Effector functions of eosinophils in schistosomiasis.
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The dual function of eosinophils is clearly illustrated in schistosomiasis. Well equipped in membrane receptors for immunoglobulins and complement, and due to the presence of granule basic proteins, eosinophils can become cytotoxic for parasite larvae and thus participate to protective immunity. However, mediators can also exert their cytolytic effect on normal cells or tissues, inducing therefore pathology. through ADCC mechanisms against schistosome larvae in vitro involving different antibody isotypes (IgG, IgE and IgA) and also in experiments performed in vivo, eosinophils have been clearly involved in protective immunity. Although no direct evidence of the protective role of eosinophils were brought in humans, the striking association of eosinophil-dependent cytotoxic antibody isotypes with resistance to reinfection (for instance IgE and IgA antibodies), whereas in vitro blocking antibody isotypes (IgG4, IgM) were detected in susceptible subjects, strongly, suggested the participation of eosinophils in antibody-dependent protective immune response. However eosinophils could also participate to granuloma formation around S. mansoni eggs and consequently to the pathological reactions induced by schistosomiasis. (+info)
Ecological studies on the intermediate host snails and the relevance to schistosomiasis control.
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A detailed knowledge of distribution patterns of schistosome intermediate hosts and their population dynamics and factors affecting these patterns will provide useful information about the possibilities and desirability of conducting snail control measures in various transmission situations. On the basis of various case studies the association between the occurrence of human water contacts and the presence of schistosome intermediate hosts or infections in the intermediate hosts is illustrated. Other parameters affecting snail distribution patterns and density fluctuations are discussed. It is concluded that ecological studies on the intermediate hosts are extremely relevant, either to optimally apply existing control measures or to develop alternative measures of snail control, such as ecological or biological control. (+info)
Holochilus brasiliensis and Nectomys squamipes (Rodentia-Cricetidae) natural hosts of Schistosoma mansoni.
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After several Brazilian researchers, the author examines the capacity of two species of rodents Cricetidae, Holochilus brasiliensis and Nectomys squamipes, to maintain the biological cycle of Schistosoma mansoni in the field and to be parasite reservoir: (a) the role they are able to play in human endemy; (b) the methods necessary to characterize the population of Schistosoma mansoni related either to man, either to rodents, either to both. (+info)
Present aspects of immunodiagnosis of schistosomiasis.
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Facilitated and improved by advances in molecular biology, techniques for the immunodiagnosis of schistosomiasis, including assays based on the detection of antigens circulating in the serum and/or excreted in the urine, have now reached the stage of multi-centre trials. There is a need to complement parasitological techniques as some national programmes are becoming increasingly successful in establishing control of the disease and the classical approach frequently fails to reveal low-intensity infection. Epidemiological survey teams in some areas have tentatively started to use serology and their experience indicates that antibody detection suffices in eradicated or controlled areas with low expected prevalence but that detection of circulating antigens is needed for assessment of the incidence of infection or reinfection in areas recently brought under control. Before reagents and procedures can be recommended for routine use of national control programmes, the assays must be standardized with sera from clinically well-characterized patients in geographically defined regions, hence emphasizing the need for a reference serum bank. Implementation of serological testing, carried out by national public health laboratories using standardized testing systems, would permit valid comparisons between different areas providing support for decisions regarding national health policies. (+info)
The susceptibility of adult schistosomes to immune attrition.
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Mouse infection models are described that demonstrate reduction of egg production in Schistosoma haematobium infections and both worm loss and reduced fecundity in S. bovis infections. Neither phenomenon could be shown in S. mansoni infected mice. The immunological basis for these anti-adult responses was inferred by comparison with infections in T-cell deprived mice and by serum transfer of the ability to reduce a S. bovis worm burden into immunocompromised hosts. Vaccination with irradiation attenuated parasites was also shown to have consequences for the adults of a challenge infection of S. haematobium and S. bovis specifically. Prior vaccination resulted in an abrogation of the anti-fecundity and adult worm elimination that occurred in non-vaccinated similarly infected mice. These models are being used to define the targets and mechanisms involved in anti-adult attrition. A serological assay, quantitation of a circulating antigen (CAA) has been assessed for its ability to measure worm burdens of different species of schistosome in mice. This assay will be used to question whether anti-adult immunity contributes to the pattern of infection with S. mansoni and S. haematobium in man. (+info)
Developmental plasticity in schistosomes and other helminths.
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Developmental plasticity in helminth life cycles serves, in most cases, to increase the probability of transmission between hosts, suggesting that the necessity to achieve transmission is a prominent selective pressure in the evolution of this phenomenon. Some evidence suggests that digenean trematodes from the genus Schistosoma are also capable of limited developmental responses to host factors. Here we review the currently available data on this phenomenon and attempt to draw comparisons with similar processes in the life cycles of other helminths. At present the biological significance of developmental responses by schistosomes under laboratory conditions remains unclear. Further work is needed to determine whether developmental plasticity plays any role in increasing the probability of schistosome transmission and life cycle propagation under adverse conditions, as it does in other helminth life cycles. (+info)
The schistosomicidal and toxic effects of some N-p-aminophenoxyalkylamides.
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Several N-(omega-p-aminophenoxyalkyl)amides were active against Schistosoma mansoni in mice. One of the most effective, N-(5-p-aminophenoxypentyl)benzamide (M&B3002), acted more rapidly than lucanthone on adult worms but less rapidly than antimony potassium tartrate. It was inactive against immature worms. This compound and M&B2948A (N-(5-p-aminophenoxypentyl)phthalimide) were both active against S. mansoni in hamsters. In monkeys M&B2948A was inactive, whilst M&B3002 was not tested for therapeutic activity. Several of the compounds were examined for the production of visual impairment in cats. Although this property was not entirely absent, its incidence was very much lower in this amide series than among other omega-p-aminophenoxyalkyl derivatives not containing an amide group. M&B3002 and M&B2948A produced impairment of vision in only a small proportion of the large number of cats tested. The general toxicology of the two drugs was studied in several species, and also their absorption and excretion in mice and rats; this was to provide information for a clinical trial. (+info)
SCHISTOSOME DERMATITIS IN SACRAMENTO, CALIFORNIA.
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Pruritus developed in two persons at different times, after contact with water in a duck pond at a motel in Sacramento. At those times (in August 1961 and June 1962) large numbers of snails infected with the dermatitis-producing cercariae T. physellae were present in the pond. Experimental lesions were produced in volunteers and by exposure to infected water while collecting snails along the shore of the pond. (+info)