The Association between Environmental Lead Exposure and Bone Density in Children

Osteoporosis is a decrease in bone mineral density (BMD) that predisposes individuals to fractures. Although an elderly affliction, a predisposition may develop during adolescence if a sufficient peak BMD is not achieved. Rat studies have found that lead exposure is associated with decreased BMD. However, human studies are limited. We hypothesized that the BMD of children with high lead exposure would be lower than the BMD of children with low lead exposure. We collected data on 35 subjects; 16 had low cumulative lead exposure (mean, 6.5 μg/dL), and 19 had high exposure (mean, 23.6 μg/dL). All were African American; there was no difference between the groups by sex, age, body mass index, socioeconomic status, physical activity, or calcium intake. Significant differences in BMD between low and high cumulative lead exposure were noted in the head (1.589 vs. 1.721 g/cm(2)), third lumbar vertebra (0.761 vs. 0.819 g/cm(2)), and fourth lumbar vertebra (0.712 vs. 0.789 g/cm(2)). Contrary to our hypothesis, subjects with high lead exposure had a significantly higher BMD than did subjects with low lead exposure. This may reflect a true phenomenon because lead exposure has been reported to accelerate bony maturation by inhibiting the effects of parathyroid hormone–related peptide. Accelerated maturation of bone may ultimately result in a lower peak BMD being achieved in young adulthood, thus predisposing to osteoporosis in later life. Future studies need to investigate this proposed model

Paleoclimate and bubonic plague: a forewarning of future risk?

Pandemics of bubonic plague have occurred in Eurasia since the sixth century ad. Climatic variations in Central Asia affect the population size and activity of the plague bacterium's reservoir rodent species, influencing the probability of human infection. Using innovative time-series analysis of surrogate climate records spanning 1,500 years, a study in BMC Biology concludes that climatic fluctuations may have influenced these pandemics. This has potential implications for health risks from future climate change

Plague: past, present and future

[Introduction] Recent experience with SARS (severe acute respiratory syndrome) [1] and avian flu shows that the public and political response to threats from new anthropozoonoses can be near-hysteria. This can readily make us forget more classical animal-borne diseases, such as plague (Box 1). Three recent international meetings on plague (Box 2) concluded that: (1) it should be re-emphasised that the plague bacillus (Yersinia pestis) still causes several thousand human cases per year [2,3] (Figure 1); (2) locally perceived risks far outstrip the objective risk based purely on the number of cases [2]; (3) climate change might increase the risk of plague outbreaks where plague is currently endemic and new plague areas might arise [2,4]; (4) remarkably little is known about the dynamics of plague in its natural reservoirs and hence about changing risks for humans [5]; and, therefore, (5) plague should be taken much more seriously by the international community than appears to be the case

The Role of Vaccine Coverage within Social Networks in Cholera Vaccine Efficacy

Traditional vaccine trial methods have an underlying assumption that the effect of a vaccine is the same throughout the trial area. There are, however, many spatial and behavioral factors that alter the rates of contact among infectious and susceptible individuals and result in different efficacies across a population. We reanalyzed data from a field trial in Bangladesh to ascertain whether there is evidence of indirect protection from cholera vaccines when vaccination rates are high in an individual's social network.We analyzed the first year of surveillance data from a placebo-controlled trial of B subunit-killed whole-cell and killed whole-cell-only oral cholera vaccines in children and adult women in Bangladesh. We calculated whether there was an inverse trend for the relation between the level of vaccine coverage in an individual's social network and the incidence of cholera in individual vaccine recipients or placebo recipients after controlling for potential confounding variables.Using bari-level social network ties, we found incidence rates of cholera among placebo recipients were inversely related to levels of vaccine coverage (5.28 cases per 1000 in the lowest quintile vs 3.27 cases per 1000 in the highest quintile; p = 0.037 for trend). Receipt of vaccine by an individual and the level of vaccine coverage of the individual's social network were independently related to a reduced risk of cholera.Findings indicate that progressively higher levels of vaccine coverage in bari-level social networks can lead to increasing levels of indirect protection of non-vaccinated individuals and could also lead to progressively higher levels of total protection of vaccine recipients

Novel Genetic Tools for Diaminopimelic Acid Selection in Virulence Studies of Yersinia pestis

Molecular studies of bacterial virulence are enhanced by expression of recombinant DNA during infection to allow complementation of mutants and expression of reporter proteins in vivo. For highly pathogenic bacteria, such as Yersinia pestis, these studies are currently limited because deliberate introduction of antibiotic resistance is restricted to those few which are not human treatment options. In this work, we report the development of alternatives to antibiotics as tools for host-pathogen research during Yersinia pestis infections focusing on the diaminopimelic acid (DAP) pathway, a requirement for cell wall synthesis in eubacteria. We generated a mutation in the dapA-nlpB(dapX) operon of Yersinia pestis KIM D27 and CO92 which eliminated the expression of both genes. The resulting strains were auxotrophic for diaminopimelic acid and this phenotype was complemented in trans by expressing dapA in single and multi-copy. In vivo, we found that plasmids derived from the p15a replicon were cured without selection, while selection for DAP enhanced stability without detectable loss of any of the three resident virulence plasmids. The dapAX mutation rendered Y. pestis avirulent in mouse models of bubonic and septicemic plague which could be complemented when dapAX was inserted in single or multi-copy, restoring development of disease that was indistinguishable from the wild type parent strain. We further identified a high level, constitutive promoter in Y. pestis that could be used to drive expression of fluorescent reporters in dapAX strains that had minimal impact to virulence in mouse models while enabling sensitive detection of bacteria during infection. Thus, diaminopimelic acid selection for single or multi-copy genetic systems in Yersinia pestis offers an improved alternative to antibiotics for in vivo studies that causes minimal disruption to virulence

Finding a Disappearing Nontimber Forest Resource: Using Grounded Visualization to Explore Urbanization Impacts on Sweetgrass Basketmaking in Greater Mt. Pleasant, South Carolina

Despite growing interest in urbanization and its social and ecological impacts on formerly rural areas, empirical research remains limited. Extant studies largely focus either on issues of social exclusion and enclosure or ecological change. This article uses the case of sweetgrass basketmaking in Mt. Pleasant, South Carolina, to explore the implications of urbanization, including gentrification, for the distribution and accessibility of sweetgrass, an economically important nontimber forest product (NTFP) for historically African American communities, in this rapidly growing area. We explore the usefulness of grounded visualization for research efforts that are examining the existence of fringe ecologies associated with NTFP. Our findings highlight the importance of integrated qualitative and quantitative analyses for revealing the complex social and ecological changes that accompany both urbanization and rural gentrification

Metapopulation structure for perpetuation of Francisella tularensis tularensis

<p>Abstract</p> <p>Background</p> <p>Outbreaks of Type A tularemia due to <it>Francisella tularensis tularensis </it>are typically sporadic and unstable, greatly hindering identification of the determinants of perpetuation and human risk. Martha's Vineyard, Massachusetts has experienced an outbreak of Type A tularemia which has persisted for 9 years. This unique situation has allowed us to conduct long-term eco-epidemiologic studies there. Our hypothesis is that the agent of Type A tularemia is perpetuated as a metapopulation, with many small isolated natural foci of transmission. During times of increased transmission, the foci would merge and a larger scale epizootic would occur, with greater likelihood that humans become exposed.</p> <p>Methods</p> <p>We sampled questing dog ticks from two natural foci on the island and tested them for tularemia DNA. We determined whether the force of transmission differed between the two foci. In addition, we examined the population structure of <it>F. tularensis </it>from ticks by variable number tandem repeat (VNTR) analysis, which allowed estimates of diversity, linkage disequilibrium, and eBURST analysis.</p> <p>Results</p> <p>The prevalence of tularemia DNA in ticks from our two field sites was markedly different: one site was stable over the course of the study yielding as many as 5.6% positive ticks. In contrast, infected ticks from the comparison site markedly increased in prevalence, from 0.4% in 2003 to 3.9% in 2006. Using 4 VNTR loci, we documented 75 different haplotypes (diversity = 0.91). eBURST analysis indicates that the stable site was essentially clonal, but the comparison site contained multiple unrelated lineages. The general bacterial population is evolving clonally (multilocus disequilibrium) and the bacteria in the two sites are reproductively isolated.</p> <p>Conclusion</p> <p>Even within an isolated island, tularemia natural foci that are no more than 15 km apart are uniquely segregated. One of our sites has stable transmission and the other is emergent. The population structure at the stable site is that of a clonal complex of circulating bacteria, whereas the emerging focus is likely to be derived from multiple founders. We conclude that the agent of tularemia may perpetuate in small stable natural foci and that new foci emerge as a result of spillover from such stable sites.</p

Nonrandom Distribution of Vector Ticks (Dermacentor variabilis) Infected by Francisella tularensis

The island of Martha's Vineyard, Massachusetts, is the site of a sustained outbreak of tularemia due to Francisella tularensis tularensis. Dog ticks, Dermacentor variabilis, appear to be critical in the perpetuation of the agent there. Tularemia has long been characterized as an agent of natural focality, stably persisting in characteristic sites of transmission, but this suggestion has never been rigorously tested. Accordingly, we sought to identify a natural focus of transmission of the agent of tularemia by mapping the distribution of PCR-positive ticks. From 2004 to 2007, questing D. variabilis were collected from 85 individual waypoints along a 1.5 km transect in a field site on Martha's Vineyard. The positions of PCR-positive ticks were then mapped using ArcGIS. Cluster analysis identified an area approximately 290 meters in diameter, 9 waypoints, that was significantly more likely to yield PCR-positive ticks (relative risk 3.3, P = 0.001) than the rest of the field site. Genotyping of F. tularensis using variable number tandem repeat (VNTR) analysis on PCR-positive ticks yielded 13 different haplotypes, the vast majority of which was one dominant haplotype. Positive ticks collected in the cluster were 3.4 times (relative risk = 3.4, P<0.0001) more likely to have an uncommon haplotype than those collected elsewhere from the transect. We conclude that we have identified a microfocus where the agent of tularemia stably perpetuates and that this area is where genetic diversity is generated