The Effect of Increasing Water Temperatures on Schistosoma mansoni Transmission and Biomphalaria pfeifferi Population Dynamics: An Agent-Based Modelling Study

Introduction

There is increasing interest in the control and elimination of schistosomiasis. Little is known, however, about the likely effects of increasing water-body temperatures on transmission.

Methods

We have developed an agent-based model of the temperature-sensitive stages of the Schistosoma and intermediate host snail life-cycles, parameterised using data from S. mansoni and Biomphalaria pfeifferi laboratory and field-based observations. Infection risk is calculated as the number of cercariae in the model, adjusted for their probability of causing infection.

Results

The number of snails in the model is approximately constant between 15–31°C. Outside this range, snail numbers drop sharply, and the snail population cannot survive outside the range 14–32°C. Mean snail generation time decreases with increasing temperature from 176 days at 14°C to 46 days at 26°C. Human infection risk is highest between 16–18°C and 1 pm and 6–10 pm in calm water, and 20–25°C and 12–4 pm in flowing water. Infection risk increases sharply when temperatures increase above the minimum necessary for sustained transmission.

Conclusions

The model suggests that, in areas where S. mansoni is already endemic, warming of the water at transmission sites will have differential effects on both snails and parasites depending on abiotic properties of the water-body. Snail generation times will decrease in most areas, meaning that snail populations will recover faster from natural population reductions and from snail-control efforts. We suggest a link between the ecological properties of transmission sites and infection risk which could significantly affect the outcomes of interventions designed to alter water contact behaviour – proposing that such interventions are more likely to reduce infection levels at river locations than lakes, where infection risk remains high for longer. In cooler areas where snails are currently found, increasing temperatures may significantly increase infection risk, potentially leading to new, high-intensity foci of infection.     

Bayesian Risk Mapping and Model-Based Estimation of Schistosoma haematobium–Schistosoma mansoni Co-distribution in C?te d′Ivoire

Background

Schistosoma haematobium and Schistosoma mansoni are blood flukes that cause urogenital and intestinal schistosomiasis, respectively. In Côte d′Ivoire, both species are endemic and control efforts are being scaled up. Accurate knowledge of the geographical distribution, including delineation of high-risk areas, is a central feature for spatial targeting of interventions. Thus far, model-based predictive risk mapping of schistosomiasis has relied on historical data of separate parasite species.

Methodology

We analyzed data pertaining to Schistosoma infection among school-aged children obtained from a national, cross-sectional survey conducted between November 2011 and February 2012. More than 5,000 children in 92 schools across Côte d′Ivoire participated. Bayesian geostatistical multinomial models were developed to assess infection risk, including S. haematobium–S. mansoni co-infection. The predicted risk of schistosomiasis was utilized to estimate the number of children that need preventive chemotherapy with praziquantel according to World Health Organization guidelines.

Principal Findings

We estimated that 8.9% of school-aged children in Côte d′Ivoire are affected by schistosomiasis; 5.3% with S. haematobium and 3.8% with S. mansoni. Approximately 2 million annualized praziquantel treatments would be required for preventive chemotherapy at health districts level. The distinct spatial patterns of S. haematobium and S. mansoni imply that co-infection is of little importance across the country.

Conclusions/Significance

We provide a comprehensive analysis of the spatial distribution of schistosomiasis risk among school-aged children in Côte d′Ivoire and a strong empirical basis for a rational targeting of control interventions.     

Schistosomiasis Control Using Piplartine against Biomphalaria glabrata at Different Developmental Stages

Background

Schistosomiasis is one of the most significant diseases in tropical countries and affects almost 200 million people worldwide. The application of molluscicides to eliminate the parasite''s intermediate host, Biomphalaria glabrata, from infected water supplies is one strategy currently being used to control the disease. Previous studies have shown a potent molluscicidal activity of crude extracts from Piper species, with extracts from Piper tuberculatum being among the most active.

Methods and Findings

The molluscicidal activity of P. tuberculatum was monitored on methanolic extracts from different organs (roots, leaves, fruit and stems). The compounds responsible for the molluscicidal activity were identified using ¹H NMR and ESIMS data and multivariate analyses, including principal component analysis and partial least squares. These results indicated that the high molluscicidal activity displayed by root extracts (LC₅₀ 20.28 µg/ml) was due to the presence of piplartine, a well-known biologically-active amide. Piplartine was isolated from P. tuberculatum root extracts, and the molluscicidal activity of this compound on adults and embryos of B. glabrata was determined. The compound displayed potent activity against all developmental stages of B. glabrata. Next, the environmental toxicity of piplartine was evaluated using the microcrustacean Daphnia similis (LC₅₀ 7.32 µg/ml) and the fish Danio rerio (1.69 µg/ml). The toxicity to these organisms was less compared with the toxicity of niclosamide, a commercial molluscicide.

Conclusions

The development of a new, natural molluscicide is highly desirable, particularly because the commercially available molluscicide niclosamide is highly toxic to some organisms in the environment (LC₅₀ 0.25 µg/ml to D. similis and 0.12 µg/ml to D. rerio). Thus, piplartine is a potential candidate for a natural molluscicide that has been extracted from a tropical plant species and showed less toxic to environment.     

Mutagenesis of Trichoderma reesei endoglucanase I: impact of expression host on activity and stability at elevated temperatures

Background

Trichoderma reesei is a key cellulase source for economically saccharifying cellulosic biomass for the production of biofuels. Lignocellulose hydrolysis at temperatures above the optimum temperature of T. reesei cellulases (~50°C) could provide many significant advantages, including reduced viscosity at high-solids loadings, lower risk of microbial contamination during saccharification, greater compatibility with high-temperature biomass pretreatment, and faster rates of hydrolysis. These potential advantages motivate efforts to engineer T. reesei cellulases that can hydrolyze lignocellulose at temperatures ranging from 60–70°C.

Results

A B-factor guided approach for improving thermostability was used to engineer variants of endoglucanase I (Cel7B) from T. reesei (TrEGI) that are able to hydrolyze cellulosic substrates more rapidly than the recombinant wild-type TrEGI at temperatures ranging from 50–70°C. When expressed in T. reesei, TrEGI variant G230A/D113S/D115T (G230A/D113S/D115T Tr_TrEGI) had a higher apparent melting temperature (3°C increase in T_m) and improved half-life at 60°C (t_1/2 = 161 hr) than the recombinant (T. reesei host) wild-type TrEGI (t_1/2 = 74 hr at 60°C, Tr_TrEGI). Furthermore, G230A/D113S/D115T Tr_TrEGI showed 2-fold improved activity compared to Tr_TrEGI at 65°C on solid cellulosic substrates, and was as efficient in hydrolyzing cellulose at 60°C as Tr_TrEGI was at 50°C. The activities and stabilities of the recombinant TrEGI enzymes followed similar trends but differed significantly in magnitude depending on the expression host (Escherichia coli cell-free, Saccharomyces cerevisiae, Neurospora crassa, or T. reesei). Compared to N.crassa-expressed TrEGI, S. cerevisiae-expressed TrEGI showed inferior activity and stability, which was attributed to the lack of cyclization of the N-terminal glutamine in Sc_TrEGI and not to differences in glycosylation. N-terminal pyroglutamate formation in TrEGI expressed in S. cerevisiae was found to be essential in elevating its activity and stability to levels similar to the T. reesei or N. crassa-expressed enzyme, highlighting the importance of this ubiquitous modification in GH7 enzymes.

Conclusion

Structure-guided evolution of T. reesei EGI was used to engineer enzymes with increased thermal stability and activity on solid cellulosic substrates. Production of TrEGI enzymes in four hosts highlighted the impact of the expression host and the role of N-terminal pyroglutamate formation on the activity and stability of TrEGI enzymes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12896-015-0118-z) contains supplementary material, which is available to authorized users.     

Thermal thresholds as predictors of seed dormancy release and germination timing: altitude-related risks from climate warming for the wild grapevine Vitis vinifera subsp. sylvestris

Background and Aims

The importance of thermal thresholds for predicting seed dormancy release and germination timing under the present climate conditions and simulated climate change scenarios was investigated. In particular, Vitis vinifera subsp. sylvestris was investigated in four Sardinian populations over the full altitudinal range of the species (from approx. 100 to 800 m a.s.l).

Methods

Dried and fresh seeds from each population were incubated in the light at a range of temperatures (10–25 and 25/10 °C), without any pre-treatment and after a warm (3 months at 25 °C) or a cold (3 months at 5 °C) stratification. A thermal time approach was then applied to the germination results for dried seeds and the seed responses were modelled according to the present climate conditions and two simulated scenarios of the Intergovernmental Panel on Climate Change (IPCC): B1 (+1·8 °C) and A2 (+3·4 °C).

Key Results

Cold stratification released physiological dormancy, while very few seeds germinated without treatments or after warm stratification. Fresh, cold-stratified seeds germinated significantly better (>80 %) at temperatures ≥20 °C than at lower temperatures. A base temperature for germination (T_b) of 9·0–11·3 °C and a thermal time requirement for 50 % of germination (θ₅₀) ranging from 33·6 °Cd to 68·6 °Cd were identified for non-dormant cold-stratified seeds, depending on the populations. This complex combination of thermal requirements for dormancy release and germination allowed prediction of field emergence from March to May under the present climatic conditions for the investigated populations.

Conclusions

The thermal thresholds for seed germination identified in this study (T_b and θ₅₀) explained the differences in seed germination detected among populations. Under the two simulated IPCC scenarios, an altitude-related risk from climate warming is identified, with lowland populations being more threatened due to a compromised seed dormancy release and a narrowed seed germination window.     

Thermal niche for in situ seed germination by Mediterranean mountain streams: model prediction and validation for Rhamnus persicifolia seeds

Background and Aims

Mediterranean mountain species face exacting ecological conditions of rainy, cold winters and arid, hot summers, which affect seed germination phenology. In this study, a soil heat sum model was used to predict field emergence of Rhamnus persicifolia, an endemic tree species living at the edge of mountain streams of central eastern Sardinia.

Methods

Seeds were incubated in the light at a range of temperatures (10–25 and 25/10 °C) after different periods (up to 3 months) of cold stratification at 5 °C. Base temperatures (T_b), and thermal times for 50 % germination (θ₅₀) were calculated. Seeds were also buried in the soil in two natural populations (Rio Correboi and Rio Olai), both underneath and outside the tree canopy, and exhumed at regular intervals. Soil temperatures were recorded using data loggers and soil heat sum (°Cd) was calculated on the basis of the estimated T_b and soil temperatures.

Key Results

Cold stratification released physiological dormancy (PD), increasing final germination and widening the range of germination temperatures, indicative of a Type 2 non-deep PD. T_b was reduced from 10·5 °C for non-stratified seeds to 2·7 °C for seeds cold stratified for 3 months. The best thermal time model was obtained by fitting probit germination against log °Cd. θ₅₀ was 2·6 log °Cd for untreated seeds and 2·17–2·19 log °Cd for stratified seeds. When θ₅₀ values were integrated with soil heat sum estimates, field emergence was predicted from March to April and confirmed through field observations.

Conclusions

T_b and θ₅₀ values facilitated model development of the thermal niche for in situ germination of R. persicifolia. These experimental approaches may be applied to model the natural regeneration patterns of other species growing on Mediterranean mountain waterways and of physiologically dormant species, with overwintering cold stratification requirement and spring germination.     

Lack of evolutionary adjustment to ambient temperature in highly specialized cave beetles

Background

A key question in evolutionary biology is the relationship between species traits and their habitats. Caves offer an ideal model to test the adjustment of species to their surrounding temperature, as they provide homogeneous and simple environments. We compared two species living under different thermal conditions within a lineage of Pyrenean beetles highly modified for the subterranean life since the Miocene. One, Troglocharinus fonti, is found in caves at 4-11°C in the ancestral Pyrenean range. The second, T. ferreri, inhabits the coastal area of Catalonia since the early Pliocene, and lives at 14-16°C.

Results

We found no differences in their short term upper thermal limit (ca. 50°C), similar to that of most organisms, or their lower thermal limit (ca. -2.5°C), higher than for most temperate insects and suggesting the absence of cryoprotectants. In longer term tests (7 days) survival between 6-20°C was almost 100% for both species plus two outgroups of the same lineage, but all four died between 23-25°C, without significant differences between them.

Conclusions

Our results suggest that species in this lineage have lost some of the thermoregulatory mechanisms common in temperate insects, as their inferred default tolerance range is larger than the thermal variation experienced through their whole evolutionary history.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-015-0288-2) contains supplementary material, which is available to authorized users.     

Recovery and fine structure variability of RGII sub-domains in wine (Vitis vinifera Merlot)

Background and Aims

Rhamnogalacturonan II (RGII) is a structurally complex pectic sub-domain composed of more than 12 different sugars and 20 different linkages distributed in five side chains along a homogalacturonan backbone. Although RGII has long been described as highly conserved over plant evolution, recent studies have revealed variations in the structure of the polysaccharide. This study examines the fine structure variability of RGII in wine, focusing on the side chains A and B obtained after sequential mild acid hydrolysis. Specifically, this study aims to differentiate intrinsic structural variations in these RGII side chains from structural variations due to acid hydrolysis.

Methods

RGII from wine (Vitis vinifera Merlot) was sequentially hydrolysed with trifluoroacetic acid (TFA) and the hydrolysis products were separated by anion-exchange chromatography (AEC). AEC fractions or total hydrolysates were analysed by MALDI-TOF mass spectrometry.

Key Results

The optimal conditions to recover non-degraded side chain B, side chain A and RGII backbone were 0·1 m TFA at 40 °C for 16 h, 0·48 m TFA at 40 °C for 16 h (or 0·1 m TFA at 60 °C for 8 h) and 0·1 m TFA at 60 °C for 16 h, respectively. Side chain B was particularly prone to acid degradation. Side chain A and the RGII GalA backbone were partly degraded by 0·1 m TFA at 80 °C for 1–4 h. AEC allowed separation of side chain B, methyl-esterified side chain A and non-methyl-esterified side chain A. The structure of side chain A and the GalA backbone were highly variable.

Conclusions

Several modifications to the RGII structure of wine were identified. The observed dearabinosylation and deacetylation were primarily the consequence of acidic treatment, while variation in methyl-esterification, methyl-ether linkages and oxidation reflect natural diversity. The physiological significance of this variability, however, remains to be determined.     

Physical and Perceptual Cooling with Beverages to Increase Cycle Performance in a Tropical Climate

Purpose

This study compares the effects of neutral temperature, cold and ice-slush beverages, with and without 0.5% menthol on cycling performance, core temperature (T_co) and stress responses in a tropical climate (hot and humid conditions).

Methods

Twelve trained male cyclists/triathletes completed six 20-km exercise trials against the clock in 30.7°C±0.8°C and 78%±0.03% relative humidity. Before and after warm-up, and before exercise and every 5 km during exercise, athletes drank 190 mL of either aromatized (i.e., with 0.5 mL of menthol (5 gr/L)) or a non-aromatized beverage (neutral temperature: 23°C±0.1°C, cold: 3°C±0.1°C, or ice-slush: −1°C±0.7°C). During the trials, heart rate (HR) was continuously monitored, whereas core temperature (T_co), thermal comfort (TC), thermal sensation (TS) and rate of perceived exertion (RPE) were measured before and after warm-up, every 5 km of exercise, and at the end of exercise and after recovery.

Results

Both the beverage aroma (P<0.02) and beverage temperature (P<0.02) had significant and positive effects on performance, which was considerably better with ice-slush than with a neutral temperature beverage, whatever the aroma (P<0.002), and with menthol vs non-menthol (P<0.02). The best performances were obtained with ice-slush/menthol and cold/menthol, as opposed to neutral/menthol. No differences were noted in HR and T_co between trials.

Conclusion

Cold water or ice-slush with menthol aroma seems to be the most effective beverage for endurance exercise in a tropical climate. Further studies are needed to explore its effects in field competition.     

Fluctuations at a Low Mean Temperature Accelerate Dengue Virus Transmission by Aedes aegypti

Background

Environmental factors such as temperature can alter mosquito vector competence for arboviruses. Results from recent studies indicate that daily fluctuations around an intermediate mean temperature (26°C) reduce vector competence of Aedes aeygpti for dengue viruses (DENV). Theoretical predictions suggest that the mean temperature in combination with the magnitude of the diurnal temperature range (DTR) mediate the direction of these effects.

Methodology/Principal Findings

We tested the effect of temperature fluctuations on Ae. aegypti vector competence for DENV serotype-1 at high and low mean temperatures, and confirmed this theoretical prediction. A small DTR had no effect on vector competence around a high (30°C) mean, but a large DTR at low temperature (20°C) increased the proportion of infected mosquitoes with a disseminated infection by 60% at 21 and 28 days post-exposure compared to a constant 20°C. This effect resulted from a marked shortening of DENV extrinsic incubation period (EIP) in its mosquito vector; i.e., a decrease from 29.6 to 18.9 days under the fluctuating vs. constant temperature treatment.

Conclusions

Our results indicate that Ae. aegypti exposed to large fluctuations at low temperatures have a significantly shorter virus EIP than under constant temperature conditions at the same mean, leading to a considerably greater potential for DENV transmission. These results emphasize the value of accounting for daily temperature variation in an effort to more accurately understand and predict the risk of mosquito-borne pathogen transmission, provide a mechanism for sustained DENV transmission in endemic areas during cooler times of the year, and indicate that DENV transmission could be more efficient in temperate regions than previously anticipated.     

The core interthreshold zone during exposure to red and blue light

Background

This study tested the hypothesis that the core interthreshold zone (CIZ) changes during exposure to red or blue light via the non-visual pathway, because it is known that light intensity affects the central nervous system. We conducted a series of human experiments with 5 or 10 male subjects in each experiment.

Methods

The air temperature in the climatic chamber was maintained at 20 to 24°C. The subjects wore suits perfused with 25°C water at a rate of 600 cm³/min. They exercised on an ergometer at 50% of their maximum work rate for 10 to 15 minutes until sweating commenced, and then remained continuously seated without exercise until their oxygen uptake increased. The rectal temperature and skin temperatures at four sites were monitored using thermistors. The sweating rate was measured at the forehead with a sweat rate monitor. Oxygen uptake was monitored with a gas analyzer. The subjects were exposed to red or blue light at 500 lx and 1000 lx in both summer and winter.

Results

The mean CIZs at 500 lx were 0.23 ± 0.16°C under red light and 0.20 ± 0.10°C under blue light in the summer, and 0.19 ± 0.20°C under red light and 0.26 ± 0.24°C under blue light in the winter. The CIZs at 1000 lx were 0.18 ± 0.14°C under red light and 0.15 ± 0.20°C under blue light in the summer, and 0.52 ± 0.18°C under red light and 0.71 ± 0.28°C under blue light in the winter. A significant difference (P <0.05) was observed in the CIZs between red and blue light at 1000 lx in the winter, and significant seasonal differences under red light (P <0.05) and blue light (P <0.01) were also observed at 1000 lx.

Conclusions

The present study demonstrated that dynamic changes in the physiological effects of colors of light on autonomic functions via the non-visual pathway may be associated with the temperature regulation system.     

The influence of environmental temperature on appetite-related hormonal responses

Background

Acute exercise in the heat has been shown to reduce appetite. However, the influence of exercise in the cold on appetite regulation remains unclear. The aim of this study was to compare exercise-induced appetite regulation under three different environmental temperatures.

Methods

Eleven male participants completed three experimental trials on the following separate days: exercise in the heat (36°C), exercise at neutral temperature (24°C), and exercise in the cold (12°C). The exercise trials consisted of pedaling exercises for 30 min at 65% of maximal oxygen uptake (VO_2max). Blood samples were collected repeatedly to determine plasma ghrelin, peptide YY (PYY) and other hormonal concentrations. Subjective feelings of hunger and tympanic temperature were also monitored.

Results

Tympanic temperature was significantly higher in the 36°C trial than that of the other two trials (P < 0.05). The subjective feelings of hunger in the 36°C and 24°C trials were significantly lower than those in the 12°C trial (P < 0.05). Plasma ghrelin concentration decreased significantly with exercise in all conditions (P < 0.05), and the responses were not significantly different among the three conditions. Plasma PYY concentration increased significantly after the exercise in the 24°C trial only (P < 0.05), with no significant difference among the three trials.

Conclusions

These results suggest that exposure to hot or cold temperatures during exercise did not affect exercise-induced plasma ghrelin and PYY responses. However, the exercise-induced reduction of subjective hunger was significantly attenuated in a cold environment.     

Chronic Schistosoma japonicum Infection Reduces Immune Response to Vaccine against Hepatitis B in Mice

Background

Hepatitis B and schistosomiasis are most prevalent in Africa and Asia, and co-infections of both are frequent in these areas. The immunomodulation reported to be induced by schistosome infections might restrict immune control of hepatitis B virus (HBV) leading to more severe viral infection. Vaccination is the most effective measure to control and prevent HBV infection, but there is evidence for a reduced immune response to the vaccine in patients with chronic schistosomiasis japonica.

Methodology/Principal Findings

In this paper, we demonstrate in a mouse model that a chronic Schistosoma japonicum infection can inhibit the immune response to hepatitis B vaccine (HBV vaccine) and lead to lower production of anti-HBs antibodies, interferon-γ (IFN-γ) and interleukin-2 (IL-2). After deworming with Praziquantel (PZQ), the level of anti-HBs antibodies gradually increased and the Th2-biased profile slowly tapered. At 16 weeks after deworming, the levels of anti-HBs antibodies and Th1/Th2 cytokines returned to the normal levels.

Conclusions/Significance

The results suggest that the preexisting Th2-dominated immune profile in the host infected with the parasite may down–regulate levels of anti-HBs antibodies and Th1 cytokines. To improve the efficacy of HBV vaccination in schistosome infected humans it may be valuable to treat them with praziquantel (PZQ) some time prior to HBV vaccination.     

Elimination of Schistosomiasis Transmission in Zanzibar: Baseline Findings before the Onset of a Randomized Intervention Trial

Background

Gaining and sustaining control of schistosomiasis and, whenever feasible, achieving local elimination are the year 2020 targets set by the World Health Organization. In Zanzibar, various institutions and stakeholders have joined forces to eliminate urogenital schistosomiasis within 5 years. We report baseline findings before the onset of a randomized intervention trial designed to assess the differential impact of community-based praziquantel administration, snail control, and behavior change interventions.

Methodology

In early 2012, a baseline parasitological survey was conducted in ∼20,000 people from 90 communities in Unguja and Pemba. Risk factors for schistosomiasis were assessed by administering a questionnaire to adults. In selected communities, local knowledge about schistosomiasis transmission and prevention was determined in focus group discussions and in-depths interviews. Intermediate host snails were collected and examined for shedding of cercariae.

Principal Findings

The baseline Schistosoma haematobium prevalence in school children and adults was 4.3% (range: 0–19.7%) and 2.7% (range: 0–26.5%) in Unguja, and 8.9% (range: 0–31.8%) and 5.5% (range: 0–23.4%) in Pemba, respectively. Heavy infections were detected in 15.1% and 35.6% of the positive school children in Unguja and Pemba, respectively. Males were at higher risk than females (odds ratio (OR): 1.45; 95% confidence interval (CI): 1.03–2.03). Decreasing adult age (OR: 1.04; CI: 1.02–1.06), being born in Pemba (OR: 1.48; CI: 1.02–2.13) or Tanzania (OR: 2.36; CI: 1.16–4.78), and use of freshwater (OR: 2.15; CI: 1.53–3.03) showed higher odds of infection. Community knowledge about schistosomiasis was low. Only few infected Bulinus snails were found.

Conclusions/Significance

The relatively low S. haematobium prevalence in Zanzibar is a promising starting point for elimination. However, there is a need to improve community knowledge about disease transmission and prevention. Control measures tailored to the local context, placing particular attention to hot-spot areas, high-risk groups, and individuals, will be necessary if elimination is to be achieved.     

Bladder Morbidity and Hepatic Fibrosis in Mixed Schistosoma haematobium and S. mansoni Infections: A Population-Wide Study in Northern Senegal

Background

The global distribution map of schistosomiasis shows a large overlap of Schistosoma haematobium- and S. mansoni-endemic areas in Africa. Yet, little is known about the consequences of mixed Schistosoma infections for the human host. A recent study in two neighboring co-endemic communities in Senegal indicated that infection intensities of both species were higher in mixed than in single infections. Here, we investigated the relationship between mixed Schistosoma infections and morbidity in the same population. So far, this has only been studied in children.

Methods

Schistosoma infection was assessed by microscopy. Schistosoma-specific morbidity was assessed by ultrasound according to WHO guidelines. Multivariable logistic regression models were used to identify independent risk factors for morbidity.

Principal Findings

Complete parasitological and morbidity data were obtained from 403 individuals. Schistosoma haematobium-specific bladder morbidity was observed in 83% and S. mansoni-specific hepatic fibrosis in 27% of the participants. Bladder morbidity was positively associated with S. haematobium infection intensity (OR = 1.9 (95% CI 1.3–2.9) for a 10-fold increase in intensity). Moreover, people with mixed infections tended to have less bladder morbidity than those with single S. haematobium infections (OR = 0.3 (95% CI 0.1–1.1)). This effect appeared to be related to ectopic S. mansoni egg elimination in urine. Hepatic fibrosis on the other hand was not related to S. mansoni infection intensity (OR = 0.9 (95% CI 0.6–1.3)), nor to mixed infections (OR = 1.0 (95% CI 0.7–1.7)).

Conclusions/Significance

This is the first population-wide study on the relationship between mixed Schistosoma infections and morbidity. Mixed infections did not increase the risk of S. mansoni-associated morbidity. They even tended to reduce the risk of S. haematobium-associated morbidity, suggesting a protective effect of S. mansoni infection on bladder morbidity. These unexpected results may have important consequences for schistosomiasis control in co-endemic areas and warrant further investigation.     

Co-infection of Long-Term Carriers of Plasmodium falciparum with Schistosoma haematobium Enhances Protection from Febrile Malaria: A Prospective Cohort Study in Mali

Background

Malaria and schistosomiasis often overlap in tropical and subtropical countries and impose tremendous disease burdens; however, the extent to which schistosomiasis modifies the risk of febrile malaria remains unclear.

Methods

We evaluated the effect of baseline S. haematobium mono-infection, baseline P. falciparum mono-infection, and co-infection with both parasites on the risk of febrile malaria in a prospective cohort study of 616 children and adults living in Kalifabougou, Mali. Individuals with S. haematobium were treated with praziquantel within 6 weeks of enrollment. Malaria episodes were detected by weekly physical examination and self-referral for 7 months. The primary outcome was time to first or only malaria episode defined as fever (≥37.5°C) and parasitemia (≥2500 asexual parasites/µl). Secondary definitions of malaria using different parasite densities were also explored.

Results

After adjusting for age, anemia status, sickle cell trait, distance from home to river, residence within a cluster of high S. haematobium transmission, and housing type, baseline P. falciparum mono-infection (n = 254) and co-infection (n = 39) were significantly associated with protection from febrile malaria by Cox regression (hazard ratios 0.71 and 0.44; P = 0.01 and 0.02; reference group: uninfected at baseline). Baseline S. haematobium mono-infection (n = 23) did not associate with malaria protection in the adjusted analysis, but this may be due to lack of statistical power. Anemia significantly interacted with co-infection (P = 0.009), and the malaria-protective effect of co-infection was strongest in non-anemic individuals. Co-infection was an independent negative predictor of lower parasite density at the first febrile malaria episode.

Conclusions

Co-infection with S. haematobium and P. falciparum is significantly associated with reduced risk of febrile malaria in long-term asymptomatic carriers of P. falciparum. Future studies are needed to determine whether co-infection induces immunomodulatory mechanisms that protect against febrile malaria or whether genetic, behavioral, or environmental factors not accounted for here explain these findings.     

Downregulation of net phosphorus-uptake capacity is inversely related to leaf phosphorus-resorption proficiency in four species from a phosphorus-impoverished environment

Background and Aims

Previous research has suggested a trade-off between the capacity of plants to downregulate their phosphorus (P) uptake capacity and their efficiency of P resorption from senescent leaves in species from P-impoverished environments.

Methods

To investigate this further, four Australian native species (Banksia attenuata, B. menziesii, Acacia truncata and A. xanthina) were grown in a greenhouse in nutrient solutions at a range of P concentrations [P]. Acacia plants received between 0 and 500 µm P; Banksia plants received between 0 and 10 µm P, to avoid major P-toxicity symptoms in these highly P-sensitive species.

Key Results

For both Acacia species, the net P-uptake rates measured at 10 µm P decreased steadily with increasing P supply during growth. In contrast, in B. attenuata, the net rate of P uptake from a solution with 10 µm P increased linearly with increasing P supply during growth. The P-uptake rate of B. menziesii showed no significant response to P supply in the growing medium. Leaf [P] of the four species supported this finding, with A. truncata and A. xanthina showing an increase up to a saturation value of 19 and 21 mg P g⁻¹ leaf dry mass, respectively (at 500 µm P), whereas B. attenuata and B. menziesii both exhibited a linear increase in leaf [P], reaching 10 and 13 mg P g⁻¹ leaf dry mass, respectively, without approaching a saturation point. The Banksia plants grown at 10 µm P showed mild symptoms of P toxicity, i.e. yellow spots on some leaves and drying and curling of the tips of the leaves. Leaf P-resorption efficiency was 69 % (B. attenuata), 73 % (B. menziesii), 34 % (A. truncata) and 36 % (A. xanthina). The P-resorption proficiency values were 0·08 mg P g⁻¹ leaf dry mass (B. attenuata and B. menziesii), 0·32 mg P g⁻¹ leaf dry mass (A. truncata) and 0·36 mg P g⁻¹ leaf dry mass (A. xanthina). Combining the present results with additional information on P-remobilization efficiency and the capacity to downregulate P-uptake capacity for two other Australian woody species, we found a strong negative correlation between these traits.

Conclusions

It is concluded that species that are adapted to extremely P-impoverished soils, such as many south-western Australian Proteaceae species, have developed extremely high P-resorption efficiencies, but lost their capacity to downregulate their P-uptake mechanisms. The results support the hypothesis that the ability to resorb P from senescing leaves is inversely related to the capacity to downregulate net P uptake, possibly because constitutive synthesis of P transporters is a prerequisite for proficient P remobilization from senescing tissues.