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PubMed1995

Summary of the Seychelles child development study on the relationship of fetal methylmercury exposure to neurodevelopment.

The Seychelles Child Development Study is examining the association between fetal methylmercury exposure from a maternal diet high in fish and subsequent child development. The study is double blind and uses maternal hair mercury as the index of fetal exposure. An initial cross-sectional pilot study of 804 infants aged 1 to 25 months suggested that mercury may affect development. A follow up of 217 pilot children at 66 months of age also suggested that neurodevelopmental effects might be present, but the result was dependent on outcomes in a small number of children. On the basis of initial results in the pilot study a prospective, longitudinal main study with more covariates and expanded endpoints was begun on a new cohort of 779 children. No association with neurodevelopment was seen at 6 1/2, 19, or 29 months of age, but there was an inverse relationship at 29 months in boys only between mercury level and activity as judged by the examiner. Adverse neurodevelopmental effects from fetal mercury exposure in the pilot study are highly dependent on how the data are analyzed and no definite effects have been detected through 29 months of age in the main study. In a related study, 32 brains were obtained at autopsy from Seychellois infants. These were examined histologically and analyzed for mercury. No clear histological abnormalities were found. Mercury levels ranged from a background of about 50 ppb up to 300 ppb, and correlated well between brain regions. For 27 brains maternal hair from delivery was available and hair mercury correlated well with brain mercury.

Child Development↗

PubMed1996

Control of intestinal parasitic infections in Seychelles: a comprehensive and sustainable approach.

Intestinal parasitic infections have been perceived as a public health problem in Seychelles for decades. A comprehensive strategy to reduce morbidity and, in the long term, transmission of intestinal parasites has been implemented successfully since 1993. Management of the programme is integrated into the well established primary health care system, with control activities being undertaken through existing health facilities. The strategy is based on periodic chemotherapy of schoolchildren, intense health education and improvement of sanitation and safe water supply. The initial objectives of the control programme were met after 2 years of activities, with an overall reduction in prevalence of intestinal parasitic infections of 44%. The intensity of infection with Trichuris trichiura, the commonest parasite, was halved (from 780 to 370 eggs per g of faeces). The programme's integrated approach, in concert with political commitment and limited operational costs, is a warranty for the future sustainability of control activities. The programme can be seen as a model for other developing countries, even where health and socioeconomic conditions are different and the control of parasitic infections will need a much longer-term commitment.

Adolescent↗

PubMed1997

Effects of prenatal methylmercury exposure from a high fish diet on developmental milestones in the Seychelles Child Development Study.

Mercury is widespread in the environment and exists in several physical and chemical forms. Prenatal exposure to methylmercury disrupts brain development. The most common mode of prenatal methylmercury exposure is maternal fish consumption. Studies of human prenatal exposure in Iraq following maternal ingestion of methylmercury treated grain suggested that maternal hair mercury concentrations above 10 ppm may be related to delayed developmental milestones and neurological abnormalities. This level of exposure can be achieved by frequent consumption of fish. The Seychelles Child Development Study analyzed developmental milestones similar to those determined in Iraq in a large controlled, prospective study of children exposed prenatally to methylmercury when their mothers ate fish. As part of this ongoing study, cohort children were evaluated at 6.5, 19, 29, and 66 months of age. At 19 months care-givers were asked at what age the child walked (n=720 out of 738) and talked (n=680). Prenatal mercury exposure was determined by atomic absorption analysis of maternal hair segments corresponding to hair growth during the pregnancy. The median mercury level in maternal hair was 5.8 ppm with a range of 0.5-26.7 ppm. The mean age (in months) at walking was 10.7 (SD = 1.9) for females and 10.6 (SD = 2.0) for males. The mean age at talking (in months) was 10.5 (SD = 2.6) for females, and 11.0 (SD = 2.9) for males. After adjusting for covariates and statistical outliers, no association was found between the age at which Seychellois children walked or talked and prenatal exposure to mercury. Normal ages at achievement of the developmental milestones walking and talking were found in Seychellois toddlers following prenatal exposure to methylmercury from a maternal fish diet. These results do not support the lowest effect levels in young children following prenatal methylmercury exposure predicted by the dose response analysis of the Iraq data. More detailed studies in older children are needed to determine if there are adverse effects in fish eating populations.

Animals↗

PubMed2003

Using measurement error models to assess effects of prenatal and postnatal methylmercury exposure in the Seychelles Child Development Study.

Studies of the effects of environmental exposures on human health typically require estimation of both exposure and outcome. Standard methods for the assessment of the association between exposure and outcome include multiple linear regression analysis, which assumes that the outcome variable is observed with error, while the levels of exposure and other explanatory variables are measured with complete accuracy, so that there is no deviation of the measured from the actual value. The term measurement error in this discussion refers to the difference between the actual or true level and the value that is actually observed. In the investigations of the effects of prenatal methylmercury (MeHg) exposure from fish consumption on child development, the only way to obtain a true exposure level (producing the toxic effect) is to ascertain the concentration in fetal brain, which is not possible. As is often the case in studies of environmental exposures, the measured exposure level is a biomarker, such as the average maternal hair level during gestation. Measurement of hair mercury is widely used as a biological indicator for exposure to MeHg and is the only indicator that has been calibrated against the target tissue, the developing brain. Variability between the measured and the true values in explanatory variables in a multiple regression analysis can produce bias, leading to either over or underestimation of regression parameters (slopes). Fortunately, statistical methods known as measurement error models (MEM) are available to account for measurement errors in explanatory variables in multiple regression analysis, and these methods can provide an (either "unbiased" or "bias-corrected") estimate of the unknown outcome/exposure relationship. In this paper, we illustrate MEM analysis by reanalyzing data from the 5.5-year test battery in the Seychelles Child Development Study, a longitudinal study of prenatal exposure to MeHg from maternal consumption of a diet high in fish. The use of the MEM approach was made possible by the existence of independent, calibration data on the magnitude of the variability of the measurement error deviations for the biomarker of prenatal exposure used in this study, the maternal hair level. Our reanalysis indicated that adjustment for measurement errors in explanatory variables had no appreciable effect on the original results.

Adult↗

PubMed2003

Sex-specific associative learning cues and inclusive fitness benefits in the Seychelles warbler.

In cooperative breeding vertebrates, indirect fitness benefits would be maximized by subordinates that accurately assess their relatedness to group offspring and preferentially help more closely related kin. In the Seychelles warbler (Acrocephalus sechellensis), we found a positive relationship between subordinate-nestling kinship (determined using microsatellite marker genotypes) and provisioning rates, but only for female subordinates. Female subordinates that helped were significantly more related to the nestlings than were nonhelpers, and the decision to help appears to be based on associative learning cues. High levels of female infidelity means that subordinates cannot trust their legitimacy through the male line, consequently they appear to use the continued presence of the primary female, but not the primary male, as a reliable cue to determine when to feed nestlings. By using effective discrimination, female subordinates are able to maximize the indirect benefits gained within a cooperative breeding system otherwise driven primarily by direct breeding benefits.

Animals↗

PubMed2001

Evidence that helping at the nest does not result in territory inheritance in the Seychelles warbler.

In an environment that has a shortage of territories, helping to rear younger siblings ('alloparenting') is proposed to facilitate territory acquisition in two ways: (i) through group augmentation that leads to an increase of the territory with subsequent partial inheritance (budding); and (ii) through site dominance that leads to greater success when competing for the natal or a nearby territory after the death of the territory owner (complete territory inheritance). Most young Seychelles warbler (Acrocephalus sechellensis) males either show alloparenting or budding behaviour. Future budders had significantly more aggressive interactions with neighbours and assisted their parents more with territory defence than similarly aged future alloparents or non-helpers. This led to an increase of the natal territory of future budders before actual budding took place, whereas the natal territories of future alloparents remained constant in size. Alloparents never became budders and vice versa, refuting partial inheritance as an advantage of alloparenting. Natural male breeding vacancies were never inherited by alloparents born on vacant or other territories, but were inherited by budders born on the vacant territory or, if these were absent, predominantly by budders from neighbouring territories. We offer explicit experimental evidence against the 'helping at the nest to inherit' hypothesis. Experimentally created male breeding vacancies, with both a male alloparent and a similarly aged sibling budder present simultaneously in the vacant territory, were filled by budders only. Site dominance over territory inheritance is linked to budding and not to alloparenting.

Animals↗

PubMed2005

Coral recovery at Aldabra Atoll, Seychelles: five years after the 1998 bleaching event.

Changes in reef benthos were assessed at Aldabra Atoll following the mass coral bleaching event of 1998. Video transects were used to survey the benthos and analysed using the Australian Institute of Marine Science five-dot method. Comparison of coral cover data collected by the Cambridge Southern Seychelles Atoll Research Programme with data collected during this study revealed that mortality of coral at Aldabra following the bleaching event was approximately 66% at 10 m depth and 38% at 20 m depth. Five years on, there are signs of hard coral recovery at some locations, but in spite of several years of high coral recruitment (7-9 recruits per m2 at 10 m depth, 4-6 recruits per m2 at 20 m depth, where recruits are defined as any colony under 5 cm maximum diameter), recovery of hard coral has not occurred at a significant level. There has been a considerable increase in soft coral cover at some locations, which was dominated by the genus Rhytisma. Macro algal cover did not increase following the bleaching event, although, as would be expected, dead corals have been colonized by coralline algae. There have been no further events leading to large-scale coral mortality at Aldabra since 1998.

Animals↗

PubMed2005

Reef fish diversity at Aldabra Atoll, Seychelles, during the five years following the 1998 coral bleaching event.

Quantitative surveys of fish-species diversity were undertaken at 10 m and 20 m water depth on the outer reef at Aldabra Atoll, southern Seychelles, between November 1999 and May 2003. No significant changes in total fish-species diversity, numbers of families represented by these species, or numbers of pomacentrid or chaetodontid species were seen, contrary to fish-diversity changes seen on coral bleaching-impacted reefs elsewhere. The lack of additional anthropogenic pressures at remote Aldabara may make this system, and others like it, more tolerant of bleaching-related population changes.

Animals↗

PubMed1995

Compliance with medication among outpatients with uncontrolled hypertension in the Seychelles.

Owing to increasing rates of hypertension and cardiovascular-related diseases in developing countries, compliance with antihypertensive medication is major public health importance. Few studies have reported on compliance in developing countries. We determined the compliance of 187 patients with uncontrolled hypertension in the Seychelles (Indian Ocean), by assessing the presence of a biologic marker (riboflavin) in the urine. The urine tested positive in 56% of the cases. Compliance varied from one physician to another (highest 72% versus lowest 33%, P = 0.003), improved with the level of literacy (62% versus 45%, P = 0.024), and depended on the presence absence of diuretics in the medication (respectively, 45% versus 66%, P = 0.005). The ability of patients to report correctly the number of antihypertensive pills to be taken daily was a predictor of compliance (62% of the patients who gave appropriate answers had positive urine for the marker versus 31% for those giving inappropriate answers).

Aged↗

PubMed1989