Strongy Detect: Preliminary Validation of a Prototype Recombinant Ss-NIE/Ss-IR Based ELISA to Detect Strongyloides stercoralis Infection.

BACKGROUND: Strongyloides stercoralis (Ss) is the etiological agent of strongyloidiasis, a neglected tropical disease of global concern. Laboratory diagnosis of strongyloidiasis is most often based on detection of antibodies against antigens in an enzyme linked immunosorbent assay (ELISA). Herein, we report a preliminary validation study of newly developed IgG4- and/or IgG- based ELISAs to detect strongyloidiasis (Strongy Detect, InBios) incorporating a cocktail of 2 previously described recombinant antigens, Ss-NIE and Ss-IR. METHODS: The sensitivity and specificity were determined by using the assay in 150 cryopreserved serum samples from humans known to be Ss infected (n = 74), helminth uninfected (n = 47), or infected with a helminth other than Ss [n = 29). The treatment associated dynamics of antibody detection were then assessed using 35 paired samples obtained before and after definitive therapy. RESULTS: The IgG and IgG4 assays were 99% and 96% sensitive, respectively, and 99% and 100% specific, respectively. Neither the IgG or IgG4 assay showed cross reactions with sera from those infected with other helminths. Although ELISA values did decline post-treatment few returned to levels below the cutoff for infection. CONCLUSION: Strongy Detect is the most sensitive and specific commercialized immunoassay for detection of strongyloidiasis. The assay remains positive for greater than a year post-treatment.

Diagnostic accuracy of a novel enzyme-linked immunoassay for the detection of IgG and IgG4 against Strongyloides stercoralis based on the recombinant antigens NIE/SsIR.

BACKGROUND: The diagnosis of strongyloidiasis is challenging. Serological tests are acknowledged to have high sensitivity, but issues due to cross-reactions with other parasites, native parasite antigen supply and intrinsic test variability do occur. Assays based on recombinant antigens could represent an improvement. The aim of this study was to assess the sensitivity and specificity of two novel immunoglobulin (Ig)G and IgG4 enzyme-linked immunosorbent assays (ELISAs) based on the recombinant antigens NIE/SsIR for the diagnosis of strongyloidiasis. METHODS: This was a retrospective diagnostic accuracy study. We included serum samples collected from immigrants from strongyloidiasis endemic areas for whom there was a matched result for Strongyloides stercoralis on agar plate culture and/or PCR assay, or a positive microscopy for S. stercoralis larvae. For the included samples, results were also available from an in-house indirect fluorescent antibody test (IFAT) and a commercial (Bordier ELISA; Bordier Affinity Products SA) ELISA. We excluded: (i) samples with insufficient serum volume; (ii) samples from patients treated with ivermectin in the previous 6 months; and (iii) sera from patients for whom only routine coproparasitology was performed after formol-ether concentration, if negative for S. stercoralis larvae. The performance of the novel assays was assessed against: (i) a primary reference standard, with samples classified as negative/positive on the basis of the results of fecal tests; (ii) a composite reference standard (CRS), which also considered patients to be positive who had concordant positive results for the IFAT and Bordier ELISA or with a single "high titer" positive result for the IFAT or Bordier ELISA. Samples with a single positive test, either for the IFAT or Bordier ELISA, at low titer, were considered to be "indeterminate," and analyses were carried out with and without their inclusion. RESULTS: When assessed against the primary reference standard, the sensitivities of the IgG and IgG4 ELISAs were 92% (95% confidence interval [CI]: 88-97%) and 81% (95% CI: 74-87%), respectively, and the specificities were 91% (95% CI: 88-95%) and 94% (95% CI: 91-97%), respectively. When tested against the CRS, the IgG ELISA performed best, with 78% sensitivity (95% CI: 72-83%) and 98% specificity (95% CI: 96-100%), when a cut-off of 0.675 was applied and the indeterminate samples were excluded from the analysis. CONCLUSION: The NIE-SsIR IgG ELISA demonstrated better accuracy than the IgG4 assay and was deemed promising particularly for serosurveys in endemic areas.

Evaluation of a Rapid IgG4 Lateral Flow Dipstick Test to Detect Strongyloides stercoralis Infection in Northeast Thailand.

Strongyloides stercoralis affects more than half a billion people worldwide, and hyperinfection in immunocompromised patients can be fatal. Elimination of this neglected tropical disease requires field-applicable diagnostic tools. We conducted a laboratory evaluation of a lateral flow rapid dipstick test (SsRapid™) using sera samples from a Strongyloides-endemic area in northeast Thailand. Group 1 was S. stercoralis-positive and larvae- and/or antibody-positive (according to the IgG ELISA) (N = 100). Group 2 had negative fecal examination and IgG ELISA results (N = 25). Group 3 had other parasitic infections and negative IgG ELISA results (N = 25). The results showed good diagnostic sensitivity (82%) and excellent specificity (96%). Suggested improvements in the SsRapid™ test include increased diagnostic sensitivity and conversion to the more robust cassette format. Field studies should be performed as well.

A new antigen detection ELISA for the diagnosis of Strongyloides infection.

Serodiagnosis is an essential component of the laboratory diagnosis of Strongyloides infection and is usually performed using an indirect IgG antibody test. A direct antigen detection method can complement the IgG assay, particularly for detecting early infection and post-treatment follow-up. In the present study, a recombinant scFv monoclonal antibody against NIE recombinant protein (rMAb23) that we had previously produced was used to develop a Strongyloides antigen detection ELISA (SsAg-ELISA). The assay is based on detecting immune complexes of circulating NIE antigens bound to Strongyloides-specific IgG antibodies. The optimized ELISA parameters were 10 µg/mL of rMAb23 coated on microtitre plate wells, 2% skim milk as blocking reagent, 1:100 serum dilution, and 1:1000 goat anti-human IgG F(ab')2 conjugated to horseradish peroxidase. Four groups of serum samples were used, i.e., Strongyloides-positive serum samples categorized into Groups IA and IB; the former were from probable chronic infections and the latter from probable early/acute infections. Strongyloides-negative samples comprising Groups II (healthy samples) and III (other infections); the latter were from eleven different types of other parasitic infections. The receiver operating characteristic (ROC) curve showed an area under the curve (AUC) of 1.00, cut-off optical density (OD405) of 0.5002, and 100% diagnostic sensitivity and specificity. The results of the commercial IgG-ELISA and SsAg-ELISA from Group IA were found to be moderately correlated (r = 0.416; p < 0.05). Notably, ANOVA showed that the average ODs405 of Group 1B were significantly higher (p < 0.05) than Group 1A, indicating that the assay may be useful to differentiate early and chronic infection. In conclusion, the developed SsAg-ELISA showed good diagnostic potential, and it merits further evaluation.

Development of rSs-NIE-1 and rSs-IR Recombinant Antigen-Based Immunoblot for Detection of Antibody to Strongyloides stercoralis.

Strongyloides stercoralis is a soil-transmitted nematode that can cause life-threatening conditions in immunocompromised persons. In the United States, strongyloidiasis should be considered mainly in immigrants, refugees, or travelers. The confirmatory laboratory diagnosis is usually performed by detecting larvae from the stool, duodenal material, and sputum. In persons who are immunocompromised with severe strongyloidiasis, adult worms and eggs can be detected from duodenal material. For serological diagnosis, most assays use crude antigens to detect anti-S. stercoralis IgG. Recently, recombinant proteins such as rSs-NIE-1 and rSs-IR have been used to detect IgG antibodies. We used rSs-NIE-1 and rSs-IR recombinant antigens to develop a biplex Western blot assay to detect the IgG4 antibody in individuals with strongyloidiasis. The sensitivities of rSs-NIE-1 and rSs-IR were 97.4% and 90.8%, respectively, whereas the specificities were 97.6% and 98%, respectively. In conclusion, the biplex rSs-NIE-1 and rSs-IR immunoblot performs well in detecting IgG4 antibody in S. stercoralis-infected persons.

Evaluation of a new Strongyloides ELISA IgG Test Kit.

BACKGROUND: Strongyloides stercoralis poses a significant clinical and public health challenge not only in endemic regions but also in non-endemic regions associated with travel. Ruling out this infection is essential in immuno-compromised hosts given the high probability of reactivation and mortality. METHODS: In this study we compared an ELISA based on two recombinant antigens in the United States with a highly sensitive and specific reference serological test. RESULTS & CONCLUSION: There was 100% agreement between the two methods. ELISA assays based on Strongyloides stercoralis recombinant antigens has the potential to improve specificity. Further studies are warranted.

Impact of Helminth Infection on Metabolic and Immune Homeostasis in Non-diabetic Obesity.

Several epidemiological and immunological studies indicate a reciprocal association between obesity/metabolic syndrome and helminth infections. Numerous studies demonstrated that obesity is concomitant with chronic low-grade inflammation, which is marked by vital changes in cellular composition and function of adipose tissue. However, the effect of helminth infection on the homeostatic milieu in obesity is not well-understood. To determine the relationship between Strongyloides stercoralis (Ss) infection and obesity, we examined an array of parameters linked with obesity both before and at 6 months following anthelmintic treatment. To this end, we measured serum levels of pancreatic hormones, incretins, adipokines and Type-1, Type-2, Type-17, and other proinflammatory cytokines in those with non-diabetic obesity with (INF) or without Ss infection (UN). In INF individuals, we evaluated the levels of these parameters at 6 months following anthelmintic treatment. INF individuals revealed significantly lower levels of insulin, glucagon, C-peptide, and GLP-1 and significantly elevated levels of GIP compared to UN individuals. INF individuals also showed significantly lower levels of Type-1, Type-17 and other pro-inflammatory cytokines and significantly increased levels of Type-2 and regulatory cytokines in comparison to UN individuals. Most of these changes were significantly reversed following anthelmintic treatment. Ss infection is associated with a significant alteration of pancreatic hormones, incretins, adipokines, and cytokines in obese individuals and its partial reversal following anthelmintic treatment. Our data offer a possible biological mechanism for the protective effect of Ss infection on obesity.

Systemic profile of immune factors in an elderly Italian population affected by chronic strongyloidiasis.

BACKGROUND: Strongyloidiasis caused by Strongyloides stercoralis is a soil-transmitted helminthiasis affecting an estimated 370 million people and considered one of the most neglected tropical diseases. Although mostly distributed in tropical and subtropical areas, autochthonous infections have also been documented in north-eastern Italy, even though the transmission presumably stopped decades ago. Because of its peculiar auto-infective cycle, strongyloidiasis can persist lifelong, but the pathophysiological mechanisms associated with the maintenance of such a chronic infection are yet to be fully deciphered. METHODS: Serum levels of 23 immune factors were retrospectively assessed in a subgroup of participants in a randomised clinical trial for the treatment of strongyloidiasis (Strong Treat). Here we included Italian subjects born between 1931 and 1964 and diagnosed with strongyloidiasis between 2013 and 2017 (Ss+, n = 32). Serum samples obtained before (BT) and 6 months (6M AT) after ivermectin treatment, as well as from age- and gender-matched uninfected controls (CTRL, n = 34) were analysed. RESULTS: The assessed immune factors showed a general reduced concertation in Ss+ patients and a lack of association with eosinophilia. In our cohort, we did not observe the classical shift towards a type 2 immune response, since Th1 and Th2 cytokines were mostly unaltered. Instead, we observed chemokines as particularly affected by the presence of the parasite, since IL-8, CCL3, CCL4 and CCL5 were significantly reduced in concentration in Ss+ subjects compared to CTRL, suggesting that immune cell recruitment to the infection site might be dampened in these patients. This observation was further sustained by a significant increase of CCL4, CCL5 and CCL11 concentrations 6M AT. A significant raised systemic concentration of three growth factors, bFGF, PDGF-BB and IL-7 (haematopoietic growth factor) was also observed post-treatment, indicating a potential involvement in restoring tissue integrity and homeostasis following parasite elimination. CONCLUSIONS: These preliminary data suggest that, in order to survive for such a long period, S. stercoralis might suppress host responses that could otherwise result in its ejection. Our results offer novel insights in the potential mechanisms of disease tolerance that might take place during this chronic infection, including a potential T-cell hypo-responsiveness and a role for chemokines.

Integrating testing for chronic strongyloidiasis within the Indigenous adult preventive health assessment system in endemic communities in the Northern Territory, Australia: An intervention study.

BACKGROUND: The life-threatening clinical manifestations of strongyloidiasis are preventable with early detection and effective treatment. The aim of this study was to assess if there was an increase to the number and proportion of persons tested for chronic strongyloidiasis, as a result of integrating Strongyloides stercoralis serology into the existing preventive health assessment system in four Aboriginal health services in endemic communities. METHODOLOGY: A prospective, longitudinal, before-and-after intervention study was conducted in four Aboriginal health services in remote endemically infected communities in the Northern Territory, Australia, from July 2012 to December 2016. The electronic patient information and recall systems enabled the integration of Strongyloides stercoralis serology into the adult preventive health assessment. Strongyloides reports for each health service were extracted half-yearly to examine the number and proportion of persons tested for chronic strongyloidiasis during the study and to measure the effect of the intervention. PRINCIPAL FINDINGS: The number and proportion of persons tested increased significantly during the study. From a total resident population of 3650 Indigenous adults over 15 years of age, 1686 persons (47.4%) were tested. The percentage of adults who had at least one serology test increased in all four health services to between 41% (446/1086) and 81.9% (172/210). Of the 1686 persons tested, 680 positive cases of chronic strongyloidiasis (40.3%) were identified. CONCLUSIONS/SIGNIFICANCE: This population health systems intervention increased the number and proportion of persons tested for chronic strongyloidiasis in four health services in endemically infected communities. This intervention is relevant to other health services with high-risk populations.

Helminth infection modulates systemic pro-inflammatory cytokines and chemokines implicated in type 2 diabetes mellitus pathogenesis.

BACKGROUND: The prevalence of helminth infections exhibits an inverse association with the prevalence of Type 2 diabetes mellitus (T2DM), and helminths are postulated to mediate a protective effect against T2DM. However, the biological mechanism behind this effect is not known. AIMS/METHODS: We postulated that helminth infections act by modulating the pro-inflammatory cytokine and chemokine milieu that is characteristic of T2DM. To examine the association of cytokines and chemokines in helminth-diabetes co-morbidity, we measured the plasma levels of a panel of pro-inflammatory cytokines and chemokines in individuals with Strongyloides stercoralis infection (Ss+) and T2DM at the time of Ss diagnosis and then 6 months after definitive anthelmintic treatment along with uninfected control individuals with T2DM alone (Ss-). PRINCIPAL FINDINGS: Ss+ individuals exhibited significantly diminished levels of the pro-inflammatory cytokines-IL-1α, IL-1ß, IL-6, IL-12, IL-18, IL-23, IL-27, G-CSF and GM-CSF and chemokines-CCL1, CCL2, CCL3, CCL11, CXCL1, CXCL2, CXCL8, CXCL9, CXCL10 and CXCL11. In contrast, Ss+ individuals exhibited significantly elevated levels of IL-1Ra. Anthelmintic treatment resulted in increased levels of all of the cytokines and chemokines. CONCLUSIONS: Thus, helminth infections alleviate and anthelmintic therapy partially restores the plasma cytokine and chemokine levels in helminth-diabetes co-morbidity. Our data therefore offer a plausible biological mechanism for the protective effect of helminth infections against T2DM.

Helminth Coinfection Alters Monocyte Activation, Polarization, and Function in Latent Mycobacterium tuberculosis Infection.

Helminth infections are known to influence T and B cell responses in latent tuberculosis infection (LTBI). Whether helminth infections also modulate monocyte responses in helminth-LTBI coinfection has not been fully explored. To this end, we examined the activation, polarization, and function of human monocytes isolated from individuals with LTBI with (n = 25) or without (n = 25) coincident Strongyloides stercoralis infection (S. stercoralis-positive and S. stercoralis-negative respectively). Our data reveal that the presence of S. stercoralis infection is associated with lower frequencies of monocytes expressing CD54, CD80, CD86 at baseline (absence of stimulation) and in response to mycobacterial-Ag stimulation than monocytes from S. stercoralis-negative individuals. In contrast, S. stercoralis infection was associated with higher frequencies of M2-like monocytes, as determined by expression of CD206 and CD163. Monocytes from S. stercoralis-positive individuals had a reduced capacity to phagocytose or exhibit respiratory burst activity following mycobacterial-Ag or LPS stimulation and were less capable of expression of IL-1ß, TNF-α, IL-6, and IL-12 at baseline and/or following Ag stimulation compared with those without S. stercoralis infection. In addition, definitive treatment of S. stercoralis infection resulted in a significant reversal of the altered monocyte function 6 mo after anthelmintic therapy. Finally, T cells from S. stercoralis-positive individuals exhibited significantly lower activation at baseline or following mycobacterial-Ag stimulation. Therefore, our data highlight the induction of dampened monocyte activation, enhanced M2 polarization, and impaired monocyte function in helminth-LTBI coinfection. Our data also reveal a different mechanism by which helminth infection modulates immune function in LTBI.

Alcohol consumption alters anti-Strongyloides stercoralis antibodies production.

Individuals infected with Strongyloides stercoralis have been reported to produce different immunoglobulins isotypes, yet few studies have evaluated their use in strongyloidiasis diagnosis. The aim of this work was to evaluate the immunoreactivity of different classes and subclasses of anti-S. stercoralis circulating antibodies in alcoholic patients by ELISA and to perform immunoblotting in samples with discordant results between parasitological and immunological methods. 345 male patients with a clinical diagnosis of alcoholism hospitalized at a reference center for alcoholics in Salvador, Bahia, Brazil, were included in this study. The fecal samples were examined by three different parasitological methods (spontaneous sedimentation, Baermann-Moraes and Agar Plate Culture methods). The ELISA was performed for the detection of IgG, IgG1, IgG4, IgE and IgA1 anti-S. stercoralis. Immunoblotting, for the detection of specific IgA1, was used to elucidate discordant results between parasitological and immunological methods. S. stercoralis infection frequency in alcoholic patients by parasitological methods was 21.4% (74/345). Although IgE-ELISA demonstrated a high sensitivity and specificity in non-alcoholic patients, about 30% (22/74) of alcoholics with larvae in feces were negative. IgG1-ELISA detected the lowest frequency of antibodies in alcoholic patients with larvae in feces, only 57% (42/74). IgG4-ELISA was the best assay for S. stercoralis infection immunodiagnosis. Immunoreactivity in the immunoblotting for IgA1 at 90, 75, 26 and/or 17 kDa bands was observed in 92% (33/36) of alcoholics with larvae excretion and negative ELISA for one or more antibody isotypes. In conclusion, IgG4-ELISA showed the highest sensitivity and specificity, thus demonstrating its superiority for strongyloidiasis immunodiagnosis in alcoholic and non-alcoholic individuals. Both, IgE and IgG1-ELISA presented high sensitivities and specificities for S. stercoralis infection diagnosis in non-alcoholics, however there was low reactivity in alcoholic individuals. This can be associated with an increased susceptibility to severe strongyloidiasis in these patients. IgA1-immunoblotting can be used to confirm S. stercoralis infection when there are discordant results between parasitological methods and ELISA.

Enhanced production of short-peptide tagged Ss3a recombinant protein as a novel potential biomarker for strongyloidiasis.

Strongyloidiasis is a mysterious yet important parasitic disease that is hard to diagnose. While microscopic examination remains a "controversial" gold standard method, improved diagnosis is achieved through confirmatory assays with serological and/or molecular diagnostic approaches. In the current serodiagnosis of strongyloidiasis, recombinant proteins have been adopted in place of the use of native parasite antigens, although the availability of diagnostically potential proteins are still limited. Here, we introduce a novel Strongyloides recombinant protein that is uniquely attached to two different short peptide tags as a potential diagnostic biomarker for serodiagnosis of strongyloidiasis, namely lysine (7K) and aspartic acid (7D). The work presented focus on improving the yield and purity of the previously unexpressed recombinant protein. Preliminary diagnostic evaluation of the recombinant favors Ss3a7K protein owing to its higher antigenicity performance with 80% sensitivity and 100% specificity, respectively.

Infection by Strongyloides stercoralis in immigrants with Chagas disease: evaluation of eosinophilia as screening method in primary care.

OBJECTIVES: To evaluate co-infection of Strongyloides stercoralis and Trypanosoma cruzi and to assess eosinophilia as a screening test for the detection of S. stercoralis infection in patients with Chagas disease (CD). METHODS: A retrospective diagnostic validation study was performed on serum samples from primary care patients diagnosed with CD in the southern Barcelona metropolitan area. All samples with eosinophilia (n = 87) and a random sample of non-eosinophilic sera (n = 180) were selected. Diagnosis of CD was based on positive serology by means of two tests: ORTHO® T. cruzi ELISA test, and BIO-FLASH® Chagas or Bioelisa CHAGAS. SCIMEDX ELISA STRONGY-96 was used to diagnose strongyloidiasis. RESULTS: Strongyloides stercoralis serology was positive in 15% of patients of whom 95% showed eosinophilia, vs. 21% of those with negative serology (P < 0.001), with differences in the mean eosinophil count (0.49 vs. 0.27 × 109 /l). Only 1.1% of patients with CD but without eosinophilia presented positive serology for S. stercoralis, whereas 44% of patients with CD and eosinophilia did (P < 0.001). Sensitivity and specificity values for eosinophilia were thus 95% and 79%, respectively. PPV was 42.5% and NPV, 98.9%. CONCLUSIONS: The prevalence of co-infection by T. cruzi and S. stercoralis is not negligible and has probably been underestimated for years in many areas, due to frequently subclinical infections. Therefore, serology seems mandatory for these patients and the use of eosinophilia as initial screening could facilitate the task, decreasing the number of analyses to be performed.

OBJECTIFS: Evaluer la coinfection par Strongyloides stercoralis et Trypanosoma cruzi et évaluer éosinophilie comme un test de dépistage pour la détection de l'infection à S. stercoralis chez les patients atteints de la maladie de Chagas (MC). MÉTHODES: Une étude de validation diagnostique rétrospective a été réalisée sur des échantillons de sérum de patients de soins primaires diagnostiqués avec la MC dans la région métropolitaine du sud de Barcelone. Tous les échantillons avec éosinophilie (n = 87) et un échantillon aléatoire de sérums non éosinophiliques (n = 180) ont été sélectionnés. Le diagnostic de la MC était basé sur une sérologie positive au moyen de deux tests: le test ELISA ORTHO® T. cruzi et le test BIO-FLASH® Chagas ou Bioelisa CHAGAS. SCIMEDX ELISA STRONGY-96 a été utilisé pour diagnostiquer la strongyloïdose. RÉSULTATS: La sérologie de S. stercoralis était positive chez 15% des patients dont 95% présentaient une éosinophilie, contre 21% de ceux avec une sérologie négative (P <0,001), avec des différences dans le taux moyen d'éosinophiles (0,49 contre 0,27 × 109 /L). Seuls 1,1% des patients avec la MC mais sans éosinophilie présentaient une sérologie positive pour S. stercoralis ; contrairement à 44% des patients atteints de la MC avec une éosinophilie (p <0,001). Les valeurs de sensibilité et de spécificité pour l'éosinophilie étaient ainsi respectivement de 95% et 79%. La VPP était de 42,5% et la VPN, 98,9%. CONCLUSIONS: La prévalence de la coinfection par T. cruzi et S. stercoralis n'est pas négligeable et a probablement été sous-estimée depuis des années dans de nombreuses régions, en raison d'infections fréquemment infracliniques. Par conséquent, la sérologie semble obligatoire pour ces patients et l'utilisation de l'éosinophilie comme dépistage initial pourrait faciliter la tâche, diminuant le nombre d'analyses à effectuer.

Rapid Progress toward Elimination of Strongyloidiasis in North Queensland, Tropical Australia, 2000-2018.

Infection with Strongyloides stercoralis can cause life-threatening disease in immunocompromised patients. Strongyloidiasis is thought to be hyper-endemic in tropical Australia, but there are limited contemporary seroprevalence data to inform local elimination strategies. To define the temporospatial epidemiology of strongyloidiasis in Far North Queensland, tropical Australia, the serology results of 2,429 individuals tested for the infection between 2000 and 2018 were examined. The proportion of positive tests fell from 36/69 (52.2%) in 2000 to 18/222 (8.1%) in 2018 (P < 0.001). Indigenous patients were more likely to have a positive result (Odds Ratio [OR]: 3.9, 95% CI: 3.0-5.0); however, by the end of the study period, residence in a rural or remote location (OR 3.9 (95% CI: 1.2-13.0), P = 0.03) was a more important risk factor for seropositivity than Indigenous status (OR 1.1 (95% CI: 0.4-3.1) P = 0.91). Ivermectin prescription data were available for the period 2004-2018, with annual prescriptions increasing from 100 to 185 boxes (P = 0.01). The volume of ivermectin dispensed correlated negatively with seropositivity (Spearman's rho = -0.62, P = 0.02). An expanded environmental health program was implemented during the study period and likely contributed to the declining seroprevalence; however, the relative contributions of the individual components of this program are difficult to quantify. The seroprevalence of strongyloidiasis has declined markedly in this region of tropical Australia despite there being no targeted campaign to address the disease. Expanded prescription of ivermectin and public health interventions targeting the few remaining high-prevalence communities would be expected to expedite disease elimination.

Strongyloidiasis in northern Vietnam: epidemiology, clinical characteristics and molecular diagnosis of the causal agent.

BACKGROUND: Strongyloidiasis is a health problem in Vietnam, but appropriate information is still limited. The aim of this study was to determine the prevalence, geographical distribution, epidemiological aspects, symptoms and other health indicators of Strongyloides stercoralis infections in patients from 27 provinces of northern Vietnam attending the Hanoi Medical University Hospital during 2016 and 2017. METHODS: Blood samples of 2000 patients were analyzed for S. stercoralis infection with an IgG ELISA test. Seroprevalence was analyzed by gender, age group, locality of origin (rural or urban areas) and symptoms. Stools from the seropositive patients were examined for the detection of worms which were subsequently used for species identification by morphology and rDNA ITS1 sequencing. RESULTS: A seroprevalence of 20% was detected, showing an increasing prevalence from young to older age groups but without significant gender difference. Seroprevalence was higher in rural areas than in urban areas, both in general and individually in all provinces without exception, and lower in the mountainous areas than in the large valley lowlands. The follow-up of the 400 patients showed eosinophilia in 100% of cases, diarrhoea in 64.5%, digestion difficulties in 58.0%, stomachache in 45.5%, stomach and duodenal ulcers in 44.5%, itching in 28.0% and fever in 9.5%. The prevalence of symptoms and signs were also higher in older age groups than in younger age groups. Worms were detected in stools of 10.5% of the patients. Sequencing of a 501-bp nuclear ribosomal DNA ITS1 fragment allowed for the verification of infection by Strongyloides stercoralis. CONCLUSIONS: To our knowledge, this study is the largest survey of human strongyloidiasis in Vietnam so far and the first molecular identification of this nematode species in this country. Long-term chronicity may probably be usual in infected subjects, mainly in the older age groups.