Roundworm Infection and Sushi: Transmission Routes
Roundworm (Ascaris lumbricoides) is NOT acquired from eating sushi—it spreads exclusively through the fecal-oral route via contaminated soil, water, or food grown in contaminated soil, not through raw fish. 1
Understanding Ascaris Transmission
Ascaris lumbricoides transmission occurs through:
- Ingestion of eggs from contaminated soil (the primary route) 2, 3
- Contaminated water and food (particularly vegetables grown in soil contaminated with human feces) 4, 2
- Poor sanitation and hygiene in endemic areas 3
The parasite has a 2-3 month prepatent period and is most common in rural settings in Africa, Asia, and South America, while being rare or absent in Europe, North America, and Australasia 1.
Why Sushi Is Not the Source
The confusion likely stems from mixing up different parasites:
- Anisakis (a different roundworm) is found in raw fish/sushi and causes anisakiasis
- Ascaris lumbricoides (the common human roundworm) is soil-transmitted, not fish-borne
Research from Japan specifically examined foodstuff contamination and found that among 10,223 plant foodstuff specimens tested, 11 were contaminated with anisakid nematodes (the fish parasite), but none with Ascaris 4. The most probable source of Ascaris infection in that study was imported kimchi, not seafood 4.
Clinical Presentation and Isolated Cases
Yes, isolated cases of roundworm infection absolutely occur:
- Most infections are asymptomatic 1
- Symptomatic cases present with abdominal pain, diarrhea, and occasionally gastrointestinal or biliary obstruction 1
- Adult worms (earthworm-sized, pink or white) may be passed in stool or rarely regurgitated 1
- Acute presentation can include Loeffler's syndrome (pulmonary symptoms) 1
- Rare gastric ascariasis has been reported in immigrants from endemic areas 5
Diagnosis and Treatment
If roundworm infection is suspected:
- Diagnosis: Concentrated stool microscopy or fecal PCR 1
- Treatment: Single-dose therapy with one of the following 1:
- Albendazole 400 mg PO
- Mebendazole 500 mg PO
- Ivermectin 200 μg/kg PO
Key Clinical Pitfall
Do not attribute roundworm infection to sushi consumption. If a patient reports eating sushi and has parasitic symptoms, consider Anisakis (which causes acute gastric symptoms within hours to days) rather than Ascaris. Ascaris requires investigation of exposure to contaminated soil, water, or vegetables—particularly in patients with travel history to endemic regions or immigrants from areas with poor sanitation 5, 3.