Wastewater-based epidemiology as a public health resource in low- and middle-income settings.

In the face of emerging and re-emerging diseases, novel and innovative approaches to population scale surveillance are necessary for the early detection and quantification of pathogens. The last decade has seen the rapid development of wastewater and environmental surveillance (WES) to address public health challenges, which has led to establishment of wastewater-based epidemiology (WBE) approaches being deployed to monitor a range of health hazards. WBE exploits the fact that excretions and secretions from urine, and from the gut are discharged in wastewater, particularly sewage, such that sampling sewage systems provides an early warning system for disease outbreaks by providing an early indication of pathogen circulation. While WBE has been mainly used in locations with networked wastewater systems, here we consider its value for less connected populations typical of lower-income settings, and in assess the opportunity afforded by pit latrines to sample communities and localities. We propose that where populations struggle to access health and diagnostic facilities, and despite several additional challenges, sampling unconnected wastewater systems remains an important means to monitor the health of large populations in a relatively cost-effective manner.

City-wide wastewater genomic surveillance through the successive emergence of SARS-CoV-2 Alpha and Delta variants.

Genomic surveillance of SARS-CoV-2 has provided a critical evidence base for public health decisions throughout the pandemic. Sequencing data from clinical cases has helped to understand disease transmission and the spread of novel variants. Genomic wastewater surveillance can offer important, complementary information by providing frequency estimates of all variants circulating in a population without sampling biases. Here we show that genomic SARS-CoV-2 wastewater surveillance can detect fine-scale differences within urban centres, specifically within the city of Liverpool, UK, during the emergence of Alpha and Delta variants between November 2020 and June 2021. Furthermore, wastewater and clinical sequencing match well in the estimated timing of new variant rises and the first detection of a new variant in a given area may occur in either clinical or wastewater samples. The study's main limitation was sample quality when infection prevalence was low in spring 2021, resulting in a lower resolution of the rise of the Delta variant compared to the rise of the Alpha variant in the previous winter. The correspondence between wastewater and clinical variant frequencies demonstrates the reliability of wastewater surveillance. However, discrepancies in the first detection of the Alpha variant between the two approaches highlight that wastewater monitoring can also capture missing information, possibly resulting from asymptomatic cases or communities less engaged with testing programmes, as found by a simultaneous surge testing effort across the city.

Assessment of aeration control strategies for biofilm-based partial nitritation/anammox systems.

The objective of this work was to compare the nitrogen removal in mainstream, biofilm-based partial nitritation anammox (PN/A) systems employing (1) constant setpoint dissolved oxygen (DO) control, (2) intermittent aeration, and (3) ammonia-based aeration control (ABAC). A detailed water resource recovery facility (WRRF) model was used to study the dynamic performance of these aeration control strategies with respect to treatment performance and energy consumption. The results show that constant setpoint DO control cannot meet typical regulatory limits for total ammonia nitrogen (NHx-N). Intermittent aeration shows improvement but requires optimisation of the aeration cycle. ABAC shows the best treatment performance with the advantages of continuous operation and over 20% lower average energy consumption as compared to intermittent aeration.

Temperature, inocula and substrate: Contrasting electroactive consortia, diversity and performance in microbial fuel cells.

The factors that affect microbial community assembly and its effects on the performance of bioelectrochemical systems are poorly understood. Sixteen microbial fuel cell (MFC) reactors were set up to test the importance of inoculum, temperature and substrate: Arctic soil versus wastewater as inoculum; warm (26.5°C) versus cold (7.5°C) temperature; and acetate versus wastewater as substrate. Substrate was the dominant factor in determining performance and diversity: unexpectedly the simple electrogenic substrate delivered a higher diversity than a complex wastewater. Furthermore, in acetate fed reactors, diversity did not correlate with performance, yet in wastewater fed ones it did, with greater diversity sustaining higher power densities and coulombic efficiencies. Temperature had only a minor effect on power density, (Q10: 2 and 1.2 for acetate and wastewater respectively): this is surprising given the well-known temperature sensitivity of anaerobic bioreactors. Reactors were able to operate at low temperature with real wastewater without the need for specialised inocula; it is speculated that MFC biofilms may have a self-heating effect. Importantly, the warm acetate fed reactors in this study did not act as direct model for cold wastewater fed systems. Application of this technology will encompass use of real wastewater at ambient temperatures.

Generalised approach to modelling a three-tiered microbial food-web.

The complexity of the anaerobic digestion process has motivated the development of complex models, such as the widely used Anaerobic Digestion Model No. 1. However, this complexity makes it intractable to identify the stability profile coupled to the asymptotic behaviour of existing steady-states as a function of conventional chemostat operating parameters (substrate inflow concentration and dilution rate). In a previous study this model was simplified and reduced to its very backbone to describe a three-tiered chlorophenol mineralising food-web, with its stability analysed numerically using consensus values for the various biological parameters of the Monod growth functions. Steady-states where all organisms exist were always stable and non-oscillatory. Here we investigate a generalised form of this three-tiered food-web, whose kinetics do not rely on the specific kinetics of Monod form. The results are valid for a large class of growth kinetics as long as they keep the signs of their derivatives. We examine the existence and stability of the identified steady-states and find that, without a maintenance term, the stability of the system may be characterised analytically. These findings permit a better understanding of the operating region of the bifurcation diagram where all organisms exist, and its dependence on the biological parameters of the model. For the previously studied Monod kinetics, we identify four interesting cases that show this dependence of the operating diagram with respect to the biological parameters. When maintenance is included, it is necessary to perform numerical analysis. In both cases we verify the discovery of two important phenomena; i) the washout steady-state is always stable, and ii) a switch in dominance between two organisms competing for hydrogen results in the system becoming unstable and a loss in viability. We show that our approach results in the discovery of an unstable operating region in its positive steady-state, where all three organisms exist, a fact that has not been reported in a previous numerical study. This type of analysis can be used to determine critical behaviour in microbial communities in response to changing operating conditions.

Emergent behaviour in a chlorophenol-mineralising three-tiered microbial 'food web'.

Anaerobic digestion enables the water industry to treat wastewater as a resource for generating energy and recovering valuable by-products. The complexity of the anaerobic digestion process has motivated the development of complex models. However, this complexity makes it intractable to pin-point stability and emergent behaviour. Here, the widely used Anaerobic Digestion Model No. 1 (ADM1) has been reduced to its very backbone, a syntrophic two-tiered microbial 'food chain' and a slightly more complex three-tiered microbial 'food web', with their stability analysed as a function of the inflowing substrate concentration and dilution rate. Parameterised for phenol and chlorophenol degradation, steady-states were always stable and non-oscillatory. Low input concentrations of chlorophenol were sufficient to maintain chlorophenol- and phenol-degrading populations but resulted in poor conversion and a hydrogen flux that was too low to sustain hydrogenotrophic methanogens. The addition of hydrogen and phenol boosted the populations of all three organisms, resulting in the counterintuitive phenomena that (i) the phenol degraders were stimulated by adding hydrogen, even though hydrogen inhibits phenol degradation, and (ii) the dechlorinators indirectly benefitted from measures that stimulated their hydrogenotrophic competitors; both phenomena hint at emergent behaviour.

An unusual barrier to gene flow: perpetually immature larvae from inter-population crosses in the flour beetle, Tribolium castaneum.

We genetically characterize an unusual hybrid incompatibility phenotype manifest in F(1) offspring of crosses between two populations of Tribolium castaneum. Hybrid larvae cease development at the third larval instar, persisting as 'perpetually immature larvae' thereafter. Although unable to produce viable adult hybrid offspring with one another, each population produces abundant, fertile hybrids with other populations, indicating a recent origin of the incompatibility and facilitating genetic studies. We mapped the paternal component of the hybrid phenotype to a single region, which exhibits two characteristics common to hybrid incompatibility: marker transmission ratio distortion within crosses and elevated genetic divergence between populations. The incompatible variation and an elevation in between-population genetic divergence is associated with a region containing the T. castaneum ecdysone receptor homologue, a major regulatory switch, controlling larval moults, pupation and metamorphosis. This contributes to understanding the genetics of speciation in the Coleoptera, one of the most speciose of all arthropod taxa.

Genetic differences among populations in sexual dimorphism: evidence for selection on males in a dioecious plant.

Genetic variation among populations in the degree of sexual dimorphism may be a consequence of selection on one or both sexes. We analysed genetic parameters from crosses involving three populations of the dioecious plant Silene latifolia, which exhibits sexual dimorphism in flower size, to determine whether population differentiation was a result of selection on one or both sexes. We took the novel approach of comparing the ratio of population differentiation of a quantitative trait (Q(ST) ) to that of neutral genetic markers (F(ST) ) for males vs. females. We attributed 72.6% of calyx width variation in males to differences among populations vs. only 6.9% in females. The Q(ST) /F(ST) ratio was 4.2 for males vs. 0.4 for females, suggesting that selection on males is responsible for differentiation among populations in calyx width and its degree of sexual dimorphism. This selection may be indirect via genetic correlations with other morphological and physiological traits.

Genetic variation and co-variation for fitness between intra-population and inter-population backgrounds in the red flour beetle, Tribolium castaneum.

Hybrids from crosses between populations of the flour beetle, Tribolium castaneum, express varying degrees of inviability and morphological abnormalities. The proportion of allopatric population hybrids exhibiting these negative hybrid phenotypes varies widely, from 3% to 100%, depending upon the pair of populations crossed. We crossed three populations and measured two fitness components, fertility and adult offspring numbers from successful crosses, to determine how genes segregating within populations interact in inter-population hybrids to cause the negative phenotypes. With data from crosses of 40 sires from each of three populations to groups of five dams from their own and two divergent populations, we estimated the genetic variance and covariance for breeding value of fitness between the intra- and inter-population backgrounds and the sire × dam population interaction variance. The latter component of the variance in breeding values estimates the change in genic effects between backgrounds owing to epistasis. Interacting genes with a positive effect, prior to fixation, in the sympatric background but a negative effect in the hybrid background cause reproductive incompatibility in the Dobzhansky-Muller speciation model. Thus, the sire × dam population interaction provides a way to measure the progress towards speciation of genetically differentiating populations on a trait by trait basis using inter-population hybrids.

The joint effects of kin, multilevel selection and indirect genetic effects on response to genetic selection.

Kin and levels-of-selection models are common approaches for modelling social evolution. Indirect genetic effect (IGE) models represent a different approach, specifying social effects on trait values rather than fitness. We investigate the joint effect of relatedness, multilevel selection and IGEs on response to selection. We present a measure for the degree of multilevel selection, which is the natural partner of relatedness in expressions for response. Response depends on both relatedness and the degree of multilevel selection, rather than only one or the other factor. Moreover, response is symmetric in relatedness and the degree of multilevel selection, indicating that both factors have exactly the same effect. Without IGEs, the key parameter is the product of relatedness and the degree of multilevel selection. With IGEs, however, multilevel selection without relatedness can explain evolution of social traits. Thus, next to relatedness and multilevel selection, IGEs are a key element in the genetical theory of social evolution.

The effect of delayed visual feedback on telerobotic surgery.

BACKGROUND: Telerobotic surgery is ideally suited for remote applications in which the instrument control console is stationed separately from the end-effectors at the patient's bedside. However, if the distance between the console and the patient is great enough, a lag effect or latency between end-effector manipulation and the depicted image leads to alterations in movement patterns. The purpose of this study was to determine the effect of visual delay on surgical task performance. METHODS: At an endoscopic skill station, an analogue delay device was interposed between the surgical field and monitor to delay the transmission of visual information, thus mimicking the distance effect of data transmission. Three surgeons with similar laparoscopic experience participated in the laparoscopic knot tying portion of the study, and seven residents participated in the accuracy and dexterity tasks. The time to complete a single throw was recorded in seconds after adding consecutively increasingly time delay in 50 ms increments. Similar time delay increments were added for the accuracy and dexterity tasks, which involved passing a needle through two adjacent circles and passing a small cylinder through a larger one to reproduce two-handed coordination and spatial resolution. Data were presented as the median time to complete each task. RESULTS: For all three tasks, an incremental increase in time delay was associated with a significant (p < 0.001) increase in the time to complete the task. For dexterity, a statistically significant (p

Spread of parasites in metapopulations: an experimental study of the effects of host migration rate and local host population size.

We established experimental metapopulations of the flour beetle, Tribolium castaneum, and its ectoparasitic mite, Acarophenax tribolii, to investigate the effects of host migration rate and local host population size on the spread of mite infections. Global prevalence across our metapopulations was less than half the observed within-patch prevalence, so that spatial structure alone afforded a great deal of protection to hosts against parasite infection. Our results showed further that migration played a determining role in occupancy, the number of patches infected within a metapopulation, while host population size played a determining role in local prevalence, the fraction of hosts infected within local patches. Local and global prevalence appeared to reach equilibrium levels on 2 different time-scales. Local host prevalence reached equilibrium values within 30 days of receiving an infected host migrant. Global prevalence increased more slowly and was clearly dependent upon occupancy, the number of host patches with at least 1 infected host, which in turn depended on the level of host migration among host patches. The effect of population size was not limited to local prevalence in patches without spatial structure but extended to sets of patches across the metapopulation. Lloyd's index of patchiness differed significantly between metapopulations with small versus large numbers of hosts. Although parasites were aggregated on hosts for both local patch sizes, they tended to aggregate to a much greater degree at the smaller host patch size. We discuss our empirical findings in light of current epidemiological theory.

Neuron number in the entorhinal cortex and CA1 in preclinical Alzheimer disease.

OBJECTIVES: To determine whether nondemented subjects with pathological evidence of preclinical Alzheimer disease (AD) demonstrate neuronal loss in the entorhinal cortex and hippocampus, and whether the onset of cognitive deficits in AD coincides with the onset of neuronal degeneration. METHODS: Preclinical AD cases have been defined by the absence of cognitive decline but with neuropathological evidence of AD. The hippocampus and entorhinal cortex were examined in 13 nondemented cases (Clinical Dementia Rating [CDR] 0) with healthy brains, 4 cases with preclinical AD, 8 cases with very mild symptomatic AD (CDR 0.5), and 4 cases with severe AD (CDR 3, hippocampus only). The volume and number of neurons were determined stereologically in 2 areas that are vulnerable to AD--the entorhinal cortex (as a whole and layer II alone) and hippocampal field CA1. RESULTS: There was no significant decrease in neuron number or volume with age in the healthy nondemented group and little or none between the healthy and preclinical AD groups. Substantial decreases were found in the very mild AD group in neuron number (35% in the entorhinal cortex, 50% in layer II, and 46% in CA1) and volume (28% in the entorhinal cortex, 21% in layer II, and 29% in CA1). Greater decrements were observed in CA1 in the severe AD group. CONCLUSIONS: There is little or no neuronal loss in aging or preclinical AD but substantial loss in very mild AD. The findings indicate that AD results in clinical deficits only when it produces significant neuronal loss.

Cultural inheritance as a mechanism for population sex-ratio bias in reptiles.

Although natural populations of most species exhibit a 1:1 sex ratio, biased sex ratios are known to be associated with non-Mendelian inheritance, as in sex-linked meiotic drive and cytoplasmic inheritance (Charnov 1982; Hurst 1993). We show how cultural inheritance, another type of non-Mendelian inheritance, can favor skewed primary sex ratios and propose that it may explain the female-biased sex ratios commonly observed in reptiles with environmental sex determination (ESD). Like cytoplasmic elements, cultural traits can be inherited through one sex. This, in turn, favors skewing the primary sex allocation in favor of the transmitting sex. Female nest-site philopatry is a sex-specific, culturally inherited trait in many reptiles with ESD and highly female-biased sex ratios. We propose that the association of nest-site selection with ESD facilitates the maternal manipulation of offspring sex ratios toward females.

Maternal effect genes and the evolution of sociality in haplo-diploid organisms.

Maternal care and female-biased sex ratios are considered by many to be essential prerequisites for the evolution of eusocial behaviors among the hymenoptera. Using population genetic models, I investigate the evolution of genes that have positive maternal effects but negative, direct effects on offspring fitness. I find that, under many conditions, such genes evolve more easily in haplo-diploids than in diplo-diploids. In fact, the conditions are less restrictive than those of kin selection theory, which postulate genes with negative direct effects but positive sib-social effects. For example, the conditions permitting the evolution of maternal effect genes are not affected if females mate multiply, whereas multiple mating reduces the efficacy of kin selection by reducing genetic relatedness within colonies. Inbreeding also differentially facilitates evolution of maternal effect genes in haplo-diploids relative to diplo-diploids, although it does not differentially affect the evolution of sib-altruism genes. Furthermore, when the direct, deleterious pleiotropic effect is restricted to sons, a maternal effect gene can evolve when the beneficial maternal effect is less than half (with inbreeding, much less) of the deleterious effect on sons. For kin selection, however, the sib-social benefits must always exceed the direct costs because genetic relatedness is always less than or equal to 1.0. The results suggest that haplo-diploidy facilitates (1) the evolution of maternal care, and (2) the evolution of maternal effect genes with antagonistic pleiotropic effects on sons. The latter effect may help explain the tendency toward female-biased sex ratios in haplo-diploids, especially those with inbreeding. I conclude that haplo-diploidy not only facilitates the evolution of sister-sister altruism by kin selection but also facilitates the evolution of maternal care and female-biased sex ratios, two prerequisites for eusociality.

Epistasis, complex traits, and mapping genes.

Using a three-locus model wherein two loci regulate a third, candidate locus, I examine physiological epistasis from the 'gene's eye view' of the regulated locus. I show that, depending upon genetic background at the regulatory loci, an allele at the candidate locus can be dominant, additive, recessive, neutral, over-dominant, or under-dominant in its effects on fitness. This kind of variation in allelic effect caused by variation in genetic background from population to population, from time to time in the same population, or sample to sample makes finding and mapping the genes underlying a complex phenotype difficult. The rate of evolution of such genes can also be slowed, especially in genetically subdivided metapopulations with migration. Nevertheless, understanding how variation in genetic background causes variation in allelic effects permits the genetic architecture of such complex traits to be dissected into the interacting component genes. While some backgrounds diminish allelic effects and make finding and mapping genes difficult, other backgrounds enhance allelic effects and facilitate gene mapping.

On indirect genetic effects in structured populations.

Indirect genetic effects (IGEs) occur when the phenotype of an individual, and possibly its fitness, depends, at least in part, on the genes of its social partners. The effective result is that environmental sources of phenotypic variance can themselves evolve. Simple models have shown that IGEs can alter the rate and direction of evolution for traits involved in interactions. Here we expand the applicability of the theory of IGEs to evolution in metapopulations by including nonlinear interactions between individuals and population genetic structure. Although population subdivision alone generates some dramatic and nonintuitive evolutionary dynamics for interacting phenotypes, the combination of nonlinear interactions with subdivision reveals an even greater importance of IGEs. The presence of genetic structure links the evolution of interacting phenotypes and the traits that influence their expression ("effector traits") even in the absence of genetic correlations. When nonlinear social effects occur in subdivided populations, evolutionary response is altered and can even oppose the direction expected due to direct selection. Because population genetic structure allows for multilevel selection, we also investigate the role of IGEs in determining the response to individual and group selection. We find that nonlinear social effects can cause interference between levels of selection even when they act in the same direction. In some cases, interference can be so extreme that the actual evolutionary response to multilevel selection is opposite in direction to that predicted by summing selection at each level. This theoretical result confirms empirical data that show higher levels of selection cannot be ignored even when selection acts in the same direction at all levels.

Early invasive versus ischaemia-guided strategies in the management of non-Q wave myocardial infarction patients with and without prior myocardial infarction; results of Veterans Affairs Non-Q Wave Infarction Strategies in Hospital (VANQWISH) trial.

AIMS: To compare the role of early invasive vs conservative management strategies in treating patients with non-Q wave myocardial infarction with or without a prior myocardial infarction. BACKGROUND: In patients recovering from non-Q wave myocardial infarction, the prognosis among patients with a first non-Q wave myocardial infarction is significantly better than in patients with a prior myocardial infarction, yet physicians often adopt an early invasive strategy to treat patients with a first non-Q wave myocardial infarction. METHODS: Non-Q wave myocardial infarction patients enrolled in the VANQWISH trial with a history of prior myocardial infarction were compared to those with a first non-Q wave myocardial infarction, for the trial primary end-point of death or myocardial infarction at 1 and 12 months, as well as for the initial randomized treatment strategy. RESULTS: Of the 920 non-Q wave myocardial infarction patients, 396 had a history of prior myocardial infarction and 524 did not. Patients with a history of prior myocardial infarction were older and had a higher incidence of multiple high-risk baseline characteristics than those with a first non-Q wave myocardial infarction. Compared to the group with a first myocardial infarction, the prior myocardial infarction group suffered more events at both 1 month (11% vs 6%, P=0.007) and at 12 months (29% vs 16%, P<0.001). This difference in outcome remained significant even after adjusting for confounding variables (P<0.0001 at 12 months). Among the non-Q wave myocardial infarction patients with a prior myocardial infarction, the frequency of death or recurrent myocardial infarction was similar in both invasive and conservative groups during the first year of follow-up. Among the first non-Q wave myocardial infarction group, those assigned to the conservative strategy had significantly fewer events (3% vs 9%, P=0.009 at 1 month; 12% vs 20%, P=0.016 at 12 months) and mortality (1% vs 5%, P=0.012 at one month; 5% vs 11%, P=0.009 at 12 months) than those assigned to early invasive strategy. CONCLUSION: A history of prior myocardial infarction identifies a moderately high-risk subset of non-Q wave myocardial infarction patients who display similar long-term outcomes regardless of the strategy assignment; however, patients with a first non-Q wave myocardial infarction may fare better with a conservative or ischaemia-guided approach during the first post infarction year.