Question
A 43-year-old man presents to the emergency department with intermittent abdominal bloating, mild diarrhoea, and an intensely itchy rash over his groin and upper thigh. He is a UK national who has lived for several years in rural Southeast Asia and recently returned to Britain to visit relatives.
He reports that the rash initially appeared near the perianal region, then faded and reappeared several centimetres away on the medial thigh. On examination, there is a linear, raised, erythematous urticarial streak approximately 8 cm long. When reviewed again 3 hours later, the rash has clearly migrated by another 8–10 cm.
Blood tests show:
- Hb 132 g/L
- WBC 8.1 × 10⁹/L
- Eosinophils 1.9 × 10⁹/L
- CRP 48 mg/L
- Renal and liver function tests within normal limits
What is the most likely diagnosis?
A. Toxocara canis
B. Schistosoma mansoni
C. Enterobius vermicularis
D. Strongyloides stercoralis
E. Taenia saginata
Answer
Strongyloides stercoralis
Detailed discussion (exam relevance)
Strongyloides stercoralis is a soil-transmitted intestinal nematode with a unique and clinically important life cycle that allows autoinfection, making it a favourite topic in MRCP exams. Infection typically occurs when filariform larvae in contaminated soil penetrate intact skin, most commonly through the soles, buttocks, or perianal area. From there, larvae migrate via the bloodstream to the lungs, ascend the tracheobronchial tree, are swallowed, and mature into adult worms in the small intestine.
The hallmark dermatological manifestation is larva currens, a rapidly migrating, pruritic, linear urticarial rash. This rash moves quickly—often several centimetres per hour—distinguishing it from cutaneous larva migrans caused by hookworms, which migrates much more slowly. The typical starting site around the perianal region is a key diagnostic clue for MRCP candidates.
Gastrointestinal symptoms include abdominal pain, bloating, diarrhoea, and malabsorption. Peripheral eosinophilia is common in chronic infection but may be absent in severe disseminated disease (hyperinfection syndrome), especially in immunosuppressed patients (e.g. those receiving corticosteroids). This is a critical exam point: unexplained Gram-negative sepsis or meningitis in an immunosuppressed patient should prompt consideration of Strongyloides hyperinfection.
Diagnosis is made by stool microscopy showing rhabditiform larvae (not eggs), though sensitivity is low with a single sample. Serology (Strongyloides IgG ELISA) is highly sensitive and commonly tested in exams. Treatment of choice is ivermectin, with albendazole as an alternative. Screening and treatment are essential before starting steroids in patients from endemic areas.
Cheat sheet (exam-oriented)
- Organism: Strongyloides stercoralis (nematode)
- Transmission: Skin penetration from soil
- Key rash: Larva currens (fast-moving urticarial streak)
- Rash speed: cm/hour (faster than cutaneous larva migrans)
- GI symptoms: Diarrhoea, bloating, abdominal pain
- Bloods: Eosinophilia (may be absent in hyperinfection)
- Stool: Rhabditiform larvae (no eggs)
- Best test: Strongyloides IgG serology
- Treatment: Ivermectin (first line)
- Exam pearl: Always consider before steroids
Flash cards
- Strongyloides mode of entry → Skin penetration
- Typical rash name → Larva currens
- Rash migration speed → Rapid (cm/hour)
- Rash origin → Perianal/buttocks
- Key GI symptoms → Diarrhoea, bloating
- Life cycle uniqueness → Autoinfection
- Stool finding → Rhabditiform larvae
- Eggs in stool? → No
- Blood abnormality → Eosinophilia
- Eosinophils in hyperinfection → May be absent
- First-line treatment → Ivermectin
- Alternative treatment → Albendazole
- Lung involvement → Loeffler-like pneumonitis
- Risk factor for dissemination → Steroids
- Geography → Tropics/subtropics
- Key exam red flag → Migrating urticaria
- Best screening test → IgG ELISA
- Human-to-human transmission → Via autoinfection
- Cutaneous larva migrans speed → Slow
- Larva currens speed → Fast
MCQs
- A rapidly migrating, linear urticarial rash beginning in the perianal region is most characteristic of which infection?
A. Ancylostoma braziliense
B. Schistosoma haematobium
C. Enterobius vermicularis
D. Strongyloides stercoralis
E. Trichuris trichiura - Which helminth has the ability to complete its life cycle entirely within the human host via autoinfection?
A. Ascaris lumbricoides
B. Taenia saginata
C. Strongyloides stercoralis
D. Enterobius vermicularis
E. Diphyllobothrium latum - What is the characteristic finding on stool microscopy in Strongyloides infection?
A. Operculated eggs
B. Hexacanth embryos
C. Adult worms
D. Rhabditiform larvae
E. Microfilariae - What is the first-line treatment for uncomplicated strongyloidiasis?
A. Praziquantel
B. Mebendazole
C. Niclosamide
D. Ivermectin
E. Metronidazole - Which blood abnormality is most commonly associated with chronic Strongyloides infection?
A. Neutropenia
B. Lymphocytosis
C. Thrombocytopenia
D. Anaemia
E. Eosinophilia - A rash migrating several centimetres per hour is best described as:
A. Erythema nodosum
B. Cutaneous larva migrans
C. Erythema multiforme
D. Urticaria pigmentosa
E. Larva currens - Which factor most strongly predisposes to Strongyloides hyperinfection syndrome?
A. Diabetes mellitus
B. HIV infection
C. Chronic kidney disease
D. Systemic corticosteroid therapy
E. Iron deficiency - Which of the following is not typically seen in the stool of a patient with Strongyloides infection?
A. Larvae
B. Motile organisms
C. Rhabditiform forms
D. Eggs
E. Occasionally adult fragments - Pulmonary involvement in Strongyloides infection most closely resembles which condition?
A. ARDS
B. Pulmonary embolism
C. Loeffler’s syndrome
D. Bronchiectasis
E. Tuberculosis - Which parasite causes a slowly migrating serpiginous rash after contact with dog or cat faeces?
A. Strongyloides stercoralis
B. Enterobius vermicularis
C. Ancylostoma braziliense
D. Trichuris trichiura
E. Ascaris lumbricoides - In patients with low parasite burden, which investigation is most sensitive for diagnosis?
A. Single stool microscopy
B. PCR on urine
C. Blood culture
D. Duodenal biopsy
E. Strongyloides IgG serology - Adult Strongyloides worms primarily reside in which part of the gastrointestinal tract?
A. Colon
B. Stomach
C. Oesophagus
D. Small intestine
E. Rectum - Which severe complication may occur during Strongyloides hyperinfection?
A. Viral myocarditis
B. Pulmonary fibrosis
C. Gram-negative sepsis
D. Splenic rupture
E. Autoimmune haemolysis - The usual route of entry of Strongyloides larvae into the human body is via:
A. Ingestion of eggs
B. Insect bite
C. Sexual transmission
D. Skin penetration
E. Blood transfusion - Strongyloides stercoralis is most commonly acquired in which setting?
A. Temperate urban environments
B. Arctic regions
C. Desert climates
D. Tropical and subtropical regions
E. High-altitude areas - Which rash is classically linear, urticarial, and intensely pruritic?
A. Erythema nodosum
B. Dermatitis herpetiformis
C. Scabies
D. Larva currens
E. Psoriasis - Which parasite is capable of causing lifelong infection without reinfection from the environment?
A. Schistosoma mansoni
B. Ascaris lumbricoides
C. Strongyloides stercoralis
D. Taenia solium
E. Enterobius vermicularis - Why is a single stool sample often insufficient to exclude Strongyloides infection?
A. Eggs are intermittently shed
B. Adult worms migrate rapidly
C. Larval output may be low
D. Parasite only appears at night
E. Stool inhibitors affect microscopy - In which situation is eosinophilia most likely to be absent despite active Strongyloides infection?
A. Early infection
B. Childhood disease
C. Mild intestinal infection
D. Pregnancy
E. Hyperinfection syndrome - Screening for Strongyloides is most important before initiating which therapy?
A. Statins
B. Proton pump inhibitors
C. Beta-blockers
D. Antibiotics
E. Systemic corticosteroids
Summary for quick exam revision
Strongyloides stercoralis is a soil-transmitted nematode that infects humans through skin penetration and uniquely causes autoinfection, allowing chronic persistence. The classic dermatological sign is larva currens, a rapidly migrating, linear, pruritic urticarial rash that typically begins in the perianal or buttock region and moves several centimetres per hour. Gastrointestinal features include diarrhoea, abdominal pain, and bloating, while eosinophilia is common in chronic disease. Diagnosis relies on stool microscopy for rhabditiform larvae and, more sensitively, Strongyloides IgG serology. Ivermectin is first-line therapy. A key MRCP concept is the risk of life-threatening hyperinfection in immunosuppressed patients, especially after corticosteroid exposure, where eosinophilia may disappear and severe sepsis can occur. Recognising the rash and epidemiological exposure is critical for exam success.
Written for MRCP candidates by a practising physician. Content aligned with UK exam patterns and standard medical teaching.
Reference:
Strongyloidiasis and larva currens are described in standard infectious disease texts such as Manson’s Tropical Diseases, which is commonly referenced for parasitic infections relevant to UK postgraduate examinations.