Neglected tropical diseases: moving beyond mass drug treatment to understanding the science

Persistent Ascaris Transmission Is Possible in Urban Areas Even Where Sanitation Coverage Is High

In low-income, urban, informal communities lacking sewerage and solid waste services, onsite sanitation (sludges, aqueous effluent) and child feces are potential sources of human fecal contamination in living environments. Working in informal communities of urban Maputo, Mozambique, we developed a quantitative, stochastic, mass-balance approach to evaluate plausible scenarios of localized contamination that could explain why the soil-transmitted helminth Ascaris remains endemic despite nearly universal coverage of latrines that sequester most fecal wastes. We used microscopy to enumerate presumptively viable Ascaris ova in feces, fecal sludges, and soils from compounds (i.e., household clusters) and then constructed a steady-state mass-balance model to evaluate possible contamination scenarios capable of explaining observed ova counts in soils. Observed Ascaris counts (mean = -0.01 log10 ova per wet gram of soil, sd = 0.71 log10) could be explained by deposits of 1.9 grams per day (10th percentile 0.04 grams, 90th percentile 84 grams) of child feces on average, rare fecal sludge contamination events that transport 17 kg every three years (10th percentile 1.0 kg, 90th percentile 260 kg), or a daily discharge of 2.7 kg aqueous effluent from an onsite system (10th percentile 0.09 kg, 90th percentile 82 kg). Results suggest that even limited intermittent flows of fecal wastes in this setting can result in a steady-state density of Ascaris ova in soils capable of sustaining transmission, given the high prevalence of Ascaris shedding by children (prevalence = 25%; mean = 3.7 log10 per wet gram, sd = 1.1 log10), the high Ascaris ova counts in fecal sludges (prevalence = 88%; mean = 1.8 log10 per wet gram, sd = 0.95 log10), and the extended persistence and viability of Ascaris ova in soils. Even near-universal coverage of onsite sanitation may allow for sustained transmission of Ascaris under these conditions.

A mechanistic model of snakebite as a zoonosis: Envenoming incidence is driven by snake ecology, socioeconomics and its impacts on snakes

Snakebite is the only WHO-listed, not infectious neglected tropical disease (NTD), although its eco-epidemiology is similar to that of zoonotic infections: envenoming occurs after a vertebrate host contacts a human. Accordingly, snakebite risk represents the interaction between snake and human factors, but their quantification has been limited by data availability. Models of infectious disease transmission are instrumental for the mitigation of NTDs and zoonoses. Here, we represented snake-human interactions with disease transmission models to approximate geospatial estimates of snakebite incidence in Sri Lanka, a global hotspot. Snakebites and envenomings are described by the product of snake and human abundance, mirroring directly transmitted zoonoses. We found that human-snake contact rates vary according to land cover (surrogate of occupation and socioeconomic status), the impacts of humans and climate on snake abundance, and by snake species. Our findings show that modelling snakebite as zoonosis provides a mechanistic eco-epidemiological basis to understand snakebites, and the possible implications of global environmental and demographic change for the burden of snakebite.

Funding patterns for biomedical research and infectious diseases burden in Gabon

Background

Biomedical research plays an important role in improving health. There seems to exist a negative correlation between the amount of biomedical research funding and disease burden from all Sub-Saharan African countries. In this study, we describe funding patterns for biomedical research, explore the correlation between funding and burden of diseases, and quantify inequalities in funds distribution across diseases in Gabon over the period 2005–2015.

Methods

Data on medical research funds from 2005 to 2015 were retrieved through a structured questionnaire distributed to Gabonese biomedical research institutions and by consulting online databases. Data on the burden of diseases were gathered from the World Health Organization and the Institute for Health Metrics and Evaluation. We used Kendall rank correlation coefficient to explore the correlation between cumulative funds over time and the burden of disease. The inequality distribution of funding across diseases was assessed through Gini coefficient and Lorenz curve.

Results

Biomedical research funding was characterized by a remarkable growth from 2005 to 2010 and a decline from 2010 to 2014. Funds were mostly from external sources and from partnerships. There was inequality in research funds allocation across diseases and malaria was far the most funded disease. There was a significant negative correlation between cumulative funding and the burden of HIV, tuberculosis, and of Helminthiasis (from 2006 to 2010) suggesting that research may be contributing to the management of such diseases. A positive, although not significant, correlation was found between cumulative funds and malaria burden.

Conclusions

The negative correlation between HIV and tuberculosis cumulative funding and burden suggests that research may be contributing to the management of such diseases but further research is needed to assess the causal direction of such as relationship. As the burden of non-communicable diseases is increasing, more research funds should be focused on those. While research partnerships have been and will remain fundamental, Gabon should increase the amount of national funds to overcome periods of reduced research funding flows from abroad.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12889-021-12201-w.

A cross-sectional study of dermatological conditions in rural and urban Timor-Leste

BACKGROUND

There is limited information about the type of skin disease in Timor-Leste. In order to determine the type and magnitude of skin disease in Timor-Leste, we conducted a cross-sectional point prevalence study of 271 patients from rural and urban Timor-Leste. The aim of the study was to estimate the magnitude and burden of dermatological disease.

METHODS

Two Australian-trained dermatologists conducted clinics in the city of Dili (urban) and village of Manusae (rural) in Timor-Leste between the period of June and July 2016. They independently recorded all patient presentations and diagnoses.

RESULTS

A total of 271 patients were reviewed over two months, of whom 37% were seen in an urban setting and 63% in a rural setting. Scabies accounted for 96% of all presentations in the rural setting, which was significantly higher than its presentation in the urban setting (8%), P < 0.001. Scabies also accounted for the majority of presentations in the paediatric population aged 10 years or younger. Fungal and bacterial skin and soft tissue infections were both more common in urban areas (P < 0.001).

CONCLUSIONS

Scabies infection remains the most prevalent dermatological condition encountered in the Timor-Leste rural population and has hopefully been addressed by a recent mass drug administration. It is important to raise awareness of the systemic problems that can arise from untreated skin infections.

A Voucher System To Speed Review Could Promote A New Generation Of Insecticides To Fight Vector-Borne Diseases

Many in the scientific community are concerned about the potential increase in prevalence of insect-borne diseases such as Chagas disease, Chikungunya, dengue fever, malaria, and Zika in the United States and around the world. Beyond vaccines and drugs to prevent and treat these diseases, a comprehensive approach to fighting these diseases should include control of disease-carrying vectors, such as mosquitoes. Vector-control methods, such as using insecticides to treat bed nets and spray the walls of homes, have prevented millions of deaths from malaria. However, mosquitoes are becoming resistant to insecticides, and no new class of insecticides for vector control has been introduced in decades. We recommend the creation of a new type of incentive for the development and commercialization of safe new insecticides: a Vector Expedited Review Voucher, to be awarded to a sponsor that introduces a novel insecticide for public health use. The voucher could be redeemed to expedite registration of a second, more profitable, product by the US Environmental Protection Agency.

DEWORMING DELUSIONS? MASS DRUG ADMINISTRATION IN EAST AFRICAN SCHOOLS

Recent debates about deworming school-aged children in East Africa have been described as the 'Worm Wars'. The stakes are high. Deworming has become one of the top priorities in the fight against infectious diseases. Staff at the World Health Organization, the Gates Foundation and the World Bank (among other institutions) have endorsed the approach, and school-based treatments are a key component of large-scale mass drug administration programmes. Drawing on field research in Uganda and Tanzania, and engaging with both biological and social evidence, this article shows that assertions about the effects of school-based deworming are over-optimistic. The results of a much-cited study on deworming Kenyan school children, which has been used to promote the intervention, are flawed, and a systematic review of randomized controlled trials demonstrates that deworming is unlikely to improve overall public health. Also, confusions arise by applying the term deworming to a variety of very different helminth infections and to different treatment regimes, while local-level research in schools reveals that drug coverage usually falls below target levels. In most places where data exist, infection levels remain disappointingly high. Without indefinite free deworming, any declines in endemicity are likely to be reversed. Moreover, there are social problems arising from mass drug administration that have generally been ignored. Notably, there are serious ethical and practical issues arising from the widespread practice of giving tablets to children without actively consulting parents. There is no doubt that curative therapy for children infected with debilitating parasitic infections is appropriate, but overly positive evaluations of indiscriminate deworming are counter-productive.

NEGLECTED TROPICAL DISEASES IN BIOSOCIAL PERSPECTIVE

The term 'neglected tropical diseases' (NTDs) points to the need for a biosocial perspective. Although 'diseases' are widely understood as biological phenomena, 'neglect' is inherently social. Social priorities, social relations and social behaviour profoundly influence the design, implementation and evaluation of control programmes. Yet, these dimensions of neglect are, themselves, neglected. Instead, emphasis is being placed on preventive chemotherapy - a technical, context-free approach which relies almost entirely on the mass distribution of drugs, at regular intervals, to populations living in endemic areas. This article reflects on the processes which have enabled an NTD 'brand' identity to emerge, and it comments on a disquieting disengagement with some of the more critical insights about the consequences of mass drug administration. Building on the work of biosocial scholars studying other aspects of health and disease, a more adequate, evidence-based approach is delineated. Developing such an approach is an iterative process, requiring on-going engagement with both biological and social insights as they emerge. Considerable theoretical, methodological and political challenges lie ahead, but it is essential they are overcome, if the sustainable control of NTDs is to become a reality.

Kicking in the Guts: Schistosoma mansoni Digestive Tract Proteins are Potential Candidates for Vaccine Development

Schistosomiasis is a debilitating disease that represents a major health problem in at least 74 tropical and subtropical countries. Current disease control strategies consist mainly of chemotherapy, which cannot prevent recurrent re-infection of people living in endemic area. In the last decades, many researchers made a remarkable effort in the search for an effective vaccine to provide long-term protection. Parasitic platyhelminthes of Schistosoma genus, which cause the disease, live in the blood vessels of definitive hosts where they are bathed in host blood for many years. Among the most promising molecules as vaccine candidates are the proteins present in the host–parasite interface, so numerous tegument antigens have been assessed and the achieved protection never got even close to 100%. Besides the tegument, the digestive tract is the other major site of host–parasite interface. Since parasites feed on blood, they need to swallow a considerable amount of blood for nutrient acquisition. Host blood ingested by schistosomes passes through the esophagus and reaches the gut where many peptidases catalyze the proteolysis of blood cells. Recent studies show the emergence of antigens related to the parasite blood feeding, such as esophageal gland proteins, proteases, and other proteins related to nutrient uptake. Herein, we review what is known about Schistosoma mansoni digestive tract proteins, emphasizing the ones described as potential vaccine candidates.

Emerging and reemerging neglected tropical diseases: a review of key characteristics, risk factors, and the policy and innovation environment

In global health, critical challenges have arisen from infectious diseases, including the emergence and reemergence of old and new infectious diseases. Emergence and reemergence are accelerated by rapid human development, including numerous changes in demographics, populations, and the environment. This has also led to zoonoses in the changing human-animal ecosystem, which are impacted by a growing globalized society where pathogens do not recognize geopolitical borders. Within this context, neglected tropical infectious diseases have historically lacked adequate attention in international public health efforts, leading to insufficient prevention and treatment options. This subset of 17 infectious tropical diseases disproportionately impacts the world's poorest, represents a significant and underappreciated global disease burden, and is a major barrier to development efforts to alleviate poverty and improve human health. Neglected tropical diseases that are also categorized as emerging or reemerging infectious diseases are an even more serious threat and have not been adequately examined or discussed in terms of their unique risk characteristics. This review sets out to identify emerging and reemerging neglected tropical diseases and explore the policy and innovation environment that could hamper or enable control efforts. Through this examination, we hope to raise awareness and guide potential approaches to addressing this global health concern.

The Impact of Nurses on Neglected Tropical Disease Management

Although Neglected Tropical Diseases (NTDs) are largely endemic in the developing nations of Africa, Asia, and South and Central America, they are reemerging with increasing frequency in developed countries. Their diagnosis, treatment, and control are an increasing public health concern that requires a different awareness by health care providers. Neglected tropical diseases (NTDs) are chronic infectious diseases which disproportionately burden poor, rural, and marginalized populations with significant mortality and high morbidity (disability, disfigurement, impaired childhood growth and cognitive development, increased vulnerability to coinfection) that reinforces their poverty. What can we learn from the nurses in developing countries already battling NTD's that could be useful in the developed world? This article provides an overview of distribution, pathophysiology, symptoms, and management of 13 NTDs, with particular attention to the role of nurses in delivering cost-effective integrated interventions. Case studies of schistosomiasis, Chagas disease, and leishmaniasis address recognition and treatment of infected individuals in developed nations where NTD infection is limited primarily to immigrants and travelers.

Schistosome syntenin partially protects vaccinated mice against Schistosoma mansoni infection

Background

Schistosomiasis is a neglected tropical disease caused by several species of trematode of the genus Schistosoma. The disease affects more than 200 million people in the world and causes up to 280,000 deaths per year, besides having high morbidity due to chronic illness that damages internal organs. Current schistosomiasis control strategies are mainly based on chemotherapy, but many researchers believe that the best long-term strategy to control disease is a combination of drug treatment and immunization with an anti-schistosome vaccine. Among the most promising molecules as vaccine candidates are the proteins present in the tegument and digestive tract of the parasite.

Methodology/Principal Findings

In this study, we describe for the first time Schistosoma mansoni syntenin (SmSynt) and we evaluate its potential as a recombinant vaccine. We demonstrate by real-time PCR that syntenin is mainly expressed in intravascular life stages (schistosomula and adult worms) of the parasite life cycle and, by confocal microscopy, we localize it in digestive epithelia in adult worms and schistosomula. Administration of siRNAs targeting SmSynt leads to the knock-down of syntenin gene and protein levels, but this has no demonstrable impact on parasite morphology or viability, suggesting that high SmSynt gene expression is not essential for the parasites in vitro. Mice immunization with rSmSynt, formulated with Freund's adjuvant, induces a Th1-type response, as suggested by the production of IFN-γ and TNF-α by rSmSynt-stimulated cultured splenocytes. The protective effect conferred by vaccination with rSmSynt was demonstrated by 30–37% reduction of worm burden, 38–43% reduction in the number, and 35–37% reduction in the area, of liver granulomas.

Conclusions/Significance

Our report is the first characterization of syntenin in Schistosoma mansoni and our data suggest that this protein is a potential candidate for the development of a multi-antigen vaccine to control schistosomiasis.

Schistosomiasis affects more than 200 million people worldwide and causes up to 280,000 deaths per year. In terms of global mortality and morbidity, this disease is the most important human helminth infection. Current control strategies are based on chemotherapy, but recurrent re-infection of people living in endemic areas makes many researchers, and also the World Health Organization, search for an effective vaccine to provide protection against schistosomiasis. Substantial efforts have been committed to the characterization of new antigens for an anti-schistosome vaccine and, in order to find new targets for vaccine and/or drug development, we searched transcriptomics and proteomics of Schistosoma mansoni and identified the protein syntenin (SmSynt) for analysis. In this study, we characterize SmSynt and evaluate its potential as a vaccine candidate to protect mice against S. mansoni infection. We demonstrate that SmSynt is expressed in schistosomula and adult worms, the intravascular stages of S. mansoni and it is located in the intestinal tract of the worms, an important host/parasite interface. Furthermore, vaccination of mice with rSmSynt confers partial protection against S. mansoni challenge infection and ameliorates parasite-induced liver pathology. Our data suggest that SmSynt is a potential candidate in the development of a vaccine against schistosomiasis.

Global burden, distribution, and interventions for infectious diseases of poverty

Infectious diseases of poverty (IDoP) disproportionately affect the poorest population in the world and contribute to a cycle of poverty as a result of decreased productivity ensuing from long-term illness, disability, and social stigma. In 2010, the global deaths from HIV/AIDS have increased to 1.5 million and malaria mortality rose to 1.17 million. Mortality from neglected tropical diseases rose to 152,000, while tuberculosis killed 1.2 million people that same year. Substantial regional variations exist in the distribution of these diseases as they are primarily concentrated in rural areas of Sub-Saharan Africa, Asia, and Latin America, with geographic overlap and high levels of co-infection. Evidence-based interventions exist to prevent and control these diseases, however, the coverage still remains low with an emerging challenge of antimicrobial resistance. Therefore, community-based delivery platforms are increasingly being advocated to ensure sustainability and combat co-infections. Because of the high morbidity and mortality burden of these diseases, especially in resource-poor settings, it is imperative to conduct a systematic review to identify strategies to prevent and control these diseases. Therefore, we attempted to evaluate the effectiveness of one of these strategies, that is community-based delivery for the prevention and treatment of IDoP. In this paper, we describe the burden, epidemiology, and potential interventions for IDoP. In subsequent papers of this series, we describe the analytical framework and the methodology used to guide the systematic reviews, and report the findings and interpretations of our analyses of the impact of community-based strategies on individual IDoPs.

Sm10.3, a member of the micro-exon gene 4 (MEG-4) family, induces erythrocyte agglutination in vitro and partially protects vaccinated mice against Schistosoma mansoni infection

BACKGROUND

The parasitic flatworm Schistosoma mansoni is a blood fluke that causes schistosomiasis. Current schistosomiasis control strategies are mainly based on chemotherapy, but many researchers believe that the best long-term strategy to control disease is a combination of drug treatment and immunization with an anti-schistosome vaccine. Numerous antigens that are expressed at the interface between the parasite and the mammalian host have been assessed. Among the most promising molecules are the proteins present in the tegument and digestive tract of the parasite.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we evaluated the potential of Sm10.3, a member of the micro-exon gene 4 (MEG-4) family, for use as part of a recombinant vaccine. We confirmed by real-time PCR that Sm10.3 was expressed at all stages of the parasite life cycle. The localization of Sm10.3 on the surface and lumen of the esophageal and intestinal tract in adult worms and lung-stage schistosomula was confirmed by confocal microscopy. We also show preliminary evidence that rSm10.3 induces erythrocyte agglutination in vitro. Immunization of mice with rSm10.3 induced a mixed Th1/Th2-type response, as IFN-γ, TNF-α, and low levels of IL-5 were detected in the supernatant of cultured splenocytes. The protective effect conferred by vaccination with rSm10.3 was demonstrated by 25.5-32% reduction in the worm burden, 32.9-43.6% reduction in the number of eggs per gram of hepatic tissue, a 23.8% reduction in the number of granulomas, an 11.8% reduction in the area of the granulomas and a 39.8% reduction in granuloma fibrosis.

CONCLUSIONS/SIGNIFICANCE

Our data suggest that Sm10.3 is a potential candidate for use in developing a multi-antigen vaccine to control schistosomiasis and provide the first evidence for a possible role for Sm10.3 in the blood feeding process.

Role of antibody dependent cell mediated cytotoxicity (ADCC) in Sm-p80-mediated protection against Schistosoma mansoni

Schistosomiasis is a major health problem in the developing world and for international travelers to the endemic countries. Existing strategies to control schistosomiasis have had limited successes so far. The addition of an effective vaccine in existing control measures would be greatly beneficial in reducing the impact of the disease. In this regard, Sm-p80 mediated protection against intestinal schistosomiasis caused by Schistosoma mansoni has been observed to be promising in two animal models of infection and disease. In this study, the role of antibody dependent cell mediated cytotoxicity (ADCC) was deciphered in Sm-p80-mediated protection especially in the elimination of lung stage schistosomula. This was achieved using lung lavage cells and lung cells that were isolated from mice immunized with and without Sm-p80 formulated in a recombinant vaccine formulation. Significant differences were observed in cytotoxicity assays using immune sera with the lung lavage cells which showed 51% more killing of schistosomula and elevated levels of nitric oxide in the supernatants were detected compared to controls.

Turning neglected tropical diseases into forgotten maladies

Because they afflict mostly poor people in poor countries, killing relatively few compared to the many who suffer from severe chronic disabilities, a large cluster of infections deserve the label of neglected tropical diseases (NTDs). That is changing as these diseases' enormous health, educational, and economic toll is better understood, including how they interact with HIV/AIDS, malaria, and other illnesses. Several NTDs could be controlled or even eliminated within a decade, using integrated, highly cost-effective mass drug administration programs together with nondrug interventions. Research is needed to provide additional means of control for these conditions and make elimination feasible for still others.

Implications of Human Microbiome Research for the Developing World

The human microbiome refers to all of the species that inhabit the human body, residing both on and in it. Over the past several years, there has been a significantly increased interest directed to the understanding of the microorganisms that reside on and in the human body. These studies of the human microbiome promise to reveal all these species and increase our understanding of the normal inhabitants, those that trigger disease and those that vary in response to disease conditions. It is anticipated that these directed research efforts, coupled with new technological advances, will ultimately allow one to gain a greater understanding of the relationships of these species with their human hosts. The various chapters in this book present a range of aspects of human microbiome research, explain the scientific and technological rationale, and highlight the significant potential that the results from these studies hold. In this chapter, we begin to address the potential and long-term implications of the knowledge gained from human microbiome research (which currently is centered in the developed world) for the developing world, which has often lagged behind in the benefits of these new technologies and their implications to new research areas.