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G Webbe

Publications and source records attributed to G Webbe.

33 records · Page 2Linked to original sources
PubMed1976

A comparative study of the death of schistosomula of Schistosoma haematobium and Schistosoma mansoni in the skin of mice and hamsters.

This study shows that some cercariae of S. haematobium and S. mansoni die during penetration of mouse or hamster skin. Approximately 30-38% of cercariae of both species die in mouse skin and 14-16% die in hamster skin. The greater number of cercariae which die in the skin of mice seems to account for the higher yield of adult worms recovered in hamsters. Adult worm recoveries from animals infected with S. haematobium were, however, only about half the worm recoveries from hosts infected with S. mansoni.

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PubMed1976

Cross-immunity to Schistosoma mansoni and S. haematobium in the hamster.

Hamsters (WO strain) with a primary infection of Schistosoma mansoni or S. haematobium rapidly developed immunity to homologous challenge judged by the lung recovery assay. Immunity was detected at 4-5 weeks and reached a plateau 6 weeks after infection. Using this information, hamsters with an 8-week primary infection with S. mansoni or S. haematobium were tested for resistance to homologous reinfection and resistance to a challenge with the other species of schistosome. Primary infection with S. mansoni or S. haematobium conferred a high level of immunity to reinfection with either species of schistosome judged by the perfusion assay, involving recovery of adult worms 6-10 weeks following challenge. Estimation of the level of immunity with the lung recovery assay, 5 days after challenge, indicated that immunity due to a primary infection with S. mansoni acted at or before migration of the challenge through the lungs but immunity stimulated by a primary S. haematobium infection was only partially effective at the lung stage and substantial destruction of challenging organisms occurred at a later stage of development. Antibodies in immune sera of hamsters with a primary S. mansoni or or S. haematobium infection were shown to bind to common antigens on the surface of young schistosomula of either species by u.v. microscopy using as detecting agent a fluorescein-labelled rabbit antiserum directed against hamster globulins.

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PubMed1976

Culture of Schistosoma haematobium in vivo and in vitro.

The maximum rate of development of Schistosoma haematobium in the hamster was determined by examination of the most advanced worms recovered at short intervals throughout the course of development. In culture S. haematobium developed at the same rate as in the hamster up to day 31 when pairing first occurs and male worms produce some spermatozoa. In vitro males formed some spermatozoa but pairing did not take place and, probably for this reason, females did not complete sexual maturation as occurs in the host between days 57-65. Somatic growth continued in vitro and at 70 days male worms had achieved almost the same length as in the hamster at this time. The culture medium, previously used for S. mansoni, consisted of equal volumes of serum and Earle's balanced saline with a final concentration of 0.25% lactalbumin hydrolysate, 100 units/ml penicillin, 100 mug/ml streptomycin and 1% rbc. The best culture results were obtained with one particular human serum; seven other human sera gave a wide range of growth support. The samples of baboon, rhesus monkey or foetal calf sera tested provided little or no growth support but prolonged survival was possible in all the sera.

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PubMed1976

Acquired resistance to Schistosoma haematobium in the baboon (Papio anubis) after cercarial exposure and adult worm transplantation.

Observations were made on the development of acquired resistance to Schistosoma haematobium in the baboon following immunization with cercariae by the percutaneous route and by the transplantation of adult worms into the mesenteric veins. In the first experiment six baboons were immunized with 1000 S. haematobium cercariae given percutaneously. They were challenged with 10 000 cercariae given 73 weeks later and the results were compared with a similar infection in non-immunized animals. The results showed that the baboon can develop a strong resistance to reinfection with S. haematobium. The manifestations of the immunity were (i) the absence of any increase in egg output after challenge (ii) the substantially lower level of adult worms and eggs in the tissues of the immunized baboons compared with the challenge control animals (iii) a reduction in the egg laying capacity of the residual worms and (iv) the virtual absence of gross pathology and the mild lesions seen in the tissue sections of all the immunized animals. The depression in egg laying of the worms was confirmed by transplanting them into non-immune baboons. This experiment indicated that the non-egg-laying worms in the immune baboons were not irreversibly damaged since they survived, some even migrating to the vesical and ureteric vessels, and egg-laying was rapidly resumed after transplantation. A further experiment was designed to see if a similar degree of immunity could be produced by an adult worm infection without previous exposure to cercariae or schistosomula. The immunization dose consisted of 50-100 S. haematobium worm pairs which were transplanted into the mesenteric veins of each of six baboons and the animals were challenged percutaneously with 7000 cercariae 35-55 weeks later. There was little difference in the worm burdens of the immunized and control animals but the worms in the immunized baboons produced fewer eggs and the pathology seen in these animals was much milder than in the challenge control animals suggesting that some degree of resistance to reinfection was produced by the transplanted worms.

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PubMed1975

The effect of sublethal concentrations of the molluscicide niclosamide on the infectivity of Schistosoma mansoni cercariae.

Experiments were conducted to assess the effect of sublethal concentrations of niclosamide on the infectivity of Schistosoma mansoni cercariae. Exposure of cercariae to 0.02 mg/l and 0.05 mg/l of niclosamide, respectively, for only two hours increased their mortality during penetration of mammalian host skin. The observed increase in mortality in the skin resulted in a consequent reduction of adult worm recovery from the liver and mesenteric veins of animals infected with the treated cercariae.

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PubMedDate not supplied

Cross protection between a laboratory passaged Chinese strain of Schistosoma japonicum and field isolates of S. japonicum from China.

Our laboratory strain of Schistosoma japonicum has been isolated for 51 years, but is comparable to the indigenous Chinese parasite in terms of its infectivity to both the intermediate and definitive hosts. Vaccination with our strain protects mice against challenge with wild isolates of S. japonicum from China. Thus any defined antigen vaccine developed using our laboratory strain would be expected to protect against S. japonicum in the field in China.

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PubMedDate not supplied

Progress in the control of schistosomiasis in Egypt 1985-1988.

Continuing epidemiological evaluation of schistosomiasis intervention measures applied in Middle and Upper Egypt since 1985 indicate that a large measure of control of Schistosoma haematobium has been achieved in relation to both prevalence and intensity of the infection and incidence of new infections. Transmission control has, however, been inadequate in many areas, since numerous re-infections occurred in treated schoolchildren. Variable compliance rates in the chemotherapy delivery system were probably, in part, an important contributory factor, and short-comings of the selective and/or focal mollusciciding strategy were also probably responsible for many new cases and re-infections. Chemotherapy delivery has now been improved following the introduction of single dose treatments with praziquantel and it is expected that there will be an increased demand for treatment following the introduction of a new information-education-communication campaign. In communities with geometric mean egg-output of less than 50 per 10 ml of urine, acceptable control of the potential for development of schistosomal disease can be expected. It is concluded, therefore, that the future maintenance control strategy in this project area may call for more frequent chemotherapy treatments in identified foci of high prevalence and intensity, with complementary focal mollusciciding and/or targeted treatment of schoolchildren, in order to prevent the serious consequences of infection. In 1988 the annual cost of schistosomiasis control measures per person throughout the project area (2 million irrigated feddans (c .800,000 hectares] containing 12 million people) was 0.5 Egyptian pounds (LE) (US$ 0.20), representing 5.2% of the annual expenditure per person in Egypt (LE 9.6) for all health services.

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PubMedDate not supplied

Immunization of baboons with attenuated schistosomula of Schistosoma haematobium: levels of protection induced by immunization with larvae irradiated with 20 and 60 krad.

We have shown previously that baboons (Papio anubis) develop high levels (greater than 80%) of protection against challenge infection following immunization with Schistosoma haematobium cercariae irradiated with 20 krad. In the present study baboons were immunized with schistosomula irradiated with either 20 krad or 60 krad, with variations in the timing and number of larvae comprising each vaccination. Baboons immunized 2 or 3 times with schistosomula irradiated with 20 krad were significantly more protected (85-90%) against challenge infection than baboons similarly immunized with larvae receiving 60 krad (56-50% protection). Baboons immunized with schistosomula irradiated with 20 krad were better protected against challenge infection at 8 weeks after immunization than at 28 weeks after immunization. Protection was manifest by a reduction in worm numbers, tissue and excreta egg counts, gross pathology and, to a lesser extent, by stability of body weight and haematological indices following challenge. Enzyme-linked immunosorbent assay (ELISA) results of selected baboon sera showed few differences related to irradiation dose alone, but titres were higher in baboons receiving booster immunizations, and there was a significant correlation between titres immediately preceding challenge and the degree of resistance. Examination of responses to individual schistosomular surface antigens by immunoprecipitation and sodium dodecyl sulphate-polyacrylamide gel electrophoresis showed no correlation between the pattern of antigens recognized and resistance status. As with the ELISA assay, an anamnestic response was detected after vaccination, while the amount of antibody present declined markedly with increasing time after individual immunizations.

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