Showing papers on "Schistosoma haematobium published in 1973"

Egg output stability and the epidemiology of Schistosoma haematobium. Part II. An analysis of the epidemiology of endemic S. haematobium

Abstract: On the basis of observations of school children described in Part I, a model for the infective process of S. haematobium in man in the Misungwi area of Tanzania is put forward. On the basis of steady challenge by cercariae, effective concomitant immunity, exponential death of worm pairs, the observed variance of egg output at age 10, and constant ranking by infection level in early life, the behaviour of egg output patterns with age in the community is predicted. Expected curves of output are compared with those observed in cross-sectional survey of over 4,000 people at Misungwi. Agreement is close. This provides additional evidence for the occurrence of concomitant immunity to S. haematobium in man and suggests that immunity cannot be disregarded in epidemiological models of the infection. It is suggested that there are 3 phases in an age-cohort's experience of endemic infection: acquisition and increase of infection, a phase of decreasing worm load combined with concomitant immunity, and a steady state phase, with loss of immunity and reinfection balancing, in later life. The need for better data on the nature of human immunity to schistosomiasis becomes apparent.

Acquired resistance to Schistosoma haematobium in the baboon (Papio anubis)

Abstract: 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.

Molluscicide for the control of schistosomiasis in irrigation schemes: a study in Southern Rhodesia.

Abstract: The development of large areas of irrigation farming in the south-eastern lowveld of Southern Rhodesia has produced the risk of severe transmission of schistosomiasis over an extent of some 30 000 ha. Control measures instituted by the Ministry of Health were primarily directed against the large and widely distributed snail populations by using molluscicides. The chemical was applied to the irrigation water by drip-feed methods once every 6-8 months. The drains, however, were treated routinely by pairs of rangers searching for snails and applying chemical where they were found. The efficacy of control operations has been assessed by longitudinal studies in children free from infection to determine the incidence of infection. The results indicate that transmission of both Schistosoma haematobium and S. mansoni has been reduced to a level below that measured in areas of the country where irrigation is not practised. The total annual cost for this work was US$ 54 800-55 500.

A comparison of Egyptian and East African strains of Schistosoma haematobium.

Abstract: The worm recoveries of two strains of S. haematobium from male hamsters and their egg laying capacities are studied. The infection rates obtained, the size of worms, and the number of testes and the distribution of eggs in hamster tissues are compared with those described for other strains of S. haematobium . It is emphasized that infra-specific variations in the host may also, in part, account for many of the differences that are attributed to different geographical strains of the parasite.

Treatment with hycanthone of Egyptian farmers infected with Schistosoma haematobium and S. mansoni.

Abstract: (1973). Treatment with hycanthone of Egyptian farmers infected with Schistosoma haematobium and S. mansoni. Annals of Tropical Medicine & Parasitology: Vol. 67, No. 2, pp. 233-236.