Global numbers of infection and disease burden of soil transmitted helminth infections in 2010

Bayesian geostatistical model-based estimates of soil-transmitted helminth infection in Nigeria, including annual deworming requirements

Background

The acceleration of the control of soil-transmitted helminth (STH) infections in Nigeria, emphasizing preventive chemotherapy, has become imperative in light of the global fight against neglected tropical diseases. Predictive risk maps are an important tool to guide and support control activities.

Methodology

STH infection prevalence data were obtained from surveys carried out in 2011 using standard protocols. Data were geo-referenced and collated in a nationwide, geographic information system database. Bayesian geostatistical models with remotely sensed environmental covariates and variable selection procedures were utilized to predict the spatial distribution of STH infections in Nigeria.

Principal Findings

We found that hookworm, Ascaris lumbricoides, and Trichuris trichiura infections are endemic in 482 (86.8%), 305 (55.0%), and 55 (9.9%) locations, respectively. Hookworm and A. lumbricoides infection co-exist in 16 states, while the three species are co-endemic in 12 states. Overall, STHs are endemic in 20 of the 36 states of Nigeria, including the Federal Capital Territory of Abuja. The observed prevalence at endemic locations ranged from 1.7% to 51.7% for hookworm, from 1.6% to 77.8% for A. lumbricoides, and from 1.0% to 25.5% for T. trichiura. Model-based predictions ranged from 0.7% to 51.0% for hookworm, from 0.1% to 82.6% for A. lumbricoides, and from 0.0% to 18.5% for T. trichiura. Our models suggest that day land surface temperature and dense vegetation are important predictors of the spatial distribution of STH infection in Nigeria. In 2011, a total of 5.7 million (13.8%) school-aged children were predicted to be infected with STHs in Nigeria. Mass treatment at the local government area level for annual or bi-annual treatment of the school-aged population in Nigeria in 2011, based on World Health Organization prevalence thresholds, were estimated at 10.2 million tablets.

Conclusions/Significance

The predictive risk maps and estimated deworming needs presented here will be helpful for escalating the control and spatial targeting of interventions against STH infections in Nigeria.

Infections with three kinds of parasitic worms—hookworm, roundworm, and whipworm—are collectively known as soil-transmitted helminths (STHs). These parasitic worm infections are widespread in Nigeria, but the exact distribution is poorly understood. In view of the global commitment to control STH infections, there is a need to accelerate the mapping of STH infections to guide control interventions, such as large-scale administration of deworming drugs. In this study, we collated survey data from the year 2011 for Nigeria. The data were utilized to predict the distribution of STH infection based on environmental and socioeconomic covariates, and employing a Bayesian geostatistical modeling approach. Our results indicated that STH infections are widely distributed across Nigeria with prevalence estimates as high as 83% for roundworm, 50% for hookworm, and 19% for whipworm infections at specific survey locations. We predict that 5.7 million school-aged children were infected with STHs. The numbers of deworming tablets for annual or bi-annual treatment of the school-aged population at local government areas level in Nigeria for 2011 were estimated to be 10.2 million.

Neglected tropical diseases among the Association of Southeast Asian Nations (ASEAN): overview and update

The ten member states of the Association of Southeast Asian Nations (ASEAN) constitute an economic powerhouse, yet these countries also harbor a mostly hidden burden of poverty and neglected tropical diseases (NTDs). Almost 200 million people live in extreme poverty in ASEAN countries, mostly in the low or lower middle-income countries of Indonesia, the Philippines, Myanmar, Viet Nam, and Cambodia, and many of them are affected by at least one NTD. However, NTDs are prevalent even among upper middle-income ASEAN countries such as Malaysia and Thailand, especially among the indigenous populations. The three major intestinal helminth infections are the most common NTDs; each helminthiasis is associated with approximately 100 million infections in the region. In addition, more than 10 million people suffer from either liver or intestinal fluke infections, as well as schistosomiasis and lymphatic filariasis (LF). Intestinal protozoan infections are widespread, while leishmaniasis has emerged in Thailand, and zoonotic malaria (Plasmodium knowlesi infection) causes severe morbidity in Malaysia. Melioidosis has emerged as an important bacterial NTD, as have selected rickettsial infections, and leptospirosis. Leprosy, yaws, and trachoma are still endemic in focal areas. Almost 70 million cases of dengue fever occur annually in ASEAN countries, such that this arboviral infection is now one of the most common and economically important NTDs in the region. A number of other arboviral and zoonotic viral infections have also emerged, including Japanese encephalitis; tick-borne viral infections; Nipah virus, a zoonosis present in fruit bats; and enterovirus 71 infection. There are urgent needs to expand surveillance activities in ASEAN countries, as well as to ensure mass drug administration is provided to populations at risk for intestinal helminth and fluke infections, LF, trachoma, and yaws. An ASEAN Network for Drugs, Diagnostics, Vaccines, and Traditional Medicines Innovation provides a policy framework for the development of new control and elimination tools. Together with prominent research institutions and universities, the World Health Organization (WHO), and its regional offices, these organizations could implement important public health improvements through NTD control and elimination in the coming decade.

Global feasibility assessment of interrupting the transmission of soil-transmitted helminths: a statistical modelling study

BACKGROUND

Emphasis is being given to the control of neglected tropical diseases, including the possibility of interrupting the transmission of soil-transmitted helminths (STH). We evaluated the feasibility by country of achieving interruption of the transmission of STH.

METHODS

Based on a conceptual framework for the identification of the characteristics of a successful STH control programme, we assembled spatial data for a range of epidemiological, institutional, economic, and political factors. Using four different statistical methods, we developed a composite score of the feasibility of interrupting STH transmission and undertook a sensitivity analysis of the data and methods.

FINDINGS

The most important determining factors in the analysis were underlying intensity of STH transmission, current implementation of control programmes for neglected tropical diseases, and whether countries receive large-scale external funding and have strong health systems. The composite scores suggested that interrupting STH transmission is most feasible in countries in the Americas and parts of Asia (eg, Argentina [range of composite feasibility scores, depending on scoring method, 9·4-10·0], Brazil [8·7- 9·7], Chile [8·84-10·0], and Thailand [9·1-10·0]; there was perfect agreement between the four methods), and least feasible in countries in sub-Saharan Africa (eg, Congo [0·4-2·7] and Guinea [2·0-5·6]; there was full agreement between methods), but there were important exceptions to these trends (eg, Ghana [7·4-10·0]; there was agreement between three methods). Agreement was highest between the scores derived with the expert opinion and principal component analysis weighting schemes (Pearson correlation coefficient, r=0·98). The largest disagreement was between benefit-of-the-doubt-derived and principal-component-analysis-derived weighting schemes (r=0·74).

INTERPRETATION

The interruption of STH transmission is feasible, especially in countries with low intensity of transmission, supportive household environments, strong health systems, and the availability of suitable delivery platforms and in-country funds, but to achieve local elimination of STH an intersectoral approach to STH control will be needed.

FUNDING

Bill & Melinda Gates Foundation and Wellcome Trust.

The human hookworm vaccine: recent updates and prospects for success

Approximately 440 million people globally are afflicted by hookworm disease, one of the 17 WHO-recognized neglected tropical diseases (NTDs). The iron-deficiency anaemia attributed to this disease contributes to at least 3.2 million disability-adjusted life years (DALYs) according to the Global Burden of Disease Study 2010. The current WHO-recommended control strategies rely primarily on mass drug administration or preventive chemotherapy. However, evidence is starting to accumulate confirming that preventive chemotherapy alone will not be sufficient to reduce the reinfection rates of hookworm, especially in areas of heavy transmission. The global health and research community is currently building a consensus stressing the need for the advancement of research and innovation to bridge the gaps and identify new public health interventions for diseases such as hookworm and other NTDs. This paper presents the strategies used by the Sabin Vaccine Institute Product Development Partnership (Sabin PDP) in their ongoing endeavour for the development of a human hookworm vaccine. Recent updates and the current prospects for success of an effective human hookworm vaccine, as a new technology to be linked to or combined with drug interventions, are presented.

Risk profiling of hookworm infection and intensity in southern Lao People's Democratic Republic using Bayesian models

BACKGROUND

Among the common soil-transmitted helminth infections, hookworm causes the highest burden. Previous research in the southern part of Lao People's Democratic Republic (Lao PDR) revealed high prevalence rates of hookworm infection. The purpose of this study was to predict the spatial distribution of hookworm infection and intensity, and to investigate risk factors in the Champasack province, southern Lao PDR.

METHODOLOGY

A cross-sectional parasitological and questionnaire survey was conducted in 51 villages. Data on demography, socioeconomic status, water, sanitation, and behavior were combined with remotely sensed environmental data. Bayesian mixed effects logistic and negative binomial models were utilized to investigate risk factors and spatial distribution of hookworm infection and intensity, and to make predictions for non-surveyed locations.

PRINCIPAL FINDINGS

A total of 3,371 individuals were examined with duplicate Kato-Katz thick smears and revealed a hookworm prevalence of 48.8%. Most infections (91.7%) were of light intensity (1-1,999 eggs/g of stool). Lower hookworm infection levels were associated with higher socioeconomic status. The lowest infection levels were found in preschool-aged children. Overall, females were at lower risk of infection, but women aged 50 years and above harbored the heaviest hookworm infection intensities. Hookworm was widespread in Champasack province with little evidence for spatial clustering. Infection risk was somewhat lower in the lowlands, mostly along the western bank of the Mekong River, while infection intensity was homogeneous across the Champasack province.

CONCLUSIONS/SIGNIFICANCE

Hookworm transmission seems to occur within, rather than between villages in Champasack province. We present spatial risk maps of hookworm infection and intensity, which suggest that control efforts should be intensified in the Champasack province, particularly in mountainous areas.

A new methodology for evaluation of nematode viability

Nematodes infections are responsible for debilitating conditions and economic losses in domestic animals as well as livestock and are considered an important public health problem due to the high prevalence in humans. The nematode resistance for drugs has been reported for livestock, highlighting the importance for development of new anthelmintic compounds. The aim of the current study was to apply and compare fluorimetric techniques using Sytox and propidium iodide for evaluating the viability of C. elegans larvae after treatment with anthelmintic drugs. These fluorescent markers were efficient to stain larvae treated with ivermectin and albendazole sulfoxide. We observed that densitometric values were proportional to the concentration of dead larvae stained with both markers. Furthermore, data on motility test presented an inverse correlation with fluorimetric data when ivermectin was used. Our results showed that lower concentrations of drugs were effective to interfere in the processes of cellular transport while higher drugs concentrations were necessary in order to result in any damage to cell integrity. The methodology described in this work might be useful for studies that aim to evaluate the viability of nematodes, particularly for testing of new anthelminthic compounds using an easy, economic, reproducible, and no time-consuming technique.

A genetic analysis of Trichuris trichiura and Trichuris suis from Ecuador

Background

Since the nematodes Trichuris trichiura and T. suis are morphologically indistinguishable, genetic analysis is required to assess epidemiological cross-over between people and pigs. This study aimed to clarify the transmission biology of trichuriasis in Ecuador.

Findings

Adult Trichuris worms were collected during a parasitological survey of 132 people and 46 pigs in Esmeraldas Province, Ecuador. Morphometric analysis of 49 pig worms and 64 human worms revealed significant variation. In discriminant analysis morphometric characteristics correctly classified male worms according to host species. In PCR-RFLP analysis of the ribosomal Internal Transcribed Spacer (ITS-2) and 18S DNA (59 pig worms and 82 human worms), nearly all Trichuris exhibited expected restriction patterns. However, two pig-derived worms showed a “heterozygous-type” ITS-2 pattern, with one also having a “heterozygous-type” 18S pattern. Phylogenetic analysis of the mitochondrial large ribosomal subunit partitioned worms by host species. Notably, some Ecuadorian T. suis clustered with porcine Trichuris from USA and Denmark and some with Chinese T. suis.

Conclusion

This is the first study in Latin America to genetically analyse Trichuris parasites. Although T. trichiura does not appear to be zoonotic in Ecuador, there is evidence of genetic exchange between T. trichiura and T. suis warranting more detailed genetic sampling.

Faecal egg counts and expulsion dynamics of the whipworm, Trichuris trichiura following self-infection

More than 400 million humans are estimated to be infected with the intestinal helminth parasite, Trichuris trichiura. The infection is chronic in nature and high-intensity infection can lead to colitis, anaemia, Trichuris Dysentery Syndrome and reduced cognitive performance. Single doses of 400 mg albendazole or 500 mg mebendazole (MBZ) are used in mass drug administration programmes, but this has been shown to be insufficient. In this study, worm expulsion dynamics are described after MBZ treatment, given as a multi-dose and single-dose treatment in two separate T. trichiura self-infection studies. Worm expulsion dynamics post-treatment showed a similar pattern regardless of the dose regime, with the first worms observed on day 2 and the last worms expelled on days 9 and 13 post-treatment. Establishment of a chronic infection was observed following the inefficient single-dose treatment. The prepatent period was 13–16 weeks in both studies and worms were found to have a lifespan of at least 1 year and 10 months. These self-infection studies provide key information on the chronicity of T. trichiura infections, expulsion dynamics after anthelmintic treatment and the prepatent period, as well as the fecundity of female worms, which was around 18,000 eggs/female per day.

The IgE response to Ascaris molecular components is associated with clinical indicators of asthma severity

Background

Asthma is a common chronic disease worldwide and Ascaris lumbricoides infection (ascariasis) is frequent in tropical regions. However, the effect of ascariasis on asthma severity has not been sufficiently explored. We sought to evaluate the influence of the IgE immune response to Ascaris extract and purified house dust mites (HDM) and Ascaris allergens on indicators of asthma severity in patients living in the tropics.

Methods

Asthmatic patients from Cartagena, Colombia were recruited. Clinical assessment included questionnaires, physical examination, allergy skin tests, spirometry, parasite stool examination and IgE antibody measurements. Asthma was diagnosed by a physician according to validated criteria. Indicators of severity were occurrence of severe dyspnea episodes, night awakenings events, > 4 emergency room (ER) visits and hospitalizations during the last year. Specific IgE to Der p 2, Ascaris spp., Blomia tropicalis and Dermatophagoides pteronyssinus extracts was determined by ImmunoCap. IgE to tropomyosins (Asc l 3, Blo t 10 and Der p 10), Blo t 5 and Asc s 1 was detected by ELISA. Logistic regression analyses were used to explore the relationships between sensitization and indicators of asthma severity.

Results

After adjustment for HDM sensitization, Ascaris sensitization remained associated with severe dyspnea (aOR: 1.90, 95% CI: 1.08 - 3.34, p = 0.03) and > 4 ER visits (aOR: 2.23, 95% CI: 1.15 - 4.30, p = 0.02). We also found that sensitization to the species specific markers Blo t 5 and Asc s 1, as well as the cross-reactive tropomyosins of D. pteronyssinus and Ascaris were associated with > 4 ER visits. Der p 2 sensitization was associated with bronchodilator responsiveness (aOR: 2.24: 1.25-4.02, p = 0.01). Remarkably, significantly higher IgE levels to HDM species specific allergens were found in Ascaris sensitized patients.

Conclusions

In this tropical population, IgE sensitization to Ascaris and the cross-reactive tropomyosins was frequent and associated with clinical indicators of asthma severity. The significant relationship between sensitization to the nematode-specific marker Asc s 1 and ER attendance supports these findings. Moreover, ascariasis increases the human IgE responses to HDM specific allergens.

Assessing the fate of Ascaris suum ova during mesophilic anaerobic digestion

There is limited knowledge about the survival of geohelminths, which are soil-transmitted human pathogens, in mesophilic anaerobic digestion processes. This study examined the fate of embryonated and unembryonated Ascaris suum ova in six laboratory-scale mesophilic (35 °C) anaerobic digesters processing swine manure to identify their survival strategies and investigate potential mechanisms to enhance their destruction. There was no significant difference in inactivation of Ascaris suum ova in digesters operated at different solids residence times (SRT) or feeding frequencies. Ova exposed to an anaerobic environment became dormant, or remained unembryonated throughout their residence in the reactors. Approximately 65% of ova were able to retain their viability for up to 16 days, after which the rate of inactivation increased until nearly all ova were nonviable by day 24. In contrast, ova exposed to aerobic conditions did not become dormant and progressed through several developmental stages until day 16, after which nearly all ova were observed to be nonviable. In addition, only 35% of fully developed ova exposed to the anaerobic environment retained their viability by day 16 compared to 65% for dormant ova. Results suggest that some ova are physically destroyed during digestion and ova can be inactivated faster if their development cycle is aerobically triggered before entering the anaerobic digestion process. Results also suggest that transfer of resource recovery technologies such as mesophilic anaerobic digestion to developing world settings must account for local climatic and health conditions so mutually beneficial outcomes can be attained.

The genome and transcriptome of the zoonotic hookworm Ancylostoma ceylanicum identify infection-specific gene families

Hookworms infect over 400 million people, stunting and impoverishing them. Sequencing hookworm genomes and finding which genes they express during infection should help in devising new drugs or vaccines against hookworms. Unlike other hookworms, Ancylostoma ceylanicum infects both humans and other mammals, providing a laboratory model for hookworm disease. We determined an A. ceylanicum genome sequence of 313 Mb, with transcriptomic data throughout infection showing expression of 30,738 genes. Approximately 900 genes were upregulated during early infection in vivo, including ASPRs, a cryptic subfamily of activation-associated secreted proteins (ASPs). Genes downregulated during early infection included ion channels and G protein-coupled receptors; this downregulation was observed in both parasitic and free-living nematodes. Later, at the onset of heavy blood feeding, C-lectin genes were upregulated along with genes for secreted clade V proteins (SCVPs), encoding a previously undescribed protein family. These findings provide new drug and vaccine targets and should help elucidate hookworm pathogenesis.

Mathematical inference on helminth egg counts in stool and its applications in mass drug administration programmes to control soil-transmitted helminthiasis in public health

In the present study, we present a hierarchical model based on faecal egg counts (FECs; expressed in eggs per 1g of stool) in which we first describe the variation in FECs between individuals in a particular population, followed by describing the variance due to counting eggs under a microscope separately for each stool sample. From this general framework, we discuss how to calculate a sample size for assessing a population mean FEC and the impact of an intervention, measured as reduction in FECs, for any scenario of soil-transmitted helminth (STH) epidemiology (the intensity and aggregation of FECs within a population) and diagnostic strategy (amount of stool examined (∼sensitivity of the diagnostic technique) and examination of individual/pooled stool samples) and on how to estimate prevalence of STH in the absence of a gold standard. To give these applications the most wide relevance as possible, we illustrate each of them with hypothetical examples.

Data-driven methods for imputing national-level incidence in global burden of disease studies

OBJECTIVE

To develop transparent and reproducible methods for imputing missing data on disease incidence at national-level for the year 2005.

METHODS

We compared several models for imputing missing country-level incidence rates for two foodborne diseases - congenital toxoplasmosis and aflatoxin-related hepatocellular carcinoma. Missing values were assumed to be missing at random. Predictor variables were selected using least absolute shrinkage and selection operator regression. We compared the predictive performance of naive extrapolation approaches and Bayesian random and mixed-effects regression models. Leave-one-out cross-validation was used to evaluate model accuracy.

FINDINGS

The predictive accuracy of the Bayesian mixed-effects models was significantly better than that of the naive extrapolation method for one of the two disease models. However, Bayesian mixed-effects models produced wider prediction intervals for both data sets.

CONCLUSION

Several approaches are available for imputing missing data at national level. Strengths of a hierarchical regression approach for this type of task are the ability to derive estimates from other similar countries, transparency, computational efficiency and ease of interpretation. The inclusion of informative covariates may improve model performance, but results should be appraised carefully.

Epidemiology. Opposite effects of anthelmintic treatment on microbial infection at individual versus population scales

Parasitic worms modulate host immune responses in ways that affect microbial co-infections. For this reason, anthelmintic therapy may be a potent tool for indirectly controlling microbial pathogens. However, the population-level consequences of this type of intervention on co-infecting microbes are unknown. We evaluated the effects of anthelmintic treatment on bovine tuberculosis (BTB) acquisition, mortality after infection, and pathogen fitness in free-ranging African buffalo. We found that treatment had no effect on the probability of BTB infection, but buffalo survival after infection was ninefold higher among treated individuals. These contrasting effects translated into an approximately eightfold increase in the reproductive number of BTB for anthelmintic-treated compared with untreated buffalo. Our results indicate that anthelmintic treatment can enhance the spread of microbial pathogens in some real-world situations.

Quality control in the diagnosis of Trichuris trichiura and Ascaris lumbricoides using the Kato-Katz technique: experience from three randomised controlled trials

Background

An accurate diagnosis of soil-transmitted helminthiasis is important for individual patient management, for drug efficacy evaluation and for monitoring control programmes. The Kato-Katz technique is the most widely used method detecting soil-transmitted helminth eggs in faecal samples. However, detailed analyses of quality control, including false-positive and faecal egg count (FEC) estimates, have received little attention.

Methods

Over a 3-year period, within the frame of a series of randomised controlled trials conducted in Pemba, United Republic of Tanzania, 10% of randomly selected Kato-Katz thick smears were re-read for Trichuris trichiura and Ascaris lumbricoides eggs. In case of discordant result (i.e. positive versus negative) the slides were re-examined a third time. A result was assumed to be false-positive or false-negative if the result from the initial reading did not agree with the quality control as well as the third reading. We also evaluated the general agreement in FECs between the first and second reading, according to internal and World Health Organization (WHO) guidelines.

Results

From the 1,445 Kato-Katz thick smears subjected to quality control, 1,181 (81.7%) were positive for T. trichiura and 290 (20.1%) were positive for A. lumbricoides. During quality control, very low rates of false-positive results were observed; 0.35% (n = 5) for T. trichiura and 0.28% (n = 4) for A. lumbricoides. False-negative readings of Kato-Katz thick smears were obtained in 28 (1.94%) and 6 (0.42%) instances for T. trichiura and A. lumbricoides, respectively. A high frequency of discordant results in FECs was observed (i.e. 10.0-23.9% for T. trichiura, and 9.0-11.4% for A. lumbricoides).

Conclusions

Our analyses show that the rate of false-positive diagnoses of soil-transmitted helminths is low. As the probability of false-positive results increases after examination of multiple stool samples from a single individual, the potential influence of false-positive results on epidemiological studies and anthelminthic drug efficacy studies should be determined. Existing WHO guidelines for quality control might be overambitious and might have to be revised, specifically with regard to handling disagreements in FECs.

Factors associated with the performance and cost-effectiveness of using lymphatic filariasis transmission assessment surveys for monitoring soil-transmitted helminths: a case study in Kenya

Transmission assessment surveys (TAS) for lymphatic filariasis have been proposed as a platform to assess the impact of mass drug administration (MDA) on soil-transmitted helminths (STHs). This study used computer simulation and field data from pre- and post-MDA settings across Kenya to evaluate the performance and cost-effectiveness of the TAS design for STH assessment compared with alternative survey designs. Variations in the TAS design and different sample sizes and diagnostic methods were also evaluated. The district-level TAS design correctly classified more districts compared with standard STH designs in pre-MDA settings. Aggregating districts into larger evaluation units in a TAS design decreased performance, whereas age group sampled and sample size had minimal impact. The low diagnostic sensitivity of Kato-Katz and mini-FLOTAC methods was found to increase misclassification. We recommend using a district-level TAS among children 8-10 years of age to assess STH but suggest that key consideration is given to evaluation unit size.

Efficacy and safety of albendazole plus ivermectin, albendazole plus mebendazole, albendazole plus oxantel pamoate, and mebendazole alone against Trichuris trichiura and concomitant soil-transmitted helminth infections: a four-arm, randomised controlled trial

BACKGROUND

Existing anthelmintic drugs (eg, albendazole and mebendazole) have low efficacy against the intestinal nematode species Trichuris trichiura and the drug pipeline is exhausted. We aimed to investigate the strategy of combination chemotherapy with existing drugs to establish whether their efficacy could be enhanced and broadened.

METHODS

In this randomised controlled trial, we compared three drug combinations and one standard drug alone in children aged 6-14 years in two schools on Pemba Island, Tanzania infected with T trichiura and concomitant intestinal nematodes. We assigned children, via a randomisation list with block sizes of either four or eight, to orally receive albendazole (400 mg) plus ivermectin (200 μg/kg); albendazole (400 mg) plus mebendazole (500 mg); albendazole (400 mg) plus oxantel pamoate (20 mg/kg); or mebendazole (500 mg) alone. The primary endpoints were the proportion of children cured of T trichiura infection and the reduction of T trichiura eggs in stool based on geometric means, both analysed by available case. This study is registered with ISRCTN, number ISRCTN80245406.

FINDINGS

We randomly assigned 440 eligible children infected with T trichiura between Sept 2, and Oct 18, 2013, to one of the four treatment groups (110 children per group). Data for 431 children were included in the analysis for the primary endpoints. Albendazole plus oxantel pamoate (74 of 108 children cured [68·5%, 95% CI 59·6-77·4]; egg reduction 99·2%, 98·7-99·6) and albendazole plus ivermectin (30 of 109 cured [27·5%, 19·0-36·0]; egg reduction 94·5%, 91·7-96·3) were significantly more effective against T trichiura than mebendazole alone (nine of 107 cured [8·4%, 3·1-13·8]; egg reduction 58·5%, 45·2-70·9). Albendazole plus mebendazole had similar low efficacy (nine of 107 cured [8·4%, 3·1-13·8; egg reduction 51·6%, 35·0-65·3) to mebendazole alone. About a fifth of the children reported adverse events, which were mainly mild. Abdominal cramps and headache were the most common adverse events after treatment; abdominal cramps were reported by 13 (12·0%) children for albendazole plus ivermectin, 10 (9·3%) for albendazole plus mebendazole, 20 (18·2%) for albendazole plus oxantel pamoate, and 16 (14·5%) for mebendazole; headaches were reported by 5 (4·6%) children for albendazole plus ivermectin, 6 (5·6%) for albendazole plus mebendazole, 12 (10·9%) for albendazole plus oxantel pamoate, and 7 (6·4%) for mebendazole.

INTERPRETATION

Our head-to-head comparison of three combination chemotherapies showed the highest efficacy for albendazole plus oxantel pamoate for the treatment of infection with T trichiura. Further studies should investigate the combination of albendazole plus oxantel pamoate so that it can be considered for soil-transmitted helminthiasis control programmes.

FUNDING

Medicor Foundation and Swiss National Science Foundation.

New tools for NTD vaccines: A case study of quality control assays for product development of the human hookworm vaccine Na-APR-1M74

Na-APR-1(M74) is an aspartic protease that is rendered enzymatically inactive by site-directed mutagenesis and is a candidate antigen component in the Human Hookworm Vaccine. The mutant protease exerts vaccine efficacy by inducing antibodies that neutralize the enzymatic activity of wild type enzyme (Na-APR-1wt) in the gut of the hookworm, thereby depriving the worm of its ability to digest its blood meal. Previously, canines immunized with Na-APR-1(M74) and challenged with Ancylostoma caninum were partially protected against hookworm challenge infection, especially from the loss in hemoglobin observed in control canines and canine immunoglobulin (Ig) G raised against Na-APR-1 was shown to inhibit the enzymatic activity of Na-APR-1 wt in vitro, thereby providing proof of concept of Na-APR-1(M74) as a vaccine antigen. The mutated version, Na-APR-1(M74), was then expressed at the cGMP level using a Nicotiana benthamiana expression system (Fraunhofer, CMB, Delaware, MD), formulated with Alhydrogel®, and used to immunize mice in a dose-ranging study to explore the enzyme-neutralizing capacity of the resulting anti- Na-APR-1(M74) IgG. As little as 0.99 μg of recombinant Na-APR-1(M74) could induce anti Na-APR-1(M74) IgG in mice that were capable of inhibiting Na-APR-1w t-mediated digestion of a peptide substrate by 89%. In the absence of enzymatic activity of Na-APR-1(M74) as a surrogate marker of protein functionality, we developed an assay based on the binding of a quenched fluorescence-labeled inhibitor of aspartic proteases, BODIPY-FL pepstatin A (BDP). Binding of BDP in the active site of Na-APR-1 wt was demonstrated by inhibition of enzymatic activity, and competitive binding with unlabelled pepstatin A. BDP also bound to Na-APR-1(M74) which was assessed by fluorescence polarization, but with an ∼ 50-fold reduction in the dissociation constant. Taken together, these assays comprise a "toolbox" that could be useful for the analyses of Na-APR-1(M74) as it proceeds through the clinical development as part of the Human Hookworm Vaccine pipeline.

Progress in research, control and elimination of helminth infections in Asia

Global health has substantially improved over the past 20 years. In low- and middle-income countries, in particular, great strives have been made in the control of communicable diseases, including helminth infections. Nevertheless, the most marginalised communities still suffer from infectious diseases that are intimately connected with poverty and lack of access to essential commodities and services, such as clean water, improved sanitation and sufficient food. A two-pronged approach is thus necessary: (i) intensifying control in remaining high-endemicity areas and pockets of high transmission; and (ii) moving from morbidity control to interruption of disease transmission in low-endemicity areas with the goal of local elimination. The latter will require new tools and strategies, going hand-in-hand with strong partnerships and new strategic alliances. In this special issue of Acta Tropica, 35 articles are featured that, together, provide an up-to-date overview of the latest progress made in research, control and elimination of helminth infections in East and Southeast Asia. The first 12 articles expound tools and approaches for improved detection, surveillance and monitoring of helminth infections. Control and elimination approaches for the most important helminth infections are revisited in the next 20 articles. The three remaining articles are cross-cutting pieces examining the interface of agriculture, environment and helminth infections and providing a rationale for integrated, multi-sectorial control approaches that are necessary for sustaining helminthiasis control and progressively moving towards elimination. An interesting aspect revealed through an in-depth analysis of the provenance of the 35 contributions is that the People's Republic of China emerges as a key player in global health, which is documented through its prominent role in research and control of helminth infection and networking throughout Asia. Policy implications are discussed and will hopefully shape the future agenda for the control and elimination of helminth infections the world over.

Repeated stool sampling and use of multiple techniques enhance the sensitivity of helminth diagnosis: a cross-sectional survey in southern Lao People's Democratic Republic

Intestinal parasitic infections are common in Lao People's Democratic Republic (Lao PDR). We investigated the accuracy of the Kato-Katz (KK) technique in relation to varying stool sampling efforts, and determined the effect of the concurrent use of a quantitative formalin-ethyl acetate concentration technique (FECT) for helminth diagnosis and appraisal of concomitant infections. The study was carried out between March and May 2006 in Champasack province, southern Lao PDR. Overall, 485 individuals aged ≥6 months who provided three stool samples were included in the final analysis. All stool samples were subjected to the KK technique. Additionally, one stool sample per individual was processed by FECT. Diagnosis was done under a light microscope by experienced laboratory technicians. Analysis of three stool samples with KK plus a single FECT was considered as diagnostic 'gold' standard and resulted in prevalence estimates of hookworm, Opisthorchis viverrini, Ascaris lumbricoides, Trichuris trichiura and Schistosoma mekongi infection of 77.9%, 65.0%, 33.4%, 26.2% and 24.3%, respectively. As expected, a single KK and a single FECT missed a considerable number of infections. While our diagnostic 'gold' standard produced similar results than those obtained by a mathematical model for most helminth infections, the 'true' prevalence predicted by the model for S. mekongi (28.1%) was somewhat higher than after multiple KK plus a single FECT (24.3%). In the current setting, triplicate KK plus a single FECT diagnosed helminth infections with high sensitivity. Hence, such a diagnostic approach might be utilised for generating high-quality baseline data, assessing anthelminthic drug efficacy and rigorous monitoring of community interventions.

Geostatistical modelling of soil-transmitted helminth infection in Cambodia: do socioeconomic factors improve predictions?

Soil-transmitted helminth infections are intimately connected with poverty. Yet, there is a paucity of using socioeconomic proxies in spatially explicit risk profiling. We compiled household-level socioeconomic data pertaining to sanitation, drinking-water, education and nutrition from readily available Demographic and Health Surveys, Multiple Indicator Cluster Surveys and World Health Surveys for Cambodia and aggregated the data at village level. We conducted a systematic review to identify parasitological surveys and made every effort possible to extract, georeference and upload the data in the open source Global Neglected Tropical Diseases database. Bayesian geostatistical models were employed to spatially align the village-aggregated socioeconomic predictors with the soil-transmitted helminth infection data. The risk of soil-transmitted helminth infection was predicted at a grid of 1×1km covering Cambodia. Additionally, two separate individual-level spatial analyses were carried out, for Takeo and Preah Vihear provinces, to assess and quantify the association between soil-transmitted helminth infection and socioeconomic indicators at an individual level. Overall, we obtained socioeconomic proxies from 1624 locations across the country. Surveys focussing on soil-transmitted helminth infections were extracted from 16 sources reporting data from 238 unique locations. We found that the risk of soil-transmitted helminth infection from 2000 onwards was considerably lower than in surveys conducted earlier. Population-adjusted prevalences for school-aged children from 2000 onwards were 28.7% for hookworm, 1.5% for Ascaris lumbricoides and 0.9% for Trichuris trichiura. Surprisingly, at the country-wide analyses, we did not find any significant association between soil-transmitted helminth infection and village-aggregated socioeconomic proxies. Based also on the individual-level analyses we conclude that socioeconomic proxies might not be good predictors at an aggregated large-scale analysis due to their large between- and within-village heterogeneity. Specific information of both the infection risk and potential predictors might be needed to obtain any existing association. The presented soil-transmitted helminth infection risk estimates for Cambodia can be used for guiding and evaluating control and elimination efforts.

Morphological diversity of Trichuris spp. eggs observed during an anthelminthic drug trial in Yunnan, China, and relative performance of parasitologic diagnostic tools

The presence of large Trichuris spp. eggs in human faecal samples is occasionally reported. Such eggs have been described as variant Trichuris trichiura or Trichuris vulpis eggs. Within the frame of a randomised controlled trial, faecal samples collected from 115 Bulang individuals from Yunnan, People's Republic of China were subjected to the Kato-Katz technique (fresh stool samples) and the FLOTAC and ether-concentration techniques (sodium acetate-acetic acid-formalin (SAF)-fixed stool samples). Large Trichuris spp. eggs were noted in faecal samples with a prevalence of 6.1% before and 21.7% after anthelminthic drug administration. The observed prevalence of standard-sized T. trichiura eggs was reduced from 93.0% to 87.0% after treatment. Considerably more cases of large Trichuris spp. eggs and slightly more cases with normal-sized T. trichiura eggs were identified by FLOTAC compared to the ether-concentration technique. No large Trichuris spp. eggs were observed on the Kato-Katz thick smears.

Multiparasitism and intensity of helminth infections in relation to symptoms and nutritional status among children: a cross-sectional study in southern Lao People's Democratic Republic

The occurrence and spatial distribution of intestinal helminth infection in children is fairly well understood. However, knowledge on how helminth infections govern intestinal morbidity is scarce. We conducted a cross-sectional study to assess and quantify the relationship between single and multiple species helminth infection with clinical and self-reported morbidity indicators and nutritional status in Champasack province, southern Lao People's Democratic Republic (Lao PDR). A random sample of 1313 children, aged 6 months to 12 years, from villages in nine rural districts were enrolled and examined for helminth infection using duplicate Kato-Katz thick smears. Morbidity was assessed by self-reported symptoms, coupled with clinical examination and appraisal of nutritional status and anaemia. Bivariate and multivariate logistic regression was employed to study associations between helminth infection and morbidity indicators and anaemia. We found considerable morbidity among the surveyed children, including hepatomegaly (13.7%), pale conjunctiva (13.2%) and abdominal pain (10.4%). Anaemia was recorded in 60.4% of the children, whilst signs of stunting and low body mass index (BMI) were observed in 49.8% and 33.3% of the surveyed children, respectively. Hookworm and Opisthorchis viverrini were the predominant helminth species with prevalences of 51.0% and 43.3%, respectively. The prevalence of Schistosoma mekongi in the surveyed children was 5.6%. Multiple species helminth infections were recorded in 40.4% of the study cohort. Morbidity was associated with specific helminth species infection (e.g. S. mekongi with hepatomegaly; adjusted odds ratio (aOR): 9.49, 95% confidence interval (CI): 2.07-43.51) and multiparasitism (e.g. two or more helminth species with abdominal pain; aOR: 2.40, 95% CI: 1.46-3.93). Anaemia was associated with hookworm infection (aOR: 1.64, 95% CI: 1.16-2.34) and multiparasitism (aOR: 1.64, 95% CI: 1.18-2.29). Low BMI was associated with O. viverrini infection (aOR: 1.68, 95% CI: 1.14-2.49) and multiparasitism (aOR: 1.42, 95% CI: 1.01-2.00). The multiple strong associations reported here between helminth infections (single or multiple species) and intestinal morbidity among children in rural parts of southern Lao PDR call for concerted efforts to control helminth infections, which in turn might improve children's health and development.

Expression, purification, and characterization of the Necator americanus aspartic protease-1 (Na-APR-1 (M74)) antigen, a component of the bivalent human hookworm vaccine

Over 400 million people living in the world's poorest developing nations are infected with hookworms, mostly of the genus Necator americanus. A bivalent human hookworm vaccine composed of the Necator americanus Glutathione S-Transferase-1 (Na-GST-1) and the Necator americanus Aspartic Protease-1 (Na-APR-1 (M74)) is currently under development by the Sabin Vaccine Institute Product Development Partnership (Sabin PDP). Both monovalent vaccines are currently in Phase 1 trials. Both Na-GST-1 and Na-APR-1 antigens are expressed as recombinant proteins. While Na-GST-1 was found to express with high yields in Pichia pastoris, the level of expression of Na-APR-1 in this host was too low to be suitable for a manufacturing process. When the tobacco plant Nicotiana benthamiana was evaluated as an expression system, acceptable levels of solubility, yield, and stability were attained. Observed expression levels of Na-APR-1 (M74) using this system are ∼300 mg/kg. Here we describe the achievements and obstacles encountered during process development as well as characterization and stability of the purified Na-APR-1 (M74) protein and formulated vaccine. The expression, purification and analysis of purified Na-APR-1 (M74) protein obtained from representative 5 kg reproducibility runs performed to qualify the Na-APR-1 (M74) production process is also presented. This process has been successfully transferred to a pilot plant and a 50 kg scale manufacturing campaign under current Good Manufacturing Practice (cGMP) has been performed. The 50 kg run has provided a sufficient amount of protein to support the ongoing hookworm vaccine development program of the Sabin PDP.

Simple fecal flotation is a superior alternative to guadruple Kato Katz smear examination for the detection of hookworm eggs in human stool

BACKGROUND

Microscopy-based identification of eggs in stool offers simple, reliable and economical options for assessing the prevalence and intensity of hookworm infections, and for monitoring the success of helminth control programs. This study was conducted to evaluate and compare the diagnostic parameters of the Kato-Katz (KK) and simple sodium nitrate flotation technique (SNF) in terms of detection and quantification of hookworm eggs, with PCR as an additional reference test in stool, collected as part of a baseline cross-sectional study in Cambodia.

METHODS/PRINCIPLE FINDINGS

Fecal samples collected from 205 people in Dong village, Rovieng district, Preah Vihear province, Cambodia were subjected to KK, SNF and PCR for the detection (and in case of microscopy-based methods, quantification) of hookworm eggs in stool. The prevalence of hookworm detected using a combination of three techniques (gold standard) was 61.0%. PCR displayed a highest sensitivity for hookworm detection (92.0%) followed by SNF (44.0%) and quadruple KK smears (36.0%) compared to the gold standard. The overall eggs per gram feces from SNF tended to be higher than for quadruple KK and the SNF proved superior for detecting low egg burdens.

CONCLUSION/SIGNIFICANCE

As a reference, PCR demonstrated the higher sensitivity compared to SNF and the quadruple KK method for detection of hookworm in human stool. For microscopic-based quantification, a single SNF proved superior to the quadruple KK for the detection of hookworm eggs in stool, in particular for low egg burdens. In addition, the SNF is cost-effective and easily accessible in resource poor countries.

Risk factors associated with malnutrition in one-year-old children living in the Peruvian Amazon

Background

Children under two years of age are in the most critical window for growth and development. As mobility increases, this time period also coincides with first exposure to soil-transmitted helminth (STH) infections in tropical and sub-tropical environments. The association between malnutrition and STH infection, however, has been understudied in this vulnerable age group.

Methodology/Principal Findings

A nested cross-sectional survey was conducted in 12 and 13-month old children participating in a deworming trial in Iquitos, an STH-endemic area of the Peruvian Amazon. An extensive socio-demo-epi questionnaire was administered to the child's parent. Length and weight were measured, and the Bayley Scales of Infant and Toddler Development were administered to measure cognition, language, and fine motor development. Stool specimens were collected to determine the presence of STH. The association between malnutrition (i.e. stunting and underweight) and STH infection, and other child, maternal, and household characteristics, was analyzed using multivariable Poisson regression. A total of 1760 children were recruited between September 2011 and June 2012. Baseline data showed a prevalence of stunting and underweight of 24.2% and 8.6%, respectively. In a subgroup of 880 randomly-allocated children whose specimens were analyzed by the Kato-Katz method, the prevalence of any STH infection was 14.5%. Risk factors for stunting in these 880 children included infection with at least one STH species (aRR = 1.37; 95% CI 1.01, 1.86) and a lower development score (aRR = 0.97; 95% CI: 0.95, 0.99). A lower development score was also a significant risk factor for underweight (aRR = 0.92; 95% CI: 0.89, 0.95).

Conclusions

The high prevalence of malnutrition, particularly stunting, and its association with STH infection and lower developmental attainment in early preschool-age children is of concern. Emphasis should be placed on determining the most cost-effective, integrated interventions to reduce disease and malnutrition burdens in this vulnerable age group.

Malnutrition, including stunting and underweight, is one of the leading causes of morbidity and mortality in preschool-age children. Children under two years of age are at a particularly critical period for growth and development, and for first exposure to worm infections in tropical and subtropical environments. The association between malnutrition and worm infection, however, is not well understood in this age group. A nested cross-sectional survey was therefore conducted between September 2011 and June 2012 in 1760 children 12 and 13 months of age living in a worm-endemic area of the Peruvian Amazon. Length, weight, development (i.e. cognitive, language and motor development), worm infection, and socio-demographic information were obtained. Results showed a high prevalence of stunting, and a significant association with worm infection and lower development. Overall, these adverse effects have the potential to negatively impact short-term and long-term health and nutrition, and educational and social achievement, into school-age and adulthood. Emphasis is needed on determining the most appropriate and effective interventions to reduce poor health and nutrition outcomes in this age group.

Enterobiasis and strongyloidiasis and associated co-infections and morbidity markers in infants, preschool- and school-aged children from rural coastal Tanzania: a cross-sectional study

Background

There is a paucity of data pertaining to the epidemiology and public health impact of Enterobius vermicularis and Strongyloides stercoralis infections. We aimed to determine the extent of enterobiasis, strongyloidiasis, and other helminth infections and their association with asymptomatic Plasmodium parasitaemia, anaemia, nutritional status, and blood cell counts in infants, preschool-aged (PSAC), and school-aged children (SAC) from rural coastal Tanzania.

Methods

A total of 1,033 children were included in a cross-sectional study implemented in the Bagamoyo district in 2011/2012. Faecal samples were examined for intestinal helminth infections using a broad set of quality controlled methods. Finger-prick blood samples were subjected to filariasis and Plasmodium parasitaemia testing and full blood cell count examination. Weight, length/height, and/or mid-upper arm circumference were measured and the nutritional status determined in accordance with age.

Results

E. vermicularis infections were found in 4.2% of infants, 16.7%, of PSAC, and 26.3% of SAC. S. stercoralis infections were detected in 5.8%, 7.5%, and 7.1% of infants, PSAC, and SAC, respectively. Multivariable regression analyses revealed higher odds of enterobiasis in children of all age-groups with a reported anthelminthic treatment history over the past six months (odds ratio (OR): 2.15; 95% confidence interval (CI): 1.22 - 3.79) and in SAC with a higher temperature (OR: 2.21; CI: 1.13 - 4.33). Strongyloidiasis was associated with eosinophilia (OR: 2.04; CI: 1.20-3.48) and with Trichuris trichiura infections (OR: 4.13; CI: 1.04-16.52) in children of all age-groups, and with asymptomatic Plasmodium parasitaemia (OR: 13.03; CI: 1.34 - 127.23) in infants. None of the investigated helminthiases impacted significantly on the nutritional status and anaemia, but moderate asymptomatic Plasmodium parasitaemia was a strong predictor for anaemia in children aged older than two years (OR: 2.69; 95% CI: 1.23 – 5.86).

Conclusions

E. vermicularis and S. stercoralis infections were moderately prevalent in children from rural coastal Tanzania. Our data can contribute to inform yet missing global burden of disease and prevalence estimates for strongyloidiasis and enterobiasis. The association between S stercoralis and asymptomatic Plasmodium parasitaemia found here warrants further comprehensive investigations.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-014-0644-7) contains supplementary material, which is available to authorized users.

Health-related quality of life among school children with parasitic infections: findings from a national cross-sectional survey in Côte d'Ivoire

Background

Parasitic infections are still of considerable public health relevance, notably among children in low- and middle-income countries. Measures to assess the magnitude of ill-health in infected individuals, however, are debated and patient-based proxies through generic health-related quality of life (HrQoL) instruments are among the proposed strategies. Disability estimates based on HrQoL are still scarce and conflicting, and hence, there is a need to strengthen the current evidence-base.

Methodology

Between November 2011 and February 2012, a national school-based cross-sectional survey was conducted in Côte d'Ivoire. Children underwent parasitological and clinical examination to assess infection status with Plasmodium and helminth species and clinical parameters, and responded to a questionnaire interview incorporating sociodemographic characteristics, self-reported morbidity, and HrQoL. Validity analysis of the HrQoL instrument was performed, assessing floor and ceiling effects, internal consistency, and correlation with morbidity scores. Multivariate regression models were applied to identify significant associations between HrQoL and children's parasitic infection and clinical status.

Principal Findings

Parasitological examination of 4,848 children aged 5–16 years revealed Plasmodium spp., hookworm, Schistosoma haematobium, Schistosoma mansoni, Ascaris lumbricoides, and Trichuris trichiura prevalences of 75.0%, 17.2%, 5.7%, 3.7%, 1.8%, and 1.3%, respectively. Anemic children showed a significant 1-point reduction in self-rated HrQoL on a scale from 0 to 100, whereas no significant negative association between HrQoL and parasite infection was observed. The 12-item HrQoL questionnaire proofed useful, as floor and ceiling effects were negligible, internally consistent (Cronbach's alpha = 0.71), and valid, as revealed by significant negative correlations and associations with children's self-reported and clinically assessed morbidity.

Conclusions/Significance

Our results suggest that HrQoL tools are not sufficiently sensitive to assess subtle morbidities due to parasitic infection in Ivorian school-aged children. However, more advanced morbid sequelae (e.g., anemia), were measurable by the instrument's health construct. Further investigations on health impacts of parasitic infection among school-aged children and refinement of generic HrQoL questionnaires are warranted.

Infectious diseases like malaria and parasitic worms affect hundreds of millions of people, and impact physical and cognitive development of children in Africa, Asia, and the Americas. Over the past 20 years, it was debated how the magnitude of ill-health due to these conditions should be assessed. One proposed strategy was to include patient-based ratings of wellbeing by administration of health-related quality of life (HrQoL) questionnaires. In order to provide new evidence on disability from parasitic infections, we conducted HrQoL interviews with children aged 5–16 years from 92 schools across Côte d'Ivoire. Children were examined for parasitic infections and clinical signs like anemia, malnutrition, and organ enlargement. We compared the self-rated HrQoL of infected and non-infected children and also considered their sociodemographic background. We could not identify lowered HrQoL in infected children, but we found that children with anemia reported a 1-point lower score on a 100-point HrQoL scale in comparison with their non-anemic counterparts. We consider our HrQoL questionnaire as useful and valid, but would recommend its further testing and development in few purposefully selected settings. Further investigation of disability induced by malaria and parasitic worm infections is warranted.

Modeling the interruption of the transmission of soil-transmitted helminths by repeated mass chemotherapy of school-age children

Background

The control or elimination of neglected tropical diseases has recently become the focus of increased interest and funding from international agencies through the donation of drugs. Resources are becoming available for the treatment of soil-transmitted helminth (STH) infection through school-based deworming strategies. However, little research has been conducted to assess the impact of STH treatment that could be used to guide the design of efficient elimination programs.

Methodology

We construct and analyse an age-structured model of STH population dynamics under regular treatment. We investigate the potential for elimination with finite rounds of treatment, and how this depends on the value of the basic reproductive number R₀ and treatment frequency.

Principal findings

Analysis of the model indicates that its behaviour is determined by key parameter groupings describing the basic reproduction number and the fraction of it attributable to the treated group, the timescale of material in the environment and the frequency and efficacy of treatment. Mechanisms of sexual reproduction and persistence of infectious material in the environment are found to be much more important in the context of elimination than in the undisturbed baseline scenario. For a given rate of drug use, sexual reproduction dictates that less frequent, higher coverage treatment is more effective. For a given treatment coverage level, the lifespan of infectious material in the environment places a limit on the effectiveness of increased treatment frequency.

Conclusions

Our work suggests that for models to capture the dynamics of parasite burdens in populations under regular treatment as elimination is approached, they need to include the effects of sexual reproduction among parasites and the dynamics infectious material in the reservoir. The interaction of these two mechanisms has a strong effect on optimum treatment strategies, both in terms of how frequently to treat and for how long.

The control or elimination of soil-transmitted helminth diseases through chemotherapy has recently become the focus of increased interest and funding from international agencies, charities, and pharmaceutical companies via drug donations for treatment in the poorer regions of the world. The design of treatment regimes and the interpretation of their impact benefit from analysis using robust and reliable mathematical models. By analyzing models of the effect of treatment on host parasite burden, we identify several aspects of parasite natural history and transmission which are often overlooked, but have a marked effect on the impact of treatment strategies. In particular, the inclusion of sexual reproduction and the dynamics of eggs or larval stages in the model changes the response of the parasite population to treatment when parasite burdens are low. This in turn has implications for the design of treatment strategies to eliminate parasites in terms of minimizing total drug use and the length of the program delivering them.

Spatial and temporal distribution of soil-transmitted helminth infection in sub-Saharan Africa: a systematic review and geostatistical meta-analysis

BACKGROUND

Interest is growing in predictive risk mapping for neglected tropical diseases (NTDs), particularly to scale up preventive chemotherapy, surveillance, and elimination efforts. Soil-transmitted helminths (hookworm, Ascaris lumbricoides, and Trichuris trichiura) are the most widespread NTDs, but broad geographical analyses are scarce. We aimed to predict the spatial and temporal distribution of soil-transmitted helminth infections, including the number of infected people and treatment needs, across sub-Saharan Africa.

METHODS

We systematically searched PubMed, Web of Knowledge, and African Journal Online from inception to Dec 31, 2013, without language restrictions, to identify georeferenced surveys. We extracted data from household surveys on sources of drinking water, sanitation, and women's level of education. Bayesian geostatistical models were used to align the data in space and estimate risk of with hookworm, A lumbricoides, and T trichiura over a grid of roughly 1 million pixels at a spatial resolution of 5 × 5 km. We calculated anthelmintic treatment needs on the basis of WHO guidelines (treatment of all school-aged children once per year where prevalence in this population is 20-50% or twice per year if prevalence is greater than 50%).

FINDINGS

We identified 459 relevant survey reports that referenced 6040 unique locations. We estimate that the prevalence of hookworm, A lumbricoides, and T trichiura among school-aged children from 2000 onwards was 16·5%, 6·6%, and 4·4%. These estimates are between 52% and 74% lower than those in surveys done before 2000, and have become similar to values for the entire communities. We estimated that 126 million doses of anthelmintic treatments are required per year.

INTERPRETATION

Patterns of soil-transmitted helminth infection in sub-Saharan Africa have changed and the prevalence of infection has declined substantially in this millennium, probably due to socioeconomic development and large-scale deworming programmes. The global control strategy should be reassessed, with emphasis given also to adults to progress towards local elimination.

FUNDING

Swiss National Science Foundation and European Research Council.

Prevalence and intensity of soil-transmitted helminth infections among pre-school age children in 12 kindergartens in Jimma Town, southwest Ethiopia

BACKGROUND

Pre-school age children (preSAC) remain difficult to reach in mass drug administration (MDA) programmes to control soil-transmitted helminth (STH) infections. Kindergartens provide a unique platform to increase the coverage of MDA in preSAC in Ethiopia, but surveys assessing STHs among preSAC in kindergartens are scarce.

METHODS

We report the prevalence and intensity of STH infections among 622 preSAC in 12 kindergartens in Jimma, Ethiopia.

RESULTS

STHs were found in all kindergartens, with prevalence exceeding 50% in 8 kindergartens. The majority of the infections were of low intensity.

CONCLUSIONS

This study highlights the importance of kindergartens as an additional opportunity for MDA in Ethiopia.

Discovery of new risk loci for IgA nephropathy implicates genes involved in immunity against intestinal pathogens

We performed a genome-wide association study (GWAS) of IgA nephropathy (IgAN), the most common form of glomerulonephritis, with discovery and follow-up in 20,612 individuals of European and East Asian ancestry. We identified six novel genome-wide significant associations, four in ITGAM-ITGAX, VAV3 and CARD9 and two new independent signals at HLA-DQB1 and DEFA. We replicated the nine previously reported signals, including known SNPs in the HLA-DQB1 and DEFA loci. The cumulative burden of risk alleles is strongly associated with age at disease onset. Most loci are either directly associated with risk of inflammatory bowel disease (IBD) or maintenance of the intestinal epithelial barrier and response to mucosal pathogens. The geo-spatial distribution of risk alleles is highly suggestive of multi-locus adaptation and the genetic risk correlates strongly with variation in local pathogens, particularly helminth diversity, suggesting a possible role for host-intestinal pathogen interactions in shaping the genetic landscape of IgAN.

Assessment of anthelmintic efficacy of mebendazole in school children in six countries where soil-transmitted helminths are endemic

Background

Robust reference values for fecal egg count reduction (FECR) rates of the most widely used anthelmintic drugs in preventive chemotherapy (PC) programs for controlling soil-transmitted helminths (STHs; Ascaris lumbricoides, Trichuris trichiura, and hookworm) are still lacking. However, they are urgently needed to ensure detection of reduced efficacies that are predicted to occur due to growing drug pressure. Here, using a standardized methodology, we assessed the FECR rate of a single oral dose of mebendazole (MEB; 500 mg) against STHs in six trials in school children in different locations around the world. Our results are compared with those previously obtained for similarly conducted trials of a single oral dose of albendazole (ALB; 400 mg).

Methodology

The efficacy of MEB, as assessed by FECR, was determined in six trials involving 5,830 school children in Brazil, Cambodia, Cameroon, Ethiopia, United Republic of Tanzania, and Vietnam. The efficacy of MEB was compared to that of ALB as previously assessed in 8,841 school children in India and all the above-mentioned study sites, using identical methodologies.

Principal Findings

The estimated FECR rate [95% confidence interval] of MEB was highest for A. lumbricoides (97.6% [95.8; 99.5]), followed by hookworm (79.6% [71.0; 88.3]). For T. trichiura, the estimated FECR rate was 63.1% [51.6; 74.6]. Compared to MEB, ALB was significantly more efficacious against hookworm (96.2% [91.1; 100], p<0.001) and only marginally, although significantly, better against A. lumbricoides infections (99.9% [99.0; 100], p = 0.012), but equally efficacious for T. trichiura infections (64.5% [44.4; 84.7], p = 0.906).

Conclusions/Significance

A minimum FECR rate of 95% for A. lumbricoides, 70% for hookworm, and 50% for T. trichiura is expected in MEB-dependent PC programs. Lower FECR results may indicate the development of potential drug resistance.

Soil-transmitted helminths (STHs; roundworms, whipworms, and hookworms) infect millions of children in sub-tropical and tropical countries, resulting in malnutrition, growth stunting, intellectual retardation, and cognitive deficits. To fight against STH, large-scale deworming programs are implemented in which anthelmintic drugs (either albendazole (ALB) or mebendazole (MEB)) are administered. Currently, these large-scale programs are intensifying, highlighting the need to closely monitor the efficacy of anthelmintic drugs to detect changes in drug efficacy that may arise through the evolution of anthelmintic drug resistance in the parasites. We have previously defined the minimum expected efficacy of ALB based on the fecal egg count reduction (FECR) rate, but these reference values are lacking for MEB. Therefore, we therefore evaluated the FECR rate of MEB against STHs in six STH endemic countries. In addition, we compared the results of the FECR rate for MEB with those we obtained previously for ALB. The results confirm that MEB treatment was highly efficacious against roundworms, and to a lesser extend against hookworms, but not against whipworms. Compared to ALB, MEB is less efficacious against hookworm, but equally efficacious against roundworms and whipworms. Based on this study we propose the minimum expected FECR rate for MEB-dependent large-scale deworming programs.

Prevalence of intestinal parasitic infections among children under five years of age with emphasis on Schistosoma mansoni in Wonji Shoa Sugar Estate, Ethiopia

Intestinal parasite infections are major public health problems of children in developing countries causing undernutrition, anemia, intestinal obstruction and mental and physical growth retardation. This study was conducted to assess the prevalence of intestinal helminthic infections among children under five years of age with emphasis on Schistosoma mansoni in Wonji Shoa Sugar Estate, Ethiopia. A cross-sectional parasitological survey was conducted in under-five children living in Wonji Shoa Sugar Estate Ethiopia, April, 2013. Stool samples were collected and examined for intestinal parasites using single Kato-Katz and single Sodium acetate-acetic acid-formalin (SAF) solution concentration methods. Out of 374 children examined using single Kato-Katz and single SAF-concentration methods, 24.3% were infected with at least one intestinal parasite species. About 10.4%, 8.8%, 4.6%, 2.9%, 1.6% and 0.8% of the children were infected with Hymenolepis nana, Schistosoma mansoni, Ascaris lumbricoides, Trichuris trichiura, Enterobius vermicularis and hookworm, respectively. Prevalence of double, triple and quadruple intestinal helminthic infection was 6.4%, 0.54% and 1.1%, respectively. A significant increase in prevalence of S. mansoni (8.3% versus 3.2%) and T. trichiura (2.7% versus 0.5%) infection was observed when determined via the single Kato-Katz method compared to the prevalence of the parasites determined via the single SAF-concentration method. On the other hand, the single SAF-concentration method (9.1%) revealed a significantly higher prevalence of H. nana infection than the single Kato-Katz (1.6%) does. In conclusion, intestinal helminths infections particularly S. mansoni and H. nana were prevalent in under-five children of Wonji Shoa Sugar Estate. Including praziquantel treatment in the deworming program as per the World Health Organization guidelines would be vital to reduce the burden of these diseases in areas where S. mansoni and H. nana infections are prevalent among under-fives. Kato-Katz can be used in estimating the prevalence of S. mansoni and other helminth infections.

An antagonist of the retinoid X receptor reduces the viability of Trichuris muris in vitro

Background

Trichuriasis is a parasitic disease caused by the human whipworm, Trichuris trichiura. It affects millions worldwide, particularly in the tropics. This nematode parasite burrows into the colonic epithelium resulting in inflammation and morbidity, especially in children. Current treatment relies mainly on general anthelmintics such as mebendazole but resistance to these drugs is increasingly problematic. Therefore, new treatments are urgently required.

Methods

The prospect of using the retinoid X receptor (RXR) antagonist HX531 as a novel anthelmintic was investigated by carrying out multiple viability assays with the mouse whipworm Trichuris muris.

Results

HX531 reduced both the motility and viability of T. muris at its L3, L4 and adult stages. Further, bioinformatic analyses show that the T. muris genome possesses an RXR-like receptor, a possible target for HX531.

Conclusions

The study suggested that Trichuris-specific RXR antagonists may be a source of much-needed novel anthelmintic candidates for the treatment of trichuriasis. The identification of an RXR-like sequence in the T. muris genome also paves the way for further research based on this new anthelmintic lead compound.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2334-14-520) contains supplementary material, which is available to authorized users.

Quantitative evaluation of a handheld light microscope for field diagnosis of soil-transmitted helminth infection

We evaluated the Newton Nm1, a commercially available handheld light microscope and compared it with conventional light microscopy for the diagnosis of soil-transmitted helminth infections. A total of 91 Kato-Katz thick smears were examined by experienced microscopists and helminth eggs were counted and expressed as eggs per gram of stool (EPG). Mean egg counts were significantly higher with the conventional light microscope (5,190 EPG versus 2,386 EPG for Ascaris lumbricoides; 826 versus 456 for Trichuris trichiura; both P < 0.05). Using regression coefficients and accounting for intensity of infection, we found that the agreement between the two devices was excellent for both species (κ = 0.90, 95% confidence interval = 0.82-0.99 for A. lumbricoides and κ = 0.96, 95% CI = 0.91-1.00 for T. trichiura). The Newton Nm1 microscope may be a useful tool for the detection and quantification of soil-transmitted helminth infection in clinical, epidemiologic, and public health settings.

WIPO Re:Search: Accelerating anthelmintic development through cross-sector partnerships

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WIPO Re:Search leverages pharmaceutical assets to advance anthelmintic research.

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BIO Ventures for Global Health (BVGH) facilitates collaborations and capacity building.

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Novartis scientists trained a Cameroonian researcher on advanced biochemistry skills.

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Researchers from Canada and Cameroon partnered to discover onchocerciasis drugs.

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Natural products were screened against schistosomes and soil-transmitted helminths.

Neglected tropical diseases (NTDs), malaria, and tuberculosis have a devastating effect on an estimated 1.6 billion people worldwide. The World Intellectual Property Organization (WIPO) Re:Search consortium accelerates the development of new drugs, vaccines, and diagnostics for these diseases by connecting the assets and resources of pharmaceutical companies, such as compound libraries and expertise, to academic or nonprofit researchers with novel product discovery or development ideas. As the WIPO Re:Search Partnership Hub Administrator, BIO Ventures for Global Health (BVGH) fields requests from researchers, identifies Member organizations able to fulfill these requests, and helps forge mutually beneficial collaborations. Since its inception in October 2011, WIPO Re:Search membership has expanded to more than 90 institutions, including leading pharmaceutical companies, universities, nonprofit research institutions, and product development partnerships from around the world. To date, WIPO Re:Search has facilitated over 70 research agreements between Consortium Members, including 11 collaborations focused on anthelmintic drug discovery.

Spatio-temporal distribution of soil-transmitted helminth infections in Brazil

Background

In Brazil, preventive chemotherapy targeting soil-transmitted helminthiasis is being scaled-up. Hence, spatially explicit estimates of infection risks providing information about the current situation are needed to guide interventions. Available high-resolution national model-based estimates either rely on analyses of data restricted to a given period of time, or on historical data collected over a longer period. While efforts have been made to take into account the spatial structure of the data in the modelling approach, little emphasis has been placed on the temporal dimension.

Methods

We extracted georeferenced survey data on the prevalence of infection with soil-transmitted helminths (i.e. Ascaris lumbricoides, hookworm and Trichuris trichiura) in Brazil from the Global Neglected Tropical Diseases (GNTD) database. Selection of the most important predictors of infection risk was carried out using a Bayesian geostatistical approach and temporal models that address non-linearity and correlation of the explanatory variables. The spatial process was estimated through a predictive process approximation. Spatio-temporal models were built on the selected predictors with integrated nested Laplace approximation using stochastic partial differential equations.

Results

Our models revealed that, over the past 20 years, the risk of soil-transmitted helminth infection has decreased in Brazil, mainly because of the reduction of A. lumbricoides and hookworm infections. From 2010 onwards, we estimate that the infection prevalences with A. lumbricoides, hookworm and T. trichiura are 3.6%, 1.7% and 1.4%, respectively. We also provide a map highlighting municipalities in need of preventive chemotherapy, based on a predicted soil-transmitted helminth infection risk in excess of 20%. The need for treatments in the school-aged population at the municipality level was estimated at 1.8 million doses of anthelminthic tablets per year.

Conclusions

The analysis of the spatio-temporal aspect of the risk of infection with soil-transmitted helminths contributes to a better understanding of the evolution of risk over time. Risk estimates provide the soil-transmitted helminthiasis control programme in Brazil with useful benchmark information for prioritising and improving spatial and temporal targeting of interventions.

Electronic supplementary material

The online version of this article (doi:10.1186/1756-3305-7-440) contains supplementary material, which is available to authorized users.

Does vitamin A supplementation protect schoolchildren from acquiring soil-transmitted helminthiasis? A randomized controlled trial

Background

Despite the intensive global efforts to control intestinal parasitic infections, the prevalence of soil-transmitted helminth (STH) infections is still very high in many developing countries particularly among children in rural areas.

Methods

A randomized, double-blind, placebo-controlled trial was conducted on 250 Aboriginal schoolchildren in Malaysia to investigate the effects of a single high-dose of vitamin A supplementation (200 000 IU) on STH reinfection. The effect of the supplement was assessed at 3 and 6 months after receiving interventions; after a complete 3-day deworming course of 400 mg/daily of albendazole tablets.

Results

Almost all children (98.6%) were infected with at least one STH species. The overall prevalence of ascariasis, trichuriasis and hookworm infection was 67.8%, 95.5% and 13.4%, respectively. Reinfection rates of Ascaris, Trichuris and hookworm were high; at 6 months, assessment reached 80% of the prevalence reported before treatment. There were no significant differences in the reinfection rates and intensities of STH between vitamin A supplemented-children and those who received placebo at 3 and 6 months (p > 0.05).

Conclusions

Vitamin A supplementation showed no protective effect against STH reinfection and this could be due to the high endemicity of STH in this community. Long-term interventions to reduce poverty will help significantly in reducing this continuing problem and there is no doubt that reducing intestinal parasitic infection would have a positive impact on the health, nutrition and education of these children.

Trial registration

This trial was registered at clinicaltrials.gov as NCT00936091.

Status of intestinal parasitic infections among residents of Jimma Town, Ethiopia

Background

Intestinal parasites cause considerable morbidity and mortality in the world, especially in developing countries like Ethiopia. Both urban and rural inhabitants are vulnerable to infection with intestinal parasites in developing countries. The aim of this study was to determine the status of intestinal parasitic infections (IPIs) among residents of Jimma Town, seven years after high prevalence was reported.

Results

Four hundred and thirty four residents of Jimma Town were included in this study. By the cross-sectional survey, the overall prevalence of intestinal parasites was 209 (48.2%). Nine species of intestinal parasites were isolated, Ascaris lumbricoides and Trichuris trichiura being the most predominant. Residence in Hermata Mentina kebele, Adjusted Odds Ratio (AOR), 3.0, 95% CI, 1.71-5.39), age less than 10 years (AOR, 3.7, 95% CI, 1.33-10.36), illiteracy (AOR, 3.2, 95% CI, 1.64-6.19), estimated monthly family income of less than 500 Ethiopian Birr (AOR, 2.9, 95% CI, 1.32-4.90) and irregular washing hands before meal (AOR, 5.3, 95% CI, 1.36-21.07) were predictors of IPI in this study. The retrospective study revealed a significant decrease (P = 0.037) in the proportion of patients infected with intestinal parasites out of those who requested stool examination over the six-year period.

Conclusion

This study confirms that IPIs are still common among residents of Jimma Town. Nearly half of the study participants were infected with at least one intestinal parasite. Public health interventions targeting prevention of IPIs should be strengthened in Jimma Town.

School hygiene and deworming are key protective factors for reduced transmission of soil-transmitted helminths among schoolchildren in Honduras

BACKGROUND

Among many neglected tropical diseases endemic in Honduras, soil-transmitted helminth (STH) infections are of particular importance. However, knowledge gaps remain in terms of risk factors involved in infection transmission. The aim of this study was to investigate risk factors associated with STH infections in schoolchildren living in rural Honduras.

METHODS

A cross-sectional study was conducted among Honduran rural schoolchildren in 2011. Demographic, socio-economic, and epidemiological data were obtained through a standardized questionnaire and STH infections were determined by the Kato-Katz method. Logistic regression models accounting for school clustering were used to assess putative risk factors for infection.

RESULTS

A total of 320 children completed the study. Prevalences for any STH and for Ascaris lumbricoides, Trichuris trichiura and hookworms were: 72.5%, 30.3%, 66.9% and 15.9%, respectively. A number of risk factors were identified at the individual, household, and school level. Boys were at increased odds of infection with hookworms (OR 2.33, 95% CI = 1.23-4.42). Higher socio-economic status in the family had a protective effect against infections by A. lumbricoides (OR 0.80, 95% CI = 0.65-0.99) and T. trichiura (OR 0.77, 95% CI = 0.63-0.94).Low school hygiene conditions significantly increased the odds for ascariasis (OR 14.85, 95% CI = 7.29-30.24), trichuriasis (OR 7.32, 95% CI = 3.71-14.45), mixed infections (OR 9.02, 95% CI = 4.66-17.46), and ascariasis intensity of infection (OR 3.32, 95% CI = 1.05 -10.52).Children attending schools not providing deworming treatment or that had provided it only once a year were at increased odds of ascariasis (OR 10.40, 95% CI = 4.39-24.65), hookworm (OR 2.92, 95% CI = 1.09-7.85) and mixed infections (OR 10.57, 95% CI = 4.53-24.66).

CONCLUSIONS

Poverty-reduction strategies will ultimately lead to sustainable control of STH infections in Honduras, but as shorter-term measures, uninterrupted bi-annual deworming treatment paired with improvements in school sanitary conditions may result in significant reductions of STH prevalence among Honduran schoolchildren.

Health education and the control of intestinal worm infections in China: a new vision

Background

The transmission of soil-transmitted helminths (STHs) is associated with poverty, poor hygiene behaviour, lack of clean water and inadequate waste disposal and sanitation. Periodic administration of benzimidazole drugs is the mainstay for global STH control but it does not prevent re-infection, and is unlikely to interrupt transmission as a stand-alone intervention.

Findings

We reported recently on the development and successful testing in Hunan province, PR China, of a health education package to prevent STH infections in Han Chinese primary school students. We have recently commenced a new trial of the package in the ethnically diverse Xishuangbanna autonomous prefecture in Yunnan province and the approach is also being tested in West Africa, with further expansion into the Philippines in 2015.

Conclusions

The work in China illustrates well the direct impact that health education can have in improving knowledge and awareness, and in changing hygiene behaviour. Further, it can provide insight into the public health outcomes of a multi-component integrated control program, where health education prevents re-infection and periodic drug treatment reduces prevalence and morbidity.

Intestinal parasitic infections among prison inmates and tobacco farm workers in Shewa Robit, north-central Ethiopia

BACKGROUND

Intestinal parasitic infections (IPIs) particularly soil-transmitted helminthiasis (STH) and schistosomiasis are among neglected tropical diseases (NTDs) globally. Apart from being associated with anemia, malabsorption and retarded cognitive development these diseases are complicating the clinical picture of more serious infections like HIV, TB and malaria. Renewed and up-to-date information on the epidemiology of IPIs in more vulnerable groups such as irrigated-farm workers and prisoners would significantly contribute towards improving the health condition of such at-risk groups.

METHODS

A cross-sectional survey was conducted to determine the prevalence of IPIs among prison inmates and tobacco farm workers in Shewa-Robit, north-central Ethiopia in November 2008. A total of 236 fecal samples were examined microscopically to detect helminths and/or protozoa using direct-smear and formol-ether concentration methods.

RESULTS

Overall, 8 intestinal parasite species have been recovered singly or in combinations from 146 (61.8 %) samples. The prevalence in prison population (88/121 = 72.7%) was significantly higher than that in tobacco farm (58/115 = 50.4%). There were no significant differences in the prevalence of IPI by most socio-demographics. Except for hookworm there was no significant difference in parasite prevalence between different age-groups though the frequency of individual parasites slightly varied between the age-groups. Multivariate logistic regression analysis showed that inmates were more likely to acquire IPIs than tobacco-farm workers (Odds Ratio (OR) = 2.62, 95% confidence interval (CI) = 1.52-4.5). In addition, participants who did not report past treatment for IPIs were more likely to acquire IPIs than participants who self-reported treatment for IPIs in the past twelve months (OR = 3.25, 95% CI = 1.75-6.06). All other socio-demographics were not significantly associated with IPIs in univariate analysis. Entamoeba histolytica/dispar/moshkovskii was the most frequently encountered species in both study sites accounting for 48.8 and 51.7 percent of the positives in prison and tobacco farm population respectively. Other intestinal parasites detected, with slight variation in prevalence in the two study areas, were hookworm, Ascaris lumbricoides, Trichuris trichiura, Schistosoma mansoni, Strongyloides stercolaris, Hymenolepis nana and Taenia sp. 35.5 and 33.0 percent of the total positive cases were mixed infections in Shewa Robit prison and tobacco farm, respectively.

CONCLUSION

The results show that IPIs are common health problems in the studied populations.

Can chemotherapy alone eliminate the transmission of soil transmitted helminths?

BACKGROUND

Amongst the world's poorest populations, availability of anthelmintic treatments for the control of soil transmitted helminths (STH) by mass or targeted chemotherapy has increased dramatically in recent years. However, the design of community based treatment programmes to achieve the greatest impact on transmission is still open to debate. Questions include: who should be treated, how often should they be treated, how long should treatment be continued for?

METHODS

Simulation and analysis of a dynamic transmission model and novel data analyses suggest refinements of the World Health Organization guidelines for the community based treatment of STH.

RESULTS

This analysis shows that treatment levels and frequency must be much higher, and the breadth of coverage across age classes broader than is typically the current practice, if transmission is to be interrupted by mass chemotherapy alone.

CONCLUSIONS

When planning interventions to reduce transmission, rather than purely to reduce morbidity, current school-based interventions are unlikely to be enough to achieve the desired results.

Exploring the relationship between access to water, sanitation and hygiene and soil-transmitted helminth infection: a demonstration of two recursive partitioning tools

BACKGROUND

Soil-transmitted helminths (STH) - a class of parasites that affect billions of people - can be mitigated using mass drug administration, though reinfection following treatment occurs within a few months. Improvements to water, sanitation and hygiene (WASH) likely provide sustained benefit, but few rigorous studies have evaluated the specific WASH components most influential in reducing infection. There is a need for alternative analytic approaches to help identify, characterize and further refine the WASH components that are most important to STH reinfection. Traditional epidemiological approaches are not well-suited for assessing the complex and highly correlated relationships commonly seen in WASH.

METHODOLOGY

We introduce two recursive partitioning approaches: classification and regression trees (C&RT) and conditional inference trees (CIT), which can be used to identify complex interactions between WASH indicators and identify sub-populations that may be susceptible to STH reinfection. We illustrate the advantages and disadvantages of these approaches utilizing school- and household-level WASH indicators gathered as part of a school-based randomized control trial in Kenya that measured STH reinfection of pupils 10 months following deworming treatment.

PRINCIPAL FINDINGS

C&RT and CIT analyses resulted in strikingly different decision trees. C&RT may be the preferred approach if interest lies in using WASH indicators to classify individuals or communities as STH infected or uninfected, whereas CIT is most appropriate for identifying WASH indicators that may be causally associated with STH infection. Both tools are well-suited for identifying complex interactions among WASH indicators.

CONCLUSIONS/SIGNIFICANCE

C&RT and CIT are two analytic approaches that may offer valuable insight regarding the identification, selection and refinement of WASH indicators and their interactions with regards to STH control programs; however, they represent solutions to two distinct research questions and careful consideration should be made before deciding which approach is most appropriate.