egr3 is a mechanosensitive transcription factor gene required for cardiac valve morphogenesis

Biomechanical forces, and their molecular transducers, including key mechanosensitive transcription factor genes, such as KLF2, are required for cardiac valve morphogenesis. However, klf2 mutants fail to completely recapitulate the valveless phenotype observed under no-flow conditions. Here, we identify the transcription factor EGR3 as a conserved biomechanical force transducer critical for cardiac valve formation. We first show that egr3 null zebrafish display a complete and highly penetrant loss of valve leaflets, leading to severe blood regurgitation. Using tissue-specific loss- and gain-of-function tools, we find that during cardiac valve formation, Egr3 functions cell-autonomously in endothelial cells, and identify one of its effectors, the nuclear receptor Nr4a2b. We further find that mechanical forces up-regulate egr3/EGR3 expression in the developing zebrafish heart and in porcine valvular endothelial cells, as well as during human aortic valve remodeling. Altogether, these findings reveal that EGR3 is necessary to transduce the biomechanical cues required for zebrafish cardiac valve morphogenesis, and potentially for pathological aortic valve remodeling in humans.

Variations in the poly-histidine repeat motif of HOXA1 contribute to bicuspid aortic valve in mouse and zebrafish

Bicuspid aortic valve (BAV), the most common cardiovascular malformation occurs in 0.5-1.2% of the population. Although highly heritable, few causal mutations have been identified in BAV patients. Here, we report the targeted sequencing of HOXA1 in a cohort of BAV patients and the identification of rare indel variants in the homopolymeric histidine tract of HOXA1. In vitro analysis shows that disruption of this motif leads to a significant reduction in protein half-life and defective transcriptional activity of HOXA1. In zebrafish, targeting hoxa1a ortholog results in aortic valve defects. In vivo assays indicates that these variants behave as dominant negatives leading abnormal valve development. In mice, deletion of Hoxa1 leads to BAV with a very small, rudimentary non-coronary leaflet. We also show that 17% of homozygous Hoxa1^-1His knock-in mice present similar phenotype. Genetic lineage tracing in Hoxa1^-/- mutant mice reveals an abnormal reduction of neural crest-derived cells in the valve leaflet, which is caused by a failure of early migration of these cells.

Expanding the phenome and variome of the ROBO-SLIT pathway in congenital heart defects: toward improving the genetic testing yield of CHD

BACKGROUND

Recent studies have shown the implication of the ROBO-SLIT pathway in heart development. Within this study, we aimed to further assess the implication of the ROBO and SLIT genes mainly in bicuspid aortic valve (BAV) and other human congenital heart defects (CHD).

METHODS

We have analyzed a cohort of singleton exome sequencing data comprising 40 adult BAV patients, 20 pediatric BAV patients generated by the Pediatric Cardiac Genomics Consortium, 10 pediatric cases with tetralogy of Fallot (ToF), and one case with coarctation of the aorta. A gene-centered analysis of data was performed. To further advance the interpretation of the variants, we intended to combine more than 5 prediction tools comprising the assessment of protein structure and stability.

RESULTS

A total of 24 variants were identified. Only 4 adult BAV patients (10%) had missense variants in the ROBO and SLIT genes. In contrast, 19 pediatric cases carried variants in ROBO or SLIT genes (61%). Three BAV patients with a severe phenotype were digenic. Segregation analysis was possible for two BAV patients. For the homozygous ROBO4: p.(Arg776Cys) variant, family segregation was consistent with an autosomal recessive pattern of inheritance. The ROBO4: c.3001 + 3G > A variant segregates with the affected family members. Interestingly, these variants were also found in two unrelated patients with ToF highlighting that the same variant in the ROBO4 gene may underlie different cardiac phenotypes affecting the outflow tract development.

CONCLUSION

Our results further reinforce the implication of the ROBO4 gene not only in BAV but also in ToF hence the importance of its inclusion in clinical genetic testing. The remaining ROBO and SLIT genes may be screened in patients with negative or inconclusive genetic tests.

SCN5A Variants as Genetic Arrhythmias Triggers for Familial Bileaflet Mitral Valve Prolapse

Mitral valve prolapse (MVP) is a common valvular heart defect with variable outcomes. Several studies reported MVP as an underestimated cause of life-threatening arrhythmias and sudden cardiac death (SCD), mostly in young adult women. Herein, we report a clinical and genetic investigation of a family with bileaflet MVP and a history of syncopes and resuscitated sudden cardiac death. Using family based whole exome sequencing, we identified two missense variants in the SCN5A gene. A rare variant SCN5A:p.Ala572Asp and the well-known functional SCN5A:p.His558Arg polymorphism. Both variants are shared between the mother and her daughter with a history of resuscitated SCD and syncopes, respectively. The second daughter with prodromal MVP as well as her healthy father and sister carried only the SCN5A:p.His558Arg polymorphism. Our study is highly suggestive of the contribution of SCN5A mutations as the potential genetic cause of the electric instability leading to ventricular arrhythmias in familial MVP cases with syncope and/or SCD history.

Identification of non-synonymous variations in ROBO1 and GATA5 genes in a family with bicuspid aortic valve disease

Bicuspid aortic valve (BAV) is the most common congenital heart defect with a high index of heritability. Patients with BAV have different clinical courses and disease progression. Herein, we report three siblings with BAV and clinical differences. Their clinical presentations include moderate to severe aortic regurgitation, aortic stenosis, and ascending aortic aneurysm. Genetic investigation was carried out using Whole-Exome Sequencing for the three patients. We identified two non-synonymous variants in ROBO1 and GATA5 genes. The ROBO1: p.(Ser327Pro) variant is shared by the three BAV-affected siblings. The GATA5: p.(Gln3Arg) variant is shared only by the two brothers who presented BAV and ascending aortic aneurysm. Their sister, affected by BAV without aneurysm, does not harbor the GATA5: p.(Gln3Arg) variant. Both variants were absent in the patients' fourth brother who is clinically healthy with tricuspid aortic valve. To our knowledge, this is the first association of ROBO1 and GATA5 variants in familial BAV with a potential genotype-phenotype correlation. Our findings are suggestive of the implication of ROBO1 gene in BAV and the GATA5: p.(Gln3Arg) variant in ascending aortic aneurysm. Our family-based study further confirms the intrafamilial incomplete penetrance of BAV and the complex pattern of inheritance of the disease.

Clinical insights into a tertiary care center cohort of patients with bicuspid aortic valve

Although bicuspid aortic valve (BAV) is one of the most common congenital heart diseases, clinical data associated with valve dysfunction are still limited. We evaluated clinical characteristics and echocardiography of French patients with BAV associated with leaking and stenosis degeneration. We initiated a prospective registry from 2014 to 2018 at a tertiary center. A total of 223 patients (168 males [75%], age 53 ± 17 years) were enrolled. Among these patients 83% had left-right coronary cusps fusion, 80% Sievers type 1 BAV and 49% showed aortic dilatation. Twenty-four patients (11%) had normal valve function, 66 patients (31%) had aortic stenosis (AS), 91 patients (41%) had aortic regurgitation (AR) and 40 patients (17%) had AR and AS. BAV phenotype did not predict neither AS nor AR (all p > 0.1). By multivariable analysis, age > 50 (41.6[10.3-248.2], p < 0.001) and presence of raphe/fusion (12.8[2.4-87.4], p < 0.001) were significantly associated with AS, whereas male gender was associated with AR (5[1.6-16.4], p = 0.005). In addition, leaking degeneration was observed at a much younger age than stenosis (44 ± 14 years vs. 66 ± 10 years, p < 0.01) and among patients with valve dysfunction younger age was independently associated with AR (1.9[1.85-1.94], p < 0.001). In this study we confirmed high prevalence of valve dysfunction at first diagnosis of BAV in a referred population. The degenerative process differs according to type of dysfunction and is mainly dependent on age and gender.

Identification of a peripheral blood gene signature predicting aortic valve calcification

Calcific aortic valve disease (CAVD) is a significant cause of illness and death worldwide. Identification of early predictive markers could help optimize patient management. RNA-sequencing was carried out on human fetal aortic valves at gestational weeks 9, 13, and 22 and on a case-control study with adult noncalcified and calcified bicuspid and tricuspid aortic valves. In dimension reduction and clustering analyses, diseased valves tended to cluster with fetal valves at week 9 rather than normal adult valves, suggesting that part of the disease program might be due to reiterated developmental processes. The analysis of groups of coregulated genes revealed predominant immune-metabolic signatures, including innate and adaptive immune responses involving lymphocyte T-cell metabolic adaptation. Cytokine and chemokine signaling, cell migration, and proliferation were all increased in CAVD, whereas oxidative phosphorylation and protein translation were decreased. Discrete immune-metabolic gene signatures were present at fetal stages and increased in adult controls, suggesting that these processes intensify throughout life and heighten in disease. Cellular stress response and neurodegeneration gene signatures were aberrantly expressed in CAVD, pointing to a mechanistic link between chronic inflammation and biological aging. Comparison of the valve RNA-sequencing data set with a case-control study of whole blood transcriptomes from asymptomatic individuals with early aortic valve calcification identified a highly predictive gene signature of CAVD and of moderate aortic valve calcification in overtly healthy individuals. These data deepen and broaden our understanding of the molecular basis of CAVD and identify a peripheral blood gene signature for the early detection of aortic valve calcification.

The MIDA Mortality Risk Score: development and external validation of a prognostic model for early and late death in degenerative mitral regurgitation

Aims

In degenerative mitral regurgitation (DMR), lack of mortality scores predicting death favours misperception of individual patients' risk and inappropriate decision-making.

Methods and results

The Mitral Regurgitation International Database (MIDA) registries include 3666 patients (age 66 ± 14 years; 70% males; follow-up 7.8 ± 5.0 years) with pure, isolated, DMR consecutively diagnosed by echocardiography at tertiary (European/North/South-American) centres. The MIDA Score was derived from the MIDA-Flail-Registry (2472 patients with DMR and flail leaflet-Derivation Cohort) by weighting all guideline-provided prognostic markers, and externally validated in the MIDA-BNP-Registry (1194 patients with DMR and flail leaflet/prolapse-Validation Cohort). The MIDA Score ranged from 0 to 12 depending on accumulating risk factors. In predicting total mortality post-diagnosis, the MIDA Score showed excellent concordance both in Derivation Cohort (c = 0.78) and Validation Cohort (c = 0.81). In the whole MIDA population (n = 3666 patients), 1-year mortality with Scores 0, 7-8, and 11-12 was 0.4, 17, and 48% under medical management and 1, 7, and 14% after surgery, respectively (P < 0.001). Five-year survival with Scores 0, 7-8, and 11-12 was 98 ± 1, 57 ± 4, and 21 ± 10% under medical management and 99 ± 1, 82 ± 2, and 57 ± 9% after surgery (P < 0.001). In models including all guideline-provided prognostic markers and the EuroScoreII, the MIDA Score provided incremental prognostic information (P ≤ 0.002).

Conclusion

The MIDA Score may represent an innovative tool for DMR management, being able to position a given patient within a continuous spectrum of short- and long-term mortality risk, either under medical or surgical management. This innovative prognostic indicator may provide a specific framework for future clinical trials aiming to compare new technologies for DMR treatment in homogeneous risk categories of patients.

Valve hemodynamic performance and myocardial strain after implantation of a third-generation, balloon-expandable, transcatheter aortic valve

BACKGROUND

Left ventricular (LV) mechanics are impaired in patients with severe aortic stenosis (AS); however, transcatheter aortic valve implantation (TAVI) may positively affect LV mechanics. Assessed herein is the performance of the SAPIEN 3 transcatheter heart valve (THV) and the effect of TAVI on LV function recovery, as assessed by global longitudinal strain (GLS).

METHODS

A subset of patients from the SOURCE 3 registry (n = 276) from 16 European centers received SAPIEN 3 balloon-expandable THV. Echocardiography was performed at baseline, postprocedure, and at 1 year, including assessment of GLS using standard two-dimensional images, and was analyzed in a core laboratory. Paired analyses between baseline and discharge, baseline and at 1 year were conducted.

RESULTS

Hemodynamic parameters were improved after TAVI and sustained to 1 year. At 1 year, the rate of moderate to severe paravalvular leaks (PVL), and moderate to severe mitral and tricuspid regurgitations were 1.8%, 1.7%, and 8.0%, respectively. The discharge GLS (-15.6 ± 5.1; p = 0.004; n = 149) improved significantly from baseline (-15.1 ± 4.8) following TAVI. This improvement was sustained at 1 year compared with baseline (-17.0 ± 4.6, p < 0.001; n = 100). Conversely, LV ejection fraction (LVEF) did not significantly change following TAVI (p = 0.47).

CONCLUSIONS

Following TAVI with a third-generation THV, valve performances were good at 1 year with low PVL rate. The LV mechanics improved immediately after the procedure and were maintained at 1 year. These findings demonstrate the benefit of TAVI on LV mechanics, and suggests that GLS may be superior to LVEF in assessing this benefit. Clinicaltrial.gov number: NCT02698956.

Long-term results of surgical treatment of secondary severe mitral regurgitation in patients with end-stage heart failure: Advantage of prosthesis insertion

BACKGROUND

Surgical treatment of secondary mitral regurgitation (SMR) is controversial.

AIM

To analyse outcome after undersizing annuloplasty (UA) and mitral valve replacement (MVR).

METHODS

Consecutive patients operated on for severe SMR, with left ventricular ejection fraction (LVEF)<40% and refractory CHF, were included. Endpoints were in-hospital mortality, mid-term cardiovascular (CV) mortality, evolution of LV variables and recurrence of mitral regurgitation (MR).

RESULTS

59 patients were included (mean age 65±10 years, preoperative LVEF 36±6%; effective regurgitant orifice [ERO] 41±17 mm²), 41 with ischaemic disease: 12 underwent UA and 47 underwent MVR; only eight had concomitant coronary revascularization. In-hospital mortality was 3.3% (8.3% in UA group; 2.1% in MVR group). Eight-year CV mortality was 39±13% (40±18% in UA group; 27±10% in MVR group). Older age (hazard ratio 1.14, 95% confidence interval 1.07 to 1.22; P<0.001) and LV end-systolic diameter (hazard ratio 1.18, 95% confidence interval 1.09 to 1.27; P<0.001) independently predicted CV mortality. LVEF did not change between the preoperative and follow-up transthoracic echocardiograms in the MVR group (36±6% vs. 35±10%; P=0.6) or the UA group (36±5% vs. 31±12%; P=0.09). Conversely, LV end-diastolic diameter decreased significantly in the MVR group (64±8m to 59±9mm; P=0.002), but not in the UA group (61±7m to 64±10mm; P=0.2). Recurrence of significant MR occurred in 81% of patients in the UA group (mean postoperative ERO 19±6 mm²) versus none in the MVR group.

CONCLUSIONS

Surgical treatment of SMR can be performed with acceptable operative risk and mid-term survival in severe heart failure, even if there is no indication for revascularization. MVR is associated with significant reverse remodelling, and UA with prohibitive risk of MR recurrence.

The Compatibility Between Biomphalaria glabrata Snails and Schistosoma mansoni: An Increasingly Complex Puzzle

This review reexamines the results obtained in recent decades regarding the compatibility polymorphism between the snail, Biomphalaria glabrata, and the pathogen, Schistosoma mansoni, which is one of the agents responsible for human schistosomiasis. Some results point to the snail's resistance as explaining the incompatibility, while others support a "matching hypothesis" between the snail's immune receptors and the schistosome's antigens. We propose here that the two hypotheses are not exclusive, and that the compatible/incompatible status of a particular host/parasite couple probably reflects the balance of multiple molecular determinants that support one hypothesis or the other. Because these genes are involved in a coevolutionary arms race, we also propose that the underlying mechanisms can vary. Finally, some recent results show that environmental factors could influence compatibility. Together, these results make the compatibility between B. glabrata and S. mansoni an increasingly complex puzzle. We need to develop more integrative approaches in order to find targets that could potentially be manipulated to control the transmission of schistosomiasis.

Krox20 heterozygous mice: A model of aortic regurgitation associated with decreased expression of fibrillar collagen genes

BACKGROUND

The mechanism involved in the onset of aortic valve (AoV) disease remains unclear despite its poor prognosis and frequency. Recently, we reported that Krox20 (EGR2 in humans) is involved in AoV development and dysfunction.

AIM

Analyze Krox20 heterozygous mice (Krox20(+/-)) to discover whether incomplete expression of Krox20 can cause valvular diseases.

METHODS

Transcriptional levels of Col1a2/COL1A2 and Krox20/EGR2 in AoVs from Krox20(+/-) mice and human patients operated on for severe aortic regurgitation were evaluated by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). Human control valves were obtained from three transplanted patients without AoV disease. Twenty-one heterozygous Krox20(+/-) mice were compared with 35 controls at different ages. Three independent measurements of valve thickness were performed on magnified tissue sections using Image J software. In vivo valve structure and function were evaluated using the high-frequency Vevo(®) 2100 echocardiogram.

RESULTS

qRT-PCR analysis using AoVs from patients with severe aortic regurgitation showed a decrease in EGR2 expression associated with significant downregulation of COL1A2 expression (P<0.05). Similar results were observed in the AoVs of Krox20(+/-) mice. Anatomical examination revealed that incomplete invalidation of Krox20 caused significant thickening of the aortic leaflet compared with controls (145±22 vs. 75±24μm; P=0.01). Within the mutant group, this thickening worsened significantly over time (Krox20(+/-) mice aged>7 vs.<7months: 136±48 vs. 102±41μm; P<0.001). Moreover, the aortic leaflets of embryonic day 18.5 Krox20(+/-) embryos were significantly more thickened than those from controls, suggesting that this disease begins during embryonic development. Echo-Doppler analysis showed a significant increase in AoV dysfunction in heterozygous versus control mice (53% vs. 17%; P<0.001), suggesting a tight relationship between valve architecture and function. Morphometric analysis revealed that the most severe AoV dysfunction was always associated with the most thickened valves. Classic histological analysis revealed that mutant AoVs had extracellular matrix disorganization, with features of human myxomatous degeneration, including excess of proteoglycan deposition in spongiosa and reduction of collagen fibre in fibrosa, but no calcification.

CONCLUSION

Decreased expression of Krox20 in mice causes degeneration of the aortic leaflets and disorganization of the extracellular matrix, causing valvular dysfunction.

Loss of Krox20 results in aortic valve regurgitation and impaired transcriptional activation of fibrillar collagen genes

AIMS

Heart valve maturation is achieved by the organization of extracellular matrix (ECM) and the distribution of valvular interstitial cells. However, the factors that regulate matrix components required for valvular structure and function are unknown. Based on the discovery of its specific expression in cardiac valves, we aimed to uncover the role of Krox20 (Egr-2) during valve development and disease.

METHODS AND RESULTS

Using series of mouse genetic tools, we demonstrated that loss of function of Krox20 caused significant hyperplasia of the semilunar valves, while atrioventricular valves appeared normal. This defect was associated with an increase in valvular interstitial cell number and ECM volume. Echo Doppler analysis revealed that adult mutant mice had aortic insufficiency. Defective aortic valves (AoVs) in Krox20(-/-) mice had features of human AoV disease, including excess of proteoglycan deposition and reduction of collagen fibres. Furthermore, examination of diseased human AoVs revealed decreased expression of KROX20. To identify downstream targets of Krox20, we examined expression of fibrillar collagens in the AoV leaflets at different stages in the mouse. We found significant down-regulation of Col1a1, Col1a2, and Col3a1 in the semilunar valves of Krox20 mutant mice. Utilizing in vitro and in vivo experiments, we demonstrated that Col1a1 and Col3a1 are direct targets of Krox20 activation in interstitial cells of the AoV.

CONCLUSION

This study identifies a previously unknown function of Krox20 during heart valve development. These results indicate that Krox20-mediated activation of fibrillar Col1a1 and Col3a1 genes is crucial to avoid postnatal degeneration of the AoV leaflets.

Vertebrate host protective immunity drives genetic diversity and antigenic polymorphism in Schistosoma mansoni

Schistosomes are gonochoric blood parasites with a complex life cycle responsible for a disease of considerable medical and veterinary importance in tropical and subtropical regions. Understanding the evolution of schistosome genetic diversity is clearly of fundamental importance to interpreting schistosomiasis epidemiology and disease transmission patterns of this parasite. In this article, we investigated the putative role of the host immune system in the selection of male genetic diversity. We demonstrated the link between genetic dissimilarity and the protective effect among male worms. We then compared the proteomes of three male clones with different genotypes and differing by their capacity to protect against reinfection. The identified differences correspond mainly to antigens known or supposed to be involved in the induction of protective immunity. These results underline the role played by host immune system in the selection of schistosome genetic diversity that is linked to antigenic diversity. We discuss the evolutionary consequences in the context of schistosome infection.

Distribution of Lymnaeidae (Mollusca: Pulmonata), intermediate snail hosts of Fasciola hepatica in Venezuela

An extensive malacological survey was carried out between 2005-2009 in order to clarify the exact number of lymnaeid species which may be intermediate hosts of Fasciola hepatica in Venezuela. Four species were discovered during this survey, including two local species: Lymnaea cubensis and Lymnaea cousini and two exotic species: Lymnaea truncatula and Lymnaea columella. The most common local species was L. cubensis which was found at 16 out of the 298 sampling sites. This species has a large distribution area throughout the Northern part of Venezuela and was encountered from sea level to an altitude of 1,802 m in state of Trujillo. The second local species L. cousini was collected at only two sites of the Andean Region at altitudes of 3,550 m and 4,040 m, respectively. The European L. truncatula was found at 24 sites all located in the states of Mérida and Táchira at an altitude varying between 1,540-4,000 m. The respective distribution areas of L. cubensis and L. truncatula do not appear to overlap, but more detailed malacological surveys are needed. The fourth lymnaeid species, L. columella was collected in a canal from Mérida at an altitude of 1,929 m and in an irrigation canal from the state of Guárico, at an altitude of 63 m. The role of these four lymnaeid species in the transmission of fascioliasis in Venezuela is discussed.

Ventricular arrhythmias during Tako-tsubo syndrome

Tako-tsubo syndrome is a recently described form of cardiomyopathy. Its pathophysiology remains unknown. However, the main demographic, clinical, electrocardiographic and biologic characteristics of the disease have been described by previous reports. Retrospective studies are essential to help describe this rare disease, although they might have several skews. Previous reports have observed a mortality rate between 0 and 8%. In our serie, demographic, clinical, electrocardiographic and biologic results are similar with those previously reported. However, the mortality rate observed was higher than expected. Refractory ventricular arrhythmias leading to death have been encountered in 15% of patients. Tako-tsubo syndrome may present as sudden death and its mortality rate may have been underestimated in previous reports.

[Left ventricular noncompaction: a cardiomyopathy in young individuals. Description of first cases in Africa]

Left ventricular noncompaction (LVNC) is a recently identified and probably rare congenital cardiomyopathy characterized by changes in the structure of the myocardium secondary to incomplete embryogenesis. The purpose of this report is to describe three cases of LVNC involving African patients. To our knowledge these are the first cases described in Africa. All three patients in this series were men from sub-Saharan Africa ranging in age from 23 to 45 years. The first patient in whom cardiomegaly was recognized on a routine chest x-ray was asymptomatic. The second who presented with exertional dyspnea developed left bundle branch block. The third was admitted to the hospital for acute pulmonary edema. In all three cases transthoracic echocardiography suggested diagnosis. The left ventricle was dilated and hypokinetic and the myocardium exhibited a spongy aspect in association with the presence of prominent trabeculations separated by crypts located at the apex and lateral wall. Color Doppler demonstrated that intratrabecular recesses were filled by intraventricular blood flow. Magnetic resonance imaging (MRI) specifically confirmed this morphological feature. Sudden death due to arrhythmia, cardiac insufficiency, and systemic emboli are the main complications of LVNC. The incidence of LVNC, which is certainly underestimated, is highest in young adults but it can be diagnosed at any age. Echocardiography and MRI are effective tools for detection of the morphologic diagnostic criteria. Recent evidence suggests that LVNC is of genetic origin and the data reported here shows that the underlying mutations are present in sub-Saharan populations. Family screening in African populations is still difficult. Therapeutic management is currently based on symptomatic treatment of cardiac insufficiency and can require techniques not readily available in tropical settings.

Are Biomphalaria snails resistant to Schistosoma mansoni?

Among Biomphalaria glabrata/Schistosoma mansoni snail–trematode combinations, it appears that some parasites succeed whilst others fail to infect snails. Snails that become infected are termed susceptible hosts. Those which are not infected are traditionally determined as ‘resistant’. Here the concept of B. glabrata resistance to S. mansoni is re-examined in the light of additional observations. It is suggested that, in B. glabrata/S. mansoni, compatibility is tested independently for each individual miracidium and host, and that the success or failure of an infection does not depend on the snail susceptibility/resistance status, but on the ‘matched’ or ‘mismatched’ status of the host and parasite phenotypes.

Geographical variations in infectivity and susceptibility in the host-parasite system Schistosoma mansoni/Biomphalaria glabrata: no evidence for local adaptation

We investigated local adaptation in the spatially structured natural Biomphalaria glabrata/Schistosoma mansoni host-parasite system in the marshy forest focus of Guadeloupe using cross-transplantation experiments. We demonstrated strong and highly significant variations in susceptibility/infectivity of host and parasite populations, respectively, but found no evidence of local adaptation neither for S. mansoni nor for B. glabrata. Environmental as well as genetic factors are discussed to explain susceptibility/infectivity variations between both host and parasite populations. The absence of local adaptation is discussed in relation to the metapopulation dynamics of both host and parasite, in particular their relative rates of dispersal at the scale under scrutiny. Our study constitutes the first cross-transplantation experiment concerning this host-parasite system of which both hosts and parasites came directly from the wild, excluding laboratory generations and experimental host passages.

Lymnaea cousini Jousseaume, 1887 (Gastropoda: Lymnaeidae): first record for Venezuela

Lymnaea cousini Jousseaume, 1887 was collected in Mucubaji, Merida State, Venezuela, from a permanent pond located at a very high altitude (3760 m). Identification of the collected specimens was made by comparison with the original description of the shell by Jousseaume and the description of the renal organ and reproductive system of topotypic specimens by Paraense.

Sex-specific genetic structure in Schistosoma mansoni: evolutionary and epidemiological implications

We studied the population genetic structure of 360 and 1247 adult Schistosoma mansoni using seven microsatellite and seven random amplified polymorphic DNA (RAPD) markers, respectively. Parasites were collected from their natural definitive host Rattus rattus in Guadeloupe (West Indies). We found a sex-specific genetic structure, a pattern never before reported in a parasitic organism. Male genotypes were more randomly distributed among rats than female genotypes. This interpretation was consistent with a lower differentiation between hosts for males relative to females, the higher genetic similarity between females in the same host and the observed local (i.e. within-individual-host) differences in allele frequencies between the two sexes. We discuss our results using ecological and immunological perspectives on host-parasite relationships. These results change our view on the epidemiology of schistosomiasis, a serious disease affecting humans in African and American intertropical zones.

Genetic structure in natural populations of flukes and snails: a practical approach and review

Several aspects of the coevolutionary dynamics in host-parasite systems may be better quantified based on analyses of population structure using neutral genetic markers. This includes, for example, the migration rates of hosts and parasites. In this respect, the current situation, especially in fluke-snail systems is unsatisfactory, since basic population genetics data are lacking and the appropriate methodology has rarely been used. After reviewing the forces acting on population structure (e.g. genetic drift or the mating system) and how they can be analysed in models of structured populations, we propose a simplified, indicative framework for conducting analyses of population structure in hosts and parasites. This includes consideration of markers, sampling, data analysis, comparison of structure in hosts and parasites and use of external data (e.g. from population dynamics). We then focus on flukes and snails, highlighting important biological traits with regard to population structure. The few available studies indicate that asexual amplification of flukes within snails strongly influences adult flukes populations. They also show that the genetic structure among populations in strongly affected by traits in other than snails (e.g. definitive host dispersal behaviour), as snails populations have limited migration. Finally more studies would allow us to deepen our current understanding of selective interference between flukes and snails (e.g. manipulation of host mating system by parasites), and evaluate how this affect population structure at neutral markers.

Studies on the biology of schistosomiasis with emphasis on the Senegal river basin

The construction of the Diama dam on the Senegal river, the Manantali dam on the Bafing river, Mali and the ensuing ecological changes have led to a massive outbreak of Schistosoma mansoni in Northern Senegal, associated with high intensity of infections, due to intense transmission, and the creation of new foci of S. haematobium. Data on the vectorial capacity of Biomphalaria pfeifferi from Ndombo, near Richard Toll, Senegal are presented with sympatric and allopatric (Cameroon) S. mansoni. Comparisons are made on infectivity, cercarial production, chronobiology of cercarial emergence and longevity of infected snails. Recent data on the intermediate host specificity of different isolates of S. haematobium from the Lower and Middle Valley of the Senegal river basin (SRB) demonstrate the existence of at least two strains of S. haematobium. The role of Bulinus truncatus in the transmission of S. haematobium in the Lower and Middle Valleys of the SRB is reviewed. Both S. haematobium and S. mansoni are transmitted in the same foci in some areas of the SRB.

Genetic diversity of Schistosoma mansoni within and among individual hosts (Rattus rattus): infrapopulation differentiation at microspatial scale

The distribution of genetic diversity in a local population of the trematode Schistosoma mansoni was determined within and between individual wild rats at a microspatial geographic scale of a standing water transmission site. Using RAPD markers, molecular variance and canonical correspondence analysis were performed to test the significance of genetic differentiation between infrapopulations. Of total gene diversity, 8 and 11% was partitioned between hosts trapped at few metres distance from each other. Significant temporal differentiation (2%) was also detected among schistosomes sampled at 6 month intervals with more infrapopulation pairs differentiated during the dry season of parasite transmission than during the rainy season (45 and 12%, respectively). A combination of factors such as restricted displacement of rats, patchy spatial aggregation of infected snails and limited cercarial dispersion in standing water are likely to promote the genetic differentiation observed between infrapopulations at this microgeographic scale.

Parasite (Schistosoma mansoni) and host (Biomphalaria glabrata) genetic diversity: population structure in a fragmented landscape

Random amplified polymorphic DNA (RAPD) markers were used to quantify genetic diversity within and between 5 populations of Schistosoma mansoni within its definitive host (Rattus rattus) and the 5 corresponding populations of the snail intermediate host (Biomphalaria glabrata) from a limited endemic area of murine schistosomiasis on the island of Guadeloupe. Analysis of molecular variance (AMOVA) and canonical correspondence analysis (CCA) were used to test the significance of genetic differentiation between populations. Both methods gave similar results. Of total gene diversity, 15.1% (AMOVA) and 18.8% (CCA) was partitioned between localities for S. mansoni with an absence of association between genetic and geographical distances. Geographical localities accounted for 20.5% (CCA) of the total diversity for B. glabrata populations. The genetic distances between pairs of parasite populations were not correlated with the genetic distances between the corresponding pairs of snail host populations. Such strong patterns of local differentiation of both parasite and snail populations are consistent with predictions based on metapopulation dynamics and may have implications on host-parasite susceptibility relationship through local adaptation processes.

Compatibility of Schistosoma mansoni Cameroon and Biomphalaria pfeifferi Senegal

The vectorial capacity of Biomphalaria pfeifferi from Ndiangue, Senegal, was investigated with an allopatric isolate of Schistosoma mansoni from Nkolbisson, Cameroon. The snail infection rate after exposure to a single miracidium per snail (MD1) was 56. 3 %, and 91.6%, for snails exposed to 5 miracidia per snail (MD5). The minimum pre-patent period was 21 days. The mean total cercarial production for the MDI group was 18,511 cercariae per snail, and 9757 cercariae for the MD5 group. The maximum production of cercariae for 1 day was 4892 observed in a snail from the MDI group at day 43 post-infection. The mean longevity of snails was higher in group MD1 (88 days p.i.) than in group MD5 (65 days p.i.). The chronobiological emergence pattern revealed a circadian rhythm with one shedding peak at mid-day. Comparisons are made with the vectorial capacity of the sympatric combination of B. pfeifferi Senegal/S. mansoni Senegal.

Metazoan parasites and resource heterogeneity: constraints and benefits

The usually narrow specificity of parasites still represents a puzzling question. We suggest that specialisation provokes aggregation of individuals at three levels (host species, hosts individuals, host microhabitats) and that one benefit for metazoan parasites lies in the frequency of genetic exchanges, in agreement with Rohde's hypothesis. We discuss two mechanisms that may maintain specificity after host speciation or host switching: alloxenic speciation by habitat preference and alloxenic speciation by assortative survival. We suggest that specialisation provokes aggregation, that aggregation increases genetic diversity, and that genetic diversity favours specialisation which is thus indefinitely restored.

Genetic diversity and recruitment pattern of Schistosoma mansoni in a Biomphalaria glabrata snail population: a field study using random-amplified polymorphic DNA markers

Random-amplified polymorphic DNA markers have been used to assess the amount and the distribution of the genetic diversity of Schistosoma mansoni within a natural population of Biomphalaria glabrata at a transmission site of the murine schistosomiasis focus of Guadeloupe. Despite high infection rate and heavy schistosome load within the definitive hosts (Ratus rattus), prevalences within intermediate snails ranged from 0.2 to 4.8%. Whatever the transmission season may be (rainy vs. dry), most of the infected snails were spatially aggregated and 88.4% of them harbored a single parasite genotype indicative of a monomiracidial infection; 4.7% had dual sex infections and a parasite intensity not exceeding 3 miracidia per snail. A substantial resistance level toward the parasite and recruitment regulatory process within snails may explain in part the observed low parasite prevalences and intensities. Considering such a distribution pattern of larval S. mansoni genetic diversity among B. glabrata, mobility of the definitive hosts, or rapid turnover of infected snails, or both, are required to maintain genetic heterogeneity within adult schistosome populations.

Compatibility of Schistosoma mansoni and Biomphalaria pfeifferi in northern Senegal

The construction of the Diama dam on the Senegal River and the ensuing ecological changes have led to a massive outbreak of Schistosoma mansoni infection in Northern Senegal, associated with very high intensity of infections, due to extremely intense transmission. The vectorial capacity of Biomphalaria pfeifferi from Ndombo, near Richard-Toll was investigated in order to assess the role of the snail-parasite relationship in this particular epidemiological situation. The results revealed an unusually high compatibility between the Senegalese S. mansoni strain and its local snail intermediate host, B. pfeifferi. The snail infection rate after exposure to a single miracidium per snail was 87%. The cercarial production of infected snails was very high, with a mean total production of 50,456 cercariae per snail. No significant difference was found in the total cercarial output between snails exposed to 1 miracidium and those exposed to 5 miracidia. The increase in the rate of cercarial output was significantly greater in snails exposed to 5 miracidia, but there was a higher mortality in this group. The chronobiological cercarial production pattern showed a peak around mid-day. The implications of these findings on the epidemiology of schistosomiasis in Northern Senegal are discussed.

Population biology of Schistosoma mansoni in the black rat: host regulation and basic transmission rate

A simple mathematical model was built to investigate the population biology of Schistosoma mansoni in its natural definitive host, the black rat (Rattus rattus). Prevalence and parasite abundance over 13 years from field studies and data from laboratory experiments were used to set up the model. Sensitivity analysis showed that the abundance of parasites is strongly influenced by variation in the values of infection parameters. The model shows that the parasite is able to control populations of definitive hosts. We discuss the factors that may explain the long-term persistence of S. mansoni among its natural definitive host, R. rattus and its intermediate host, the snail Biomphalaria glabrata in Guadeloupe (French West Indies). The impact of the parasite does not appear to explain the apparent persistence of the host-parasite association over a 13 year period. Our results seem to support the influence of environmental factors, which may act on the infection process by reducing, or increasing, the rate of encounters between hosts and free-living stages of the parasite.

Recombinant human interleukin-1-mediated killing of Schistosoma mansoni primary sporocysts in Biomphalaria glabrata

Previous work has indicated that injection of recombinant-human interleukin (rhIL)-1beta in Schistosoma mansoni-infected M-line Biomphalaria glabrata resulted in a significant reduction in the number of cercariae shed. The purpose of the present work was to determine if primary sporocysts were killed following rhIL-1beta injection in susceptible snails and, if so, to determine if killing was the direct result of hemocyte activity. Counting of primary sporocysts indicated a 50% reduction in the number surviving at 3 days PE in snails from 2 susceptible strains following injection. Histological analysis indicated that killing occurred with little-to-no observable hemocyte/parasite contact, whereas short-term culture of primary sporocysts with cell-free plasma (hemolymph) from injected snails rapidly initiated killing in vitro. Because levels of a snail IL-1-like molecule (SnaIL-1) drop significantly following schistosome exposure in M-line snails, because resistant snails maintain higher SnaIL-1 levels following infection, and because rhIL-1beta upregulates hemocyte cytotoxic mechanisms, these data support the contention that SnaIL-1 plays a role in determining resistance in B. glabrata. These data also indicate that schistosome death may be separated from parasite encapsulation by hemocytes and that an as yet unidentified humoral killing mechanism/factor may exist in B. glabrata. Lastly, these data further support the hypothesis that cytokine-like molecules are important, functionally conserved immunodefense mediators in both vertebrates and invertebrates.

Host choice by larval parasites: a study of Biomphalaria glabrata snails and Schistosoma mansoni miracidia related to host size

Within snail/trematode associations the age/size of the host at infection has consequences with regard to miracidial infection success, further intramolluscan parasite development and reproduction, and the host response, mainly in terms of growth and reproductive effort. Taking into account these differences, we were interested in determining whether miracidia could discriminate and make a choice between snails of different sizes. Using the Schistosoma mansoni/Biomphalaria glabrata system, we compared data on the snail infection rate and the mother sporocyst abundance among three size classes of snails (juvenile, subadult, and adult) exposed separately or together to the parasite larvae. When exposed individually, juvenile snails (3-5 mm) had significantly higher prevalence and abundance values than did subadult snails, followed by adult snails. In contrast, when snails of the three size classes were exposed together in heterogeneous size groups the prevalence and abundance values were always significantly higher for subadult snails of the 7- to 9-mm class than for juvenile and adult snails. A host choice experiment confirmed that significantly more miracidia were attracted by subadult snails, suggesting that the parasite has been selected for specific locating and recognition mechanisms increasing the infection rate of subadult snails when the latter have been exposed in a heterogeneous size group. Selective forces that may be responsible for such a preferential infectivity of the parasite vis-à-vis particular host age/size class are discussed in relation to host resources and host responses.

Age/size- and time-specific effects of Schistosoma mansoni on energy allocation patterns of its snail host Biomphalaria glabrata

Snail hosts of different ages constitute different resource environments for larval trematodes because each individual has a particular energy budget and energy allocation pattern at the time of infection. Effects of monomiracidial trematode infections on shell growth, body dry weight and reproductive effort of the snail host were compared between controls and infected juvenile and adult snails during the prepatent and patent periods. The results demonstrate phenotypic plasticity in the host response. There is an age/size-specific effect characterized by limitation of growth rate when snails are infected as juveniles and reduction of reproductive effort when snails are infected as adults, and a time-specific effect with early enhancement of growth rate and reproductive effort for infected juvenile and adult snails respectively during prepatency, before reduction and cessation during patency. The parasite is considered as a generalist in its energy exploitation strategy of the snail host, but taking into account the differential host responses observed relative to the host age, the possibility of a host preference for juvenile or adult snails is discussed.

Natural Schistosoma mansoni infection in wild rats from Guadeloupe: parasitological and immunological aspects

Rattus rattus is the predominant rodent in the mangrove area of Guadeloupe. Between 1990 and 1991 we found 73 R. rattus and five R. norvegicus. Among the infected rats with Schistosoma mansoni, 59% for R. rattus and 80% for R. norvegicus, the comparison of the median of the worm load was not statistically different. Both species of infected rats showed adult worms and eggs in the lungs and 20% of them showed, at the same time, two and even three generations of worms. Neither adults nor eggs were seen in the intestinal wall or stools of R. norvegicus, instead R. rattus had eggs in the liver, in the intestinal wall and the stools. Therefore, R. norvegicus gets infection as well as R. rattus, but does not participate in the transmission of the schistosomiasis. In order to elucidate this difference, we looked at the humoral recognition of these two rats, to the molecular antigens of the three stages of the parasite: cercaria, adult worm (AWA) and egg (SEA). In general, R. norvegicus recognized cercarial antigens more frequently than R. rattus, 73, 81 and 172 kDa being statistically different. Regarding AWA, molecules 82, 86, 117 and 150 kDa were recognized more often by R. rattus as compared to R. norvegicus. The reverse was true for the 18, 33 and 61 kDa. Only the differences between 61 and 150 kDa molecules were statistically significant. With respect to SEA, R. norvegicus recognized more 28, 45, 47, 49, 64 and 92 kDa molecules than R. rattus, but the latter recognized the 140 kDa molecules of SEA to a higher degree (95 and 140 kDa were significantly different). It is plausible that the immune response to cercarial invasion is more effective in R. norvegicus in allowing the parasites to reach adulthood, but it does not let them live in the mesenteric veins and therefore to lay their eggs in the intestinal wall and feces.

Intraspecific diversity of Schistosoma haematobium in west Africa: chronobiology of cercarial emergence

Cercarial emergence patterns were used to analyse the intraspecific variability within and between nine populations of Schistosoma haematobium collected along a transect line from the north to the South of the Ivory Coast (Africa) and using Bulinus truncatus or Bulinus globosus as intermediate snail hosts. Statistical comparison demonstrated the existence of a chronobiological polymorphism and the existence of three homogeneous groups of S. haematobium isolates with mean shedding times of the cercariae decreasing from the North to the South. The chronobiological variability observed was not correlated with the species of Bulinus (B. truncatus vs. B. globosus) implicated in the parasite transmission but with the climatic and vegetal features of the transmission area. S. haematobium from shaded sites of the forest zone (South) showed cercarial emergence patterns significantly earliest than that of S. haematobium from open sites of the savanna zone (North). Differences in sensitivity to light intensity could characterize the existence of eco-geographical races of S. haematobium one of the forest, the other from the savanna.