In This Issue

doi:10.1073/iti4819116

New Research In

Civil unrest and Ebola control

Transmission electron micrograph of the Ebola virus. Image courtesy of the Centers for Disease Control and Prevention/Cynthia Goldsmith.

Violence targeting healthcare workers and treatment centers in the Democratic Republic of Congo (DRC) has affected Ebola treatment and prevention efforts, but the degree to which civil unrest has obstructed public health responses to Ebola in the DRC is unclear. To determine how conflict affected the Ebola epidemic in North Kivu and Ituri between April 30, 2018, and June 23, 2019, Chad Wells, Abhishek Pandey, et al. (pp. 24366–24372) constructed a timeline of conflict events throughout the course of the Ebola epidemic, an ethnographic appraisal of the local conditions that preceded and followed conflict events, and a model of Ebola transmission and control using data from the World Health Organization. The time from symptom onset to case isolation varied, as did population-level effectiveness of vaccination, due to preceding unrest and subsequent impacts of conflict events. Surges of Ebola incidence coincided with intensified conflict. Moreover, during the first week of vaccine administration, prior to any disruptive events, vaccination effectiveness was 52%; following disruptive conflict, vaccination effectiveness dropped to a minimum of 4.8% over the course of the epidemic. The results suggest that conflict events repeatedly reversed a declining phase of the Ebola epidemic in the DRC, according to the authors. — M.S.

Nonneuronal cells and human brain evolution

Studies of human brain evolution have largely focused on changes in the number and functions of neurons. As a result, the contribution of nonneuronal brain cell types to human brain evolution has not been clear, even though the cells have been implicated in brain development, cognitive function, and neuropsychiatric disorders. Stefano Berto, Isabel Mendizabal, Noriyoshi Usui, Kazuya Toriumi, et al. (pp. 24334–24342) used RNA sequencing to compare whole-genome levels of gene expression in nuclei from different cell types in the prefrontal cortex of humans, chimpanzees, and rhesus macaques. Compared with neurons, nonneuronal cells called oligodendrocytes showed greater changes in gene expression in the human lineage relative to the chimpanzee lineage. The findings suggest that gene expression in oligodendrocytes has undergone more rapid evolution than in neurons within the human lineage. In addition, genes showing human-specific expression in oligodendrocytes are associated with neuropsychiatric diseases such as attention deficit hyperactivity disorder, bipolar disorder, major depressive disorder, autism spectrum disorder, and schizophrenia. Moreover, analysis of whole-transcriptome data from oligodendrocytes in the prefrontal cortex of 23 patients with schizophrenia and healthy donors revealed that genes dysregulated in schizophrenia overlap with genes showing human-specific expression. According to the authors, the findings suggest that oligodendrocytes may have played an important role in the evolution of the human brain and cognitive diseases. — J.W.

Artisanal gold mining and sediment transport in the Amazon

Satellite images from dry season in the Madre de Dios region showing increased deforestation and suspended sediment in rivers (orange) associated with artisanal gold mining from 1984 to 2019. Landsat imagery courtesy of NASA Goddard Space Flight Center and US Geological Survey.

Artisanal-scale gold mining (ASGM), which has been expanding worldwide, often facilitates deforestation and can lead to increased sediment transport into nearby rivers. The subsequent impacts of ASGM on river hydrological properties in tropical systems, such as the Peruvian Amazon, are not well understood. Evan Dethier et al. (pp. 23936–23941) examined 34 years of satellite images to determine the effects of ASGM on suspended sediment concentrations (SSC) in 32 river reaches in the Madre de Dios River (MDDR) watershed in the Peruvian Amazon, a global biodiversity hotspot. Eighteen of the sites were classified as affected by ASGM, having a significant amount of upstream deforestation associated with ASGM activity. The authors observed significant increases in SSC in 16 out of 18 affected sites. By contrast, only 5 out of 14 unaffected sites exhibited significant SSC increases. Increases tended to be large during the dry season, when SSC at unaffected sites is low, leading to inversion of natural seasonal SSC cycles. Such increases in SSC and the resulting elevated turbidity are likely to substantially affect fish community structure. Additionally, ASGM-associated sediments tend to be associated with mercury and their increase may facilitate mercury transport to nearby communities. The results suggest that ASGM has contributed to deteriorating water quality in the MDDR region, and provide a framework for further evaluating environmental impacts of ASGM worldwide, according to the authors. — B.D.

Gut microbes and colorectal cancer

Previous studies have found that alterations in colon-associated microbes can raise the risk of colorectal cancer (CRC) in humans. Iradj Sobhani et al. (pp. 24285–24295) attempted to uncover genetic mechanisms by which alterations in colon-associated microbes might promote CRC. Experiments in which fecal microbes were transferred from patients with CRC or from healthy controls to germ-free mice exposed to the carcinogen azoxymethane revealed that after 7–14 weeks of transfer, mice that received fecal microbes from CRC patients exhibited greater numbers of aberrant crypts in colonic tissues, as well as increased epithelial cell division, increased inflammation, and greater epigenetic changes in the colonic mucosa, compared with mice that received fecal microbes from healthy controls. Next, the authors computed a cumulative methyl index (CMI)—a measure of DNA methylation changes in gene promoters—in blood samples from a cohort of participants with normal colonoscopies as well as patients with CRC. In a pilot study of 266 people, blood DNA methylation levels of 3 genes—Wif1, PENK, and NPY—were tied to CRC-associated colon microbe changes. In a separate cohort of 1,000 people, patients with CRC exhibited higher CMI for these 3 genes, compared with healthy controls. Metagenomic analysis revealed that the abundance of some bacterial species, such as Parvimonas, was directly associated with increased blood CMI. According to the authors, alterations in colon-associated microbes may trigger DNA methylation changes that promote CRC, raising the possibility that changes in gut microbes and DNA methylation may serve as potential biomarkers of CRC. — P.N.

Puberty and stress reactivity in humans

Humans exposed to adversity in infancy show a blunted response of the stress hormone cortisol. Megan Gunnar et al. (pp. 23984–23988) report that puberty may open a window of opportunity for the recalibration of the hypothalamic–pituitary–adrenocortical (HPA) axis, a hormonal system that controls stress responses. Two hundred ninety-nine youths, aged 7–15 years at the start of the study, participated in 3 sessions across consecutive years. Of the participants, 129 individuals were previously institutionalized as infants or toddlers before being adopted into generally supportive, well-resourced homes, whereas 170 individuals were born and raised in their natal families. Using saliva samples, the authors measured cortisol reactivity to social evaluative stress as the participants engaged in public speaking and mental arithmetic while being evaluated by judges. At the individual level, cortisol reactivity in postinstitutionalized participants rose with increasing pubertal stage, becoming more similar to that of nonadopted individuals. By contrast, cortisol reactivity did not rise significantly with increasing pubertal stage in nonadopted participants. According to the authors, the findings suggest that interventions to improve the supportiveness of caregiving environments during puberty may have a strong impact on HPA axis function. — J.W.

Hurricane damage in the United States

In the United States, hurricanes are among the most expensive natural disasters, but comparing the damage from recent and historical storms is challenging because of changing factors, such as the value of vulnerable property over time. Aslak Grinsted et al. (pp. 23942–23946) developed a method to compare the impact of hurricanes across the centuries and report that storms have become more damaging over time. The authors’ method accounts for, or normalizes, changes in exposed wealth. Instead of framing storms in terms of economic damage, the method frames losses in terms of a more easily quantified factor: land area. Using an insurance industry database, the authors calculated the amount of land totally destroyed by 247 storms from 1900 to 2018. Using the normalization method, the authors found that the frequency of more damaging storms is increasing faster than that of moderately damaging storms. According to the authors, the approach accounts for differences in wealth, population, and spatial differences, and provides evidence for the impact of climate change on increasing storm intensity, but it does not address changes in vulnerability. — T.H.D.

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