Pattern of cercarial emergence of Schistosoma curassoni from Niger and comparison with three sympatric species of schistosomes.
TL;DR: The emergence pattern of Schistosoma curassoni cercariae from Bulinus umbilicatus, whose adult worms parasitize bovine, caprine, and ovine ungulates in Niger, is of a circadian type with a mean emission time at 0855 hr 1 hr 6 min, characteristic of the schistosome species parasitizing domestic or wild cattle as mentioned in this paper.
Abstract: The emergence pattern of Schistosoma curassoni cercariae from Bulinus umbilicatus, whose adult worms parasitize bovine, caprine, and ovine ungulates in Niger, is of a circadian type with a mean emission time at 0855 hr 1 hr 6 min, characteristic of the schistosome species parasitizing domestic or wild cattle. The comparison of this cercarial emergence pattern with those of the other 3 sympatric species of schistosomes (Schistosoma haematobium, Schistosoma bovis, and Schistosoma mansoni) shows a significant difference between the chronobiology of the cercariae infective for human and those infective for bovine hosts. This difference may improve epidemiological surveys based on snail prevalences by allowing the distinction between bulinids infected with human and bovine parasites.
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01 Jan 2003
247 citations
Cites background from "Pattern of cercarial emergence of S..."
...bovis cercariae are timed for early morning, when the definitive hosts of these parasites, the bulls, come to drink water (Pages and Théron, 1990b; Mouchet et al., 1992), those of S....
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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: 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
TL;DR: This chapter provides an updated and comprehensive review on the main features of cattle schistosomiasis and indicates that suitable drugs are not available for mass treatment in domestic stock and are unlikely to be developed in the near future.
Abstract: Publisher Summary This chapter provides an updated and comprehensive review on the main features of cattle schistosomiasis. The adult worms are obligate parasites of the blood vascular system of vertebrates. They live in the perivesical, nasal or mesenteric, and hepatic veins of the host where they feed on blood and produce nonoperculated eggs with a characteristic terminal or lateral spine. As many as 10 different species of schistosomes have been reported to naturally infect cattle. The geographical distribution of schistosome species infecting cattle is mainly determined by the distribution of their respective intermediate host snails. It is noted that most infections in endemic areas occur at a subclinical level. However, it has been established that high rates of prevalence of subclinical infections cause significant losses due to long-term effects on animal growth and productivity and increased susceptibility to other parasitic or bacterial disease. Despite this, schistosomes of veterinary concern have received relatively little attention. In addition, suitable drugs are not available for mass treatment in domestic stock and are unlikely to be developed in the near future. However, recent progress in identifying potentially protective parasite antigens has opened new perspectives in the control strategy against schistosomiasis.
70 citations
TL;DR: Together, exogenous and endogenous factors control emergence of trematode cercariae, mitigating the vagaries of an intertidal environment.
Abstract: Trematode parasites in intertidal estuaries ex- perience constantly varying conditions, with the presence or absence of water potentially limiting larval transport be- tween hosts. Given the short life spans (24 h) of cercariae, emergence timing should be optimized to enhance the prob- ability of successful transmission. In the present study, field measurements and laboratory experiments identified pro- cesses that regulate the emergence of cercariae from their first intermediate snail hosts in an intertidal marsh. Larvae emerged over species-specific temperature ranges, exclu- sively during daylight hours, and only when snails were submerged. The three factors operate over different tempo- ral scales: temperature monthly, light diurnally (24-h pe- riod), and water depth tidally (12-h period). Each stimulus creates a necessary condition for the next, forming a hier- archy of environmental cues. Emergence as the tide floods would favor transport within the estuary, and light may trigger direct (downward or upward) swimming toward host habitats. Abbreviated dispersal would retain asexually re- produced cercariae within the marsh, and local mixing would diversify the gene pool of larvae encysting on sub- sequent hosts. In contrast to the timing of cercarial release, emergence duration was under endogenous control. Dura- tion of emergence decreased from sunrise to sunset, perhaps in response to the diminishing lighted interval as the day progresses. Circadian rhythms that control cercarial emer- gence of freshwater species (including schistosomes) are often set by the activity patterns of subsequent hosts. In this estuary, however, the synchronizing agent is the tides. To-
67 citations
References
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TL;DR: A survey of 5722 sheep and 1752 goats at the abatoir in Dakar, Senegal showed that the overall prevalence of schistosomiasis was 2·1%, and this species is shown to be distinct from S. bovis and S. mattheei.
Abstract: A survey of 5722 sheep and 1752 goats at the abatoir in Dakar, Senegal showed that the overall prevalence of schistosomiasis was 2·1%. Of the 112 animals where identification of the schistosome species was possible, all were infected with Schistosoma curassoni, and 2·7% had mixed infections with S. bovis. The adult worms of S. curassoni are described, and on the basis of egg morphology this species is shown to be distinct from S. bovis and S. mattheei. Eggs of S. curassoni measured 146 μm ± 16·8 × 63·3 μm ± 4·5 from sheep and 149·4 μm ± 13·2 × 62·8 μm ± 4·9 from mouse liver, and appear to be indistinguishable from the eggs of S. haematobium Guede Chantier, Senegal which measure 153·1 μm ± 11·1 × 62·4 μm ± 12·1 from mouse liver. However, S. curassoni differs from S. haematobium in that it develops more quickly than S. haematobium in hamsters, uterine eggs becoming visible at least 20 days earlier; the adult worms of S. curassoni are nearly double the size of S. haematobium in hamsters at 70 days post infec...
30 citations
TL;DR: Three chronobiological patterns were distinguished for the parasite populations studied, and statistical tests for the homogeneity of samples in each group and the significant differences between groups were also carried out.
Abstract: Chronobiological data concerning the emergence rhythms of Schistosoma mansoni cercariae were transformed into circular variables and analysed using circular statistics. The method proposed allowed three chronobiological patterns to be distinguished for the parasite populations studied, and statistical tests for the homogeneity of samples in each group and the significant differences between groups were also carried out.
27 citations
TL;DR: The chronobiology of the emergence rhythms of the cercariae seems to be an additional marker to estimate the genetic variability of this species and to characterize the 2 strains of Schistosoma intercalatum.
Abstract: An experimental study of the cercarial emergence rhythm was conducted to compare 2 geographical strains of Schistosoma intercalatum from Cameroon and Zaire. For the Cameroon strain, the peak emergence time was between 1300 hr and 1400 hr, and the mean emergence time was 1359 hr. For the Zaire strain, the peak emergence time was between 1200 hr and 1300 hr, and the mean emergence time was 1213 hr. These results were shown to be significantly different by statistical analysis. Thus, the chronobiology of the emergence rhythms of the cercariae seems to be an additional marker to estimate the genetic variability of this species and to characterize the 2 strains.
19 citations
TL;DR: The results support the hypothesis that cercarial emission rhythms are determined primarily by the parasite in these snail/parasite associations.
17 citations