was still present on the surface of the tegument. Within 72 h the tegument was covered with a heptalaminate membrane over a greater part of the body, and the amorphous material was very reduced. Large vacuoles in the tegument disappeared and tegumental folds developed in some regions. No amorphous material existed on the surface of 10-day schistosomulum and the outer membrane of the tegument was heptalaminate in almost all regions of the body.
When rabbits infected with 48-52 Schistosoma japonicum cercariae once every wk for 6 times or every other day for 5 times were treated ig with artemether (Art) 10 or 15 mg.kg-1 on d7 after the first infection, followed by the repeated administration of the same dose once every 1-2 wk, a promising effect was seen in the groups treated with Art at higher dose. In another group of rabbits with the same drug administration regimens of praziquantel (Pra) were also used in early treatment, but the initial dose was given on d21 after the first infection. The results showed that Pra given at 40 mg.kg-1 in each administration was more promising than the lower dose of 30 mg.kg-1 especially in group treated at 2 wk intervals. Further study indicated that the presence of adult schistosomes in rabbits increased the effect of Pra not only on 21-day-old schistosomule, but also on 14-day-old schistosomules. The results suggest that Art and Pra could be used in field trial for controlling acute schistosomiasis and decreasing the intensity of schistosomal infection.
Following a single percutaneous vaccination with optimally irradiated cercariae of Schistosoma mansoni, C57BL/6 mice mount a T-helper type-1 (Th1) lymphocyte-dominant immune response and are highly resistant to challenge infection. In this study, we show that, besides interferon-gamma (IFN-gamma), lymph node (LN) cells draining the site of vaccination produce significant amounts of interleukin (IL)-4 and IL-10 in culture with parasite antigen. After a challenge infection at the original site of vaccination, these LN cells did not generate an anamnestic Th1 response. Paradosically, IFN-gamma production and cell proliferation were profoundly down-regulated, whereas IL-4 production was enhanced and occurred earlier than in challenge control cultures. When challenge was applied to a site remote from vaccination, IFN-gamma down-regulation was less evident, but the IL-4 response was consistently enhanced. Neutralization of IL-10 in vitro restored IFN-gamma production by LN cells, whilst IL-4 levels were reduced. These data indicate that down-regulation of IFN-gamma is controlled by IL-10 and/or IL-4. Mice showing down-regulated Th1 responses in the LN after S. mansoni challenge infection did not have a reduced ability to eliminate challenge parasites, indicating that the post-vaccination Th1 response had already armed the lungs with effector T cells before administration of challenge parasites. The observed phenomena of down-regulated Th1 and enhanced Th2 responses may be of relevance to other systems involving multiple infections or vaccination/boosting. Repeated applications to percutaneous sites having common lymphatic drainage would be expected to favour Th2 responses. Alternatively, in order to induce Th1-dominant responses and avoid unwanted IL-4/IL-10 induction, the use of remote sites is indicated.
The present paper describes the ultrastructure of the surface topography, head organ, tegument, musculature, glandular system, primary alimentary tract and flame cells of the Chinese mainland strain of Schistosoma japonicum cercaria, as visualized with both scanning and transmission electron microscopes. The results not only illustrate the morphological features of the cercarial surface and its internal structure reflecting an adaptation to the aqueous habitat but also reveal the correlation between the morphological structure and physiological function.
When rabbits infected with Schistosoma japonicum cercariae for 7 d were treated ig with artemether (Art) 30 mg.kg-1, and repeated at 1-wk intervals (i.e. on d 14, 21, 28 after infection) for 4 times, dead worms were found in the liver sections, but no egg or egg granuloma was detected. In infected rabbits treated repeatedly with the above-mentioned dosage of Art at 2-wk intervals (i.e. on d 21, 35, 49) after the first dosing on d 7 after infection, few eggs and egg granulomas were seen occasionally. In another experiment, praziquantel (Pra) 40 mg.kg-1 was given ig to rabbits on d 21 after infection and the same dosage was administered repeatedly at 1- or 2-wk intervals for 2 times, the numbers of eggs and egg granulomas detected in the liver sections of these 2 groups were much less as compared with the control. In the latter group treated at 2-wk intervals, only degenerated eggs and egg granulomas were detected occasionally in the liver sections. The results indicate that if Art or Pra was given to rabbits in the early stage after infection, no apparent or only slight damage of the liver induced by the eggs was seen due to the fact that most or even all of the female worms were killed.
Cercarial sex determination protocol which utilizes nonradioactive nucleic acid labelling with digoxigenin (DIG)-11-dUTR, offers a rapid "clean" identification of the sex of Schistosoma mansoni cercaria. DIG labelled pW1-DNA (plasmid female-specific genomic DNA clone--W1) hybridized with the native cercarial DNA, and hybridization signals are visualized with Lumigen PPD. Results obtained are comparable with those obtained with the 32P labelled pW1.