Detection of Strongyloides stercoralis infection particularly in asymptomatic individuals is often hampered due to the lack of standard diagnostic tools. In this study, the use of serological and molecular approaches were investigated for the detection of S. stercoralis infection among an Orang Asli (indigenous) community following a preliminary detection by microscopic examination of faecal samples. Out of 54 individuals studied, 17/54 (31.5%) were detected to be positive for S. stercoralis infection by enzyme-linked immunosorbent assay (ELISA), compared to 0/54 (0%) by faecal examination. Further confirmation performed by a nested polymerase chain reaction (PCR) using DNA extracted from faecal samples of these 17 individuals yielded 3/17 (17.6%) positives for S. stercoralis DNA amplification. No amplification was seen with the other 37 faecal samples, which were negative by microscopy and ELISA. As the high ELISA positive results were suspected to be false-positives, ELISA is not recommended for use as a detection tool but may be beneficial for evaluating the effectiveness of anti-Strongyloides drugs. The present finding indicated that PCR should be considered as an alternative diagnostic tool for the detection of S. stercoralis infection.
This cross-sectional study aimed to determine the prevalence and risk factors of S. stercoralis infection among 1142 Orang Asli primary schoolchildren in six different states of Peninsular Malaysia. Fecal samples were examined using direct smear, formalin-ether sedimentation (FES), agar plate culture (APC) and PCR techniques. Overall, 15.8% of the children were found to be infected with S. stercoralis. The prevalence was 0.2, 1.3, 15.2 and 13.7% by direct smear, FES, APC and PCR, respectively. Multivariate analysis showed that an age of >10 years, being male, belonging to a Proto-Malay tribe, belonging to the Senoi tribe, indiscriminate defecation, using an unimproved water source for drinking water and not wearing shoes when outside were the significant risk factors of infection among these children. In conclusion, we provide new evidence on the occurrence of S. stercoralis in Malaysia to show that there is a relatively high prevalence of infection among Orang Asli schoolchildren. Therefore, the use of specific methods for detecting S. stercoralis should be considered when screening these children for intestinal parasites. Moreover, prevention and control measures specific to S. stercoralis should be integrated into the intestinal parasitic infections control programme in Malaysia.
Strongyloides stercoralis is an intestinal nematode infecting humans. The actual prevalence of infestation with this parasite in our setting is not well established. Thus, this study was conducted to determine the age, sex and co-morbid conditions among patients with S. stercoralis infestation as well as to study the common manifestations of strongyloidiasis in our patients. Records of patients with positive S. stercoralis larvae from January 2000 to December 2012 in Hospital Universiti Sains Malaysia, Kubang Kerian, Kelantan were reviewed. Ten patients were male and two were female. Their ages ranged from 19 to 78 years old. The majority (92%) of cases, presented with intestinal symptoms and 50% with moderate to severe anaemia. Thirty percent of cases had extraintestinal manifestations such as cough, sepsis and pleural effusion. Ninety-two percent of the patients had a comorbid illness. Most patients were immunocompromised, with underlying diabetes mellitus, retroviral disease, lymphoma and steroid therapy contributing to about 58% of cases. Only 58% were treated with anti-helminthic drugs. Strongyloidiasis is present in our local setting, though the prevalence could be underestimated.
Two laboratory trials were conducted to determine the effect of the addition of spores (conidia) of the nematophagous fungus, Arthrobotrys oligospora, on the development of the ruminant parasite, Strongyloides papillosus, in cultures of bovine faeces. Both studies showed that at a concentration of 2000 conidia/g faeces virtually eliminated infective larvae (> 99% reduction), following 14 days incubation under ideal conditions (25 degrees C and saturated humidity) for free-living development of this parasite species. In one trial, a high level of control was also observed at a 10-fold decrease in conidia concentration (200 spores/g faeces). This work has demonstrated, in principle, that A. oligospora could provide a practical biological control agent against S. papillosus infecting intensively raised young ruminants in the humid tropics/subtropics.
Laboratory diagnosis of Strongyloides infections can be grouped into direct and indirect detection methods, and a combination of the two methods is often needed to reach an accurate and timely diagnosis. This review focuses on non-conventional direct detection via molecular and antigen detection assays. Conventional PCR is the most commonly used molecular diagnostic for Strongyloides. Real-time PCR is accurate and highly sensitive for quantitative and qualitative analysis. Meanwhile, PCR-RFLP can efficiently distinguish human and dog isolates of S. stercoralis, S. fuelleborni (from monkey), and S. ratti (from rodent). Loop-mediated isothermal amplification (LAMP) amplifies DNA isothermally with high specificity, efficiency, and rapidity, and has potential for point-of-care (POC) translation. As for antigen detection assay, coproantigen detection ELISAs for strongyloidiasis traditionally relied on raising rabbit polyclonal antibodies against the parasite antigens for use as capture or detection reagents. Subsequently, hybridoma technology using animals has enabled the discovery of monoclonal antibodies specific to Strongyloides antigens and was utilised to develop antigen detection assays. In recent times, phage display technology has facilitated the discovery of scFv antibody against Strongyloides protein that can accelerate the development of such assays. Improvements in both direct detection methods are being made. Strongyloides molecular diagnostics is moving from the detection of a single infection to the simultaneous detection of soil-transmitted helminths. Meanwhile, antigen detection assays can also be multiplexed and aptamers can be used as antigen binders. In the near future, these two direct detection methods may be more widely used as diagnostic tools for strongyloidiasis.
The conventional method of detecting Strongyloides stercoralis in fecal samples has poor diagnostic sensitivity. Detection of Strongyloides-specific antibodies increases the sensitivity; however, most tests are ELISAs that use parasite extract which may cross-react with the sera of other helminth infections. To improve the serological diagnosis of strongyloidiasis, this study aimed at developing a sensitive and specific lateral flow rapid dipstick test. Two recombinant proteins, recombinant NIE (rNIE) and recombinant Ss1a (rSs1a), were used in preparing the dipstick, with gold-conjugated antihuman IgG4 as detector reagent. In parallel, the corresponding ELISA was performed. Both assays demonstrated diagnostic sensitivity of 91.3% (21/23) when tested with serum samples of patients with Strongyloides infection, and 100% specificity with 82 sera of asymptomatic (healthy) and those with other parasitic infections. The ELISA and dipstick test results were positively correlated to each other (r = 0.6114, P = 0.0019). The developed lateral flow dipstick test may improve the serodiagnosis of strongyloidiasis and merit further validation studies.
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.
Enzyme-linked immunosorbent assays (ELISAs) were developed for the detection of IgG, IgG4 and IgE antibodies against Strongyloides stercoralis. A commercial ELISA (IVD Research, USA) was also used, and the sensitivities and specificities of the four assays were determined. Serum samples from 26 patients with S. stercoralis infection and 55 patients with other infections or no infection were analysed. Sensitivities of the IgG4 , IgG, IgE and IgG (IVD) assays were 76.9%, 84.6%, 7.7% and 84.6%, respectively, while the specificities were 92.7%, 81.8%, 100% and 83.6%, respectively. If filariasis samples were excluded, the specificities of the IgG4 -ELISA and both IgG-ELISAs increased to 100% and 98%, respectively. A significant positive correlation was observed between IgG- and IgG4 -ELISAs (r = 0.4828; P = 0.0125). IgG- and IgG- (IVD) ELISAs (r = 0.309) were positively correlated, but was not significant (P = 0.124). Meanwhile there was no correlation between IgG4 - and IgG- (IVD) ELISAs (r = 0.0042; P = 0.8294). Sera from brugian filariasis patients showed weak, positive correlation between the titres of antifilarial IgG4 and the optical densities of anti-Strongyloides IgG4 -ELISA (r = 0.4544, P = 0.0294). In conclusion, the detection of both anti-Strongyloides IgG4 and IgG antibodies could improve the serodiagnosis of human strongyloidiasis. Furthermore, patients from lymphatic filariasis endemic areas who are serologically diagnosed with strongyloidiasis should also be tested for filariasis.
Strongyloides stercoralis infection is prevalent worldwide and can cause lifelong infection in immunocompetent individuals, and potentially death in immunosuppressed patients. The diagnosis is hindered by the low sensitivity of microscopic examination, thus making serology an important complementary test to improve the detection rate. However, there were reports that some Strongyloides-infected individuals were negative with specific IgG and IgG4 assays, and other helminth infections were positive with commercial Strongyloides IgG-ELISAs. Thus, there is a need to develop better serodiagnostic methods for strongyloidiasis. We investigated the diagnostic potential of IgE-ELISAs using Strongyloides larval lysate. Sera from two groups infected with Strongyloides served as the positive reference, that is, 1) positive by commercial IgG-ELISAs and IgG4 rapid test, and stool samples positive by microscopy and/or PCR (group IA; n = 20); and 2) negative by IgG-ELISAs and IgG4 rapid test, but stool samples were PCR positive (group IB sera; n = 11). Sera from another two groups served as negative reference (controls), that is, 1) infected with other parasites (group II; n = 73) and 2) healthy donors (group III; n = 22). Results showed a 100% diagnostic sensitivity in detecting sera from groups IA and IB. The latter group of individuals probably had early infection because their IgG and IgG4 assays were negative. The optical density values of group IB sera were also significantly lower than those of group IA (P < 0.003). The IgE-ELISA was 100% specific when tested against sera from groups II and III. This study highlights the diagnostic potential of IgE-ELISA using larval lysate to detect strongyloidiasis, especially those with probable early infection.
Strongyloides callosciureus n. sp. (Nematoda: Rhabditoidea), from Asian sciurids, is described based on morphology, morphometry, and the small and large subunit (SSU/LSU) ribosomal RNA gene (rDNA) sequences. This new species was collected from Pallas's squirrels (Callosciurus erythraeus) in the central part of mainland Japan (Honshu), which were originally introduced from Taiwan some decades ago, and plantain squirrels (Callosciurus notatus) imported from Malaysia as personal pets. For comparison, Strongyloides robustus Chandler, 1942 was collected from American red squirrels (Tamiasciurus hudsonicus) and southern flying squirrels (Glaucomys volans) imported from the United States as personal pets. The parasitic females found in North American and Asian sciurids shared some key morphological features such as the ovary running spirally around the gut, and the shapes of the stoma in the apical view and the tail. However, morphometric features of parasitic females in North American and Asian sciurids differed significantly from each other; the former was larger than the latter, and the relative position of the vulva to the whole body length from the mouth was different. The SSU/LSU rDNA sequences supported the division of sciurid Strongyloides isolates by geographical distribution of the host and morphological features, leading us to propose the erection of new species.
Infections and mTalignancies are common causes of pleural effusion. Among infectious causes, hyperinfection syndrome of Strongyloides stercoralis may occur in immunosuppressive patient. A 62-year-old man, known case of Non-Hodgkin lymphoma (NHL) was presented with recurrent NHL stage IV and had undergone salvage chemotherapy. Patient subsequently developed pneumonia with bilateral pleural effusion and ascites. We reported rhabditiform larvae of S. stercoralis in pleural fluid of both lungs without infiltration by lymphoma cells. Stool for microscopic examination also revealed rhabditiform larvae of S. stercoralis. This patient was a known case of NHL receiving chemotherapy resulting in immunosuppression state. Although S. stercoralis infection is not very common compared to other parasitic infections, it is common in immunosuppressive patients and may present with hyperinfection. Therefore, awareness of this parasite should be kept in mind in immunosuppressive patients.
Understanding determinants shaping infection risk of endangered wildlife is a major topic in conservation medicine. The proboscis monkey, Nasalis larvatus, an endemic primate flagship species for conservation in Borneo, is endangered through habitat loss, but can still be found in riparian lowland and mangrove forests, and in some protected areas. To assess socioecological and anthropogenic influence on intestinal helminth infections in N. larvatus, 724 fecal samples of harem and bachelor groups, varying in size and the number of juveniles, were collected between June and October 2012 from two study sites in Malaysian Borneo: 634 samples were obtained from groups inhabiting the Lower Kinabatangan Wildlife Sanctuary (LKWS), 90 samples were collected from groups of the Labuk Bay Proboscis Monkey Sanctuary (LBPMS), where monkeys are fed on stationary feeding platforms. Parasite risk was quantified by intestinal helminth prevalence, host parasite species richness (PSR), and eggs per gram feces (epg). Generalized linear mixed effect models were applied to explore whether study site, group type, group size, the number of juveniles per group, and sampling month predict parasite risk. At the LBPMS, prevalence and epg of Trichuris spp., strongylids, and Strongyloides spp. but not Ascaris spp., as well as host PSR were significantly elevated. Only for Strongyloides spp., prevalence showed significant changes between months; at both sites, the beginning rainy season with increased precipitation was linked to higher prevalence, suggesting the external life cycle of Strongyloides spp. to benefit from humidity. Higher prevalence, epgs, and PSR within the LBPMS suggest that anthropogenic factors shape host infection risk more than socioecological factors, most likely via higher re-infection rates and chronic stress. Noninvasive measurement of fecal parasite stages is an important tool for assessing transmission dynamics and infection risks for endangered tropical wildlife. Findings will contribute to healthcare management in nature and in anthropogenically managed environments.
INTRODUCTION: Strongyloidiasis is one of the most commonly neglected but clinically important parasitic infections worldwide, especially among immunocompromised patients. Evidence of infection among immunocompromised patients in Malaysia is, however, lacking. In this study, microscopy, real-time polymerase chain reaction (PCR) and enzyme-linked immunosorbent assays (ELISAs) were used to detect Strongyloides stercoralis (S. stercoralis) infection among cancer patients in a Malaysian hospital.
METHODS: A total of 192 stool and serum samples were collected from cancer patients who were receiving chemotherapy with or without steroid treatment at a hospital in northeastern Malaysia. Stool samples were examined for S. stercoralis using parasitological methods and real-time PCR. Serology by ELISA was performed to detect parasite-specific immunoglobulin G (IgG), IgG4 and immunoglobulin E (IgE) antibodies. For comparison, IgG4- and IgG-ELISAs were also performed on the sera of 150 healthy individuals from the same area.
RESULTS: Of the 192 samples examined, 1 (0.5%) sample was positive for S. stercoralis by microscopy, 3 (1.6%) by real-time PCR, 8 (4.2%) by IgG-ELISA, 6 (3.1%) by IgG4-ELISA, and none was positive by IgE-ELISA. In comparison, healthy blood donors had significantly lower prevalence of parasite-specific IgG (2.67%, p < 0.05) and IgG4 (2.67%, p < 0.05) responses.
CONCLUSION: This study showed that laboratory testing may be considered as a diagnostic investigation for S. stercoralis among immunocompromised cancer patients.
Strongyloides stercoralis infection is of low prevalence in Malaysia. We report an unusual case presenting primarily with gastric symptoms. The patient was a 72 years old Chinese male admitted for progressive weight loss and abdominal bloating. Gastroscopic examination revealed mucosal prepyloric elevations in the gastric mucosa. Gastric strongyloidiasis was confirmed by the presence of adult forms, as well as ova and larval rhabditiform stages of the worm in the gastric mucosal crypts. We believe that this is the first histologically documented case of gastric strongyloidiasis in Malaysia.
Strongyloidiasis is a major neglected tropical disease with the potential of causing lifelong infection and mortality. One of the ways for effective control of this disease is developing improved diagnostics, particularly using serological approaches. A serological test can achieve high diagnostic sensitivity and specificity, has the potential for point-of-care translation, and can be used as a screening tool for early detection. More research is needed to find clinically important antibody biomarkers for early disease detection, mapping, and epidemiological surveillance. This article summarizes human strongyloidiasis and the available diagnostic tools for the disease, focusing on describing the current antibody assays for strongyloidiasis. Finally, prospects of developing a more effective serodiagnostic tool for strongyloidiasis are discussed.
Soil-transmitted helminth infections remain a major public health burden in low- and middle-income countries. The traditional diagnosis by microscopic examination of fecal samples is insensitive and time-consuming. In this study, a pentaplex real-time polymerase chain reaction (PCR) was evaluated for the simultaneous detection of Ancylostoma, Necator americanus, Ascaris lumbricoides, and Strongyloides stercoralis. The results were compared with those obtained by conventional parasitological diagnostic methods. Real-time PCR was positive in 48 of 77 samples (62.3%) and microscopic examination was positive in six samples (7.8%) only (P < 0.05). In conclusion, the real-time PCR assay described in this study provides a specific and sensitive diagnostic tool for the detection of these four helminth species in epidemiological studies and monitoring of treatment programs.