Real-time PCR for detection of Strongyloides stercoralis in human stool samples from Côte d'Ivoire: diagnostic accuracy, inter-laboratory comparison and patterns of hookworm co-infection

'A comparative study of traditional and molecular diagnostic methods for detection of gastrointestinal parasites in Nepalese migrants to the UK'

BACKGROUND

We evaluated the results of examining a single faecal sample for gastrointestinal parasites (GIP) using a combination of traditional methods with multiplex qPCR for helminths and protozoa, compared to a reference standard of examining three faecal samples from each person using traditional diagnostic methods alone.

METHODS

Three faecal samples were collected at weekly intervals from 596 healthy Nepalese men. Each sample underwent formalin-ethyl acetate (FEA) concentration and light microscopy, and charcoal culture. The combined results of these investigations for all three stool samples were designated the reference standard. The first sample was also analysed using a multiplex TaqManTM qPCR assay, screening for five helminths and three protozoa. We compared sensitivity and specificity of analysing the first faecal sample with qPCR alone, or a hybrid approach combining qPCR with traditional methods, to the reference standard. Additionally, a serum sample was taken from each participant for Strongyloides stercoralis IgG ELISA.

RESULTS

The reference standard identified 139 GIP infections in 133 (22.3%) participants. Use of qPCR alone in one stool identified 176 infections in 147 (24.8%) participants, rising to 187 infections in 156 (26.3%) when combined with FEA microscopy and charcoal culture. The sensitivity of this latter hybrid approach was 100% for Strongyloides spp., 90.9% for Trichuris trichiura, 86.8% for hookworm species and 75% for Giardia duodenalis compared to the reference standard. The hybrid approach increased the detected cases of G. duodenalis by 4.5% (46 cases) overall, T. trichiura by 2.9% (18 cases), Strongyloides spp. by 1% (6 cases), and hookworm by 0.5% (8 cases), compared to the reference standard.

CONCLUSION

Examination of a single faecal sample using qPCR alone showed superior or equivalent sensitivity to traditional methods for most GIP infections when both were compared to the reference standard. Combining molecular and traditional methods to analyse a single stool improved the detection rate for most studied parasites. This approach has value in settings where repeated sampling and/or faecal culture for helminths is impractical, but molecular diagnostics are available.

Effectiveness of one and two doses of ivermectin mass drug administration in reducing the prevalence and intensity of soil-transmitted helminth (STH) infections in Western Province, Solomon Islands: a cluster-randomised, before-after analysis

Background

Ivermectin mass drug administration (MDA) is effective for controlling onchocerciasis and scabies, with evidence supporting its role in some species of soil-transmitted helminth (STH) infections. In the context of RISE, a cluster-randomised trial for scabies, this study evaluated the effectiveness of ivermectin MDA in reducing STH burden in the Western Province of Solomon Islands.

Methods

Twenty villages were randomised 1:1 to receive ivermectin MDA as one dose (IVM-1) or two doses (IVM-2) for scabies. The effectiveness of one and two doses in reducing STH prevalence and intensity was evaluated before (May 2019) and 21 months after (February 2021) MDA in May 2019. All residents aged 12 months or older in the study villages were eligible to participate and provide stool specimens. Species-specific STH infection and intensity were assessed using quantitative PCR. We compared prevalence and intensity of infection between baseline and 21 months in each intervention arm individually using cluster-level analysis (adjusted for clustering) and individual-level analysis (adjusted for sex, age, and clustering). The primary outcomes were the prevalence risk difference (RD) from the cluster-level analysis, and the change in adjusted odds of infection from the individual-level analysis. Secondary outcomes included change in incident rates of mean eggs per gram (epg) of stool from baseline to 21 months, relative risk difference in prevalence and relative change in odds of infection between arms at 21 months. Sex data (male/female) were self-reported.

Findings

Overall, STH infection was assessed in 830 participants from 18 villages at baseline and 1172 from 20 villages at follow-up. Females represented 58% (n = 478) of the sample at baseline and 59% (n = 690) at follow-up. We observed a reduction in Strongyloides spp. prevalence following two doses of ivermectin MDA in the cluster-level analysis from 7.0% (32/458 participants) to 1.2% (8/674 participants), corresponding to a RD of -0.07 (95% CI -0.14 to -0.01, p = 0.036), and in the individual-level analysis (OR 0.11, 95% CI 0.04-0.33, p < 0.001). T. trichiura prevalence decreased following one dose from 19.4% (74/372 participants) to 11.7% (56/505 participants) (OR 0.44, 95% CI 0.26-0.73, p = 0.0040), while egg count reduced in both arms (IVM-1: IRR 0.28, 95% CI 0.11-0.70, p = 0.0070; IVM-2: IRR 0.18, 95% CI 0.08-0.40, p < 0.001), in the individual-level analysis. We did not detect a significant difference in effect measures between the one- and two-dose arms for any species after 21 months.

Interpretation

Our study highlights the long-term benefits of ivermectin MDA in reducing the burden of Strongyloides spp. and T. trichiura. STH control programs should leverage the geographical overlap of NTDs, existing drug distribution channels, and broad-spectrum agents.

Funding

The National Health and Medical Research Council of Australia.

Identification and treatment of Strongyloides stercoralis infection in a Boston Terrier dog from south-eastern Australia

Strongyloides stercoralis, the causative agent of strongyloidiasis, is a potentially zoonotic intestinal nematode endemic to northern Australia. Strongyloidiasis is typically observed in immunocompromised hosts and is characterised by gastrointestinal signs, respiratory symptoms and a failure to thrive. In immunocompromised hosts, hyperinfection syndrome and disseminated infections can prove life-threatening. A 24-month-old Boston Terrier dog was referred for investigation of chronic small and large intestinal watery hematochezic diarrhoea, emaciation and hematemesis. Small intestinal histology identified a nematode despite consecutive negative faecal flotations. A real-time polymerase chain reaction and Baermann test subsequently confirmed infection with S. stercoralis. The dog had received an oral parasiticide comprising milbemycin oxime and afoxolaner every month for the 11 months prior to this diagnosis. Despite fenbendazole being reported as successful in the treatment of canine strongyloidiasis, a course of fenbendazole failed to clear the infection. Eradication of S. stercoralis infection was confirmed after the administration of off-label ivermectin fortnightly for 12 doses. Attention should be paid to this nematode as the failure of routine copromicroscopic methods to diagnose S. stercoralis infections can result in misdiagnosis, mistreatment and progression of the disease. Off-label ivermectin may be an alternative to fenbendazole for the treatment of Strongyloides spp. infection in dogs.

Strongyloidiasis in humans and dogs in Southern Italy: an observational study

Strongyloidiasis is a clinical issue both in humans and in dogs. Moreover, there are concerns about its zoonotic potential. We aimed to explore Strongyloides stercoralis epidemiology in Southern Italy in humans and dogs sharing the same environment in three different settings: (1) kennels (group K); (2) livestock farms (group L) and (3) agricultural farms (group A). For humans, a commercial ELISA test was used for screening. RT-PCR on faecal samples was done for people testing positive or equivocal at serology. On dog's faecal samples, Baermann test and RT-PCR were performed. A total of 145 dogs and 139 persons were tested. Based on faecal tests in dogs and serology in humans, a S. stercoralis positivity of 4.1% and 6.5% was revealed, respectively. The sites where cases were found were different for animals and humans. In dogs the highest positivity was in group K (6.7% against 2% and 0% in L and A). Differently, in humans the proportion of positive results was similar between the groups (p = 0.883). Fifty percent (3/6) of positive dogs were healthy; the other dogs presented weight loss and/or diarrhoea. ELISA-positive persons (n=9) were all in health, but abdominal pain (37.5%), urticaria (22.2%) and asthma (22.2%) were reported, resolving after treatment with oral ivermectin 200 μg/kg. RT-PCR performed on 13 human faecal samples resulted negative. These findings suggest that strongyloidiasis is present in humans and dogs in Southern Italy, and screening in larger cohorts would be needed for more accurate estimates.

Strongyloides infection screening in transplant candidates: What is the best strategy?

BACKGROUND

The potential that Strongyloides stercoralis infection has to cause major morbidity and high mortality when the disseminated form occurs in transplant patients is of particular concern.

METHODS

In this study, the objective was to observe S. stercoralis infection in patients who are candidates for transplantation by using parasitological, serological, and molecular techniques and to propose an algorithm for the detection of that infection in transplant candidates.

RESULTS

By parasitological techniques, 10% of fecal samples were positive. Anti-Strongyloides antibodies immunoglobulin G were detected in 19.3% and 20.7% of patients by immunofluorescence assay and enzyme-linked immunosorbent assay, respectively. S. stercoralis DNA was observed in 17.3% of samples by conventional polymerase chain reaction and 32.7% of samples by quantitative polymerase chain reaction (qPCR).

CONCLUSION

The set of results allows us to reinforce that a positive result by parasitological techniques and/or qPCR indicates that the specific treatment should be applied. However, the improvement of diagnostic techniques may suggest changes in the screening for strongyloidiasis in these patients.

From past to present: opportunities and trends in the molecular detection and diagnosis of Strongyloides stercoralis

Strongyloides stercoralis is a soil-transmitted helminth that is mainly found in the tropical and subtropical regions and affects approximately 600 million people globally. The medical importance of strongyloidiasis lies in its capacity to remain asymptomatic and chronically unnoticed until the host is immunocompromised. Additionally, in severe strongyloidiasis, hyperinfection syndrome and larva dissemination to various organs can occur. Parasitological techniques such as Baermann-Moraes and agar plate culture to detect larvae in stool samples are the current gold standard. However, the sensitivity might be inadequate, especially with reduced worm burden. Complementing parasitological techniques, immunological techniques including immunoblot and immunosorbent assays are employed, with higher sensitivity. However, cross-reactivity to other parasites may occur, hampering the assay's specificity. Recently, advances in molecular techniques such as polymerase chain reaction and next-generation sequencing technology have provided the opportunity to detect parasite DNA in stool, blood, and environmental samples. Molecular techniques, known for their high sensitivity and specificity, have the potential to circumvent some of the challenges associated with chronicity and intermittent larval output for increased detection. Here, as S. stercoralis was recently included by the World Health Organization as another soil-transmitted helminth targeted for control from 2021 to 2030, we aimed to present a review of the current molecular techniques for detecting and diagnosing S. stercoralis in a bid to consolidate the molecular studies that have been performed. Upcoming molecular trends, especially next-generation sequencing technologies, are also discussed to increase the awareness of its potential for diagnosis and detection. Improved and novel detection methods can aid in making accurate and informed choices, especially in this era where infectious and non-infectious diseases are increasingly commonplace.

Seroprevalence of Strongyloides stercolaris in Patients about to Receive Immunosuppressive Treatment in Gran Canaria (Spain)

Strongyloides stercoralis infection is generally asymptomatic or mildly symptomatic, but in the immunosuppressed host, it is associated with more severe and complicated forms with a worse prognosis. S. stercoralis seroprevalence was studied in 256 patients before receiving immunosuppressive treatment (before kidney transplantation or starting biological treatments). As a control group, serum bank data of 642 individuals representative of the population of the Canary Islands were retrospectively analyzed. To avoid false positives due to cross-reactivity with other similar helminth antigens present in the study area, IgG antibodies to Toxocara spp. and Echinococcus spp. were evaluated in cases positive for Strongyloides. The data show this is a prevalent infection: 1.1% of the Canarian population, 2.38% of Canarian individuals awaiting organ transplants and 4.8% of individuals about to start biological agents. On the other hand, strongyloidiasis can remain asymptomatic (as observed in our study population). There are no indirect data, such as country of origin or eosinophilia, to help raise suspicion of the disease. In summary, our study suggests that screening for S. stercoralis infection should be performed in patients who receive immunosuppressive treatment for solid organ transplantation or biological agents, in line with previous publications.

Seroprevalence and microscopy detection rates of strongyloidiasis in Croatian patients with eosinophilia

Infection with the parasitic nematode Strongyloides stercoralis is characteristic for tropical and subtropical regions of the world, but autochthonous cases have been reported in European countries as well. Here we present the first nation-wide survey of S. stercoralis seroprevalence in Croatian individuals presenting with eosinophilia, and evaluate the fraction of positive microscopy rates in stool specimens of seropositive individuals. In our sample of 1407 patients tested between 2018 and 2021, the overall prevalence of strongyloidiasis was 9.31%, with significantly higher rates in those older than 60 years of age (P = 0.005). Of those, one-quarter (25.95%) were also positive following microscopy examination of faeces after using the merthiolate-iodine-formaldehyde concentration method. Our findings reinforce the notion of endemic strongyloidiasis transmission in Croatia, particularly in older individuals, and highlight the need to consider the presence of S. stercoralis in patients with eosinophilia.

Advantages and Limitations of Microscopy and Molecular Detections for Diagnosis of Soil-transmitted Helminths: An Overview

World Health Organization (WHO) reported that over 1.5 billion people are infected by soil-transmitted helminths (STH) worldwide in sub-Saharan Africa, the United States of America, China, and East Asia. Heavy infections and polyparasitism are associated with higher morbidity rates, and the patients are exposed to increased vulnerability to other diseases. Therefore, accurate diagnosis followed by mass treatment for morbidity control is necessary.STH diagnosis commonly involves the microscopic observation of the presence of the STH eggs and larvae in the faecal samples. Furthermore, molecular approaches are increasingly utilised in monitoring and surveillance as they show higher sensitivity. Their capability to differentiate hookworm species is an advantage over the Kato-Katz technique. This review discusses the advantages and limitations of microscopy and various molecular tools used for STH detection.

The diagnosis of human and companion animal Strongyloides stercoralis infection: Challenges and solutions. A scoping review

Strongyloidiasis is the infection caused by soil-transmitted nematodes of Strongyloides species, infecting humans and some animals. Strongyloides stercoralis is the species with most clinical and epidemiological relevance in humans and dogs, due to its high prevalence and its capacity of inducing a life-threatening hyperinfection. Diagnosis of strongyloidiasis is challenging, due to the absence of a single reference standard test with high sensitivity and specificity, which also hampers the estimation of the accuracy of other diagnostic tests. In this chapter, we review the deployment and performance of the parasitological, immunological, molecular tests for the diagnosis of strongyloidiasis in humans and in dogs. Further, we comment the available evidence from genotyping studies that have addressed the zoonotic potential of S. stercoralis. Finally, we discuss the use of different diagnostic methods in relation to the purpose (i.e., screening, individual diagnosis, inclusion in a clinical trial) and the setting (endemic/non-endemic areas) and report the accuracy figures reported by systematic reviews on either parasitological, serological or molecular techniques published in literature.

Faecal prevalence, distribution and risk factors associated with canine soil-transmitted helminths contaminating urban parks across Australia

Dog parks provide an ideal urban space where dogs and their owners can exercise, play, and socialize in a safe environment. However, these parks can also increase the risk of exposure to a series of infectious agents including canine soil-transmitted helminths (cSTHs) such as hookworms, roundworms, Strongyloides stercoralis, and Trichuris vulpis, which are endemic to Australia. In this study, we collected 1581 canine faecal samples in 190 urban parks across Australia and subjected these to faecal floatation and multiplex real-time PCRs (qPCR) to detect a range of cSTHs. In total, 44.2% of the parks sampled were contaminated with at least one species of cSTH, with hookworms being the most prevalent parasites (10.2%) followed by Trichuris spp. (1.3%) and Strongyloides spp. (1.2%). This is the first large-scale study investigating the contamination of urban parks with cSTHs in Australia, and the first nation-wide study to demonstrate the occurrence of Strongyloides spp. in canine faecal samples from urban areas in the country. This study reveals a high rate of contamination with cSTHs in dog parks in urban Australia, most of which having proven zoonotic potential. Preventive measures, including awareness-raising educational programs promoting responsible pet ownership, should be encouraged to minimise the health risks associated with cSTHs for both dogs and humans.

Evaluation of five diagnostic methods for Strongyloides stercoralis infection in Amhara National Regional State, northwest Ethiopia

Background

Strongyloides stercoralis is an intestinal parasite that can cause chronic infection, hyperinfection and/or a dissemination syndrome in humans. The use of techniques targeting ova fails to detect S. stercoralis, as only larvae of the parasite are excreted in faeces. Due to the absence of “Gold” standard diagnostic method for S. stercoralis, there is a paucity of reported data worldwide.

Objective

This study aimed to evaluate the performance of diagnostic methods of S. stercoralis infection by taking the composite reference as a “Gold” standard.

Methods

A cross-sectional study was conducted among 844 schoolchildren in Amhara Region, Ethiopia, from April to December 2019. Stool samples were collected and processed with formol-ether concentration technique (FECT), spontaneous tube sedimentation technique (STST), Baermann concentration technique (BCT), agar plate culture (APC) and real-time polymerase chain reaction (RT-PCR). Sensitivity, specificity, positive predictive value, and negative predictive value of each diagnostic method were computed against the composite reference. The agreements of diagnostic methods were evaluated by Kappa value at 95% CI.

Results

The composite detection rate of S. stercoralis by the five diagnostic methods was 39.0% (329/844). The detection rate of the parasite from stool samples by FECT, STST, BCT, APC and RT-PCR was 2.0% (17/844), 4.0% (34/844), 10.2% (86/844), 10.9% (92/844) and 28.8% (243/844), respectively. The highest detection rate (37.8%; 319/844) of S. stercoralis was recorded by a combination of BCT, APC, and RT-PCR followed by a combination of STST, BCT, APC and RT-PCR (37.3%; 315/844). The sensitivity of FECT, STST, BCT, APC and RT-PCR against the composite reference was 5.2%, 10.3%, 26.4%, 28.0% and 73.9%, respectively. The diagnostic agreements of RT-PCR, APC, BCT, STST and FECT with the composite reference in detection of S. stercoralis were substantial (0.775), fair (0.321), fair (0.305), slight (0.123), and slight (0.062), respectively.

Conclusion

RT-PCR detected the highest number of S. stercoralis infections. A combination of RT-PCR with APC and/or BCT better detected S. stercoralis from stool samples compared to other combinations or single diagnostic methods. Therefore, RT-PCR and combination of RT-PCR with APC and/or BCT diagnostic methods should be advocated for detection of S. stercoralis infection.

A Practical Approach to Screening for Strongyloides stercoralis

Strongyloides stercoralis, causative agent of a neglected tropical disease, is a soil-transmitted helminth which may cause lifelong persisting infection due to continuous autoinfection. In the case of immunosuppression, life-threatening hyperinfection and disseminated strongyloidiasis can develop. We propose a pragmatic screening algorithm for latent strongyloidiasis based on epidemiologic exposure and immunosuppression status that can be applied for any kind of immunosuppressive therapy. The algorithm allows the diagnosis of latent strongyloidiasis with optimal accuracy in a well-equipped setting, while for endemic settings where the complete testing array is unavailable, an empiric treatment is generally recommended. Accurate diagnosis and extensive empiric treatment will both contribute to decreasing the current neglect of strongyloidiasis.

Scope and limitations of a multiplex conventional PCR for the diagnosis of S. stercoralis and hookworms

OBJECTIVES

Describe the diagnostic characteristics of a conventional multiplex PCR for the diagnosis of S. stercoralis, N. americanus and Ancylostomas spp.

METHODS

Fecal samples were collected from a cross-sectional study in Orán department, Salta province, Argentina. The stool samples were analyzed using concentration-sedimentation, Harada Mori, McMaster, and Baermann techniques. DNA was extracted from 50 mg fecal sample using the FastPrep® Spin Kit for Soil. Three pairs of primers were used for the amplification of three products of 101, 330, and 577 base pairs (bp) for S. stercoralis, N. americanus and Ancylostoma spp, respectively. The sensitivity and analytical specificity of multiplex PCR were evaluated, as well as the sensitivity and diagnostic specificity, using a composite standard and Bayesian approach.

RESULTS AND CONCLUSIONS

Multiplex PCR did not present cross-reaction with other intestinal parasites, and the detection limit for multiplex PCR was between 2 and 20 pg of genomic DNA. In addition it presented a diagnostic sensitivity of 97.4% for S. stercoralis and 90.3% for hookworms with a specificity of 100% and 87.6%, respectively. PCR identified a higher proportion (p <0.01) of coinfections (15.3%) than microscopic techniques (3.5%). Also, multiplex PCR showed that there was a positive association between S. stercoralis and hookworms (odds ratio = 2.12). However, this association was due to N. americanus (odds ratio= 3.22), since no association was observed between S. stercoralis and Ancylostoma spp. Neither was an association observed between the two species of hookworms.

Diagnosis of human strongyloidiasis: Application in clinical practice

This review considers the advantages and disadvantages of parasitological techniques, methods of detecting antibodies and antigens, as well as molecular biology techniques in the diagnosis of human strongyloidiasis. In addition, it elucidates the potential of different techniques for rapid and effective detection of clinical cases, thus enabling early treatment and preventing fatal consequences of this helminthiasis.

Evaluation of targets for Strongyloides genus specific molecular diagnosis in experimental strongyloidiasis

Strongyloides venezuelensis has been used in different experimental studies, such as those aimed at the evaluation of diagnostic techniques for human strongyloidiasis, mainly the molecular diagnosis. In this study, three regions (genus, 18S and 28S targets) of Strongyloides ribosomal DNA were evaluated for the molecular diagnosis of experimental strongyloidiasis. Rats were infected subcutaneously with 400 or 4000 S. venezuelensis infective larvae (400iL3 and 4000iL3), and kept for 35 days. Fecal samples were collected daily to count eggs per gram of feces (EPG) and to perform the polymerase chain reaction (PCR). Egg count started on the 5th day post-infection (pi) and ended on days 33 and 34 pi, in 400iL3 and 4000iL3 groups, respectively. Based in EPG, fecal samples were selected from days 2, 5, 8, 11, 15, 23 and 35 pi for DNA extraction; PCR (genus, 18S and 28S); and sequencing. The PCR-28S products showed higher values of identity (95-100%) in the database with the Strongyloides sequences. Therefore, it is possible to reinforce the application of PCR-28S in the diagnosis of experimental and human strongyloidiasis.

Evaluation of the Allplex™ GI-Helminth(I) Assay, the first marketed multiplex PCR for helminth diagnosis

Molecular biology has been gaining more importance in parasitology. Recently, a commercial multiplex PCR assay detecting helminths was marketed: the Allplex™ GI-Helminth(I) Assay. It targets Ancylostoma spp., Ascaris spp., Enterobius vermicularis, Hymenolepis spp., Necator americanus, Strongyloides spp., Taenia spp. and Trichuris trichiura, but also the two most common microsporidia genera in human health, i.e. Enterocytozoon spp. and Encephalitozoon spp. This study aimed to evaluate and compare the Allplex™ GI-Helminth(I) Assay to classical diagnostic methods, based on a cohort of 110 stool samples positive for helminths (microscopy) or for microsporidia (PCR). Samples were stored at −80 °C until analysis by the Allplex™ GI-Helminth(I) Assay. False-negatives were re-tested with bead-beating pretreatment. Without mechanical lysis, concordance and agreement between microscopy and Allplex™ GI-Helminth(I) Assay ranged from 91% to 100% and from 0.15 to 1.00, respectively depending on the target. Concordance was perfect for Taenia spp. (n = 5) and microsporidia (n = 10). False-negative results were observed in 54% (6/13), 34% (4/11) and 20% (7/35) of cases, for hookworms, E. vermicularis and Strongyloides spp. detection, respectively. For these targets, pretreatment improved the results, but only slightly. Trichuris trichiura detection was critically low without pretreatment, as only 9% (1/11) of the samples were positive, but detection reached 91% (10/11) with bead-beating pretreatment. Mechanical lysis was also needed for Ascaris spp. and Hymenolepis spp. to reduce false-negative results from 1/8 to 1/21, respectively, to none for both. Overall, with an optimized extraction process, the Allplex™ GI-Helminth(I) Assay allows the detection of numerous parasites with roughly equivalent performance to that of microscopy, except for hookworms.

Efficacy and safety of ascending doses of moxidectin against Strongyloides stercoralis infections in adults: a randomised, parallel-group, single-blinded, placebo-controlled, dose-ranging, phase 2a trial

BACKGROUND

Strongyloidiasis represents a major public health issue, particularly in resource-limited countries. Preliminary studies suggest that moxidectin might serve as an alternative to the only available treatment option, ivermectin. We aimed to evaluate the efficacy and safety of ascending doses of moxidectin in Strongyloides stercoralis-infected patients.

METHODS

We did a randomised, parallel-group, single-blinded, placebo-controlled, dose-ranging, phase 2a trial in four villages in northern Laos. Eligible adults (aged 18-65 years) with S stercoralis infection intensities of at least 0·4 larvae per g of stool in at least two stool samples were randomly assigned (1:1:1:1:1:1:1) by use of computerised, stratified, block randomisation into seven treatment groups: 2 mg of moxidectin, 4 mg of moxidectin, 6 mg of moxidectin, 8 mg of moxidectin, 10 mg of moxidectin, 12 mg of moxidectin, or placebo. Participants and primary outcome assessors were masked to treatment allocation, but study site investigators were not. Participants received a single oral dose of their allocated dose of moxidectin in 2 mg tablets, or four placebo tablets. Three stool samples were collected at baseline and two stool samples were collected 28 days after treatment from each participant. A Baermann assay was used to quantify S stercoralis infection and Kato-Katz thick smears were used to qualitatively identify coinfections with additional helminths species. The primary endpoint was cure rate against S stercoralis and was analysed in an available case analysis set, defined as all randomly assigned participants with primary endpoint data. Predicted cure rates and associated CIs were estimated with hyperbolic E_max models. Safety was evaluated in the intention-to-treat population. This trial is registered at ClinicalTrials.gov, NCT04056325, and is complete.

FINDINGS

Between Nov 27, 2019, and March 15, 2020, 785 adults were screened for trial eligibility. Of these, 223 participants were randomly assigned to treatment groups and 209 completed the study and were analysed for the primary outcome. 2 mg of moxidectin had a predicted cure rate of 75% (95% CI 59-87; 22 [73%] of 30 cured) against S stercoralis compared with a predicted cure rate of 14% (5-31; four [14%] of 29 cured) for placebo. With escalating doses, the probability of cure increased from 83% (95% CI 76-88; 26 [90%] of 29 cured) at 4 mg to 86% (79-90; 27 [84%] of 32 cured) at 6 mg, and to 87% (80-92; 24 [83%] of 29 cured) at 8 mg, levelling off at 88% (80-93; 29 [97%] of 30 cured) at 10 mg and 88% (80-93; 26 [87%] of 30 cured) at 12 mg. Moxidectin was well tolerated across all treatment groups, with no serious adverse events being recorded and all reported symptoms being classified as mild.

INTERPRETATION

4-12 mg of moxidectin showed promising tolerability and efficacy profiles in the treatment of S stercoralis infections in adults. Because 8 mg of moxidectin is used for the treatment of onchocerciasis and has been evaluated for other helminth infections, we recommend this dose for phase 2b and phase 3 trials of strongyloidiasis therapy.

FUNDING

Fondazione Adiuvare.

Prevalence of Strongyloidiasis in a Cohort of Migrants in Italy and Accuracy of a Novel ELISA Assay for S. stercoralis Infection, a Cross-Sectional Study

Strongyloides stercoralis infection is a life-threatening neglected tropical disease. Diagnostic issues have caused an underestimation of its global burden. The choice of appropriate diagnostic tests for the screening of populations at risk of the infection, such as migrants from endemic countries, is of paramount importance. From November 2017 to July 2018, all migrants presenting to the National Institute for Health Migration and Poverty (INMP) in Rome, Italy were offered screening tests for S. stercoralis infection. The study objective was to estimate the prevalence of strongyloidiasis in the study population and the accuracy of a novel ELISA assay. The following tests were carried out at the IRCCS Sacro Cuore Don Calabria hospital in Negrar, Verona: stool microscopy, real-time PCR for S. stercoralis, in-house immunofluorescence test (IFAT), a commercial ELISA assay (Bordier ELISA), and a novel ELISA assay (Euroimmun ELISA). A latent class analysis (LCA) model set up with test results, clinical variables, and eosinophilia indicated a prevalence around 7.5%, in line with previous findings. The sensitivity and the specificity of Euroimmun ELISA were 90.6% (95% CI 80.5–100) and 87.7% (95CI 84.5–91.0); these results indicate that the novel ELISA assay would be suitable for screening of migrants from endemic countries.

Strongyloidiasis in Africa: Systematic Review and Meta-Analysis on Prevalence, Diagnostic Methods, and Study Settings

BACKGROUND

Strongyloidiasis is an intestinal parasitic infection mainly caused by Strongyloides stercoralis. Although it is a predominant parasite in tropics and subtropics where sanitation and hygiene are poorly practiced, the true prevalence of strongyloidiasis is not known due to low-sensitivity diagnostic methods.

OBJECTIVE

This systematic review and meta-analysis is aimed at determining the pooled prevalence of strongyloidiasis in African countries, stratified by diagnostic methods, study settings, and patients.

METHODS

Cross-sectional studies on strongyloidiasis published in African countries from the year 2008 up to 2018 in PubMed and Google Scholar databases and which reported at least one Strongyloides spp. infection were included. Identification and screening of eligible articles were also done. Articles whose focus was on strongyloidiasis in animals, soil, and foreigners infected by Strongyloides spp. in Africa were excluded. The random effects model was used to calculate the pooled prevalence of strongyloidiasis across African countries as well as by diagnostic methods and study settings. The heterogeneity between studies was also computed.

RESULT

A total of 82 studies were included. The overall pooled prevalence of strongyloidiasis was 2.7%. By individual techniques, the pooled prevalence of strongyloidiasis was 0.4%, 1.0%, 3.4%, 9.3%, 9.6%, and 19.4% by the respective direct saline microscopy, Kato-Katz, formol ether concentration, polymerase chain reaction, Baermann concentration, and culture diagnostic techniques. The prevalence rates of strongyloidiasis among rural community, school, and health institution studies were 6.8%, 6.4%, and 0.9%, respectively. The variation on the effect size comparing African countries, diagnostic methods, study settings, and patients was significant (P ≤ 0.001).

CONCLUSIONS

This review shows that strongyloidiasis is overlooked and its prevalence is estimated to be low in Africa due to the use of diagnostic methods with low sensitivity. Therefore, there is a need for using a combination of appropriate diagnostic methods to approach the actual strongyloidiasis rates in Africa.

Comparison of real-time PCR and the Kato-Katz method for the diagnosis of soil-transmitted helminthiasis and assessment of cure in a randomized controlled trial

Background

Diagnosis of soil-transmitted helminths (STHs) in developing countries is commonly based on microscopic detection of eggs in stool samples, using the Kato-Katz (KK) method, which has a poor sensitivity for detecting light intensity infections. We compared the performance of the KK method and real-time PCR in the framework of a randomized trial, which evaluated four novel treatments against Trichuris trichiura and concomitant STH infections.

Results

Two stool samples obtained from 320 participants were examined at baseline and follow-up with quadruplicate KK and PCR analyses of one of the two samples using “bead-beating” for DNA extraction. At follow-up, 80 samples were negative according to both PCR and KK and 173 were positive with both methods for any of the STHs. Relative to PCR, the calculated sensitivity of KK at follow-up was 83.6%, 43.0% and 53.8% for T. trichiura, for hookworm and for Ascaris lumbricoides, respectively. The sensitivity of PCR compared with KK at this time point was 89.1% for T. trichiura, 72.7% for hookworm and 87.5% for A. lumbricoides. Cure rates (CRs) for T. trichiura and A. lumbricoides were slightly lower with the PCR method. For hookworm CRs with KK were mostly significantly lower, namely 36.7%, 91.1%, 72.2% and 77.8% for moxidectin, moxidectin in combination with tribendimidine, moxidectin in combination with albendazole and albendazole in combination with oxantel pamoate, respectively, whereas with PCR the CRs were 8.3%, 82.6%, 37.1% and 57.1%, respectively.

Conclusions

In conclusion, a single real-time PCR is as sensitive as quadruplicate KK for T. trichiura and A. lumbricoides detection but more sensitive for hookworm, which has an influence on the estimated treatment efficacy. PCR method with DNA extraction using the “bead-beating protocol” should be further promoted in endemic areas and laboratories that can afford the needed equipment.

The study is registered at ISRCTN (no. 20398469).

Strongyloides stercoralis prevalence and diagnostics in Vientiane, Lao People's Democratic Republic

Background

Despite the high prevalence of strongyloidiasis in the Laotian population, Laotian hospitals still lack diagnostic capacity to appropriately diagnose Strongyloides stercoralis infections. This cross-sectional hospital-based study was conducted to assess the prevalence of Strongyloides stercoralis infection among hospitalized patients treated at Mahosot Hospital, the primary reference hospital of Lao People’s Democratic Republic (Lao PDR), and to validate feasible methods for diagnosing S. stercoralis infection at hospital’s laboratory.

Methods

Between September and December 2018, stool samples of 104 inpatients were investigated for S. stercoralis infection by wet smear, Baermann technique, Koga Agar plate culture (KAPC), and real-time detection polymerase chain reaction (RTD-PCR) at the Infectious Diseases Ward of the Mahosot Hospital in Vientiane. The sensitivity, the specificity, the negative predictive value (NPV) of each diagnostic test, as well as their combination(s) was calculated using a composite reference standard (CRS). The correlation of the different test methods was assessed by chi-square or Fisher’s exact test. Cohen’s kappa coefficient was used to assess the diagnostic agreement of the different test methods.

Results

The overall prevalence of S. stercoralis infections among the study population was 33.4%. The cumulative infection prevalence statistically significantly increased from the lowest age group of 40 years and below (22.4%), to the medium (40.0%) and to the oldest age group of 61 year and above (72.7%)(P = 0.003). The cumulative infection prevalence of CRS was considerably higher in male (40.4%) compared to female patients (28.1%), but not statistically different (P = 0.184). The diagnostic sensitivity of Baermann technique, KAPC, RTD-PCR, and the combination of Baermann technique and KAPC were 60.0, 60.0, 74.3, and 77.1%, respectively. Only 13 patients (37.1%) of the total 35 S. stercoralis patients diagnosed with any technique had a simultaneously positive diagnostic test with Baermann, KAPC and RTD-PCR.

Conclusions

We identified Baermann technique and KAPC to be currently the most feasible and implementable standard methods for diagnosing S. stercoralis at a hospital setting such as Mahosot Hospital and provincial and district hospitals in Lao PDR and other low- and middle income countries in Southeast Asia.

Trial registration

This study was approved by the National Ethics Committee for Health Research in Lao PDR (reference no. 083/NECHR) and by the Ethics Committee Northwest and Central Switzerland (reference no. 2018–00594).

Epidemiology and risk factors of Strongyloides stercoralis infection in Papua, Indonesia: a molecular diagnostic study

Strongyloides stercoralis is a parasitic worm that is of considerable clinical relevance. Indeed, it may persist asymptomatically for many years, but can lead to potentially fatal dissemination when the host's immune status is impaired. As commonly employed stool microscopy techniques (e.g. Kato-Katz thick smear) fail to detect S. stercoralis, the epidemiology is poorly understood. In 2013, we conducted a cross-sectional household survey in the district of Mimika in Papua, Indonesia. A total of 331 individuals, aged 1 month to 44 years, had a single stool sample subjected to real-time polymerase chain reaction (PCR) for S. stercoralis diagnosis. The prevalence of S. stercoralis infection was 32.0% (106/331 individuals); higher than any of the three main soil-transmitted helminths (Ascaris lumbricoides, 23.9%; Trichuris trichiura, 18.4%; and hookworm, 17.2%). Amongst the S. stercoralis-infected individuals, 73.6% were concurrently infected with another helminth, with hookworm being the most frequent co-infection (27.4%). Fourteen percent of the S. stercoralis infections had low cycle threshold values on real-time PCR, which may indicate a higher infection intensity. Multivariate logistic regression analysis revealed that age ≥5 years (adjusted odds ratio (OR) 5.8, 95% confidence interval (CI): 3.1-10.8) was significantly associated with S. stercoralis infection. There is a need for in-depth clinical and diagnostic studies to elucidate the public health impact of S. stercoralis infection in Indonesia.

Strongyloides stercoralis Infection at Different Altitudes of the Cusco Region in Peru

Strongyloides stercoralis affects 30-100 million people worldwide. The burden is underestimated because of the paucity of studies, limited geographical areas surveyed, and poor quality of diagnostic tests. This study aimed at determining the epidemiology of strongyloidiasis using sensitive microscopy testing in rural populations living at different altitudes in Cusco, Peru. Data were collected from subjects aged > 3 years living in Quellouno (elevation 2,600 ft) and Limatambo (elevation 8,379 ft) districts. Subjects provided one fresh stool sample and answer a standardized questionnaire. Fresh stool was tested on site using the Baermann's test and agar plate culture. Formalin-preserved stool was tested by rapid sedimentation. Eighty percent (585/715) of eligible subjects consented to participate; after excluding subjects with missing data, 65% (462/715) were included. Fifty-five percentage were female; the median age was 33 years (interquartile range 13-52), and 72% had government health insurance. Half had intestinal parasites, and Strongyloides was the most common (24.5%) followed by Giardia (15.5%), Blastocystis (14.9%), and hookworm (11.5%). The agar plate culture detected more cases of Strongyloides than Baermann's or sedimentation tests. Strongyloides infection was more common at low altitude (26.4%) than at high altitude (18.6%), but the difference was not statistically significant (P = 0.08). Older age, walking barefoot, bathing in rivers/streams, and using municipal sewage were associated with strongyloidiasis. Strongyloides was the most prevalent parasite in the areas studied and was associated with demographic, socioeconomic, and sanitary factors.

An optimized agar plate culture improves diagnostic efficiency for Strongyloides stercoralis infection in an endemic community

We aimed to compare the efficacy of modified agar plate fecal culture (mAPC) and standard agar plate culture (sAPC) for diagnosis of Strongyloides stercoralis infection in a community at Khon Kaen Province, Thailand. Fecal samples were collected from participants individually (n = 1076) and were tested using these two methods. Modified APC and sAPC detected 129 (11.99%) and 91 (8.46%) infected individuals, respectively. Thirty-eight participants were negative according to sAPC, but positive for mAPC. Moreover, in the participants who were positive for both methods, the number of worm developmental stages obtained was higher for mAPC than for sAPC. Our study suggests that mAPC is an effective and useful tool for S. stercoralis diagnosis and can be applied for mass-screening in community and/or control programs.

Diagnostic comparison of Baermann funnel, Koga agar plate culture and polymerase chain reaction for detection of human Strongyloides stercoralis infection in Maluku, Indonesia

Human infection with the nematode Strongyloides stercoralis, which may have a life-threatening course, primarily occurs in tropical settings. Epidemiological data on the occurrence of strongyloidiasis are scarce, and microscopic stool-based detection methods are insensitive. Polymerase chain reaction (PCR) assays have been developed, yet conflicting results have been reported. Our goal was to determine whether there was diagnostic agreement between an in-house PCR and two microscopic techniques, the Baermann funnel (BM) and the Koga agar plate culture (KAP) for the detection of S. stercoralis in stool samples. Eighty ethanol-fixed stool samples stemming from a cross-sectional survey in Maluku, Indonesia, were purposefully selected for PCR analysis. The final sample size comprised four groups, each with 20 samples: group 1, positive for S. stercoralis on both BM and KAP; group 2, positive only by BM; group 3, positive only by KAP; and group 4, negative on both BM and KAP. A Strongyloides-specific PCR targeting the internal transcribed spacer 2 (ITS2) region was carried out in an Indonesian reference laboratory. The overall agreement between PCR and microscopy was 61% (49/80 samples), being highest in group 1 (15/20, 75%) and lowest in group 3 (9/20, 45%). PCR revealed eight additional S. stercoralis infections in group 4. Future studies should elucidate the 'true' infection status of samples that are negative by PCR, but positive upon microscopy. Taken together, there is a lack of agreement between microscopy and PCR results for the diagnosis of human S. stercoralis infection in Indonesia. ClinicalTrials.gov (identifier: NCT02105714).

Molecular diagnosis of Strongyloides stercoralis among transplant candidates

Strongyloidiasis can occur without any symptoms or as a potentially fatal hyperinfection or disseminated infection, principally in immunosuppressed patients. Our study aimed to evaluate the application of conventional polymerase chain reaction (cPCR) and real-time PCR (qPCR). Polymerase chain reaction (PCR) and real-time PCR (qPCR) targeting the 18S rRNA gene for detection of Strongyloides stercoralis infection among transplant candidates were applied in stool samples obtained from 150 transplant candidates, preliminarily analyzed by parasitological methods. S. stercoralis larvae were visualized in 15/150 (10.0%) transplant candidates by parasitological methods. DNA from S. stercoralis was amplified in 26/150 (17.3%) and 49/150 (32.7%) stool samples of transplant candidates, using cPCR and qPCR, respectively. The results suggest that molecular methods, especially qPCR, should be used as an additional tool for diagnostic of S. stercoralis infection among transplant candidates.

Evaluation of Two DNA Extraction Methods for Detection of Strongyloides stercoralis Infection

Strongyloides stercoralis is present worldwide, but its prevalence is still uncertain, mainly due to the lack of sensitivity of diagnostic methods. Molecular techniques are under development, but a standardized protocol is still unavailable. We compared the sensitivity of real-time PCR, using two extraction protocols, with that of the Baermann technique. Samples were collected in the framework of the baseline screening of a randomized clinical trial evaluating moxidectin against S. stercoralis in Lao People's Democratic Republic. Two stool samples from each participant were processed by the Baermann method, and one subsample was processed by PCR. DNA was extracted using the QIAamp DNA stool minikit based on the standard protocol for the QIAamp DNA minikit (QIA) and using a modification of the QIA procedure (POL). Subsequently, all extracted samples were analyzed by real-time PCR. Overall, 95 samples were analyzed by the three diagnostic methods. Sixty-nine (72.6%) samples were positive according to the Baermann method, 25 (26.3%) by the QIA method, and 62 (65.3%) by the POL method. The sensitivities were 86% (95% confidence interval [CI], 76.7 to 92.9), 31.0% (95% CI, 21.3 to 42.6), and 78.0% (95% CI, 66.8 to 86.1) for the Baermann, QIA, and POL methods, respectively. The sensitivities calculated for each day of the Baermann method separately were 60% (48.4 to 70.8%) and 64% (52.2 to 74.2%) for days 1 and 2, respectively. In conclusion, the POL method revealed a good performance and was comparable to the Baermann test performed on two stool samples and superior to the Baermann method performed on one stool sample. Additional studies are needed to standardize a PCR protocol for S. stercoralis diagnosis.

Accuracy of molecular biology techniques for the diagnosis of Strongyloides stercoralis infection-A systematic review and meta-analysis

Background

Strongyloides stercoralis infection is a neglected tropical disease which can lead to severe symptoms and even death in immunosuppressed people. Unfortunately, its diagnosis is hampered by the lack of a gold standard, as the sensitivity of traditional parasitological tests (including microscopic examination of stool samples and coproculture) is low. Hence, alternative diagnostic methods, such as molecular biology techniques (mostly polymerase chain reaction, PCR) have been implemented. However, there are discrepancies in the reported accuracy of PCR.

Methodology

A systematic review with meta-analysis was conducted in order to evaluate the accuracy of PCR for the diagnosis of S. stercoralis infection. The protocol was registered with PROSPERO International Prospective Register of Systematic Reviews (record: CRD42016054298). Fourteen studies, 12 of which evaluating real-time PCR, were included in the analysis. The specificity of the techniques resulted high (ranging from 93 to 95%, according to the reference test(s) used). When all molecular techniques were compared to parasitological methods, the sensitivity of PCR was assessed at 71.8% (95% CI 52.2–85.5), that decreased to 61.8% (95% CI 42.0–78.4) when serology was added among the reference tests. Similarly, sensitivity of real-time PCR resulted 64.4% (95% CI 46.2–77.7) when compared to parasitological methods only, 56.5% (95% CI 39.2–72.4) including serology.

Conclusions

PCR might not be suitable for screening purpose, whereas it might have a role as a confirmatory test.

Strongyloides stercoralis is a worm that can potentially kill affected immunosuppressed individuals. The parasite is not easily detected with stool microscopy, hence novel tests have been implemented, such as polymerase chain reaction (PCR), that can detect the DNA of the parasite. This work aims at evaluating the performance of PCR for the diagnosis of S. stercoralis through a revision of diagnostic studies available in literature. According to the results of this work, PCR for S. stercoralis still misses a relevant proportion of infected people, while a positive result confirms the presence of the infection.

Isothermal diagnostic assays for the detection of soil-transmitted helminths based on the SmartAmp2 method

Background

Diagnosis of soil-transmitted helminths (STHs) has traditionally relied on stool microscopy, which has a number of critical deficiencies. Molecular diagnostics are powerful tools to identify closely related species, but the requirement for costly equipment makes their implementation difficult in low-resource or field settings. Rapid, sensitive and cost-effective diagnostic tools are crucial for accurate estimation of STH infection intensity in MDA programmes in which the goal is to reduce morbidity following repeated rounds of chemotherapy.

Results

In this study, colourimetric isothermal assays were developed using SmartAmp2 primer sets and reagents in loop-mediated amplification (LAMP) assays. Species-specific primer sets, designed on a specific target sequence in the β-tubulin gene, were used to identify Necator americanus, Trichuris trichiura and Ascaris lumbricoides. After initial optimization on control plasmids and genomic DNA from adult worms, assays were evaluated on field samples. Assays showed high sensitivity and demonstrated high tolerance to inhibitors in spiked faecal samples. Rapid and sensitive colourimetric assays were successfully developed to identify the STHs in field samples using hydroxy napthol blue (HNB) dye.

Conclusions

Rapid and simple colourimetric diagnostic assays, using the SmartAmp2 method, were developed, with the potential to be applied in the field for detection of STH infections and the estimation of response to treatment. However, further validation on large numbers of field samples is needed.

Electronic supplementary material

The online version of this article (10.1186/s13071-017-2420-1) contains supplementary material, which is available to authorized users.

Combination of five diagnostic tests to estimate the prevalence of hookworm infection among school-aged children from a rural area of colombia

BACKGROUND

Public health programs for the control of soil-transmitted helminthiases require valid diagnostic tests for surveillance and parasitic control evaluation. However, there is currently no agreement about what test should be used as a gold standard for the diagnosis of hookworm infection. Still, in presence of concurrent data for multiple tests it is possible to use statistical models to estimate measures of test performance and prevalence. The aim of this study was to estimate the diagnostic accuracy of five parallel tests (direct microscopic examination, Kato-Katz, Harada-Mori, modified Ritchie-Frick, and culture in agar plate) to detect hookworm infections in a sample of school-aged children from a rural area in Colombia.

METHODS AND RESULTS

We used both, a frequentist approach, and Bayesian latent class models to estimate the sensitivity and specificity of five tests for hookworm detection, and to estimate the prevalence of hookworm infection in absence of a Gold Standard. The Kato-Katz and agar plate methods had an overall agreement of 95% and kappa coefficient of 0.76. Different models estimated a sensitivity between 76% and 92% for the agar plate technique, and 52% to 87% for the Kato-Katz technique. The other tests had lower sensitivity. All tests had specificity between 95% and 98%. The prevalence estimated by the Kato-Katz and Agar plate methods for different subpopulations varied between 10% and 14%, and was consistent with the prevalence estimated from the combination of all tests. The Harada-Mori, Ritchie-Frick and direct examination techniques resulted in lower and disparate prevalence estimates. Bayesian approaches assuming imperfect specificity resulted in lower prevalence estimates than the frequentist approach.

Prevalence of Strongyloides stercoralis and Other Intestinal Parasite Infections in School Children in a Rural Area of Angola: A Cross-Sectional Study

Strongyloides stercoralis is widely distributed in the tropics and subtropics. The aim of this study was to determine the prevalence of S. stercoralis and other intestinal parasites and identify the risk factors for infection with S. stercoralis in a rural area of Angola. A cross-sectional study was conducted in school-age children (SAC) in Cubal, Angola. A questionnaire collecting clinical and epidemiological variables was used, and two stool samples were collected. A concentration technique (Ritchie) and a technique for detection of larvae migration (Baermann) were performed. Of 230 SAC, 56.1% were female and the mean age was 9.3 years (SD 2.45). Severe malnutrition, according to body mass index (BMI)-for-age, was observed in 20.4% of the SAC, and anemia was found in 59.6%. Strongyloides stercoralis was observed in 28 of the 230 (12.8%) SAC. Eggs of other helminths were observed in 51 (22.2%) students: Hymenolepis spp. in 27 students (11.7%), hookworm in 14 (6.1%), Schistosoma haematobium in four (1.7%), Enterobius vermicularis in four (1.7%), Ascaris lumbricoides in three (1.3%), Taenia spp. in two (0.9%), and Fasciola hepatica in one (0.4%). Protozoa were observed in 17 (7.4%) students. Detection of S. stercoralis was higher using the Baermann technique versus using formol-ether (11.3 vs. 3%). Overall prevalence of S. stercoralis in the school population of 16 studied schools in the municipal area of Cubal was greater than 10%. This fact must be considered when designing deworming mass campaigns. The use of specific tests in larvae detection is needed to avoid overlooking this parasite.

Strongyloides stercoralis in solid organ transplantation: early diagnosis gets the worm

PURPOSE OF REVIEW

Strongyloidiasis is a parasitic infection affecting millions of people worldwide. Complications of infection are strongly associated with alcoholism, immunosuppression, and organ transplantation. Delayed diagnosis results in hyperinfection syndrome and disseminated strongyloidiasis leading to mortality rates approaching 80%. Early detection, and prevention of infection and transmission are key to diminish this illness.

RECENT FINDINGS

In this review, we cover the basic concepts in immunity, immunosuppression, and disorder necessary for understanding the infectious syndromes associated with Strongyloides stercoralis infection. Focused discussion on donor-derived transmission and recipient risk in solid organ transplantation is presented. Current methodology for diagnosis, screening algorithms, and treatment are also reviewed.

SUMMARY

Strongyloidiasis complicated by hyperinfection and dissemination remains associated with a poor outcome. The poor outcome pleads for a high level of suspicion and aggressive treatment in at-risk patients. As the population of transplant patients continues to increase, the risk of infection also increases, compelling us to address this highly fatal infectious complication in solid organ transplantation (SOT). Here we review the pathology, immunology, diagnosis, and treatment of strongyloides infection in the immunosuppressed SOT population.

Epidemiology of Strongyloides stercoralis in northern Italy: results of a multicentre case-control study, February 2013 to July 2014

Strongyloides stercoralis is a soil-transmitted helminth widely diffused in tropical and subtropical regions of the world. Autochthonous cases have been also diagnosed sporadically in areas of temperate climate. We aimed at defining the epidemiology of strongyloidiasis in immigrants and Italians living in three northern Italian Regions. Screening for S. stercoralis infection was done with serology, confirmation tests were a second serological method or stool agar culture. A case–control approach was adopted and patients with a peripheral eosinophil count ≥ 500/mcL were classified as cases. Of 2,701 individuals enrolled here 1,351 were cases and 1,350 controls; 86% were Italians, 48% women. Italians testing positive were in 8% (97/1,137) cases and 1% (13/1,178) controls (adjusted odds ratio (aOR) 8.2; 95% confidence interval (CI): 4.5–14.8), while positive immigrants were in 17% (36/214) cases and in 2% (3/172) controls (aOR 9.6; 95% CI: 2.9–32.4). Factors associated with a higher risk of infection for all study participants were eosinophilia (p < 0.001) and immigration (p = 0.001). Overall, strongyloidiasis was nine-times more frequent in individuals with eosinophilia than in those with normal eosinophil count.

Parasitological versus molecular diagnosis of strongyloidiasis in serial stool samples: how many?

Strongyloidiasis is usually an asymptomatic disease in immunocompetent patients, caused by Strongyloides stercoralis. However, in immunocompromised patients it can produce a severe clinical profile. Therefore, a correct diagnosis is necessary in these cases and in those chronic asymptomatic patients. The low sensitivity of classical parasitological techniques requires the analysis of multiple serial stool samples. Molecular diagnostic techniques represent an improvement in the detection of the parasite. The objective of this study was to evaluate the minimum number of samples necessary to achieve maximum sensitivity by real-time polymerase chain reaction (PCR). A total of 116 stool samples from 39 patients were analysed by direct microscopic observation, agar culture, Harada–Mori and real-time PCR, in one, two, three and four or more consecutive samples. After two serial samples, 6 out of 39 patients were positive by parasitological and molecular techniques, while 16 of them were real-time PCR positive, and all the patients detected by parasitology were also detected by the molecular technique, reaching 100.00% sensitivity versus 83.00% when analysing a single sample. These data also reflect apparently low specificity (51.52%) and positive predictive value (PPV) (27.27 %) values, due to the high number of cases detected by real-time PCR and not by parasitological techniques. These cases were confirmed as true positives when analysing three, four or more samples from the same patient. In conclusion, the application of molecular techniques decreases the number of serial stool samples necessary to give a diagnosis with the maximum sensitivity.

Strongyloidiasis Current Status with Emphasis in Diagnosis and Drug Research

Strongyloidiasis is a parasitic neglected disease caused by the nematode Strongyloides stercoralis affecting 30 to 100 million people worldwide. Complications, strongly associated with alcoholism, organ transplants, and HTLV-1 virus, often arise due to late diagnosis, frequently leading to patient death. Lack of preemptive diagnosis is not the only difficulty when dealing with this parasite, since there are no gold standard diagnostic techniques, and the ones used have problems associated with sensitivity, resulting in false negatives. Treatment is also an issue as ivermectin and benzimidazoles administration leads to inconsistent cure rates and several side effects. Researching new anti-Strongyloides drugs is a difficult task since S. stercoralis does not develop until the adult stages in Mus musculus (with the exception of SCID mice), the main experimental host model. Fortunately, alternative parasite models can be used, namely, Strongyloides ratti and S. venezuelensis. However, even with these models, there are other complications in finding new drugs, which are associated with specific in vitro assay protocol steps, such as larvae decontamination. In this review, we highlight the challenges associated with new drug search, the compounds tested, and a list of published in vitro assay methodologies. We also point out advances being made in strongyloidiasis diagnosis so far.

A retrospective study comparing agar plate culture, indirect immunofluorescence and real-time PCR for the diagnosis of Strongyloides stercoralis infection

Strongyloides stercoralis is a parasite that can cause death in immunocompromised people. A proper diagnosis is hence essential. The real-time polymerase-chain reaction (RT–PCR) is a novel, promising diagnostic method, that detects the DNA of the parasite in stool samples. In this retrospective study, we compared the sensitivity of agar plate coproculture (APC), an in-house immunofluorescence test (IFAT) and an in-house RT–PCR for the diagnosis of S. stercoralis infection. The study sample was composed by 223 samples. Samples resulting positive to APC, IFAT and RT–PCR were 20, 140 and 25, respectively. When sensitivity was calculated against a composite reference standard, serology confirmed the best performance (sensitivity 95%), followed by RT–PCR (57%) and APC (45%). In conclusion, in a non-endemic setting, serology is the best screening method, while the combination of APC and RT–PCR does not seem a reasonable approach to increase sensitivity. Both methods can have a role as confirmatory tests for selected cases.

High prevalence of Strongyloides stercoralis in school-aged children in a rural highland of north-western Ethiopia: the role of intensive diagnostic work-up

Background

Soil-transmitted helminthiases (hookworms, Ascaris lumbricoides and Trichuris trichiura) are extremely prevalent in school-aged children living in poor sanitary conditions. Recent epidemiological data suggest that Strongyloides stercoralis is highly unreported. However, accurate data are essential for conducting interventions aimed at introducing control and elimination programmes.

Methods

We conducted a cross-sectional survey of 396 randomly selected school-aged children in Amhara region in rural area in north-western Ethiopia, to assess the prevalence of S. stercoralis and other intestinal helminths. We examined stools using three techniques: conventional stool concentration; and two S. stercoralis-specific methods, i.e. the Baermann technique and polymerase chain reaction. The diagnostic accuracy of these three methods was then compared.

Results

There was an overall prevalence of helminths of 77.5%, with distribution differing according to school setting. Soil-transmitted helminths were recorded in 69.2%. Prevalence of S. stercoralis and hookworm infection was 20.7 and 54.5%, respectively, and co-infection was detected in 16.3% of cases. Schistosoma mansoni had a prevalence of 15.7%. Prevalence of S. stercoralis was shown 3.5% by the conventional method, 12.1% by the Baermann method, and 13.4% by PCR, which thus proved to be the most sensitive.

Conclusions

Our results suggest that S. stercoralis could be overlooked and neglected in Ethiopia, if studies of soil-transmitted helminths rely on conventional diagnostic techniques alone. A combination of molecular and stool microscopy techniques yields a significantly higher prevalence. In view of the fact that current control policies for triggering drug administration are based on parasite prevalence levels, a comprehensive diagnostic approach should instead be applied to ensure comprehensive control of helminth infections.

Strongyloidiasis in Ontario: Performance of diagnostic tests over a 14-month period

BACKGROUND

We evaluated the performance of stool microscopy, serology, and real time PCR (qPCR) for the diagnosis of strongyloidiasis at our reference laboratory.

METHODS

Using a convenience sample of specimens submitted between April 1, 2014 and May 31, 2015, positivity rates and performance characteristics were calculated.

RESULTS

During the enrolment period, 17,933 stool specimens were examined for O&P, 14 of which were positive for Strongyloides larvae. For stool specimens serially positive for larvae, mean duration of larval shedding was 12.7 days following the initial positive specimen, while for sputum and urine, it was 12 and 2 days, respectively. During the enrolment period, 3258 specimens were processed for Strongyloides serology, 200 of which were reactive (6.1%), 210 indeterminate (6.5%), and 2848 non-reactive (87.4%). qPCR was positive in 11 of 12 (91.7%) stool specimens containing larvae, and negative in all stool specimens without larvae by microscopy. There was no cross-reactivity of Strongyloides-specific qPCR to other stool protozoa or helminths.

CONCLUSIONS

In the absence of immunosuppression, larval burden in strongyloidiasis is low, limiting the utility of microscopy, and favoring serologic testing. However, false negative serology can occur in those with hyperinfection necessitating a combined diagnostic approach. qPCR was insufficiently sensitive to replace microscopy for detection of larvae.

Soil-Transmitted Helminths: Mathematical Models of Transmission, the Impact of Mass Drug Administration and Transmission Elimination Criteria

Infections caused by soil-transmitted helminthias (STHs) affect over a billion people worldwide, causing anaemia and having a large social and economic impact through poor educational outcomes. They are identified in the World Health Organization (WHO) 2020 goals for neglected tropical diseases as a target for renewed effort to ameliorate their global public health burden through mass drug administration (MDA) and water and hygiene improvement. In this chapter, we review the underlying biology and epidemiology of the three causative intestinal nematode species that are mostly considered under the STH umbrella term. We review efforts to model the transmission cycle of these helminths in populations and the effects of preventative chemotherapy on their control and elimination. Recent modelling shows that the different epidemiological characteristics of the parasitic nematode species that make up the STH group can lead to quite distinct responses to any given form of MDA. When connected with models of treatment cost-effectiveness, these models are potentially a powerful tool for informing public policy. A number of shortcomings are identified; lack of critical types of data and poor understanding of diagnostic sensitivities hamper efforts to test and hence improve models.

Molecular Diagnostics for Soil-Transmitted Helminths

Historically, the diagnosis of soil-transmitted helminths (STHs) (e.g., Strongyloides stercoralis, Trichuris trichiura, Ancylostoma duodenale, Necator americanus, and Ascaris lumbricoides) has relied on often-insensitive microscopy techniques. Over the past several years, there has been an effort to use molecular diagnostics, particularly quantitative polymerase chain reaction (qPCR), to detect intestinal pathogens. While some platforms have been approved by regulatory bodies (e.g., Food and Drug Administration) to detect intestinal bacteria, viruses, and protozoa, there are no approved tests currently available for STH. Although studies comparing qPCR to microscopy methods for STH are imperfect, due in large part to a lack of a sufficient gold standard, they do show a significant increase in sensitivity and specificity of qPCR compared with microscopic techniques. These studies, as well as the advantages and disadvantages of using qPCR for STH diagnosis, are discussed. Guidelines for those designing future studies utilizing qPCR are proposed for optimizing results, as is the proposition for using standardized molecular diagnostics routinely for STH in clinical laboratories and for field-based studies when possible.

Comparison between PCR and larvae visualization methods for diagnosis of Strongyloides stercoralis out of endemic area: A proposed algorithm

Underdiagnosis of chronic infection with the nematode Strongyloides stercoralis may lead to severe disease in the immunosuppressed. Thus, we have set-up a specific and highly sensitive molecular diagnosis in stool samples. Here, we compared the accuracy of our polymerase chain reaction (PCR)-based method with that of conventional diagnostic methods for chronic infection. We also analyzed clinical and epidemiological predictors of infection to propose an algorithm for the diagnosis of strongyloidiasis useful for the clinician. Molecular and gold standard methods were performed to evaluate a cohort of 237 individuals recruited in Buenos Aires, Argentina. Subjects were assigned according to their immunological status, eosinophilia and/or history of residence in endemic areas. Diagnosis of strongyloidiasis by PCR on the first stool sample was achieved in 71/237 (29.9%) individuals whereas only 35/237(27.4%) were positive by conventional methods, requiring up to four serial stool samples at weekly intervals. Eosinophilia and history of residence in endemic areas have been revealed as independent factors as they increase the likelihood of detecting the parasite according to our study population. Our results underscore the usefulness of robust molecular tools aimed to diagnose chronic S. stercoralis infection. Evidence also highlights the need to survey patients with eosinophilia even when history of an endemic area is absent.