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Few studies have addressed co-occurring methylmercury (MeHg) from maternal origin and ethylmercury (EtHg) from Thimerosal-containing vaccines (TCVs) during infant's neurodevelopment. We studied children (n=1139) from the Western Amazon based on combined (low, intermediate, and high) exposure to chronic MeHg from fish consumption and acute TCV- EtHg. Neurodevelopment outcomes were age of walking and age of talking, and the Bayley Scale of Infant Development (BSID). The Mental Developmental Index (MDI) and Psychomotor Developmental Index (PDI) were measured at six and 24 months of age. Median hair-Hg (HHg) at birth was 6.4µgg(-1) in mothers, and 1.94µgg(-1) in newborns; total (pregnancy and infancy) EtHg exposure ranged from 0 to 187.5µg. The combined (MeHg+EtHg) exposure showed significant differences for MDI but not for PDI; however, there was a significant decrease in both MDI and PDI scores at 24 months. The increase in BSID delays (scores <80) between six and 24 months was not discernible with regards to EtHg or MeHg exposure. We found a statistically significant increase in neurodevelopmental (BSID) delays related to the combined exposure to Hg (MeHg>EtHg). Neurodevelopment delays due to low-doses of organic mercury (albeit undiscernible) are not predictable but can be avoided by choosing low-Hg fish and providing Thimerosal-free vaccines., (Copyright © 2015 Elsevier Inc. All rights reserved.)

The variance of variables associated with neurodevelopment at 180 days, pre-natal variables (Hg in placenta, blood and hair) and post-natal Hg exposure (including Thimerosal-containing vaccines, TCV) were examined in 82 exclusively breastfed infants using principal component analysis (PCA). This multivariate method was applied to identify hierarchy and sets of interrelated variables. The PCA yielded a two-factor solution, explaining 92% of variance and summarizing most of the relevant information in the dataset matrix: the first component represented birth weight and vaccine (first doses of Hepatitis B and DTP) variability and explained 57% of variance; the second component represented a gradient of neurodevelopment (Gesell scores) and explained 35% of variance. The third component explained only 3% of the remaining 8% variance. Beside CNS priming by breastfeeding, infant development (birth weight) and time of immunization with TCV should be considered in epidemiological studies. PCA can classify sets of variables related to vaccination and neuromotor development schedules, clearly discriminating between earlier and later TCV exposures of exclusively breastfed infants. In conclusion, the incommensurable concept of the chance of toxic risk caused by TCV-EtHg exposure against the proven benefit of immunization is in no way disputed here. However, infant neurodevelopmental (ND) disorders linked to Thimerosal-Hg stands in need of proof, but PCA points to the possibility of identifying exposure risk variables associated with ND schedules.

Aim: Brazilian newborns immunized with hepatitis-B (thimerosal containing vaccine, TCV) receive the first dose within 24 h if delivered in public hospitals, but at a later time if born in private hospitals. We compared neurodevelopment (ND) in infants born in a state hospital (immunized within 24 h) and in privately run hospitals (immunized 2-4 days postnatally)., Methods: We used the Gesell Developmental Schedules in 82 healthy exclusively breastfed infants at 6 months to assess motor skills, language development, comprehension capacity and social skills., Results: Compared to the group immunized 2-4 days after hospital discharge, the group immunized within 24 h showed no significant difference in ND delays. Despite the variation in gestational age (range 36-42 weeks) and TCV-ethylmercury (EtHg) dose (5.7-11.3 microg Hg/kg b.w.) at birth, time of exposure to TCV showed no significant association with ND. Gesell Developmental Score was not significantly correlated with total parenteral EtHg/unit of body mass neither with the relative increase in hair-Hg (as an additional challenge to prenatal Hg exposure)., Conclusion: In breastfed infants, differences in early exposure to TCV-EtHg cannot portend clinical neurodevelopment delays at 6 months. We speculate that breastfeeding remains a significant strategy to improve central nervous system protection of infants facing early exposure challenges.

In the transitioning Amazon, we addressed birth environment (home vs hospital) and associated perinatal organic-Hg exposures: methylmercury (MeHg) from maternal fish consumption and ethylmercury (EtHg) from pediatric Thimerosal-containing vaccines (TCVs) taken systematically during hospital delivery. We studied 365 children in relation to linear growth at 60 months and neurodevelopment (milestone achievements, Bayley Scale of Infant Development/BSID at 24 months, and Stanford-Binet intelligence tests at 60 months). Mothers delivered in hospitals vs those gave birth at home had significantly (p<0.0001) lower hair-Hg (HHg) concentrations (12.2 vs 23.9μg/g respectively) and shorter length of breastfeeding (8.5 vs 9.7 months respectively). Home-born children had significantly (p<0.0001) higher HHg (7.1μg/g) than hospital-born children (4.6μg/g). Hospital-born children also had significantly earlier (p<0.0001) hepatitis B vaccine than home-born children (1.5 vs 24.1days respectively) and higher (p<0.0001) exposures to total TCV-EtHg (75.8 vs 49.3μg respectively). Neither anthropometric indices nor neurodevelopment (except for fluid reasoning) were directly affected by birth environment. The percentage of hospital-born children with BSID (MDI or PDI) scores <80 was not significantly different from those born at home. In spite of the differences in HHg and EtHg levels between hospital-born and home-born children, no impact on neurodevelopment was observed. [ABSTRACT FROM AUTHOR]