Schistosome monogamy: who, how, and why?

Beltran‐Bech, Sophie; Boissier, Jérôme

doi:10.1016/j.pt.2008.05.009

Cited by 33 publications

(27 citation statements)

References 46 publications

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“…This relationship could be further complicated if treatment induces acquired immunity [65]. There is also uncertainty regarding the biology of the long-term mating behaviour of the adult worms [66, 67] and therefore the most appropriate mating function to use within the models [6, 68]. Furthermore, it important to note that the model does not account for migration or animal reservoirs.…”

Section: Discussionmentioning

confidence: 99%

Evaluating the variation in the projected benefit of community-wide mass treatment for schistosomiasis: Implications for future economic evaluations

et al. 2017

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BackgroundThe majority of schistosomiasis control programmes focus on targeting school-aged children. Expanding the use of community-wide mass treatment to reach more adults is under consideration. However, it should be noted that this would require a further increase in programmatic resources, international aid, and commitment for the provision of praziquantel. Consequently, it is important to understand (i) where a change of strategy would have the greatest benefit, and (ii) how generalisable the conclusions of field trials and analytical studies based on mathematical models investigating the impact of community-wide mass treatment, are to a broad range of settings.MethodsIn this paper, we employ a previously described deterministic fully age-structured schistosomiasis transmission model and evaluate the benefit of community-wide mass treatment both in terms of controlling morbidity and eliminating transmission for Schistosoma mansoni, across a wide range of epidemiological settings and programmatic scenarios. This included variation in the baseline relative worm pre-control burden in adults, the overall level of transmission in defined settings, choice of effectiveness metric (basing morbidity calculations on prevalence or intensity), the level of school enrolment and treatment compliance.ResultsCommunity-wide mass treatment was found to be more effective for controlling the transmission of schistosome parasites than using a school-based programme only targeting school-aged children. However, in the context of morbidity control, the potential benefit of switching to community-wide mass treatment was highly variable across the different scenarios analysed. In contrast, for areas where the goal is to eliminate transmission, the projected benefit of community-wide mass treatment was more consistent.ConclusionWhether community-wide mass treatment is appropriate will depend on the local epidemiological setting (i.e. the relative pre-control burden in adults and transmission intensity), and whether the goal is morbidity control or eliminating transmission. This has important implications regarding the generalisability of cost-effectiveness analyses of schistosomiasis interventions. Our results indicate that areas with poor school-enrolment/coverage could benefit more from community-wide treatment of praziquantel and should potentially be prioritised for any change in strategy. This work highlights the importance of not over-generalising conclusions and policy in this area, but of basing decisions on high quality epidemiological data and quantitative analyses of the impact of interventions in a range of settings.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-017-2141-5) contains supplementary material, which is available to authorized users.

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Section: Discussionmentioning

confidence: 99%

Evaluating the variation in the projected benefit of community-wide mass treatment for schistosomiasis: Implications for future economic evaluations

et al. 2017

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“…Molecular markers and parentage analyses are powerful tools for uncovering mating patterns in internal parasites and can help determine who is mating with whom and their reproductive success. Most human-infecting schistosomes are thought to be monogamous because the male typically mates with a single female at a time and sequesters her within his gynecophoral canal (LoVerde et al, 2004; Beltran and Boissier, 2008), although polygyny (a single male with multiple females in its gynecophoral canal) has been reported (Steinauer, 2009). Although schistosomes typically mate with one individual at a time, they are known to change mates, and there is also evidence for mate choice and mate competition (Tchuem Tchuenté et al, 1995; Beltran et al, 2008a; Steinauer, 2009).…”

Section: Mating Systemsmentioning

confidence: 99%

Applying evolutionary genetics to schistosome epidemiology

Steinauer¹,

Blouin²,

Criscione³

2010

Infection, Genetics and Evolution

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We review how molecular markers and evolutionary analysis have been applied to the study of schistosome parasites, important pathogens that infect over 200 million people worldwide. Topics reviewed include phylogenetics and biogeography, hybridization, infection within snails, mating systems, and genetic structure. Some interesting generalizations include that schistosome species hybridize frequently and have switched definitive hosts repeatedly in evolutionary time. We show that molecular markers can be used to infer epidemiologically-relevant processes such as spatial variation in transmission, or to reveal complex patterns of mate choice. Analysis of genetic structure data shows that transmission foci can be structured by watershed boundaries, habitat types, and host species. We also discuss sampling and analytical problems that arise when using larvae to estimate genetic parameters of adult schistosome populations. Finally, we review pitfalls in methodologies such as genotyping very small individuals, statistical methods for identifying clonemates or for identifying sibling groups, and estimating allele frequencies from pooled egg samples.

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“…Another way half-sibships could be produced is through mate switching. However, mate-switching is not likely to occur in our samples because each fecal sample represents a small window of reproduction and schistosomes are primarily monogamous [10], [11], [65].…”

Section: Discussionmentioning

confidence: 99%

“…Schistosome parasites are one such example. Schistosomes are dioecious blood flukes that become reproductively mature in the vasculature (mesenteric veins or the veins of the bladder plexus) of their hosts where they reside in primarily monogamous pairs [10], [11]. The adults are inaccessible, but their offspring can be collected as eggs that are shed in urine or feces.…”

Section: Introductionmentioning

confidence: 99%

Non-Invasive Sampling of Schistosomes from Humans Requires Correcting for Family Structure

et al. 2013

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For ethical and logistical reasons, population-genetic studies of parasites often rely on the non-invasive sampling of offspring shed from their definitive hosts. However, if the sampled offspring are naturally derived from a small number of parents, then the strong family structure can result in biased population-level estimates of genetic parameters, particularly if reproductive output is skewed. Here, we document and correct for the strong family structure present within schistosome offspring (miracidia) that were collected non-invasively from humans in western Kenya. By genotyping 2,424 miracidia from 12 patients at 12 microsatellite loci and using a sibship clustering program, we found that the samples contained large numbers of siblings. Furthermore, reproductive success of the breeding schistosomes was skewed, creating differential representation of each family in the offspring pool. After removing the family structure with an iterative jacknifing procedure, we demonstrated that the presence of relatives led to inflated estimates of genetic differentiation and linkage disequilibrium, and downwardly-biased estimates of inbreeding coefficients (FIS). For example, correcting for family structure yielded estimates of FST among patients that were 27 times lower than estimates from the uncorrected samples. These biased estimates would cause one to draw false conclusions regarding these parameters in the adult population. We also found from our analyses that estimates of the number of full sibling families and other genetic parameters of samples of miracidia were highly intercorrelated but are not correlated with estimates of worm burden obtained via egg counting (Kato-Katz). Whether genetic methods or the traditional Kato-Katz estimator provide a better estimate of actual number of adult worms remains to be seen. This study illustrates that family structure must be explicitly accounted for when using offspring samples to estimate the genetic parameters of adult parasite populations.

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Schistosome monogamy: who, how, and why?

Cited by 33 publications

References 46 publications

Evaluating the variation in the projected benefit of community-wide mass treatment for schistosomiasis: Implications for future economic evaluations

Evaluating the variation in the projected benefit of community-wide mass treatment for schistosomiasis: Implications for future economic evaluations

Applying evolutionary genetics to schistosome epidemiology

Non-Invasive Sampling of Schistosomes from Humans Requires Correcting for Family Structure

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