African Sources Research Articles

Out of Africa: novel source of small hive beetles infesting Eastern and Western honey bee colonies in China

Small hive beetles (SHB, Aethina tumida Murray, Coleoptera: Nitidulidae) are parasites of social bee colonies endemic to sub-Saharan Africa and have become an invasive species. Even though the global spread of SHB seems inevitable, the origin of novel introductions and their impact on new host populations need to be investigated to foster mitigation. Here, we report a case of SHBs from China and use COI gene sequencing to trace their origin. Since July 2018, beetle infestations of Eastern (Apis cerana) and Western (Apis mellifera) honey bee colonies with clinical symptoms were repeatedly reported from two Chinese provinces. These infestations apparently had a severe impact on A. cerana. Using morphometrics, genetics and clinical symptoms in the field, the beetles were confirmed to be A. tumida. The DNA sequences suggest an introduction from a yet unidentified African source similar to the Philippines, but very different to any other previously reported SHB haplotypes. The establishment of SHB in China underlines the need to limit novel introductions. Given that Eastern honey bees and possibly other Apis spp. are susceptible to SHB infestations, our findings highlight the need for adequate protection measures of endemic Asian honey bees.

Food and waterborne protozoan parasites: The African perspective

Parasitic food-borne diseases, particularly those caused by the protozoan parasites Cryptosporidium, Giardia, Cyclospora cayetanensis and Entamoeba are increasingly becoming common and have received considerable attention in the last two decades. The ability of the transmission stages of the parasites to survive in the environment for prolonged periods, globalization of the food industry and changes in eating habits have contributed to the numbers of human infections. This systematic scoping review highlights these important water- and foodborne parasites in the African context, detailing the burden in African water sources, wastewater/effluents and fresh produce. A scoping review search targeting African countries was conducted in Medline, Web of science and African journals online as well as back referencing from included studies covering the period 1990 to January 2020. Out of 1134 studies, 68 were included in the review. The articles covered 17 out of 54 African countries. There were 39/68 studies reporting on water sources while the rest reported on fresh produce. Cryptosporidium prevalence ranged from 6 to 100% in surface water, 4 to 100% in tap water and up to 100% in wastewater and sludge. In fresh produce, Cryptosporidium was reported from five countries with prevalence of 0.8–75%. Giardia was reported in 47 out of 68 articles; prevalence ranged from 2.4% in surface water; 1% to over 70% in tap water; 28–100% in wastewater and 2% - 99% in fresh produce. Prevalence of Cyclospora cayetanensis was lower. Prevalence of Entamoeba was 78% in surface water; 100% in wastewater and up to 99% in fresh produce. This study finds that Africa is no exception to the risk presented by the subject parasites from water and/or food sources. Routine screening for these parasites particularly at household level and provision of adequate and safe drinking water would help to control the parasites.

6. FROM DECOLONIAL INDIGENOUS KNOWLEDGES TO VERNACULAR IDEAS IN SOUTHEAST ASIA

ABSTRACTRelations between humans and orangutans in present‐day Malaysia show the historiographic and ethnographic problem of using the term “Indigenous knowledge.” Iban and Malay relationships with nonhuman animals are intersubjective and informed by particular subject formations, and indigeneity explains only one kind of relation. To analyze their relations simply in terms of decolonial Indigenous knowledge would be a culturally imperialist act from the Americas: decoloniality is specific to the development of racialization in the West via white settler colonialism, antiblack enslavement, and anti‐Indigenous exploitation and genocide. Instead, this article draws from southern African historical sources and Southeast Asian ethnographic sources to advocate a historiography and ethnography of vernaculars, both vernacular knowledge and vernacular ignorance, in order to avoid autochthonous and potentially xenophobic claims.

Western and Chinese media representation of Africa in COVID-19 news coverage

ABSTRACT In news production and dissemination, media represent communities, countries, and continents by constructing concepts, images, and identities as viewed by selected information sources. It is often assumed that foreign countries are labelled ‘Others’ by global media and misrepresented. This study aims to explore how differently Western and Chinese media source and frame events in Africa. Comparative content analysis of news coverage of COVID-19 prevention in Africa revealed that Western media used African official, African non-official, and Western non-official channels as information sources whereas Chinese media mainly used African and Chinese official sources. The result demonstrated that Western media covered events in Africa in Conflict, Negativity, Human interest, Impact, Eminence, and Novelty frames in positive, neutral, and negative tones whereas Chinese media covered mainly in Impact, Eminence and Novelty frames mostly in positive tone. Overall, the results suggest that Western media coverage of the events is not predominantly negative; and Chinese media coverage is uncommonly affirmative. The findings also suggest that sourcing shapes frames, tones, and representation of ‘Others’ by news media.

The Holocene Cedrus pollen record from Sierra Nevada (S Spain), a proxy for climate change in N Africa

Comprehending the effects of climate variability and disturbance on forested ecosystems is paramount to successfully managing forest environments under future climate scenarios (e.g., global warming, aridification increase). Changes in fossil pollen abundance in sedimentary archives record past vegetation dynamics at regional scales, mainly related to climate changes and, in the last few millennia, to human impact. Pollen records can thus provide long databases with information on how the environment reacted to climate change before the historical record. In this study, we synthesized fossil pollen data from seven sites from the Sierra Nevada in southern Spain to investigate the response of forests in the western Mediterranean area to millennial-scale climate changes and to human impact during the Holocene. In particular, here we focused on Cedrus pollen abundances, which most-likely originated from Northern Africa and were carried to Sierra Nevada by wind. Cedrus pollen has received little attention in the Iberian Peninsula palynological records, for it occurs in low concentrations and has an African source, and thus this article explores the potential to reconstruct its past history and climate. Although Cedrus abundances are generally lower than 1% in the studied pollen samples, a comparison with North African (Moroccan) Cedrus pollen records shows similar trends at long- and short-term time-scales. Therefore, this record could be used as a proxy for changes in this forest species in North Africa. As observed in the Sierra Nevada synthetic record, the increasing trend of Cedrus pollen during the Middle and Late Holocene closely correlates with decreasing summer insolation. This would have produced overall cooler annual temperatures in Northern Africa (Middle Atlas and Rif Mountains) as well as lower summer evaporation, benefiting the growth of this cool-adapted montane tree species while increasing available moisture during the summer, which is critical for this water-demanding species. Millennial-scale variability also characterizes the Sierra Nevada Cedrus synthetic pollen record. Cedrus abundance oscillations co-vary with well-known millennial-scale climatic variability that controlled cedar abundance and altitudinal distribution in montane areas of N Africa.

Disproving the Bodélé Depression as the Primary Source of Dust Fertilizing the Amazon Rainforest

AbstractMotivated by the ongoing debates about the relative contribution of specific North African dust sources to the transatlantic dust transport to the Amazon Basin, the current study integrates a suite of satellite observations into a novel trajectory analysis framework to investigate dust transport from the leading two North African dust sources, namely, the Bodélé depression and El Djouf. In particular, this approach provides observation‐constrained quantification of the dust's dry and wet deposition along its transport pathways and is validated against multiple satellite observations. The current large ensemble trajectory simulations identify favorable transport pathways from the El Djouf across the Atlantic Ocean with respect to seasonal rain belts. The limited potential for long‐range transport of dust from the Bodélé depression is attributed to the currently identified extensive near‐source dust removal primarily by dry and wet deposition during boreal winter and summer, respectively.

Impact of Potential COVID-19 Treatment on South African Water Sources Already Threatened by Pharmaceutical Pollution.

After a cluster of human pneumonia cases in Wuhan City (China) on 7 January 2020 a novel coronavirus, the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS‐CoV‐2) was identified as the causative agent of the disease COVID‐19 (World Health Organization (WHO). 2020).This article is protected by copyright. All rights reserved.

Steep Declines in Pediatric AIDS Mortality in South Africa, Despite Poor Progress Toward Pediatric Diagnosis and Treatment Targets.

Few attempts have been made to monitor progress toward HIV diagnosis and antiretroviral treatment (ART) coverage targets in children, and the impact that ART and prevention of mother-to-child transmission (PMTCT) programs have had on pediatric HIV incidence and mortality. A multiparameter evidence synthesis approach was adopted to integrate South African pediatric HIV data sources. A previously developed model of HIV in South Africa was calibrated to household survey HIV prevalence data, routine antibody testing data, data on numbers and ages of children on ART, vital registration data and data on HIV diagnosis at death. The impact of ART and PMTCT was estimated by comparing validated model outputs against model predictions of the trends that would have been expected in the absence of ART and PMTCT. By mid-2018, the model estimated that 75.2% (95% CI: 73.9%-76.8%) of HIV-positive children were diagnosed, substantially lower than the corresponding estimates in HIV-positive adults (91.0%). ART coverage in children in 2018 (51.2%, 95% CI: 49.4%-52.7%) was also lower than that in adults (62.0%). In 2017-2018, the numbers of new cases of mother-to-child transmission and pediatric AIDS deaths were reduced by 84% and 94%, respectively, relative to what would have been expected in the absence of interventions, but reductions in mortality were driven largely by PMTCT. Although levels of AIDS mortality in children have declined dramatically in South Africa, this has mostly been due to successful PMTCT programs, and progress toward the 90-90-90 targets appears relatively poor when compared with that in adults.

Physico-chemical characterization of urban aerosols from specific combustion sources in West Africa at Abidjan in Côte d'Ivoire and Cotonou in Benin in the frame of the DACCIWA program

Abstract. Urban air pollution in West Africa has yet to be well characterized. In the frame of DACCIWA (Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa) program, intensive measurement campaigns were performed in Abidjan (Côte d'Ivoire) and Cotonou (Benin), in dry (January 2016 and 2017) and wet (July 2015 and 2016) seasons, at different sites chosen to be representative of African urban combustion sources, i.e., domestic fires (ADF), traffic (AT) and waste burning (AWB) sources in Abidjan and traffic source in Cotonou (CT). Both the size distribution of particulate matter (PM) and their chemical composition including elemental carbon (EC), organic carbon (OC), water-soluble organic carbon (WSOC), water-soluble inorganic ions (WSI) and trace metals were examined. Results show very high PM concentrations at all sites and a well-marked seasonality as well as a strong spatial variation. The average PM2.5 mass concentrations during the wet season are 517.3, 104.1, 90.3, and 69.1 µg m−3 at the ADF, CT, AT, and AWB sites, respectively. In the dry season, PM2.5 concentrations decrease to 375.7 µg m−3 at the ADF site, while they increase to 269.7, 141.3, and 175.3 µg m−3 at the CT, AT, and AWB sites, respectively. The annual PM2.5 levels at almost all sites are significantly higher than the WHO guideline level of 10 µg m−3. As for PM mass, (EC) and (OC) concentrations are also maximal at the ADF site, accounting for up to 69 % of the total PM mass. Such a high content is mainly linked to wood burning for domestic cooking and commercial food smoking activities. Dust contributions are dominant at CT (57 %–80 %), AT (20 %–70 %), and AWB (30 %–69 %) sites and especially in the coarse and fine-particle modes at the CT site and in the coarse fraction at the AT site, which may be explained by the impact of long-range desert-dust transport and resuspended particles from the roads, in addition to anthropogenic sources. The contributions of WSI to the total PM mass, mainly driven by chloride, nitrate, and calcium in the fine and/or large particles, are highly variable according to the sites but remain less than 30 %. Values are generally 1–3 times higher in the wet season than in the dry season. This is due not only to anthropogenic emissions but also to nitrate formation by reaction processes and natural emissions. The concentrations of trace elements reflect well the trends in dust at the traffic and AWB sites, with a predominance of Al, Na, Ca, Fe, and K, keys markers of crustal dust. This study constitutes an original database that characterizes specific African combustion sources.

Evolution of defense and herbivory in introduced plants-Testing enemy release using a known source population, herbivore trials, and time since introduction.

The enemy release hypothesis is often cited as a potential explanation for the success of introduced plants; yet, empirical evidence for enemy release is mixed. We aimed to quantify changes in herbivory and defense in introduced plants while controlling for three factors that might have confounded past studies: using a wide native range for comparison with the introduced range, measuring defense traits without determining whether they affect herbivore preferences, and not considering the effect of time since introduction. The first hypothesis we tested was that introduced plants will have evolved lower levels of plant defense compared to their source population. We grew South African (source) and Australian (introduced) beach daisies (Arctotheca populifolia) in a common‐environment glasshouse experiment and measured seven defense traits. Introduced plants had more ash, alkaloids, and leaf hairs than source plants, but were also less tough, with a lower C:N ratio and less phenolics. Overall, we found no difference in defense between source and introduced plants. To determine whether the feeding habits of herbivores align with changes in defense traits, we conducted preference feeding trials using five different herbivore species. Herbivores showed no overall preference for leaves from either group. The second hypothesis we tested was that herbivory on introduced plant species will increase through time after introduction to a new range. We recorded leaf damage on herbarium specimens of seven species introduced to eastern Australia and three native control species. We found no change in the overall level of herbivory experienced by introduced plants since arriving in Australia.ConclusionIn the field of invasion ecology, we need to rethink the paradigm that species introduced to a new range undergo simple decreases in defenses against herbivores. Instead, plants are likely to employ a range of defense traits that evolve in both coordinated and opposing ways in response to a plethora of different biotic and abiotic selective pressures.

Six-year observations of aerosol optical properties at a southern African grassland savannah site

Atmospheric aerosols have a significant effect on earth's radiative budget, particularly on regional scales. This paper presents a ~6 year, in situ, ground level aerosol scattering and absorption dataset, measured at a background site strategically positioned to enable differentiation of the effect of anthropogenic, population density and open biomass burning activities on a regional scale. Relatively well-defined seasonal and diurnal patterns were observed for all the aerosol optical properties, i.e. scattering coefficient (σ SP ), absorption coefficient (σ AP ), single scattering albedo (ω 0 ) and Ångström exponent of scattering (α SP ). These patterns were explained by considering southern African specific sources and metrological conditions. Using a receptor modelling method (auto-generated source maps) it was found that air masses that had higher σ SP , σ AP and ω 0 , and lower α SP , if compared with the relatively clean background, passed over source regions with significant industrial or other anthropogenic activities, higher population density, re-circulation of polluted air masses and higher open biomass burning frequency. To quantify differences, four source regions were defined, i.e. Karoo, Kalahari, anti-cyclonic recirculation pattern and the industrial hub of South Africa. Air masses that had passed over the Karoo source region represented the cleanest regional background conditions, while air masses that had passed either over the industrial hub and/or the anti-cyclonic recirculation pattern represented the most significant anthropogenically impacted, as indicated by the aerosol optical properties. The ω 0 medians of air masses that had passed over the Karoo (0.80–0.86) were 9, 12 and 7% lower than in air masses that had passed over source regions with the highest ω 0 median, in the warmest/wettest, coldest, and driest, peak open biomass burning periods, respectively. • A six-year, ground level aerosol optical property dataset is presented. • Well-defined seasonal and diurnal patterns were evident for the optical properties. • Auto-generated source maps were used to explain results within a regional context. • Air masses passing over the Karoo region represented the most natural background. • Anthropogenic influences were evident in air masses passing over all other regions.

Sources, frequency, and chemical nature of dust events impacting the United States East Coast.

This study examines 14 years (2004-2017) of surface aerosol composition data from the EPA IMPROVE network with a focus on the monthly profile, sources, and chemical nature of extreme dust events (>92nd percentile of fine soil concentration each month) impacting ten sites along the United States East Coast ranging in latitude from Florida to Maine. Based on trajectory, remote sensing, and reanalysis data, dust events were categorized into four source categories: African, Asian, Mix (African + Asian), and Other (anything other than African and Asian). The results reveal that extreme dust events account for between 3.3% and 4.6% of total available days depending on the site. March-April-May (MAM) had the most (174) dust events, followed by June-July-August (JJA) with 172, and then by September-October-November (SON) with 160 and December-January-February (DFJ) with 150. There is a variability in the predominant dust sources based on latitude, with African and Other sources more influential from North Carolina to the south, while Asian and Other were most important from New Jersey to the north. The Mix category is consistently the least frequent dust category at all sites. The African dust category was linked to the highest fine soil levels across the entire East Coast relative to other sources regardless of location. JJA is mostly impacted by African dust for sites ranging from Florida to New Jersey, while MAM is dominated by Asian dust for all sites. Mix events occurred mostly between April and October and Other events were most common outside of MAM and JJA seasons. Seven out of ten sites had Other as the most dominant source. Aerosol constituents organic carbon (OC) and elemental carbon (EC) had higher average concentrations in Other events (2.39 ± 0.78 μg m-3 and 0.79 ± 0.81 μg m-3, respectively) as compared to the other three source categories, suggestive of regional anthropogenic emissions. Moreover, the ratios of elements (Si:Al, K:Fe, Fe:Ca, Al:Ca) contributing to fine soil and PM2.5:PM10 exhibited distinct values depending on the dust source category and the site. This study builds on the growing evidence of the importance of long-range transport of dust in impacting distant regions and how a variety of sources can impact the U.S. East Coast at all times of the year.

Evaluating the Impact of Assimilating Aerosol Optical Depth Observations on Dust Forecasts Over North Africa and the East Atlantic Using Different Data Assimilation Methods.

This study evaluates the impact of assimilating moderate resolution imaging spectroradiometer (MODIS) aerosol optical depth (AOD) data using different data assimilation (DA) methods on dust analyses and forecasts over North Africa and tropical North Atlantic. To do so, seven experiments are conducted using the Weather Research and Forecasting dust model and the Gridpoint Statistical Interpolation analysis system. Six of these experiments differ in whether or not AOD observations are assimilated and the DA method used, the latter of which includes the three‐dimensional variational (3D‐Var), ensemble square root filter (EnSRF), and hybrid methods. The seventh experiment, which allows us to assess the impact of assimilating deep blue AOD data, assimilates only dark target AOD data using the hybrid method. The assimilation of MODIS AOD data clearly improves AOD analyses and forecasts up to 48 hr in length. Results also show that assimilating deep blue data has a primarily positive effect on AOD analyses and forecasts over and downstream of the major North African source regions. Without assimilating deep blue data (assimilating dark target only), AOD assimilation only improves AOD forecasts for up to 30 hr. Of the three DA methods examined, the hybrid and EnSRF methods produce better AOD analyses and forecasts than the 3D‐Var method does. Despite the clear benefit of AOD assimilation for AOD analyses and forecasts, the lack of information regarding the vertical distribution of aerosols in AOD data means that AOD assimilation has very little positive effect on analyzed or forecasted vertical profiles of backscatter.

Analysis of the Transport of Aerosols over the North Tropical Atlantic Ocean Using Time Series of POLDER/PARASOL Satellite Data

The time series of total, fine and coarse POLAC/PARASOL aerosol optical depth (AOD) satellite products (2005–2013) processed by the POLAC algorithm are examined to investigate the transport of aerosols over the North Tropical Atlantic Ocean, a region that is characterized by significant dust aerosols events. First, the comparison of satellite observations with ground-based measurements acquired by AERONET ground-based measurements shows a satisfactory consistency for both total AOD and coarse mode AOD (i.e., correlation coefficients of 0.75 and bias ranging from −0.03 to 0.03), thus confirming the robustness and performance of POLAC/PARASOL data to investigate the spatio-temporal variability of the aerosols over the study area. Regarding fine mode aerosol, POLAC/PARASOL data present a lower performance with correlation coefficient ranging from 0.37 to 0.73. Second, the analysis of POLAC/PARASOL aerosol climatology reveals a high contribution of the coarse mode of aerosols ( AOD c between 0.1 and 0.4) at long distance from the African sources, confirming previous studies related to dust transport. The POLAC/PARASOL data were also compared with aerosol data obtained over the North Tropical Atlantic Ocean from MACC and MERRA-2 reanalyses. It is observed that the total AOD is underestimated in both reanalysis with a negative bias reaching −0.2. In summary, our results thus suggest that satellite POLAC/PARASOL observations of fine and coarse modes of aerosols could provide additional constraints useful to improve the quantification of the dust direct radiative forcing on a regional scale but also the biogeochemical processes such as nutrient supply to the surface waters.

Assessment of a new detection threshold for [formula omitted] concentrations linked to African dust events in the Caribbean Basin

The Lesser Antilles is an intermediate zone located between the Caribbean Sea and the Atlantic Ocean. This area is frequently affected by the major long range Saharan dust transportation from West African desert sources. The aerosols optical properties are provided by the AEronet Robotic NETwork (AERONET) measurement sites in Puerto Rico, Guadeloupe, and Barbados. Thus, Aerosols Optical Depth (AOD), Angstrom Exponent (AE), Volume Particle Size Distribution (VPSD), complex refractive indexes, and Single Scattering Albedo (SSA) were used to define the predominant type of atmospheric particles namely sea salt aerosols, mineral dust or aerosols mixture. Obtained results show that aerosols in the atmospheric column (AOD) and surface dust measurements (PM10) are well correlated with correlation coefficients of 0.72 and 0.81 respectively for Puerto Rico, and Guadeloupe. Detailed analysis of optical data associated to daily PM10 concentrations highlighted that dust phenomenon can be observable below PM10 threshold of 50 μg∕m3 given by the European directives to detect dust episodes. Indeed, for Caribbean islands, episodes of desert dust phenomenon have been detected from 35 μg∕m3. The climatological assessment of monthly dust events observed in Puerto Rico, Guadeloupe, and Martinique between 2006 and 2016 highlighted a low dust season from November to February and a high dust season from May to August. Both seasons are separated by two transition dust periods: March to April and September to October. Lastly, the day-to-day back trajectories (NOAA-HYSPLIT) illustrated the general atmospheric circulation and show three main dust transportation routes: the North West African Path (62.7%); the South West African Path (20.8%) ; and the North East Atlantic Path (15.1%). By computing the average PM10 concentrations bring from each path, we notice that South West African Path is the most loaded in mineral dust because he comes from one of the most persistently active and intense dust sources in the world, i.e. Bodélé Depression in northern Chad.

The first mitogenome of the Nile pufferfish Tetraodon lineatus from Lake Turkana in East Africa: new insights into the genus

A complete mitogenome of T. lineatus from Lake Turkana in the Kenyan part was determined. It had a length of 16 470 bp, including 37 genes as found in teleosts with the typical gene order in these fishes. Mitogenomic comparison and phylogenetic analysis supported not only the morphology-based recognition of the pufferfish specimen from Lake Turkana as the Nile pufferfish, but also the identification of the Chinese specimen recently recorded as T. lineatus and its African source. The mitochondrial genome here amplified for the sample of T. lineatus from Lake Turkana also provides conclusive molecular evidence for the monophyletic nature of Tetraodon s.s., as it serves as a reference genome of this species used to clarify ambiguity in its identification in previous molecular studies.

Rapid changes of dust geochemistry in the Saharan Air Layer linked to sources and meteorology

Based at Izaña Observatory (~2400 m a.s.l. in Tenerife), we performed 1-h resolution measurements of elemental composition of dust in the Saharan Air Layer (SAL) and studied the variability of the ratios of these elements to aluminium (elemental ratios). In a period (~1 week) of continuous dust presence (50–200 μg/m3), we observed rapid variations of dust composition; some elemental ratios changed by a factor 2 in a few (5–8) hours. The lowest variability (Normalized Variability Range, %) was found for Si/Al (9%) and Fe/Al (9%), followed by the ratios of K, Ti, Mg, Mn, Ca and Sr to Al (20–80%), and the highest for S/Al, Na/Al and Cl/Al (110–160%) and a number of trace metals (Cr, Cu, Ni, Zn, Zr) and Br (>200%). This variability was induced by the alternating impacts of three of the large North African dust sources: NE Algeria (rich in evaporite minerals bearing Ca, S, Sr, K and Mg and in illite mineral), Western Sahara to Bechar region (containing Na, S and Cl rich Yermosol soils) and SW Sahara – Western Sahel (rich in illite and hematite). We traced the variability in large-scale meteorology using the so-called North African Dipole Intensity (NAFDI: strength of the subtropical Saharan high -Morocco-to the monsoon tropical low -Nigeria-). The mobilization of dust from the different sources was associated with westward propagating Harmattan pulses linked to the change of phase of NAFDI (- to +), the associated westward shifts of the Saharan Heat Low and convective monsoon inflow. We found a correlation between dust composition in the SAL and NAFDI: moderate NAFDI values (0 to +2.5) were associated with Ca, K, Na, Mg and S rich dust linked to dust sources in NE Algeria, whereas higher NAFDI values (+2.5 to +4) were linked to Fe rich dust (Ca, Na and S depleted) linked to dust sources in SW Sahara – Western Sahel. The results of this study also show that some trace elements (Br, Cr, Ni, Zn and Zr) are influenced by industrial emissions into North Africa.

South African Abietane Diterpenoids and Their Analogs as Potential Antimalarials: Novel Insights from Hybrid Computational Approaches.

The hemoglobin degradation process in Plasmodium parasites is vital for nutrient acquisition required for their growth and proliferation. In P. falciparum, falcipains (FP-2 and FP-3) are the major hemoglobinases, and remain attractive antimalarial drug targets. Other Plasmodium species also possess highly homologous proteins to FP-2 and FP-3. Although several inhibitors have been designed against these proteins, none has been commercialized due to associated toxicity on human cathepsins (Cat-K, Cat-L and Cat-S). Despite the two enzyme groups sharing a common structural fold and catalytic mechanism, distinct active site variations have been identified, and can be exploited for drug development. Here, we utilize in silico approaches to screen 628 compounds from the South African natural sources to identify potential hits that can selectively inhibit the plasmodial proteases. Using docking studies, seven abietane diterpenoids, binding strongly to the plasmodial proteases, and three additional analogs from PubChem were identified. Important residues involved in ligand stabilization were identified for all potential hits through binding pose analysis and their energetic contribution determined by binding free energy calculations. The identified compounds present important scaffolds that could be further developed as plasmodial protease inhibitors. Previous laboratory assays showed the effect of the seven diterpenoids as antimalarials. Here, for the first time, we demonstrate that their possible mechanism of action could be by interacting with falcipains and their plasmodial homologs. Dynamic residue network (DRN) analysis on the plasmodial proteases identified functionally important residues, including a region with high betweenness centrality, which had previously been proposed as a potential allosteric site in FP-2.

Withholding tax on interest: Who has the withholding obligation?

Orientation: Non-residents receiving interest from a South African source will be taxable in terms of the gross income definition in the South African Income Tax Act . Effective 01 March 2015, new provisions for withholding of tax on interest (WTI) to non-residents were incorporated in the Act with the purpose of simplifying the collection of tax from non-residents. Research purpose: This article aimed to seek clarity on who ‘the person is who makes payment’ of the interest in order to suggest an amendment to the Act. Motivation for the study: When dealing with debt instruments, the issuer of the instrument and the ‘payer’ of the interest might not always be the same person as intermediaries might be involved in the transactions. The provisions on WTI do not clarify who has the withholding obligation in the case of an intermediary, and uncertainty may therefore arise on who the ‘payer’ of the interest is. Research approach/design and method: Using a doctrinal method, the article reviewed and interpreted South African legislation and commentary related to the topic and also turned to international legislation dealing with WTI for guidance. Main findings: It was found that the only person who would be in a position to withhold the withholding tax is the person who is seen as the last client-facing entity or intermediary. Practical/managerial implications: Two suggestions are offered with regard to amending the provisions on WTI, namely to split the withholding obligation between the issuer and the intermediary and to define ‘intermediary’. Contribution/value-add: This study provides clarity on ‘who the payer of the interest’ is on whom the withholding obligation rests.

Smoothed Spherical Truncation based on Fuzzy Membership Functions: Application to the Molecular Encoding.

A novel spherical truncation method, based on fuzzy membership functions, is introduced to truncate interatomic (or interaminoacid) relations according to smoothing values computed from fuzzy membership degrees. In this method, the molecules are circumscribed into a sphere, so that the geometric centers of the molecules are the centers of the spheres. The fuzzy membership degree of each atom (or aminoacid) is computed from its distance with respect to the geometric center of the molecule, by using a fuzzy membership function. So, the smoothing value to be applied in the truncation of a relation (or interaction) is computed by averaging the fuzzy membership degrees of the atoms (or aminoacids) involved in the relation. This truncation method is rather different from the existing ones, at considering the geometric center for the whole molecule and not only for atom-groups, as well as for using fuzzy membership functions to compute the smoothing values. A variability study on a set comprised of 20,469 compounds (15,050 drug-like compounds, 2994 drugs approved, 880 natural products from African sources, and 1545 plant-derived natural compounds exhibiting anti-cancerous activity) demonstrated that the truncation method proposed allows to determine molecular encodings with better ability for discriminating among structurally different molecules than the encodings obtained without applying truncation or applying non-fuzzy truncation functions. Moreover, a principal component analysis revealed that orthogonal chemical information of the molecules is encoded by using the method proposed. Lastly, a modeling study proved that the truncation method improves the modeling ability of existing geometric molecular descriptors, at allowing to develop more robust models than the ones built only using non-truncated descriptors. In this sense, a comparison and statistical assessment were performed on eight chemical datasets. As a result, the models based on the truncated molecular encodings yielded statistically better results than 12 procedures considered from the literature. It can thus be stated that the proposed truncation method is a relevant strategy for obtaining better molecular encodings, which will be ultimately useful in enhancing the modeling ability of existing encodings both on small-to-medium size molecules and biomacromolecules. © 2019 Wiley Periodicals, Inc.