A Practical Approach to Screening for Strongyloides stercoralis

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.

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.

Locally acquired strongyloidiasis in remote Australia: why are there still cases?

In Australia, strongyloidiasis primarily affects returned travellers, Vietnam veterans and refugees or asylum seekers, and First Nations people. Non-overseas acquired cases are seen almost exclusively in Australian First Nations remote communities. Australian First Nations communities have one of the highest rates of strongyloidiasis in the world. Our work has shown that strongyloidiasis is a disease of poverty. Acknowledging this is important-we need to shift the lens to socioeconomic factors, particularly environmental health hardware such as working toilets and sewerage systems, showers and laundries, and effective wastewater and rubbish removal. The rates of strongyloidiasis in First Nations communities is a result of decades of inadequate, poorly constructed and/or poorly maintained housing, and poor environmental health hardware (hereafter hardware). The solution lies in adequate funding, resulting in well designed and maintained housing and appropriate hardware. Governments need to allow First Nations communities themselves to take the lead role in funding allocation, and design, construction and maintenance of their housing and hardware. This will ensure housing and hardware fulfils cultural and physical needs and desires, and protects health. Improving housing and hardware will also improve other health outcomes. This article is part of the Theo Murphy meeting issue 'Strongyloides: omics to worm-free populations'.

Improved diagnostic sensitivity of human strongyloidiasis using point-of-care mixed recombinant antigen-based immunochromatography

Strongyloidiasis is a neglected tropical disease that can cause fatal complications due to hyperinfection and disseminated strongyloidiasis in immunocompromised patients. We used two Strongyloides stercoralis recombinant antigenic proteins, L3NieAg.01 (NIE) and IgG-immunoreactive antigen (SsIR), to develop the recombinant antigen-based immunochromatography test (ICT) kit. We constructed and compared kits using either the NIE (NIE ICT kit) or the SsIR (SsIR ICT kit) antigens and a kit using a mixture of both (NIE-SsIR ICT kit) for detection of anti-Strongyloides IgG antibody in human serum samples. Serum samples from normal healthy individuals (Group I, n = 40), proven strongyloidiasis patients (Group II, n = 100), and those with other parasitic infections (Group III, n = 154) were evaluated. Sensitivity and specificity were 81.0% and 84.0% for the NIE ICT kit, 89.0% and 83.5% for the SsIR ICT kit, and 95.0% and 90.2% for the NIE-SsIR ICT kit, respectively. The NIE-SsIR ICT kit provided the best diagnostic results; it can supplement stool examination for clinical diagnosis and can be used to screen for asymptomatic S. stercoralis infection in people at risk in endemic areas. The NIE-SsIR ICT kit can also be used in large-scale sero-epidemiological investigations in endemic areas without the need for additional facilities or ancillary supplies.

MANAGEMENT OF A FATAL OUTBREAK OF STRONGYLOIDIASIS IN A CAPTIVE POPULATION OF PANTHER CHAMELEONS (FURCIFER PARDALIS) WITH IVERMECTIN

An outbreak of the nematode Strongyloides sp. occurred in a population of 18 male and 29 female panther chameleons (Furcifer pardalis) at the Singapore Zoo. The parasite was first detected in one individual during routine microscopic examination of feces using the direct examination and magnesium sulfate flotation methods. The parasite was later found to have a closest match (98.96%) with Strongyloides sp. Okayama by DNA sequencing. Over a period of 6 mon, 97.9% (46/47) of the panther chameleons tested positive for the parasite, and 25.5% (12/47) of the animals died due to the disease. All the animals that died were female. Of the positive tests, magnesium sulfate flotation identified the parasite 98.1% (105/107) of the time, compared to direct fecal microscopy, which identified the parasite only 43.9% (47/107) of the time. Parasite eggs were detected in 100% (105/105) of the positive magnesium sulfate flotation tests but only 66.0% (31/47) of the positive direct fecal microscopy tests. Parasite larvae were detected in 61.7% (29/47) of the positive direct fecal microscopy tests but only 9.5% (10/105) of the magnesium sulfate flotation tests. Treatments with fenbendazole and pyrantel pamoate at published doses were ineffective at eliminating the parasite. Ivermectin (0.2 mg/kg PO q2wk for two doses) was successful at treating the parasite, with all animals testing negative for the parasite at the end of the treatment course without any observed adverse reactions. However, complete eradication of the parasite could not be achieved, as Strongyloides sp. could still be detected in the population on routine coproscopy intermittently over 3 yr. There were no further mortalities due to the disease with prompt treatment with ivermectin. Strongyloidiasis may cause high morbidity in panther chameleons, but severe disease leading to mortality can be prevented with the use of ivermectin.

Efficacy of Oral Ivermectin as Empirical Prophylaxis for Strongyloidiasis in Patients Treated with High-Dose Corticosteroids: A Retrospective Cohort Study

People living in areas endemic for strongyloidiasis are at risk of latent Strongyloides stercoralis infection. Corticosteroid therapy is a well-established risk factor for life-threatening hyperinfection syndrome and disseminated disease owing to suppression of the immune system. There are limited data available on the efficacy and cost of providing oral ivermectin prophylaxis to all patients receiving high-dose corticosteroids for strongyloidiasis in endemic areas. We thus conducted this retrospective cohort study at Khon Kaen University's Srinagarind Hospital from 2015 to 2019. Inclusion criteria were as follows: age ≥ 18 years, having received ≥ 0.5 mg/kg/day of prednisolone or equivalent for at least 14 days, and hospitalization during the study period. A total of 250 patients were included in the study: 125 in the empirical prophylaxis group (prescribed ivermectin even if fecal examination results were negative or nonexistent) and the remaining patients in the definite therapy group (prescribed ivermectin only if S. stercoralis was detected by fecal examination). The prevalence of strongyloidiasis at enrollment estimated by fecal examination was 5.5%. Ivermectin was given to 125 patients (100%) in the prophylaxis group compared with 12 (9.6%) in the definite therapy group (P value < 0.001). During the 12-month follow-up period, S. stercoralis was detected in three patients, two in the prophylaxis group and one in the definite therapy group (P value = 1.000). No cases of hyperinfection syndrome or disseminated disease were found. The empirical prophylaxis strategy had a significantly higher cost than the definite therapy strategy (563 versus 254, P value < 0.001) and did not demonstrate superior efficacy in strongyloidiasis prevention.

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.

Strongyloides and COVID-19: Challenges and Opportunities for Future Research

Strongyloides stercoralis is a soil transmitted helminth endemic to tropical and subtropical areas that can persist for decades in immunocompetent human hosts as a chronic asymptomatic infection. The use of corticosteroids, a mainstay of treatment for patients hospitalized with severe coronavirus disease (COVID-19), can trigger a life-threatening Strongyloides hyperinfection syndrome and disseminated disease. We identified 22 previously published cases of strongyloidiasis occurring in individuals with COVID-19, with one death reported among the seven patients who had Strongyloides hyperinfection syndrome. A total of seventeen patients had previously received corticosteroids, and of the five with no prior corticosteroid use, one presented with hyperinfection syndrome. We identify the key challenges in the diagnosis and treatment of Strongyloides within the context of COVID-19, including our imprecise knowledge of the global distribution of Strongyloides, the overlapping symptoms and signs of COVID-19 and Strongyloides hyperinfection syndrome, the limited utility of eosinophilia as a clinical marker for strongyloidiasis in this setting, the lack of validated algorithms to screen for Strongyloides prior to corticosteroid use, and the paucity of treatment options for critically ill patients with COVID-19 who cannot take oral ivermectin. Future research should focus on improved diagnostic methods and population prevalence estimates, optimizing the approaches for Strongyloides screening in persons with COVID-19 (including clinical trial participants and strategies for resource-limited settings) and better defining the role of pre-emptive treatment.

Strongyloides stercoralis: A Neglected but Fatal Parasite

Strongyloidiasis is a disease caused by Strongyloides stercoralis and remains a neglected tropical infection despite significant public health concerns. Challenges in the management of strongyloidiasis arise from wide ranging clinical presentations, lack of practical high sensitivity diagnostic tests, and a fatal outcome in immunocompromised hosts. Migration, globalization, and increased administration of immunomodulators, particularly during the COVID-19 era, have amplified the global impact of strongyloidiasis. Here, we comprehensively review the diagnostic tests, clinical manifestations, and treatment of strongyloidiasis. The review additionally focuses on complicated strongyloidiasis in immunocompromised patients and critical screening strategies. Diagnosis of strongyloidiasis is challenging because of non-specific presentations and low parasite load. In contrast, treatment is simple: administration of single dosage ivermectin or moxidectin, a recent anthelmintic drug. Undiagnosed infections result in hyperinfection syndrome and disseminated disease when patients become immunocompromised. Thus, disease manifestation awareness among clinicians is crucial. Furthermore, active surveillance and advanced diagnostic tests are essential for fundamental management.