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Biomedical subjects

G Webbe

Publications and source records attributed to G Webbe.

At least 19 recordsLinked to original sources
PubMed1990

Antibody is responsible for the passive transfer of immunity to mice from rabbits, rats or mice vaccinated with attenuated Schistosoma japonicum cercariae.

Sera from rabbits, rats and mice multiply-vaccinated with attenuated cercariae of Schistosoma japonicum conferred high levels of resistance against challenge to naive recipient mice (up to 97, 64 and 60% respectively). Vaccinated rabbit and rat sera were given before challenge and vaccinated mouse serum 5 days after challenge. To show that the protective factors in these sera were antibodies, vaccinated rabbit and mouse sera were fractionated by protein A-Sepharose and the fractions precipitated by 50% ammonium sulphate. The protein A-Sepharose binding or non-binding fractions in vaccinated rabbit serum transferred approximately equal levels of significant resistance to mice, suggesting that both the IgG and non-IgG components of vaccinated rabbit serum are protective. The major part of the protective activity in vaccinated mouse serum was transferred to recipients by the protein A-Sepharose binding fraction, i.e. the IgG antibodies. Heat inactivation of sera at 56 degrees C for 3 h affected the protective capacity of vaccinated rat sera, but not that of vaccinated rabbit or mouse sera.

Animals↗
PubMed1989

Pathology resulting from the administration of a live attenuated anti-Schistosoma haematobium vaccine in baboons.

Baboons (Papio anubis) were injected in the leg muscle with 18,000 20 Krad irradiated schistosomula of Schistosoma haematobium. Four protocols were followed: single, primary injection; single injection into animals primed by patent S. haematobium infection; secondary vaccine injection following an earlier injection; and single injection following praziquantel treatment of infected animals. Injection of the putative vaccine elicited localized mixed inflammatory infiltration at the site of injection which was both intense and prolonged. Three grades of tissue reaction were seen: the relatively mild primary response; the response in infected animals which had enhanced tissue eosinophilia; and the response in animals primed by prior injection and drug-treated prior infection. The latter 2 showed intensification of eosinophilia, stellate abscesses in the lesion centers, and perischistosomular Hoeppli precipitates. Intramuscular lesions peaked at 14 days for the primary response and at 7 days for all secondary responses. Traces of the milder lesions persisted beyond 4 weeks; more severe reactions healed more rapidly. Some schistosomula survived for 14 days in the milder reactions. A few larvae were deposited in the skin by backflushing of the injectate which produced local inflammation. Compared to mice, live schistosome vaccines injected into baboons elicited greater local inflammation; however, while evidence suggested that sporadic vaccine schistosomula did reach the lymphatic nodes draining the injection sites, no systemic lesions were found and the injection sites healed in approximately 5-6 weeks without permanent damage.

Animals↗
PubMed1979

Control of schistosomiasis: report of a workshop.

Nineteen scientists, field workers, and representatives of funding agencies active in schistosomiasis research and control met in Bellagio, Italy in October 1977 to attempt to evaluate the effectiveness of current control methods and what might be accomplished with available technology. The deliberations included summaries of knowledge on the biology, transmission, and control of schistosomiasis and assessment of major control programs and methodologies. The groups concluded that in the major endemic areas considerable gains in control of schistosomiasis could be made with current technology. However, maintenance of control in most countries, and establishment of serious control programs in countries in which schistosomiasis is a less severe public health problem, would require development of less expensive modalities which would need little monitoring and possibly have benefits extending beyond schistosomiasis control.

Agriculture↗
PubMed1976

Immunisation of baboons against Schistosoma mansoni using irradiated S. mansoni cercariae and schistosomula and non-irradiated S. rodhaini cercariae.

In an attempt to develop a non-pathogenic procedure for immunising baboons against S. mansoni, groups of five baboons were exposed to three doses of 5000 6 Kr-irradiated S. mansoni cercariae or to similar numbers of normal S. rodhaini cercariae and challenged at week 15 with 500 normal S. mansoni cercariae. Faecal egg counts, worm and tissue egg counts, and histopathological examination, showed that neither of the immunising schedules had produced significant protection. In the second experiment baboons were injected by the intramuscular route with 31000 schistosomula of S. mansoni in three doses and the irradiation dose was reduced to near the minimum required for worm sterilisation (2-1--2-4 Kr). Challenge with 3500 normal cercariae of S. mansoni 21 weeks after the first immunising dose again showed no significant protection, although reductions of 20--30% were found in egg and worm counts resulting from the challenge. These results indicate that it may be difficult to develop an effective live vaccine for S. mansoni unless the antigenicity of the immunising larvae can be greatly increased.

Animals↗
PubMed1976

Immunisation of sheep against Schistosoma mattheei using either irradiated cercariae or irradiated schistosomula.

Irradiated cercariae, irradiated schistosomula, or heterologous infections were used to vaccinate sheep against Schistosoma mattheei infection. In the first experiment four doses of 10(4) S. mattheei cercariae irradiated at 6Kr were administered to sheep by percutaneous infection at 4 week intervals. This induced a 74% reduction in a challenge infection compared to control sheep while only 13% protection was achieved in a third group of sheep immunised with normal cercariae of the heterologous parasite S. mansoni. No significant differences were seen in histopathology of the liver of any of the sheep but the pathological changes were more severe in the large and small intestines of sheep vaccinated with the heterologous parasite. In the second experiment with irradiated cercariae only one or two immunising exposures were used. The degree of protection in the adult worm load (9-11%) was not significant and no significant differences were noticed in the pathology of the vaccinated and control animals. In the third experiment four doses of irradiated organisms were used to vaccinate five groups of sheep: 3Kr or 6Kr cercariae were administered by percutaneous infection; 6Kr skin-transformed schistosomula were administered by intra muscular injection; the same 6Kr skin-transformed schistosomula were given by intravenous injection and 6Kr syringe transformed schistosomula were administered by intramuscular injection. The degree of protection (determined as the reduction in worm burden) achieved by these different procedures was respectively 72%, 61%, 77%, 56% and 78%. These results indicate the possibility of making a live vaccine against ovine schistosomiasis and show that effective immunisation is not dependent on the presence of a mature worm infection or on cercarial penetration of the skin by the immunising infection.

Animals↗
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.

Animals↗
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.

Animals↗
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.

Animals↗
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.

Animals↗
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.

Animals↗