Conventional parasitology and DNA-based diagnostic methods for onchocerciasis elimination programmes

Beyond Tradition: Exploring Cutting-Edge Approaches for Accurate Diagnosis of Human Filariasis

Filariasis is recognised as a global public health threat, particularly in tropical and subtropical regions. It is caused by infection with a nematode parasite of the superfamily Filarioidea, including Wuchereria bancrofti, Brugia malayi, Onchocerca volvulus, and Onchocerca lupi. Three main types of filariasis have been classified: lymphatic filariasis, subcutaneous filariasis, and serous cavity filariasis. The symptoms exhibited by individuals afflicted with filariasis are diverse and contingent upon several variables, including the species of parasite, the host's health and immune response, and the stage of infection. While many classical parasitological techniques are considered indispensable tools for the diagnosis of parasitic infections in humans, alternative methods are being sought due to their limitations. Novel tests based on host-parasite interactions offer a rapid, simple, sensitive, and specific diagnostic tool in comparison to traditional parasitological methods. This article presents methods developed in the 21st century for the diagnosis of filariasis caused by invasion from W. bancrofti, B. malayi, O. volvulus, and O. lupi, as well as techniques that are currently in use. The development of modern diagnostic methods based on molecular biology constitutes a significant advancement in the fight against filariasis.

Causes of infectious pediatric uveitis: A review

Infectious pediatric uveitis is a rare disease that can cause severe ocular damage if not detected rapidly and treated properly. Additionally, early identification of an infection can protect the child from life-threatening systemic infection. Infectious uveitis can be congenital or acquired and may manifest as a primary ocular infection or as a reactivation. Nevertheless, publications on infectious paediatric uveitis are usually limited to a small number of patients or a case report. So far, most studies on uveitis in children have focused primarily on noninfectious uveitis, and a systematic study on infectious uveitis is lacking. In this review, we summarize the literature on infectious uveitis in pediatric populations and report on the epidemiology, pathophysiology, clinical signs, diagnostic tests, and treatment. We will describe the different possible pathogens causing uveitis in childhood by microbiological group (i.e. parasites, viruses, bacteria, and fungi). We aim to contribute to early diagnosis and management of infectious pediatric uveitis, which in turn might improve not only visual outcome, but also the general health outcome.

Optimized strategy for real-time qPCR detection of Onchocerca volvulus DNA in pooled Simulium sp. blackfly vectors

BACKGROUND

Onchocerca volvulus is a filarial parasite that is a major cause of dermatitis and blindness in endemic regions primarily in sub-Saharan Africa. Widespread efforts to control the disease caused by O. volvulus infection (onchocerciasis) began in 1974 and in recent years, following successful elimination of transmission in much of the Americas, the focus of efforts in Africa has moved from control to the more challenging goal of elimination of transmission in all endemic countries. Mass drug administration (MDA) with ivermectin has reached more than 150 million people and elimination of transmission has been confirmed in four South American countries, with at least two African countries having now stopped MDA as they approach verification of elimination. It is essential that accurate data for active transmission are used to assist in making the critical decision to stop MDA, since missing low levels of transmission and infection can lead to continued spread or recrudescence of the disease.

METHODOLOGY/PRINCIPAL FINDINGS

Current World Health Organization guidelines for MDA stopping decisions and post-treatment surveillance include screening pools of the Simulium blackfly vector for the presence of O. volvulus larvae using a PCR-ELISA-based molecular technique. In this study, we address the potential of an updated, practical, standardized molecular diagnostic tool with increased sensitivity and species-specificity by comparing several candidate qPCR assays. When paired with heat-stable reagents, a qPCR assay with a mitochondrial DNA target (OvND5) was found to be more sensitive and species-specific than an O150 qPCR, which targets a non-protein coding repetitive DNA sequence. The OvND5 assay detected 19/20 pools of 100 blackfly heads spiked with a single L3, compared to 16/20 for the O150 qPCR assay.

CONCLUSIONS/SIGNIFICANCE

Given the improved sensitivity, species-specificity and resistance to PCR inhibitors, we identified OvND5 as the optimal target for field sample detection. All reagents for this assay can be shipped at room temperature with no loss of activity. The qPCR protocol we propose is also simpler, faster, and more cost-effective than the current end-point molecular assays.

Ivermectin and doxycycline treatments against Onchocerciasis: Adaptations and impact among semi-nomadic population in Massangam Health District, Cameroon

We trialed strategies to reach semi-nomadic population with interventions targeting onchocerciasis including a combination of community knowledge and Geographical Information System (GIS) technology; nomad-specific sensitization; and mobile outreach. The interventions included ivermectin (ivm) mass drug administration (MDA) and treating infected individuals (found upon skin snip microscopy test) with doxycycline for 35 days. Microscopy-negative snips were further tested by Polymerase Chain Reaction (PCR). After 8 months, individuals immigrating or emigrating constituted 47% of the initial population; 59% of individuals not born in the area have immigrated during the last five years; 28% (age>9) reportedly never taken ivm; 72% (compared to 51% previously) of eligible population (age ≥ 5 years) took ivm; and 47% (age > 8, not pregnant, not breastfeeding, not severely ill,) participated in the test. A high prevalence of onchocerciasis,15.1%, was found upon microscopy & PCR test; 9/10 tested by skin snip microscopy and PCR at follow-up were all negative. Microfilaria prevalence and intensity upon skin snip microscopy reduced significantly from baseline following the intervention (8.9% to 4.1%, p = 0.032; 0.18 to 0.16, p = 0.013, respectively). The strategies considerably increased reach to nomadic camps. Treating with doxycycline in combination with ivm is feasible and has led to a significant reduction in infection level within one year among the semi-nomads. Being potentially curative in one intervention round, this combination should be considered for population group faced with challenges of achieving adequate coverage and adhesion to ivm MDA over prolonged period (>10 years).

A Systematic Review on Suitability of Molecular Techniques for Diagnosis and Research into Infectious Diseases of Concern in Resource-Limited Settings

Infectious diseases significantly impact the health status of developing countries. Historically, infectious diseases of the tropics especially have received insufficient attention in worldwide public health initiatives, resulting in poor preventive and treatment options. Many molecular tests for human infections have been established since the 1980s, when polymerase chain reaction (PCR) testing was introduced. In spite of the substantial innovative advancements in PCR technology, which currently has found wide application in most viral pathogens of global concern, the development and application of molecular diagnostics, particularly in resource-limited settings, poses potential constraints. This review accessed data from sources including PubMed, Google Scholar, the Web of Knowledge, as well as reports from the World Health Organization’s Annual Meeting on infectious diseases and examined these for current molecular approaches used to identify, monitor, or investigate some neglected tropical infectious diseases. This review noted some growth efforts in the development of molecular techniques for diagnosis of pathogens that appear to be common in resource limited settings and identified gaps in the availability and applicability of most of these molecular diagnostics, which need to be addressed if the One Health goal is to be achieved.

Single-Nucleotide Polymorphism Associates' β-Tubulin Isotype-1 Gene in Onchocerca volvulus Populations in Ivermectin-Treated Communities in Taraba State, Nigeria

PURPOSE

The occurrence of Single-Nucleotide Polymorphisms (SNPs) associated with repeated ivermectin treatment and sub-optimal responses reported by previous findings is of great concern in Onchocerciasis endemic areas. This study investigated SNPs' occurrence after 15 years of ivermectin intervention in Onchocerciasis endemic communities in two Local Government Areas of Taraba State, Nigeria.

METHODS

Microfilariae samples were collected by skin snip from individuals treated with ivermectin for 10-15 years of annual distribution and preserved in RNAlater^® in a 1.5 ml micro-centrifuge tube. Genomic DNA was extracted from microfilariae and residual skin, amplification in two regions within the β-tubulin gene, sequenced and analyzed for SNPs using Bioinformatics tools.

RESULTS

Three distinct SNP positions: 1183 (T/G), 1188 (T/C) and 1308 (C/T) on the β-tubulin gene on the targeted 1083-1568 bp fragment, associate's with the ivermectin-treated population. Furthermore, SNPs positions detected in this study are 1730 (A/G) and 1794 (T/G) in the β-tub gene in the 1557-1857 (bp) region. The 1794 (T/G) SNP position (Phe243Val) in the exon within the β-tubulin gene region were observed in this study.

CONCLUSION

The present study indicates that SNPs are observed in Onchocerca volvulus, thus strengthening the warning that genetic changes could occur in some parasite populations in some ivermectin-treated areas.

Whole blood transcriptome analysis in onchocerciasis

Identifying the molecular mechanisms controlling the host’s response to infection with Onchocerca volvulus is important to understand how the human host controls such parasitic infection. Little is known of the cellular immune response upon infection with O. volvulus. We performed a transcriptomic study using PAXgene-preserved whole blood from 30 nodule-positive individuals and 21 non-endemic controls. It was found that of the 45,042 transcripts that were mapped to the human genome, 544 were found to be upregulated and 447 to be downregulated in nodule-positive individuals (adjusted P-value < 0.05). Pathway analysis was performed on this set of differentially expressed genes, which demonstrated an impact on oxidative phosphorylation and protein translation. Upstream regulator analysis showed that the mTOR associated protein RICTOR appears to play an important role in inducing the transcriptional changes in infected individuals. Functional analysis of the genes affected by infection indicated a suppression of antibody response, Th17 immune response and proliferation of activated T lymphocytes. Multiple regression models were used to select 22 genes that could contribute significantly in the generation of a classifier to predict infection with O. volvulus. For these 22 genes, as well as for 8 reference target genes, validated RT-qPCR assays were developed and used to re-analyze the discovery sample set. These data were used to perform elastic net regularized logistic regression and a panel of 7 genes was found to be the best performing classifier. The resulting algorithm returns a value between 0 and 1, reflecting the predicted probability of being infected. A validation panel of 69 nodule-positive individuals and 5 non-endemic controls was used to validate the performance of this classifier. Based on this validation set only, a sensitivity of 94.2% and a specificity of 60.0% was obtained. When combining the discovery test set and validation set, a sensitivity of 96.0% and a specificity of 92.3% was obtained. Large-scale validation approaches will be necessary to define the intended use for this classifier. Besides the use as marker for infection in MDA efficacy surveys and epidemiological transmission studies, this classifier might also hold potential as pharmacodynamic marker in macrofilaricide clinical trials.

•

Whole blood transcriptome analysis was performed in onchocerciasis patients.

•

Suppression of antibodies, Th17, and proliferation of activated T cells.

•

RICTOR plays an important role in inducing the transcriptional changes.

•

A 7-gene expression classifier was built as a tool for onchocerciasis detection.

Molecular diagnosis of scabies using a novel probe-based polymerase chain reaction assay targeting high-copy number repetitive sequences in the Sarcoptes scabiei genome

Background

The suboptimal sensitivity and specificity of available diagnostic methods for scabies hampers clinical management, trials of new therapies and epidemiologic studies. Additionally, parasitologic diagnosis by microscopic examination of skin scrapings requires sample collection with a sharp scalpel blade, causing discomfort to patients and difficulty in children. Polymerase chain reaction (PCR)-based diagnostic assays, combined with non-invasive sampling methods, represent an attractive approach. In this study, we aimed to develop a real-time probe-based PCR test for scabies, test a non-invasive sampling method and evaluate its diagnostic performance in two clinical settings.

Methodology/Principal findings

High copy-number repetitive DNA elements were identified in draft Sarcoptes scabiei genome sequences and used as assay targets for diagnostic PCR. Two suitable repetitive DNA sequences, a 375 base pair microsatellite (SSR5) and a 606 base pair long tandem repeat (SSR6), were identified. Diagnostic sensitivity and specificity were tested using relevant positive and negative control materials and compared to a published assay targeting the mitochondrial cox1 gene. Both assays were positive at a 1:100 dilution of DNA from a single mite; no amplification was observed in DNA from samples from 19 patients with other skin conditions nor from house dust, sheep or dog mites, head and body lice or from six common skin bacterial and fungal species. Moderate sensitivity of the assays was achieved in a pilot study, detecting 5/7 (71.4% [95% CI: 29.0% - 96.3%]) of clinically diagnosed untreated scabies patients). Greater sensitivity was observed in samples collected by FLOQ swabs compared to skin scrapings.

Conclusions/Significance

This newly developed qPCR assay, combined with the use of an alternative non-invasive swab sampling technique offers the possibility of enhanced diagnosis of scabies. Further studies will be required to better define the diagnostic performance of these tests.

As scabies control efforts continue to grow, scarcity of diagnostic options hinders success of elimination efforts in endemic areas. Efficiency in large-scale monitoring is further obstructed by invasive sample collection techniques, which are often uncomfortable for patients, and lack sensitivity. We have developed two PCR-based diagnostic assays targeting repetitive DNA elements. These were identified using new data on the S. scabiei genome. Targeting these elements by PCR improved the detection of scabies DNA. Enhanced sensitivity was demonstrated when tested against routine microscopy and a published PCR-based diagnostic assay. When combined with a non-invasive, effective FLOQ swab sampling method, the developed qPCR-based assays may provide a useful complementary tool for diagnosis of scabies, and its application will likely improve scabies control in target populations.

Duplex Real-Time PCR Assay for Clinical Differentiation of Onchocerca lupi and Onchocerca volvulus

In the United States and Europe, human onchocerciasis is a rare disease caused by zoonotic or anthropophilic parasites in the genus Onchocerca. The zoonotic species identified in focal areas of Europe and United States is Onchocerca lupi, and Onchocerca volvulus, the anthroponotic species, may be found among people who had lived in endemic areas of Africa, the Arabian Peninsula, or Latin America. Onchocerciasis due to O. lupi is an emergent parasitic disease, with limited diagnostic methods, in addition to the lack of information on its biology, transmission, and epidemiology. Cutaneous nodules are the disease's most prevalent manifestation but lack diagnostic specificity. To address the diagnosis of onchocerciasis at reference laboratories, we developed a duplex TaqMan real-time PCR (qPCR) method, targeting the cytochrome oxidase subunit I locus which has species-specific probes to identify and differentiate O. lupi from O. volvulus. We determined the performance of the duplex with a panel of 45 samples: 11 positives for O. lupi, six for O. volvulus, five samples with negative results for Onchocerca spp., and 23 non-Onchocerca nematodes. The duplex qPCR correctly detected 10 of 11 O. lupi- and six of six O. volvulus-positive specimens. The new duplex assay allowed the simultaneous detection and discrimination of O. lupi and O. volvulus in clinical specimens, expediting and facilitating the clinical diagnosis of O. lupi in non-endemic settings where the disease is an infrequent finding.

Differential susceptibility of Onchocerca volvulus microfilaria to ivermectin in two areas of contrasting history of mass drug administration in Cameroon: relevance of microscopy and molecular techniques for the monitoring of skin microfilarial repopulation within six months of direct observed treatment

Background

Ivermectin is an excellent microfilaricide against Onchocerca volvulus. However, in some regions, long term use of ivermectin has resulted in sub-optimal responses to the treatment. More data to properly document the phenomenon in various contexts of ivermectin mass drug administration (IVM-MDA) is needed. Also, there is a need to accurately monitor a possible repopulation of skin by microfilariae following treatment. Skin snip microscopy is known to have a low sensitivity in individuals with light infections, which can be the case following treatment. This study was designed with two complementary objectives: (i) to assess the susceptibility of O. volvulus microfilariae to ivermectin in two areas undergoing IVM-MDA for different lengths of time, and (ii) to document the repopulation of skin by the O. volvulus microfilariae following treatment, using 3 independent diagnostic techniques.

Method

Identified microfilaridermic individuals were treated with ivermectin and re-examined after 1, 3, and 6 months using microscopy, actin real-time PCR (actin-qPCR) and O-150 LAMP assays. Susceptibility to ivermectin and trends in detecting reappearance of skin microfilariae were determined using three techniques. Microscopy was used as an imperfect gold standard to determine the performance of actin-qPCR and LAMP.

Results

In Bafia with over 20 years of IVM-MDA, 11/51 (21.6%) direct observe treated microfilaridemic participants were still positive for skin microfilariae after 1 month. In Melong, with 10 years of IVM-MDA, 2/29 (6.9%) treated participants were still positive. The microfilarial density reduction per skin biopsy within one month following treatment was significantly lower in participants from Bafia.

In both study sites, the molecular techniques detected higher proportions of infected individuals than microscopy at all monitoring time points. LAMP demonstrated the highest levels of sensitivity and real-time PCR was found to have the highest specificity.

Conclusion

Patterns in skin mirofilariae clearance and repopulation were established. O. volvulus worms from Bafia with higher number of annual MDA displayed a lower clearance and higher repopulation rate after treatment with ivermectin. Molecular assays displayed higher sensitivity in monitoring O. volvulus microfilaridemia within six months following treatment.

Status of parasitological indicators and morbidity burden of onchocerciasis after years of successive implementation of mass distribution of ivermectin in selected communities of Yeki and Asosa districts, Ethiopia

Background

Control and elimination of onchocerciasis requires regular follow-up and evaluation of community directed treatment with ivermectin (CDTi) program implementation. This research was aimed to assess the epidemiological status of onchocerciasis in disease endemic communities of Asosa and Yeki districts of Ethiopia after 5 and 15 years of successive CDTi respectively, and to evaluate the decline in infection and morbidity burden.

Methods

A community-based cross-sectional study was conducted from August 2017 to January 2018 (i.e. within 2–7 months since the last treatment) using interview, physical and parasitological examinations. Pre-CDTi epidemiological data were obtained from studies conducted prior to the launch of CDTi.

Results

A total of 3002 individuals (1567 from Asosa and 1435 from Yeki) were included. No infection was detected from Yeki. In Asosa, the prevalence of infection was 1.6%. The geometric mean intensity of infection was 0.02 mf/mg of skin snip. The prevalence rates of dermatitis, depigmentation, nodule, and atrophy in Yeki were 33(2.3%), 57(4%), 37(2.6%) and 11(0.7%), respectively. The prevalence rates of papular dermatitis, depigmentation, palpable nodule, atrophy, and blindness in Asosa were 94(6%), 38(2.4%), 30(1.9%), 28(1.8%) and 2(0.1%), respectively. Five years of CDTi had significantly reduced prevalence and intensity of infection by 91.8% (p < 0.001) and 99.7% (p < 0.001), respectively. Moreover, CDTi reduced prevalence of papular dermatitis by 95.9% (p < 0.001), palpable nodule by 90.5% (p < 0.001), and atrophy by 30% (p = 0.6) in Yeki. Similarly, CDTi reduced prevalence of papular dermatitis by 88.6% (p < 0.001), depigmentation by 90.3% (p < 0.001), atrophy by 89.5% (p < 0.001), and blindness by 90% (p < 0.001) in Asosa.

Conclusions

Fifteen years of successive CDTi had brought the infection from high to zero in Yeki. However, thorough entomological and serological data need to be generated to ascertain whether complete interruption of parasite transmission has been attained, and for considerations of an evidence-based CDTi cessation. Five years of CDTi in Asosa has significantly reduced the infection and morbidity of onchocerciasis to very low level. We, hereby, recommend biannual CDTi to continue in Asosa and its surroundings until the infection transmission is fully interrupted.

NTD Diagnostics for Disease Elimination: A Review

Neglected Tropical Diseases (NTDs) marked out for disease elimination provide a lens through which to explore the changing status of diagnosis in global health. This paper reports on the findings of a scoping review, which set out to explore the main debates around diagnosis for the elimination of NTDs, including the multiple roles diagnostic technologies are being ascribed and the ideal characteristics of tests. It also attempts to summarise the state of diagnosis for three NTDs with elimination goals. The review places special emphasis on point-of-care testing in acknowledgement of the remote and underserved areas where NTDs proliferate. Early NTD campaigns were largely focused on attack phase planning, whereby a similar set of interventions could be transplanted anywhere. Now, with elimination goals in sight, strategies must be tailored to local settings if they are to attain and sustain success. Diagnostic data helps with local adaptation and is increasingly used for programmatic decision-making. The review finds that elimination goals reframe whom diagnosis is for and the myriad roles diagnostics can play. The exigencies of elimination also serve to highlight deficiencies in the current diagnostic arsenal and development pipeline for many NTDs. Moving forward, a guiding framework is needed to drive research and stimulate investment in diagnosis to support NTD goals.

The insufficiency of circulating miRNA and DNA as diagnostic tools or as biomarkers of treatment efficacy for Onchocerca volvulus

Skin snip evaluation for onchocerciasis has insufficient sensitivity when skin microfilarial (mf) densities are low, such as following ivermectin treatment. Mf density is suitable for assessing microfilaricidal efficacy but only serves as an indirect indicator of macrofilaricidal activity. We assessed circulating nucleic acids from Onchocerca volvulus as an alternative to skin snips. We screened a plasma sample set of infected individuals followed up at four, 12 and 21 months after microfilaricidal (ivermectin, n = four), macrofilaricidal (doxycycline, n = nine), or combination treatment (n = five). Two parasite-derived miRNAs, cel-miR-71-5p and bma-lin-4, and O-150 repeat DNA were assessed. Highly abundant DNA repeat families identified in the O. volvulus genome were also evaluated. miRNAs were detected in two of 72 plasma samples (2.8%) and two of 47 samples (4.3%) with microfilaridermia using RT-qPCR. O-150 DNA was detected in eight (44.4%) baseline samples by qPCR and the number of positives declined post-treatment. One doxycycline-treated individual remained O-150 positive. However, only 11 (23.4%) samples with microfilaridermia were qPCR-positive. Analysis by qPCR showed novel DNA repeat families were comparatively less abundant than the O-150 repeat. Circulating parasite-derived nucleic acids are therefore insufficient as diagnostic tools or as biomarkers of treatment efficacy for O. volvulus.

Ivermectin: From theory to clinical application

Approximately 250 million people have been using ivermectin (IVM) annually to combat many parasitic diseases including filariasis, onchocerciasis, strongyloidiasis, scabies and pediculosis. Many clinical studies have proven its efficacy against these diseases and have reported the optimum dose and duration of treatment. Moreover, its antiparasitic range has increased to cover more parasitic infections, but it still requires further exploration, e.g. for trichinosis and myiasis. Furthermore, IVM showed high efficacy in killing vectors of disease-causing parasites such as mosquitoes, sandflies and tsetse flies. The World Health Organization (WHO) has managed many control programmes involving the use of IVM to achieve elimination of onchocerciasis and lymphatic filariasis and to reduce malaria transmission. However, IVM is not exempt from the possibility of resistance and, certainly, its intensive use has led to the emergence of resistance in some parasites. Recent research is investigating the possibility of novel drug delivery systems for IVM that increase its potential to treat a new range of diseases and to overcome the possibility of drug resistance. This review highlights the most common human uses of IVM, with special reference to the new and promising properties of IVM.

Population Genetics and Molecular Epidemiology of Eukaryotes

Molecular epidemiology uses the distribution and organization of a pathogen's DNA to understand the distribution and determinants of disease. Since the biology of DNA for eukaryotic pathogens differs substantially from that of bacteria, the analytic approach to their molecular epidemiology can also differ. While many of the genotyping techniques presented earlier in this series, "Advances in Molecular Epidemiology of Infectious Diseases," can be applied to eukaryotes, the output must be interpreted in the light of how DNA is distributed from one generation to the next. In some cases, parasite populations can be evaluated in ways reminiscent of bacteria. They differ, however, when analyzed as sexually reproducing organisms, where all individuals are unique but the genetic composition of the population does not change unless a limited set of events occurs. It is these events (migration, mutation, nonrandom mating, selection, and genetic drift) that are of interest. At a given time, not all of them are likely to be equally important, so the list can easily be narrowed down to understand the driving forces behind the population as it is now and even what it will look like in the future. The main population characteristics measured to assess these events are differentiation and diversity, interpreted in the light of what is known about the population from observation. The population genetics of eukaryotes is important for planning and evaluation of control measures, surveillance, outbreak investigation, and monitoring of the development and spread of drug resistance. *This article is part of a curated collection.

PCR-coupled sequencing achieves specific diagnosis of onchocerciasis in a challenging clinical case, to underpin effective treatment and clinical management

This study demonstrates the utility of a PCR-based DNA sequencing approach to make a specific diagnosis of onchocerciasis in a returned traveller. Although a clinical diagnosis was not possible, the surgical excision of a suprascapular nodule from this patient, combined with an histological examination of this nodule and PCR-based sequencing of DNA from a nematode from this lesion solved the case. The analysis of DNA sequence data confirmed the presence of Onchocerca volvulus infection, supporting an effective treatment-clinical management strategy for the patient.

Interruption of onchocerciasis transmission in Bioko Island: Accelerating the movement from control to elimination in Equatorial Guinea

Background

Onchocerciasis, also known as river blindness, is a parasitic disease. More than 99 percent of all cases occur in Africa. Bioko Island (Equatorial Guinea) is the only island endemic for onchocerciasis in the world. Since 2005, when vector Simulium yahense was eliminated, there have not been any reported cases of infection. This study aimed to demonstrate that updated WHO criteria for stopping mass drug administration (MDA) have been met.

Methodology/Principal findings

A cross-sectional study was conducted from September 2016 to January 2017. Participants were 5- to 9-year-old school children. Onchocerciasis/lymphatic Filariasis (LF, only in endemic districts) rapid diagnostic tests (RDTs) were performed. Blood spots were collected from RDT positive children and 10 percent of the RDT negatives to determine Ov16 and Wb123 IgG4 antibodies through enzyme-linked immunosorbent assay (ELISA). Skin snips were collected from RDT positives. Filarial detection was performed by PCR in positives and indeterminate sera. Black fly collection was carried out in traditional breeding sites. A total of 7,052 children, ranging from 5 to 9 years of age, were included in the study. Four children (0.06%) were Ov16 IgG4 RDT positives, but negative by ELISA Ov16, while 6 RDT negative children tested positive by ELISA. A total of 1,230 children from the Riaba and Baney districts were tested for LF. One child was Wb123 RDT positive (0.08%), but ELISA negative, while 3 RDT negative children were positive by Wb123 ELISA. All positive samples were negative by PCR for onchocerciasis and LF (in blood spot and skin snip). All fly collections and larval prospections in the traditional catching and prospection sites were negative.

Conclusions/Significance

WHO criteria have been met, therefore MDA in Bioko Island can be stopped. Three years of post-treatment surveillance should be implemented to identify any new occurrences of exposure or infection.

Onchocerciasis, commonly called river blindness, is a chronic parasitic disease particularly prevalent in Africa. It is transmitted through the bites of infected Simulium blackflies. Onchocerciasis is endemic in Equatorial Guinea. Huge achievements have been made in human and vector control during the last two decades, especially on Bioko Island. Eliminating onchocerciasis transmission on Bioko is feasible given its isolation from other landmasses, which also reduces the risk of reinvasion by the disease vector. Recently updated WHO guidelines for stopping mass drug administration (MDA) and verifying elimination of human onchocerciasis (2016) established a new critical threshold to verify elimination of onchocerciasis transmission based on novel serological tests. We applied these techniques in a representative sample of 5- to 9-year-old school children. An entomological assessment was also carried out. We found no evidence of current infection or recent transmission. There was no evidence of onchocerciasis vectors, and our results from the sample population meet the current WHO serologic criteria for stopping MDA. Based on these results, we recommended to the Ministry of Health and Social Welfare of Equatorial Guinea that MDA on Bioko Island be stopped and that 3 years of post-treatment surveillance should be undertaken to identify any new occurrences of exposure or infection.

Comparison of PCR Methods for Onchocerca volvulus Detection in Skin Snip Biopsies from the Tshopo Province, Democratic Republic of the Congo

Defining the optimal diagnostic tools for evaluating onchocerciasis elimination efforts in areas co-endemic for other filarial nematodes is imperative. This study compared three published polymerase chain reaction (PCR) methods: the Onchocerca volvulus-specific qPCR-O150, the pan-filarial qPCR melt curve analysis (MCA), and the O150-PCR enzyme-linked immunosorbent assay (ELISA) currently used for vector surveillance in skin snip biopsies (skin snips) collected from the Democratic Republic of the Congo. The pan-filarial qPCR-MCA was compared with species-specific qPCRs for Loa loa and Mansonella perstans. Among the 471 skin snips, 47.5%, 43.5%, and 27.0% were O. volvulus positive by qPCR-O150, qPCR-MCA, and O150-PCR ELISA, respectively. Using qPCR-O150 as the comparator, the sensitivity and specificity of qPCR-MCA were 89.3% and 98.0%, respectively, whereas for O150-PCR ELISA, they were 56.7% and 100%, respectively. Although qPCR-MCA identified the presence of L. loa and Mansonella spp. in skin snips, species-specific qPCRs had greater sensitivity and were needed to identify M. perstans. Most of the qPCR-MCA misclassifications occurred in mixed infections. The reduced sensitivity of O150-PCR ELISA was associated with lower microfilaria burden and with lower amounts of O. volvulus DNA. Although qPCR-MCA identified most of the O. volvulus-positive skin snips, it is not sufficiently robust to be used for stop-mass drug administration (MDA) evaluations in areas co-endemic for other filariae. Because O150-PCR ELISA missed 43.3% of qPCR-O150-positive skin snips, the qPCR-O150 assay is more appropriate for evaluating skin snips of OV-16 + children in stop-MDA assessments. Although improving the sensitivity of the O150-PCR ELISA as an alternative to qPCR might be possible, qPCR-O150 offers distinct advantages aside from increased sensitivity.

Diagnostics for onchocerciasis in the era of elimination

In the past few years, efforts to eliminate onchocerciasis from Africa have intensified. These efforts are primarily based on the mass distribution of the anti-helminthic drug Mectizan™ (ivermectin). This program has led to the development of new guidelines by the World Health Organization for the verification that transmission has been suppressed and eventually eliminated. The requirements of diagnostic tools for this purpose differ in many ways from tests used to diagnose infection in individuals. In this review, we summarize the progress that has been made to identify diagnostics that meet the specialized requirements needed to verify onchocerciasis elimination, discuss why these tests were selected and summarize the needs that still exist to complete the arsenal of diagnostic tools that will be useful as the goal of elimination is achieved.

O-5S quantitative real-time PCR: a new diagnostic tool for laboratory confirmation of human onchocerciasis

Background

Onchocerciasis is a parasitic disease caused by the filarial nematode Onchocerca volvulus. In endemic areas, the diagnosis is commonly confirmed by microscopic examination of skin snip samples, though this technique is considered to have low sensitivity. The available melting-curve based quantitative real-time PCR (qPCR) using degenerated primers targeting the O-150 repeat of O. volvulus was considered insufficient for confirming the individual diagnosis, especially in elimination studies. This study aimed to improve detection of O. volvulus DNA in clinical samples through the development of a highly sensitive qPCR assay.

Methods

A novel hydrolysis probe based qPCR assay was designed targeting the specific sequence of the O. volvulus O-5S rRNA gene. A total of 200 clinically suspected onchocerciasis cases were included from Goma district in South-west Ethiopia, from October 2012 through May 2013. Skin snip samples were collected and subjected to microscopy, O-150 qPCR, and the novel O-5S qPCR.

Results

Among the 200 individuals, 133 patients tested positive (positivity rate of 66.5%) and 67 negative by O-5S qPCR, 74 tested positive by microscopy (37.0%) and 78 tested positive by O-150 qPCR (39.0%). Among the 133 O-5S qPCR positive individuals, microscopy and O-150 qPCR detected 55.6 and 59.4% patients, respectively, implying a higher sensitivity of O-5S qPCR than microscopy and O-150 qPCR. None of the 67 individuals who tested negative by O-5S qPCR tested positive by microscopy or O-150 qPCR, implying 100% specificity of the newly designed O-5S qPCR assay.

Conclusions

The novel O-5S qPCR assay is more sensitive than both microscopic examination and the existing O-150 qPCR for the detection of O. volvulus from skin snip samples. The newly designed assay is an important step towards appropriate individual diagnosis and control of onchocerciasis.

Electronic supplementary material

The online version of this article (10.1186/s13071-017-2382-3) contains supplementary material, which is available to authorized users.

The Current Status of Molecular Xenomonitoring for Lymphatic Filariasis and Onchocerciasis

The capacity of vector insect surveillance to provide estimates of pathogen prevalence and transmission potential has long been recognized within the global communities tasked with eliminating lymphatic filariasis (LF), the underlying cause of elephantiasis and hydrocele, and onchocerciasis (river blindness). Initially restricted to the practice of dissection, the potential of vector monitoring has grown due to the advent of molecular methods capable of increasing the sensitivity and throughput of testing. However, despite such advancement, operational research gaps remain. If insufficiently addressed, these gaps will reduce the utility of molecular xenomonitoring (MX) for onchocerciasis as elimination efforts expand into Africa. Similarly, such shortcomings will limit the programmatic usefulness of MX for LF, resulting in this technique's significant underutilization.

Characterizing Reactivity to Onchocerca volvulus Antigens in Multiplex Bead Assays

Multiplex bead assays (MBAs) may provide a powerful integrated tool for monitoring, evaluation, and post-elimination surveillance of onchocerciasis and co-endemic diseases; however, the specificity and sensitivity of Onchocerca volvulus antigens have not been characterized within this context. An MBA was developed to evaluate three antigens (OV-16, OV-17, and OV-33) for onchocerciasis. Receiver operating characteristics (ROC) analyses were used to characterize antigen performance using a panel of 610 specimens: 109 O. volvulus-positive specimens, 426 non-onchocerciasis controls with filarial and other confirmed parasitic infection, and 75 sera from patients with no other parasitic infection. The IgG and IgG4 assays for OV-16 demonstrated sensitivities of 95.4% and 96.3%, and specificities of 99.4% and 99.8%, respectively. The OV-17 IgG and IgG4 assays had sensitivities of 86.2% and 76.1% and specificities of 79.2% and 82.8%. For OV-33, the IgG and IgG4 assays had sensitivities of 90.8% and 96.3%, and specificities of 96.8% and 98.6%. The OV-16 IgG4-based MBA had the best assay characteristics, followed by OV-33 IgG4. The OV-16 IgG4 assay would be useful for monitoring and evaluation using the MBA platform. Further evaluations are needed to review the potential use of OV-33 as a confirmatory test in the context of program evaluations.

Pre-control relationship of onchocercal skin disease with onchocercal infection in Guinea Savanna, Northern Nigeria

Background

Onchocerca volvulus infection can result in blindness, itching and skin lesions. Previous research concentrated on blindness.

Methods

A clinical classification system of the cutaneous changes in onchocerciasis was used for the first time in this study within the context of an early ivermectin drug trial in the savanna region of Kaduna State, northern Nigeria. Skin examinations were performed in 6,790 individuals aged 5+ years in endemic communities and 1,343 individuals in nonendemic communities.

Results / Discussion

There was increased risk for all forms of onchocercal skin disease in endemic communities with the most common finding being the presence of nodules (1,438 individuals, 21.2%), followed by atrophy (367, 6.1% of those < 50 years), acute papular onchodermatitis, APOD (233, 3.4%), depigmentation (216, 3.2%) and chronic papular onchodermatitis, CPOD (155, 2.3%). A further 645 individuals (9.5%) complained of pruritus but had completely normal skin. APOD was more common in males whereas atrophy, hanging groin and nodules were more common in females. After controlling for age and sex, microfilarial positivity was a risk factor for CPOD, depigmentation, hanging groin and nodules (OR 1.54, p = 0.046; OR 2.29, p = 0.002; OR 2.18, p = 0.002 and OR 3.80, p <0.001 respectively). Comparable results were found using presence of nodules as the marker for infection. Microfilarial load showed similar, though weaker, results. A total of 2621(38.6%) endemic residents had itching with normal skin, or had one or more types of onchocercal skin disease including nodules, which may be considered as a composite index of the overall prevalence of onchocercal skin disease.

Conclusion

Significant levels of onchocercal skin disease were documented in this savanna area, which subsequently resulted in a reassessment of the true burden of skin disease in onchocerciasis. This paper represents the first detailed report of the association of onchocercal skin disease with markers for onchocercal infection.

Onchocerciasis is a tropical parasitic infection caused by the nematode worm Onchocerca volvulus. The disease mainly occurs across tropical Africa and infection can result in blindness, debilitating itching and a variety of skin changes. Initial research concentrated mainly on the problem of blindness. A number of studies on onchocercal skin disease were performed but were difficult to interpret and compare because of the use of inconsistent terminology. Within the setting of one of the early trials of ivermectin in a savanna area of northern Nigeria, where there were known high rates of onchocercal blindness, we used a novel clinical classification of the skin changes in onchocerciasis. We identified significant levels of itching and various forms of onchocercal skin disease within these endemic communities. A positive skin-snip result proved to be a significant risk factor for the presence of chronic papular onchodermatitis (CPOD), depigmentation, hanging groin and onchocercal nodules. Comparable results were found when the presence of nodules was used as the marker for infection and similar, though weaker odds ratios were found with microfilarial load per se. The findings triggered a reassessment of the true burden of skin disease in onchocerciasis. It is the first detailed report of the association between onchocercal skin disease and markers of infection.

An isothermal DNA amplification method for detection of Onchocerca volvulus infection in skin biopsies

Background

Diagnostic procedures for the diagnosis of infection with the nematode parasite Onchocerca volvulus are currently based on the microscopic detection of microfilariae in skin biopsies. Alternative approaches based on amplification of parasitic DNA in these skin biopsies are currently being explored. Mostly this is based on the detection of the O-150 repeat sequence using PCR based techniques.

Methods

An isothermal, loop-mediated amplification method has been designed using the mitochondrial O. volvulus cox1 gene as a target.

Results

Analysis of dilution series of synthetic DNA containing the targeted sequence show a non-linear dose-response curve, as is usually the case for isothermal amplification methods. Evaluation of cross-reactivity with the heterologous sequence from the closely related parasites Wuchereria bancrofti, Loa loa and Brugia malayi demonstrated strong specificity, as none of these sequences was amplified. The assay however amplified both O. volvulus and O. ochengi DNA, but with a different melting point that can be used to discriminate between the species. Evaluation of this assay in a set of skin snip biopsies collected in an endemic area in Ghana showed a high correlation with O-150 qPCR and also demonstrated a similar sensitivity. Compared to qPCR, LAMP had a sensitivity of 88.2% and a specificity of 99.2%.

Conclusions

We have developed a sensitive and specific loop-mediated amplification method for detection of O. volvulus DNA in skin biopsies that is capable of providing results within 30 min.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1913-7) contains supplementary material, which is available to authorized users.

Evaluation of onchocerciasis seroprevalence in Bioko Island (Equatorial Guinea) after years of disease control programmes

BACKGROUND

Onchocerciasis or "river blindness" is a chronic parasitic disease caused by the filarial worm Onchocerca volvulus, transmitted through infected blackflies (Simulium spp.). Bioko Island (Equatorial Guinea) used to show a high endemicity for onchocerciasis. During the last years, the disease control programmes using different larvicides and ivermectin administration have considerably reduced the prevalence and intensity of infection. Based on this new epidemiological scenario, in the present work we aimed to assess the impact of the strategies applied against onchocerciasis in Bioko Island by an evaluation of IgG4 antibodies specific for recombinant Ov-16 in ELISA.

METHODS

A cross-sectional study was conducted in Bioko Island from mid-January to mid-February, 2014. Twenty communities were randomly selected from rural and urban settings. A total of 140 households were chosen. In every selected household, all individuals aged 5 years and above were recruited; 544 study participants agreed to be part of this work. No previous data on onchocerciasis seroprevalence in the selected communities were available. Blood samples were collected and used in an "ELISA in-house" prepared with recombinant Ov-16, expressed and further purified. IgG4 antibodies specific for recombinant Ov-16 were evaluated by ELISA in all of the participants.

RESULTS

Based on the Ov-16 ELISA, the onchocerciasis seroprevalence was 7.9 %, mainly concentrated in rural settings; samples from community Catedral Ela Nguema (# 16) were missed during the field work. Among the rural setups, communities Inasa Maule (# 7), Ruiché (# 20) and Barrios Adyacentes Riaba (# 14), had the highest seropositivity percentages (29.2, 26.9 and 23.8 %, respectively). With respect to the urban settings, we did not find any positive case in communities Manzana Casa Bola (# 3), Colas Sesgas (# 6), Getesa (# 8), Moka Bioko (# 9), Impecsa (# 10), Baney Zona Baja (# 12) and Santo Tomás de Aquino (# 1). No onchocerciasis seropositive samples were found in 10-year-old individuals or younger. The IgG4 positive titles increased in older participants.

CONCLUSIONS

A significant decline in onchocerciasis prevalence was observed in Bioko Island after years of disease-vector control and CDTI strategy. The seroprevalence increased with age, mainly in rural settings that could be due to previous exposure of population to the filarial parasite, eliminated by the control programmes introduced against onchocerciasis. A new Ov-16 serological evaluation with a larger sample size of children below 10 years of age is required to demonstrate the interruption of transmission of O. volvulus in the human population of Bioko Island (Equatorial Guinea) according to the WHO criteria.

Comparison of a new visual isothermal nucleic acid amplification test with PCR and skin snip analysis for diagnosis of onchocerciasis in humans

Accurate, simple and affordable diagnostics are needed to detect Onchocerca volvulus infection in humans. A newly developed colorimetric loop-mediated isothermal amplification (LAMP) assay was compared to PCR and skin snip analysis for diagnosis of onchocerciasis. The robustness and simplicity of the assay indicates that it may be a useful field tool for surveillance in endemic countries.

Evidence for Suppression of Onchocerciasis Transmission in Bioko Island, Equatorial Guinea

Onchocerciasis or "river blindness" is a chronic parasitic neglected tropical disease which is endemic both in mainland and insular Equatorial Guinea. We aim to estimate the current epidemiological situation of onchocerciasis in Bioko Island after vector elimination in 2005 and more than sixteen years of Community Directed Treatment with Ivermectin (CDTI) by using molecular and serological approaches for onchocerciasis diagnosis. A community-based cross-sectional study was carried out in Bioko Island from mid-January to mid-February 2014. A total of 544 study participants were recruited. A complete dermatological examination was performed and three skin snips were performed in every participant for parasitological and molecular assessments. Blood spots were also taken for determination of Ov16 IgG4 antibodies trough an “in-house” ELISA assay. Overall, we found 15 out of 522 individuals suffering any onchocerciasis specific cutaneous lesions and 16 out of 528 (3.0%) with onchocercal nodules in the skin. Nodules were significantly associated with age, being more common in subjects older than 10 years than in younger people (3.9% vs. 0%, p = 0.029). Regarding the onchocerciasis laboratory assessment, no positive parasitological test for microfilaria detection was found in the skin snips. The calculated seroprevalence through IgG4 serology was 7.9%. No children less than 10 years old were found to be positive for this test. Only one case was positive for Onchocerca volvulus (O. volvulus) after skin PCR. The present study points out that the on-going mass ivermectin treatment has been effective in reducing the prevalence of onchocerciasis and corroborates the interruption of transmission in Bioko Island. To our knowledge, this is the first time that accurate information through molecular and serological techniques is generated to estimate the onchocerciasis prevalence in this zone. Sustained support from the national program and appropriate communication and health education strategies to reinforce participation in CDTI activities are essential to ensure progress towards onchocerciasis elimination in the country.

Onchocerciasis or “river blindness” is a chronic parasitic disease which is mainly found in Sub-Saharan Africa. Onchocerciasis is endemic in both mainland and insular Equatorial Guinea. Huge achievements have been made on onchocerciasis control in Bioko Island in the last years, and the country is moving fast towards elimination. In the new elimination context, monitoring and evaluation activities with more sensitive diagnostic tools become especially necessary in order to confirm that transmission has been interrupted. Previous data on the epidemiological situation of onchocerciasis in Bioko Island are mainly based on microfilaria (MF) skin snip assessments. We aim to create evidence towards the fact that onchocerciasis transmission might have been achieved in Bioko Island after more than sixteen years of onchocerciasis control activities by using molecular and serological technics for onchocerciasis diagnosis.

Analysis of age-dependent trends in Ov16 IgG4 seroprevalence to onchocerciasis

Background

Diagnostics provide a means to measure progress toward disease elimination. Many countries in Africa are approaching elimination of onchocerciasis after successful implementation of mass drug administration programs as well as vector control. An understanding of how markers for infection such as skin snip microfilaria and Onchocerca volvulus-specific seroconversion perform in near-elimination settings informs how to best use these markers.

Methods

All-age participants from 35 villages in Togo were surveyed in 2013 and 2014 for skin snip Onchocerca volvulus microfilaria and IgG4 antibody response by enzyme-linked immunosorbent assay (ELISA) to the Onchocerca volvulus-specific antigen Ov16. A Gaussian mixture model applying the expectation-maximization (EM) algorithm was used to determine seropositivity from Ov16 ELISA data. For a subset of participants (n = 434), polymerase chain reaction (PCR) was performed on the skin snips taken during surveillance.

Results

Within the 2,005 participants for which there was Ov16 ELISA data, O. volvulus microfilaremia prevalence and Ov16 seroprevalence were, 2.5 and 19.7 %, respectively, in the total population, and 1.6 and 3.6 % in children under 11. In the subset of 434 specimens for which ELISA, PCR, and microscopy data were generated, it was found that in children under 11 years of age, the anti-Ov16 IgG4 antibody response demonstrate a sensitivity and specificity of 80 and 97 %, respectively, against active infections as determined by combined PCR and microscopy on skin snips. Further analysis was performed in 34 of the 35 villages surveyed. These villages were stratified by all-age seroprevalence into three clusters: < 15 %; 15–20 %; and > 20 %. Age-dependence of seroprevalence for each cluster was best reflected by a two-phase force-of-infection (FOI) catalytic model. In all clusters, the lower of the two phases of FOI was associated with a younger age group, as reflected by the seroconversion rates for each phase. The age at which transition from lower to higher seroconversion, between the two phases of FOI, was found to be highest (older) for the cluster of villages with < 15 % seroprevalence and lowest (younger) for the cluster with the highest all-age seroprevalence.

Conclusions

The anti-Ov16 IgG4 antibody response is an accurate marker for active infection in children under 11 years of age in this population. Applying Ov16 surveillance to a broader age range provides additional valuable information for understanding progression toward elimination and can inform where targeted augmented interventions may be needed. Clustering of villages by all-age sero-surveillance allowed application of a biphasic FOI model to differentiate seroconversion rates for different age groups within the village cluster categories.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1623-1) contains supplementary material, which is available to authorized users.

Onchocerciasis, an undiagnosed disease in Mozambique: identifying research opportunities

BACKGROUND

The objective of this paper is to summarise and critically review the available data about onchocerciasis in Mozambique, in order to report epidemiological and clinical aspects related to the disease and identify gaps in knowledge. The paper is intended to raise awareness of the existence and importance of this disease and to define research priorities.

METHODS

We examined the scarce epidemiological data at our disposal: two diagnostic studies in 1997 and 1998 (first reports on the existence of onchocerciasis in Mozambique), and two Rapid Epidemiological Mapping of Onchocerciasis (REMO) surveys in 2001 and 2007. We examined differences in study designs and methodologies as well as the differing geographical locations to explain the divergence in findings among the studies.

RESULTS

Evidence indicates that onchocerciasis is hypoendemic in Mozambique (with national and imported cases), but still largely remains an undiagnosed illness. There is no awareness of the clinical aspects of the disease and nor of the differential diagnosis with lepromatous leprosy and dermatitis caused by Scabies spp. The use of skin biopsy and a symptom screening questionnaire, combined with nodule rate, in the first two studies may have captured even atypical or subacute presentations. Both REMO surveys relied solely on nodule detection and in the six years between the two studies, the prevalence of nodules detected more than doubled.

CONCLUSIONS

The epidemiology and clinical aspects of the disease are unknown in Mozambique. Since the last REMO took place in 2007 and since the population is subject to large-scale movement and displacement, it is important to develop tools to identify and analyse populations that are at high risk for onchocerciasis. Cases of onchocerciasis may be misdiagnosed as leprosy or scabies that fail to improve despite being subjected to treatment against leprosy. Techniques to enable a differential diagnosis need to be established by training health professionals on the recognition of this undiagnosed disease. It is equally necessary to identify the blackfly vectors and where they breed.

Detection of Onchocerca volvulus in Skin Snips by Microscopy and Real-Time Polymerase Chain Reaction: Implications for Monitoring and Evaluation Activities

Microscopic evaluation of skin biopsies is the monitoring and evaluation (M and E) method currently used by multiple onchocerciasis elimination programs in Africa. However, as repeated mass drug administration suppresses microfilarial loads, the sensitivity and programmatic utility of skin snip microscopy is expected to decrease. Using a pan-filarial real-time polymerase chain reaction with melt curve analysis (qPCR-MCA), we evaluated 1) the use of a single-step molecular assay for detecting and identifying Onchocerca volvulus microfilariae in residual skin snips and 2) the sensitivity of skin snip microscopy relative to qPCR-MCA. Skin snips were collected and examined with routine microscopy in hyperendemic regions of Uganda and Ethiopia (N= 500 each) and "residual" skin snips (tissue remaining after induced microfilarial emergence) were tested with qPCR-MCA. qPCR-MCA detected Onchocerca DNA in 223 residual snips: 139 of 147 microscopy(+) and 84 among microscopy(-) snips, suggesting overall sensitivity of microscopy was 62.3% (139/223) relative to qPCR-MCA (75.6% in Uganda and 28.6% in Ethiopia). These findings demonstrate the insufficient sensitivity of skin snip microscopy for reliable programmatic monitoring. Molecular tools such as qPCR-MCA can augment sensitivity and provide diagnostic confirmation of skin biopsies and will be useful for evaluation or validation of new onchocerciasis M and E tools.

River Blindness: Mathematical Models for Control and Elimination

Human onchocerciasis (river blindness) is one of the few neglected tropical diseases (NTDs) whose control strategies have been informed by mathematical modelling. With the change in focus from elimination of the disease burden to elimination of Onchocerca volvulus, much remains to be done to refine, calibrate and validate existing models. Under the impetus of the NTD Modelling Consortium, the teams that developed EPIONCHO and ONCHOSIM have joined forces to compare and improve these frameworks to better assist ongoing elimination efforts. We review their current versions and describe how they are being used to address two key questions: (1) where can onchocerciasis be eliminated with current intervention strategies by 2020/2025? and (2) what alternative/complementary strategies could help to accelerate elimination where (1) cannot be achieved? The control and elimination of onchocerciasis from the African continent is at a crucial crossroad. The African Programme for Onchocerciasis Control closed at the end of 2015, and although a new platform for support and integration of NTD control has been launched, the disease will have to compete with a myriad of other national health priorities at a pivotal time in the road to elimination. However, never before had onchocerciasis control a better arsenal of intervention strategies as well as diagnostics. It is, therefore, timely to present two models of different geneses and modelling traditions as they come together to produce robust decision-support tools. We start by describing the structural and parametric assumptions of EPIONCHO and ONCHOSIM; we continue by summarizing the modelling of current treatment strategies with annual (or biannual) mass ivermectin distribution and introduce a number of alternative strategies, including other microfilaricidal therapies (such as moxidectin), macrofilaricidal (anti-wolbachial) treatments, focal vector control and the possibility of an onchocerciasis vaccine. We conclude by discussing challenges, opportunities and future directions.

Diagnostic Tools for Onchocerciasis Elimination Programs

Onchocerciasis (river blindness) is a major public health problem in sub-Saharan Africa. Major disease-control programs have greatly reduced both disease and infection prevalence by mass distribution of donated ivermectin. Recent studies have shown that local elimination was achieved in some areas following many years of ivermectin. The global health community has recently decided to build on these successes with a new program that aims to eliminate onchocerciasis. Diagnostic tests that were useful for identifying priority areas for disease prevention may not be adequate tools for elimination programs. This paper reviews available and emerging diagnostic tests for onchocerciasis and considers how they might be best employed during different stages of onchocerciasis elimination programs.

Monitoring the efficacy of drugs for neglected tropical diseases controlled by preventive chemotherapy

In the last decade, pharmaceutical companies, governments and global health organisations under the leadership of the World Health Organization (WHO) have pledged large-scale donations of anthelmintic drugs, including ivermectin (IVM), praziquantel (PZQ), albendazole (ALB) and mebendazole (MEB). This worldwide scale-up in drug donations calls for strong monitoring systems to detect any changes in anthelmintic drug efficacy. This review reports on the outcome of the WHO Global Working Group on Monitoring of Neglected Tropical Diseases Drug Efficacy, which consists of three subgroups: (i) soil-transmitted helminthiases (ALB and MEB); (ii) onchocerciasis and lymphatic filariasis (IVM); and (iii) schistosomiasis (PZQ). Progress of ongoing work, challenges and research needs for each of the four main drugs used in helminthic preventive chemotherapy (PC) are reported, laying the ground for appropriate implementation of drug efficacy monitoring programmes under the co-ordination and guidelines of the WHO. Best practices for monitoring drug efficacy should be made available and capacity built as an integral part of neglected tropical disease (NTD) programme monitoring. Development of a disease-specific model to predict the impact of PC programmes, to detect outliers and to solicit responses is essential. Research studies on genetic polymorphisms in relation to low-efficacy phenotypes should be carried out to identify markers of putative resistance against all NTD drugs and ultimately to develop diagnostic assays. Development of combination and co-administration of NTD drugs as well as of new drug entities to boost the armamentarium of the few drugs available for NTD control and elimination should be pursued in parallel.