Genetic analysis of cercarial emergence rhythms of Schistosoma mansoni.
TL;DR: Experimental crossbreeding between schistosomes with an early and those with a late cercarial shedding pattern demonstrates that the cercaria emergence rhythms of schistOSomes are genetically determined.
Abstract: Using two chronobiological variants ofSchistosoma mansoni (a blood fluke infecting man) from Guadeloupe (French West Indies), we carried out experimental crossbreeding between schistosomes with an early and those with a late cercarial shedding pattern. The results obtained on the F1 (intermediate shedding patterns) and F2 generations (early, intermediate, and late patterns) demonstrate that the cercarial emergence rhythms of schistosomes are genetically determined. This genetic variability is interpreted as a consequence of the selective pressure exerted by the two different hosts (man and rat) implicated in the life cycle ofS. mansoni from the Guadeloupean focus of schistosomiasis.
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01 Jan 2003
247 citations
Cites background from "Genetic analysis of cercarial emerg..."
...This process is not stable and undergoes periodic fluctuations which are genetically controlled (Théron and Combes, 1988; Théron, 1989; Pages and Théron, 1990a) and are referred to as “cercarial emergence rhythms”....
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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
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
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.
Abstract: Many parasitic worms enter their hosts by active invasion. Their transmission success is often based on a mass production of invasive stages. However, most stages show a highly specific host-finding behaviour. Information on host-finding mechanisms is available mainly for trematode miracidia and cercariae and for nematode hookworms. The larvae find and recognise their hosts, in some cases even with species specificity, via complex sequences of behavioural patterns with which they successively respond to various environmental and host cues. There is often a surprisingly high diversity of host-recognition strategies. Each parasite species finds and enters its host using a different series of cues. For example, different species of schistosomes enter the human skin using different recognition sequences. The various recognition strategies may reflect adaptations to distinct ecological conditions of transmission. Another question is how, after invasion, parasitic worms find their complex paths through their host's tissues to their often very specific microhabitats. Recent data show that the migrating parasite stages can follow local chemical gradients of skin and blood compounds, but their long-distance navigation within the host body still remains puzzling. 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
TL;DR: Biological factors central to the transmission of schistosomes, including cercarial emergence rhythms and interactions with other parasites and abiotic factors including temperature, rainfall, water velocity, desiccation and salinity are shown to impact on the intermediate host-parasite relationship.
Abstract: Within each of the four species groups of Bulinus there are species that act as intermediate hosts for one or more of the seven species of schistosomes in the Schistosoma haematobium group, which includes the important human pathogens S. haematobium and S. intercalatum. Bulinus species have an extensive distribution throughout much of Africa and some surrounding islands including Madagascar, parts of the Middle East and the Mediterranean region. Considerable variation in intermediate host specificity can be found and differences in compatibility between snail and parasite can be observed over small geographical areas. Molecular studies for detection of genetic variation and the discrimination of Bulinus species are reviewed and two novel assays, allele-specific amplification (ASA) and SNaPshot™, are introduced and shown to be of value for detecting nucleotide changes in characterized genes such as cytochrome oxidase 1. The value and complexity of compatibility studies is illustrated by case studies of S. haematobium transmission. In Senegal, where B. globosus, B. umbilicatus, B. truncatus and B. senegalensis may act as intermediate hosts, distinct differences have been observed in the infectivity of different isolates of S. haematobium. In Zanzibar, molecular characterization studies to discriminate between B. globosus and B. nasutus have been essential to elucidate the roles of snails in transmission. B. globosus is an intermediate host on Unguja and Pemba. Further studies are required to establish the intermediate hosts in the coastal areas of East Africa. Biological factors central to the transmission of schistosomes, including cercarial emergence rhythms and interactions with other parasites and abiotic factors including temperature, rainfall, water velocity, desiccation and salinity are shown to impact on the intermediate host-parasite relationship.
83 citations
References
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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-
102 citations
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
"Genetic analysis of cercarial emerg..." refers background in this paper
...These chronobiological differences, well known at the interspecific level (Yamaguti, 1970; Pitchford et al., 1969), are generally believed to result from a selective adaptation of the parasite to the behavior of the host to be infected; they have their place among This work received financial…...
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TL;DR: Development of a method of infecting of the molluscan host by microsurgical transplantation of the parasite's sporocysts enables the researcher to maintain the host cycle of Schistosoma mansoni exclusively by asexual means and without the participation of a vertebrate host.
Abstract: Development of a method of infecting of the molluscan host by microsurgical transplantation of the parasite's sporocysts enables the researcher to maintain the host cycle of Schistosoma mansoni exclusively by asexual means and without the participation of a vertebrate host. After transplantation, larval morphogenesis becomes altered to form an additional generation of sporocysts. These invade the digestive gland of the recipient mollusc progressively, producing normally infective cercariae. The maintenance of the life cycle of S. mansoni in the laboratory for 1 year, solely in the mollusc, has been obtained through six successive transplantations. Thus, a true cloning of S. mansoni has been achieved, the original transplant material being derived from a monomiracidial infection. From the practical viewpoint, this transplantation technique is of definite utility in the maintenance of the cycle, the vertebrate stage having been eliminated. From the theoretical viewpoint, unexpected analogies become apparent with the two types of larval demography found in Digenea (Digenea with sporocyst and Digenea with rediae).
55 citations
TL;DR: Dans la mangrove lacustre de Dubelloy-Devarieux (Guadeloupe), la dynamique des populations de B. glabrata et de the transmission de S. mansoni est etroitement dependante de l’alternance saison seche, saison des pluies.
Abstract: Dans la mangrove lacustre de Dubelloy-Devarieux (Guadeloupe), la dynamique des populations de B. glabrata et de la transmission de S. mansoni est etroitement dependante de l’alternance saison seche, saison des pluies. La remise en eau de la mangrove (septembre) permet chaque annee un renouvellement des peuplements malacologiques. L’analyse des classes de taille montre que le cycle de developpement d’une population de B. glabrata comporte deux saisons des pluies separees par une saison seche. La prevalence d’infestation des Mollusques (0,25 %) et les densites de cercaires de S. mansoni (0,8 c/l) sont faibles. Le rythme de presence des cercaires en milieu stagnant montre une acrophase a 14 heures. L’homme et le rat sont parasites. La contamination des populations murines passe de 20 % a la remise en eau, a pres de 100 % en fin de saison des pluies. Les facteurs pouvant favoriser l’infestation des rats sont discutes.
16 citations