Chronic schistosomiasis and strongyloidiasis mimicking irritable bowel syndrome over multiple decades: A case report

Abstract

Chronic infections caused by Strongyloides stercoralis and Schistosoma spp. can present with longstanding gastrointestinal symptoms that mimic irritable bowel syndrome (IBS). In this case report, we describe a patient who was misdiagnosed with IBS for several decades before receiving a definitive diagnosis of chronic helminthiasis. Treatment with first-line antihelminthics resulted in complete and sustained resolution of symptoms. We review the life cycle, epidemiology, clinical presentations, diagnosis, and management of chronic helminthiases in the context of IBS. We further discuss the impact of misdiagnosis on both the patient and the healthcare system. Given the significant individual and economic burdens of IBS and the diagnostic uncertainty associated with low sensitivity of standard diagnostic tests for helminth infections, healthcare professionals should maintain a low threshold for testing and empiric treatment in patients with relevant travel and medical history.

1. Introduction

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder characterized by irregular bowel movements, bloating, abdominal distention, and pain. Although its underlying pathophysiology remains incompletely understood, IBS has been associated with enteric nerve hypersensitivity, family history, sensitivity to certain foods, and psychological distress. IBS is highly prevalent, affecting approximately 4%–15% of the population in the United States, and incurs substantial economic burden, with estimated annual costs in excess of USD 1 billion of USD for direct medical care alone.^[1,2]

The symptoms of IBS often overlap with those of traveler’s diarrhea and parasitic infections such as schistosomiasis and strongyloidiasis. The Rome criteria are typically used in both clinical research and practice for IBS diagnosis.^[3] Current guidelines recommend a positive approach to IBS diagnosis based on clinical history, physical examination, and limited testing rather than one of exclusion. However, despite similarities in clinical presentation, due to widespread perception of low prevalence and lack of awareness there are no specific recommendations in the American, Canadian, or British IBS guidelines to screen for schistosomiasis or strongyloidiasis in high-risk patients.^{[3,4 and 5]} Recognizing the epidemiology, clinical manifestations, diagnostic methods, and treatment strategies for these infections is important for identifying and managing these globally prevalent IBS mimics.

We present a case of chronic symptomatic schistosomiasis and strongyloidiasis in a patient with remote travel to sub-Saharan Africa who had been diagnosed with IBS following extensive investigations and diagnosis that persisted for decades before the underlying infections were identified and treated.

2. Case presentation

A 64-year-old Canadian-born male with a history of travel to former Zaire (now the Democratic Republic of Congo) was referred to Toronto General Hospital, an academic teaching hospital member of the Temerty Faculty of Medicine in 2022 for chronic gastrointestinal symptoms. His relevant past medical history included childhood duodenal ulcer, remote pancreatitis, and sigmoid diverticulitis for which he underwent surgical resection at age 62. He was also known to have coronary artery disease. His medication use and family history were non-contributory. In the 1970s, the patient had spent several months in a refugee camp in former Zaire as part of a humanitarian effort. He also reported travel to China, Costa Rica, Mexico, India, Malaysia, Thailand, and Nepal (see Table 1).

Table 1.

Travel history and geographic distribution of Strongyloides stercoralis and Schistosoma spp.

Patient travel history (Chronologic)	Strongyloides stercoralis prevalence (%) (95% Confidence Interval)[14]	Report on Schistosoma spp. cases (Yes/No)[15]
Democratic Republic of the Congo (former Zaire)	13 (6.6–19.4)	Yes
India	10.4 (5.3–15.4)	Yes
Thailand	10.8 (5.5–16.1)	No
Mexico	7 (3.6–10.5)	No
Costa Rica	15.7 (8–23.4)	No
China	6.6 (3.3–9.8)	Yes
Malaysia	15.9 (8.1–23.7)	No
Nepal	14.2 (7.2–21.1)	No

Shortly after visiting former Zaire, the patient developed soft stools, which gradually worsened over time. In the five years preceding presentation, he experienced non-bloody, watery diarrhea approximately twice per week, progressing to near-daily episodes. These symptoms persisted even after sigmoid resection for diverticulitis. He also reported chronic pruritus ani. A review of systems was negative for rash, generalized pruritus, respiratory symptoms such as cough and shortness of breath, neurological sequelae, and constitutional symptoms such as fever, drenching sweats, or weight loss.

Because he had been recently examined by his family physician and there were no significant findings, upon referral to our center, an initial physical examination was deferred due to COVID-19 precautions. Laboratory investigations revealed a normal complete blood count: hemoglobin 146 g/L, white blood cell count 6.92 × 10⁹/L, and platelets 221 × 10⁹/L. Differential counts, including eosinophils, were within normal limits. Renal function, electrolytes, alanine transaminase, alkaline phosphatase, and total bilirubin were also normal. Stool cultures were negative for Campylobacter spp., Escherichia coli O157, Salmonella spp., and Shigella spp. A single stool specimen submitted for ova and parasite microscopy was negative for pathogenic parasites. Celiac serology was negative (normal anti-tissue transglutaminae [tTG] immunoglobulin A [IgA] and total IgA). Colonoscopy performed two years prior to presentation, shortly before resection for diverticulitis, revealed diverticulosis without polyps or malignancy. Serologic testing for Schistosoma spp. was indeterminate (immunoglobulin G [IgG] enzyme immunoassay [EIA] 0.26 optical density [OD]; reference: non-reactive <0.2 OD, indeterminate 0.2–0.4 OD, reactive >0.4 OD). Strongyloides stercoralis serology was non-reactive (IgG EIA 0.18 OD; reference: non-reactive <0.2 OD, indeterminate 0.2–0.3 OD, reactive >0.3 OD).

Given the indeterminate Schistosoma result, further investigations were pursued. Urinalysis was unremarkable Abdominal ultrasound revealed mild to moderate hepatic steatosis without periportal fibrosis. Considering his extensive travel history, he was empirically treated for Schistosoma japonicum with praziquantel 60 mg/kg per day, divided into three doses, for one day. This regimen was repeated six weeks later. Based on his body weight (84 kg) and the fact that the Praziquantel tablets are 600 mg each and cannot be split, the calculated dosages are rounded up to the nearest 600 - mg increment that surpasses the precise mg/kg dosage, the total daily dose was 5400 mg, divided into three doses of 1800 mg each day.

Although the Strongyloides serology was reported as non-reactive, the 0.18 OD approached the indeterminate threshold. Considering the 92% sensitivity of the assay employed at our center^[6] and the patient’s exposure history in endemic areas along with highly suggestive symptoms, such as pruritus ani, empiric treatment was also provided with ivermectin 18 mg orally once, and repeated after two weeks.

The patient reported resolution of diarrhea within one week of the first dose of both medications. At six-month follow-up, he described sustained relief of gastrointestinal symptoms. Physical examination at that time was unremarkable. Repeat serology for S. stercoralis was not performed given the initial non-reactive result and complete symptom resolution. At both 12-month and two-year follow-up, the patient remained asymptomatic, supporting a clinical diagnosis of chronic helminth infection as the underlying etiology.

Verbal informed consent has been obtained from the patient to publish this paper and documented in his medical record in accordance with PHIPA.

3. Discussion

In primary care, IBS is commonly diagnosed using the Rome IV criteria.^[3] Diagnosis requires that a patient have abdominal pain at least one day per week over a three-month period, accompanied by at least two of the following: (1) pain related to defecation, (2) changes in stool frequency, and (3) changes in stool consistency. These symptom-based criteria, although widely adopted, overlap with the clinical manifestations of several other gastrointestinal conditions, including helminthic infections. When such parasitic infections are not adequately considered or investigated, they may be misdiagnosed as IBS.

Strongyloidiasis, caused by the nematode S. stercoralis, is prevalent in tropical and warm temperate regions such as Southeast Asia, Africa, and the Western Pacific. Transmission occurs primarily through skin contact with contaminated soil. Acute symptoms reflect larval migration and may manifest as a papular rash at the site of skin penetration and a dry cough as the larvae migrate into the lungs and trachea via lymphatic circulation. After expectoration and swallowing, the filariform larvae reach the gastrointestinal tract, leading to auto-infection and potentially resulting in lifelong carriage if untreated.

Chronic strongyloidiasis is often asymptomatic but can cause abdominal pain (typically epigastric and reflux-like), nausea, irregular bowel habits, pruritus ani due to autoinfection, and mild eosinophilia or elevated IgE. Immunocompromised patients, including those with human T-lymphotropic virus type 1 infection, transplant recipients, or individuals on immunosuppressive therapy, are at increased risk of developing disseminated infection and life-threatening hyperinfection syndrome. In immunocompetent patients, uncomplicated infections are generally treated with two doses of ivermectin. In areas endemic for Loa loa, screening for microfilaremia prior to treatment is essential due to the risk of ivermectin-induced encephalopathy and other severe adverse effects.

Laboratory diagnosis relies on serology or microscopic and molecular analysis of stool, sputum, or urine. Unconcentrated stool microscopy has low sensitivity, often requiring up to seven samples to achieve 100% sensitivity.^[7] Even with formalin–ethyl acetate concentration techniques, the sensitivity remains limited (22%; 95% confidence interval, 14.3%–32.1%).^[8] In our case, the patient submitted a single stool sample, which tested negative for ova and parasites using this method.

Serology is considered the gold standard in non-endemic areas due to its higher sensitivity compared to stool ova and parasite microscopy. However, it may cross-react with other helminths, remain positive after treatment, or yield false negatives in immunosuppressed patients. If both stool and serologic tests are negative or indeterminate and empirical treatment is considered, then follow-up at or before 12 months is recommended to confirm symptom resolution. CDC guidelines advise repeat testing and treatment 2–4 weeks after initial therapy if stool tests are positive and symptoms persist. For isolated positive serologies, repeat serologic testing should be performed 6–12 months post-treatment, as IgG levels begin to decrease significantly within 6 months of cure.^[9]

Schistosomiasis also mimics IBS and is highly prevalent in tropical and subtropical regions, affecting approximately 220 million people globally. Transmission occurs through contact with contaminated freshwater. Intestinal schistosomiasis, caused by Schistosoma mansoni, S. japonicum, and Schistosoma mekongi, is prevalent in Africa, the Middle East, Southeast Asia, and the Caribbean. Urogenital schistosomiasis caused by Schistosoma haematobium is endemic to Africa, the Middle East, and parts of Europe. Many infected individuals remain asymptomatic during both acute and chronic stages of infection. Acute schistosomiasis may present with rash, nocturnal fever, myalgia, and respiratory symptoms. Chronic schistosomiasis results from the immune response to the parasite, causing abdominal pain, diarrhea, and hematochezia. Chronic inflammation can cause bowel ulceration, hepatosplenomegaly with left lobe involvement, hepatic fibrosis, and portal hypertension. Intestinal granulomas secondary to egg deposition may appear as intestinal wall thickening on computed tomography imaging, and periportal fibrosis seen on ultrasound is suggestive of chronic schistosomiasis according to the World Health Organization’s criteria. Liver stiffening assessed through transient elastography informs prognosis and management in advanced chronic disease. Praziquantel is the recommended treatment and may require multiple courses depending on host immune status.

Diagnostic approaches include stool or urine microscopy and serology. In endemic areas, circulating cathodic antigen and circulating anodic antigen detection in serum or urine supports diagnosis and confirmation of cure. Although Kato-Katz stool microscopy for S. mansoni performs poorly in low-burden areas, it shows 89%–99% sensitivity in endemic areas.^[10] Serologic and nucleic acid amplification techniques offer improved specificity and sensitivity, although cross-reactivity with other helminths can occur. Reinfection with Schistosoma spp. is common, and chronic infections may persist for decades. Immunologic sequalae from past infections further complicate serologic interpretation.

Given the low sensitivity of laboratory diagnostics, detailed epidemiological history is critical. In our case, the patient had lived in a refugee camp for a prolonged period in the 1970s and reported longstanding, non-specific gastrointestinal symptoms. He underwent extensive investigations for non-parasitic causes. He further traveled to regions where Strongyloides and Schistosoma infections are prevalent (Table 1), which increased the pre-test probability. Despite indeterminate serology and negative stool results, we opted for empiric therapy based on exposure history, prolonged symptom duration, and lack of alternative explanation. The patient’s rapid and sustained resolution of symptoms strongly supports our decision.

Cases of helminth infections misdiagnosed as IBS have sporadically been reported in the literature.^[11] Misdiagnosis can negatively impact quality of life and increase healthcare resource utilization and costs. IBS has also been associated with mental health concerns, including health anxiety and depression.^[12] In Canada, the economic impact is significant, with IBS-related care costing an estimated CAD 131 million annually in Ontario alone.^[13]

Given the personal and economic burdens IBS and the diagnostic uncertainty associated with low-sensitivity tests for parasitic infections, healthcare professionals must maintain a low threshold for testing in patients with an appropriate travel or exposure history. Empiric treatmentcan be considered, in consultation with a tropical medicine specialist, even decades after exposure, and even when laboratory tests are inconclusive.

Acknowledgments

The authors acknowledge the Departments of Medicine at the University of Toronto and University Health Network, which support Andrea K. Boggild as a Clinician Scientist, thereby enabling her to train and mentor learners in the Temerty Faculty of Medicine.

Author Contributions

Jonathan D. Cook and Kara G. Hounsell were responsible for the conceptualization of the report, conducting the literature review and synthesis, drafting the original manuscript, and reviewing and critically revising the manuscript. Ranie Ahmed, Candice Madakadze, and Angelica J. Vidal contributed to the literature review and synthesis, as well as the original drafting of the manuscript. Andrea K. Boggild contributed to conceptualizing the report, the literature review and synthesis, drafting the manuscript, critically revising it, and the overall supervision for the entire project. All authors have read and agreed to the published version of the manuscript.

Conflicts of Interest

Andrea K. Boggild oversees the Tropical Disease Fund for Excellence at the University Health Network (UHN) Foundation, which has received an unrestricted educational grant from Seegene Canada. Neither Seegene nor UHN contributed to the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Data Availability Statement

The datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request.

Funding Statement

None.