Accuracy, acceptability, and feasibility of diagnostic tests for the screening of Strongyloides stercoralis in the field (ESTRELLA): a cross-sectional study in Ecuador

An evaluation of a lateral flow rapid diagnostic test for Strongyloides stercoralis infection

Strongyloides stercoralis in humans often presents as a chronic asymptomatic infection. Diagnosis can be challenging due to the limited sensitivity of faecal-based parasitological techniques. A prototype lateral flow rapid diagnostic test (RDT) for the detection of specific antibodies against Strongyloides stercoralis (SsRapid) was evaluated using 143 samples from the serum bank of the Swiss Tropical and Public Health Institute. Group 1 (n = 30) comprised serum samples from larvae-positive individuals; the RDT's diagnostic sensitivity was 97 % (29/30). Group II comprised serum samples from patients with other parasitic infections (n = 86) and Swiss blood donors (n = 27); the RDT's diagnostic specificity for this group was 90 % (102/113). The RDT showed good diagnostic performance and is a promising point-of-care test for detecting human Strongyloides stercoralis infection.

Prevalence of Strongyloides stercoralis and other helminths in four districts of Madagascar

BACKGROUND

Estimation of prevalence of Strongyloides stercoralis infection is required in endemic areas, in order to identify areas in need of control programmes. Data on prevalence of strongyloidiasis in Madagascar are scant. Aim of this work was to estimate prevalence of S. stercoralis in four districts of Madagascar.

METHODS

Fecal and serum samples collected in the context of a previous study on schistosomiasis were tested with S. stercoralis real-time PCR and serology, respectively. A multiplex real-time PCR for Ascaris lumbricoides, Ancylostoma duodenalis, Necator americanus, and Trichuris trichiura was done on fecal samples collected in the areas demonstrating higher prevalence of strongyloidiasis. Comparisons between proportions were made using Fisher exact test, with false discovery rate correction used for post-hoc comparisons. A multivariable Firth logistic regression model was used to assess potential risk factors for S. stercoralis infection.

RESULTS

Overall, 1775 serum samples were tested, of which 102 of 487 (20.9%) and 104 of 296 (35.2%) were serological-positive in Marovoay and in Vatomandry districts (both coastal areas), respectively, compared to 28 of 496 (5.6%) and 30 of 496 (6.1%) in Tsiroanomandidy and in Ambositra districts (both highlands), respectively (adj. p < 0.001). PCR for S. stercoralis was positive in 15 of 210 (7.1%) and in 11 of 296 (3.7%) samples from Marovoay from Vatomandry, respectively, while was negative for all samples tested in the other two districts. High prevalence of A. lumbricoides (45.9%), hookworm (44.6%) and T. trichiura (32.1%) was found in Vatomandry. In the multivariable analysis, strongyloidiasis was associated with hookworm infection. Hookworm infection was also associated with male sex and lower education level.

CONCLUSIONS

S. stercoralis prevalence proved higher in coastal areas compared to highlands. Different climatic conditions may explain this distribution, along with previous rounds of anthelminthics distributed in the country, which may have reduced the parasite load in the population. The high prevalence of the other soil-transmitted helminths (STH) in Vatomandry was unexpected, given the good coverage with benzimidazole in control campaigns. Further studies are needed to explore the risk factors for STH and S. stercoralis infections in Madagascar, in order to align with the WHO recommendations.

Design and expression of a chimeric recombinant antigen (SsIR-Ss1a) for the serodiagnosis of human strongyloidiasis: Evaluation of performance, sensitivity, and specificity

BACKGROUND

The sensitivity of parasitological and molecular methods is unsatisfactory for the diagnosis of strongyloidiasis, and serological techniques are remaining as the most effective diagnostic approach. The present study aimed to design and produce a chimeric recombinant antigen from Strongyloides stercoralis immunoreactive antigen (SsIR) and Ss1a antigens, using immune-informatics approaches, and evaluated its diagnostic performance in an ELISA system for the diagnosis of human strongyloidiasis.

METHODOLOGY/PRINCIPAL FINDINGS

The coding sequences for SsIR and Ss1a were selected from GenBank and were gene-optimized. Using bioinformatics analysis, the regions with the highest antigenicity that did not overlap with other parasite antigens were selected. The chimeric recombinant antigen SsIR- Ss1a, was constructed. The solubility and physicochemical properties of the designed construct were analyzed and its tertiary structures were built and evaluated. The construct was expressed into the pET-23a (+) expression vector and the optimized DNA sequences of SsIR-Ss1a (873 bp) were cloned into competent E. coli DH5α cells. Diagnostic performances of the produced recombinant antigen, along with a commercial kit were evaluated in an indirect ELISA system, using a panel of sera from strongyloidiasis patients and controls. The physicochemical and bioinformatics evaluations revealed that the designed chimeric construct is soluble, has a molecular with of 35 KDa, and is antigenic. Western blotting confirmed the immunoreactivity of the produced chimeric recombinant antigen with the sera of strongyloidiasis patients. The sensitivity and specificity of the indirect ELISA system, using the produced SsIR-Ss1a chimeric antigen, were found to be 93.94% (95% CI, 0.803 to 0.989) and 97.22% (95% CI, 0.921 to 0.992) respectively.

CONCLUSIONS/SIGNIFICANCE

The preliminary findings of this study suggest that the produced SsIR-Ss1a chimeric antigen shows promise in the diagnosis of human strongyloidiasis. However, these results are based on a limited panel of samples, and further research with a larger sample size is necessary to confirm its accuracy. The construct has potential as an antigen in the ELISA system for the serological diagnosis of this neglected parasitic infection, but additional validation is required.

Serological diagnosis of strongyloidiasis: An evaluation of three commercial assays

BACKGROUND

Strongyloidiasis is caused by a neglected nematode, manifesting as chronic intestinal infection with potentially severe manifestations. The disease is an emerging problem in non-endemic countries affecting travelers and migrants. Diagnosis of strongyloidiasis is hampered by the lack of standardization and absence of a gold standard. Since adequate direct methods to detect the motile larvae in stool samples are not widely available, other techniques such as serology have been developed.

METHODS

We evaluated three commercial ELISA kits (DRG Instruments, IVD Research, and Bordier Affinity Products) to detect IgG antibodies against Strongyloides stercoralis assays utilizing serum samples from travelers with microscopically confirmed strongyloidiasis (n = 50) and other imported helminthic infections (n = 159) as well as healthy controls (n = 50).

RESULTS

The DRG, IVD, and Bordier assays showed sensitivities of 58.0%, 64.0%, and 56.0%, respectively. Specificity values were 96.0%, 96.0%, and 92.0% in healthy controls, and 67.3%, 62.9%, and 76.7% in cases with other helminth infections, respectively. Cross-reactions were mostly observed in cases with other nematodes (37.5%, 42.5%, and 20.0%, respectively), but also in trematode (33.3%, 38.1%, and 19.0%, respectively) and in cestode infections (25.0%, 30.0%, and 32.5%, respectively).

CONCLUSION

The study demonstrates the diagnostic limitations of serological assays to detect or exclude cases of strongyloidiasis in returning travelers, who frequently present with recent or acute infections.

Evaluation of the SsIR/NIE recombinant antigen ELISA for the follow up of patients infected by Strongyloides stercoralis: a diagnostic study

Some serology assays demonstrated useful for post-treatment monitoring of Strongyloides stercoralis infection. Serology frequently has low specificity, which might be improved by the use of recombinant antigens. The Strongy Detect ELISA is based on 2 recombinant antigens (SsIR and NIE) and proved good accuracy. Aim of this study was to evaluate the performance of this test for the post-treatment monitoring of strongyloidiasis. We tested 38 paired sera, with matched fecal tests results, stored in our biobank and originating from a randomized controlled trial. At baseline, all patients tested positive for at least 1 fecal assay among PCR, direct stool microscopy and agar plate culture. Patients were re-tested with both serology and fecal assays 12 months after treatment. Primary outcome was the relative reduction in optical density (OD) between baseline and follow up. We observed that about 95% samples showed a reduction between pre and post-treatment OD, with a median relative reduction of 93.9% (IQR 77.3%–98.1%). In conclusion, the test proved reliable for post-treatment monitoring. However, some technical issues, including that the threshold for positivity has not be predefined, and that a substantial number of samples showed overflow signals, need to be fixed to permit use in routine practice.

Strongyloidiasis

Strongyloidiasis is a neglected tropical disease caused primarily by the roundworm Strongyloides stercoralis. Strongyloidiasis is most prevalent in Southeast Asia and the Western Pacific. Although cases have been documented worldwide, global prevalence is largely unknown due to limited surveillance. Infection of the definitive human host occurs via direct skin penetration of the infective filariform larvae. Parasitic females reside in the small intestine and reproduce via parthenogenesis, where eggs hatch inside the host before rhabditiform larvae are excreted in faeces to begin the single generation free-living life cycle. Rhabditiform larvae can also develop directly into infectious filariform larvae in the gut and cause autoinfection. Although many are asymptomatic, infected individuals may report a range of non-specific gastrointestinal, respiratory or skin symptoms. Autoinfection may cause hyperinfection and disseminated strongyloidiasis in immunocompromised individuals, which is often fatal. Diagnosis requires direct examination of larvae in clinical specimens, positive serology or nucleic acid detection. However, there is a lack of standardization of techniques for all diagnostic types. Ivermectin is the treatment of choice. Control and elimination of strongyloidiasis will require a multifaceted, integrated approach, including highly sensitive and standardized diagnostics, active surveillance, health information, education and communication strategies, improved water, sanitation and hygiene, access to efficacious treatment, vaccine development and better integration and acknowledgement in current helminth control programmes.

Human strongyloidiasis: complexities and pathways forward

Strongyloidiasis is a World Health Organization neglected tropical disease usually caused by Strongyloides stercoralis, a parasitic worm with a complex life cycle. Globally, 300-600 million people are infected through contact with fecally contaminated soil. An autoinfective component of the life cycle can lead to chronic infection that may be asymptomatic or cause long-term symptoms, including malnourishment in children. Low larval output can limit the sensitivity of detection in stool, with serology being effective but less sensitive in immunocompromise. Host immunosuppression can trigger catastrophic, fatal hyperinfection/dissemination, where large numbers of larvae pierce the bowel wall and disseminate throughout the organs. Stable disease is effectively treated by single-dose ivermectin, with disease in immunocompromised patients treated with multiple doses. Strategies for management include raising awareness, clarifying zoonotic potential, the development and use of effective diagnostic tests for epidemiological studies and individual diagnosis, and the implementation of treatment programs with research into therapeutic alternatives and medication safety.

Screening for Neglected Tropical Diseases and other infections in African refugees and asylum seekers in Rome and Lazio region, Italy

BACKGROUND

Few reliable data are available on Neglected Tropical Diseases (NTDs) and other infections among African refugees and asylum seekers in Italy. We aimed to estimate the prevalence of NTDs and other infections in a large cohort of African refugees and asylum seekers living in reception centers in Lazio, Italy.

MATERIAL AND METHODS

This is an observational, prospective prevalence study on infectious diseases in a large population of African refugees and asylum seekers (936 overall) consecutively enrolled for screening purpose at the Infectious and Tropical diseases outpatient clinic of the National Institute of Migrant and Poverty (INMP), Rome from August 2019 to December 2020.

RESULTS

We found a prevalence of 8.8 % and 31 % for Strongyloides and schistosoma infection, respectively, while the prevalence of human immunodeficiency virus (HIV) infection was 0.7 %, HCV antibodies 2.5%, hepatitis B virus surface antigen 10.8 % and syphilis serological tests 2.9 %.

CONCLUSION

Strongyloidiasis and schistosomiasis are highly prevalent among African refugees and asylum seekers in Italy, in contrast to communicable diseases (with the exception of hepatitis B). Raising awareness of NTDs among health professionals and implementing guidelines seems to be of paramount importance to prevent these diseases and their sufferers from becoming even more "neglected".