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Journal ArticleDOI

Early and late shedding patterns of schistosoma mansoni cercariae: ecological significance in transmission to human and murine hosts

01 Oct 1984-Journal of Parasitology (J Parasitol)-Vol. 70, Iss: 5, pp 652-655
TL;DR: A comparative analysis of the cercarial shedding of 2 Schistosoma mansoni populations originating from the same endemic area (Guadeloupe) allows us to distinguish an early (peak emergence at 1100 hr) and a late (peak at 1600 hr) shedding patterns of cercariae.
Abstract: A comparative analysis of the cercarial shedding of 2 Schistosoma mansoni populations originat- ing from the same endemic area (Guadeloupe) allows us to distinguish an early (peak emergence at 1100 hr) and a late (peak at 1600 hr) shedding patterns of cercariae. This intraspecific variation in the chronobiology of S. mansoni cercariae may be related to the ecology in the transmission site. The early shedding pattern char- acterizes schistosome populations originated from urbanized foci where man plays the main role in the parasite transmission; the late shedding pattern characterizes schistosome populations originated from sylvatic focus where a rat (R. rattus) is the main host. The late shedding of cercariae is considered as an adaptation favoring transmission to a murine host whose behavior is preferentially crepuscular. All studies concerned with the cercarial shed-
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BookDOI
01 Jan 2003

247 citations


Cites background from "Early and late shedding patterns of..."

  • ...cariae, as stated above, mostly during the daytime, the strain of murine origin has its shedding peak in the evening (Théron, 1984)....

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  • ...mansoni cercariae, for the daytime, when people are active (Théron, 1984; Pages and Théron, 1990b) and those of S....

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Journal ArticleDOI
TL;DR: Mass drug administration has already made significant improvements to global health and productivity and has the potential for further successes, particularly where incorporated into sanitation and education programmes, however logistical, financial and biological challenges remain.
Abstract: Mass drug administration (MDA) is a means of delivering safe and inexpensive essential medicines based on the principles of preventive chemotherapy, where populations or sub-populations are offered treatment without individual diagnosis. High-coverage MDA in endemic areas aims to prevent and alleviate symptoms and morbidity on the one hand and can reduce transmission on the other, together improving global health. MDA is the recommended strategy of the World Health Organisation to control or eliminate several neglected tropical diseases (NTDs). More than 700 million people now receive these essential NTD medicines annually. The combined cost of integrated NTD MDA has been calculated to be in the order of $0.50 per person per year. Activities have recently been expanded due, in part, to the proposed attempt to eliminate certain NTDs in the coming two decades. More than 1.9 billion people need to receive MDA annually across several years if these targets are to be met. Such extensive coverage will require additional avenues of financial support, expanded monitoring and evaluation focusing on impact and drug efficacy, as well as new diagnostic tools and social science strategies to encourage adherence. MDA is a means to help reduce the burden of disease, and hence poverty, among the poorest sector of populations. It has already made significant improvements to global health and productivity and has the potential for further successes, particularly where incorporated into sanitation and education programmes. However logistical, financial and biological challenges remain.

217 citations

Journal ArticleDOI
TL;DR: Cercariae, like miracidia, are non-parasitic larval stages implicated in the life cycle of all trematodes for the host-to-host parasite transmission.
Abstract: Cercariae, like miracidia, are non-parasitic larval stages implicated in the life cycle of all trematodes for the host-to-host parasite transmission. Almost all cercariae are free-living in the external environment. With a few exceptions (cercariae of Halipegus occidualis (Halipegidae) can live several months, Shostak & Esch, 1990a), cercariae have a short active life during which they do not feed, living on accumulated reserves. Most cercariae encyst as metacercariae in second intermediate hosts which are prey of the definitive host; in certain species, the interruption of the active life is achieved by an encystment in the external environment (or a simple immobile waiting strategy in a few species). In some two-host life cycles, the cercariae develop into adults after penetration (this is the case for various species causing human schistosomiasis). Some cercariae do not leave the mollusc which must then be ingested by the definitive host.

180 citations

Journal ArticleDOI
TL;DR: In parasitic life cycles, transmission events, that is, the passage of a parasite from an "upstream" host to a "downstream"Host, often involve behavioral adaptations that result in an increase of the chances of the parasite's being actually transmitted.
Abstract: In parasitic life cycles, transmission events, that is, the passage of a parasite from an "upstream" host to a "downstream" host, often involve behavioral adaptations that result in an increase of the chances of the parasite's being actually transmitted These behaviors stem from evolutionary changes in the parasites' genomes: either the parasites select responses (their own responses or those they provoke in upstream hosts) to stimuli arising from downstream hosts or from the environment where they live, or they select stimuli (arising from themselves, or from alterations they provoke in upstream hosts) that are addressed to downstream hosts The various processes are differentiated on the basis of behavioral adaptations and illustrated by examples The difficulty of demonstrating that the traits are actually the result of a selective process favoring transmission and several unresolved questions are discussed

178 citations

Journal ArticleDOI
01 Jan 2003-Zoology
TL;DR: The high complexity, specificity and diversity of host-recognition strategies suggest that host finding and host recognition are important determinants in the evolution of parasite life cycles.

161 citations

References
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Journal ArticleDOI
TL;DR: In this paper, the shedding patterns of various schistosome species under outdoor conditions in the Transvaal were investigated and the results showed that the shedding pattern of various species in South Africa is similar to that of the USA.
Abstract: (1969). Cercarial shedding patterns of various schistosome species under outdoor conditions in the Transvaal. Annals of Tropical Medicine & Parasitology: Vol. 63, No. 3, pp. 359-371.

71 citations

Journal ArticleDOI
TL;DR: A delayed pattern of Schistosoma mansoni cercarial emergence from Biomphalaria glabrata is presented, in which cercariae did not emerge from the snail under a diurnal photoperiod until after 12 noon.

19 citations

Journal ArticleDOI
TL;DR: In the chanel studied, the role of the rat in the transmission of the parasite seems less important than that of the Man, and the infection of the rats during consumption of snails can be foreseen.
Abstract: The study of the rate of contamination of B. glabrata and the cercarial densities of S. mansoni in the chanels of Beaugendre valley (Guadeloupe, French West Indies) concentrates attention on the focalisation of the sites with high risk of contamination. This focalization of the sites of transmission is directly related to the regular deposition of human faeces. A small number of contamined people is enough to maintain high cercarial densities (230 c/1). In the chanel studied, the role of the rat in the transmission of the parasite seems less important than that of the Man. The infection of the rats during consumption of snails can be foreseen.

16 citations