GPAtlas🧭 When to suspect
Roundworm (Ascaris lumbricoides) is the largest intestinal nematode – adult worms reach 15–35 cm – and the most common soil-transmitted helminth infection worldwide, part of a global burden the World Health Organization (WHO) estimates affects around 1.5 billion people.
In UK primary care, suspect ascariasis in someone who has recently travelled to or migrated from an endemic area – typically a tropical or subtropical region with poor sanitation. Transmission is faecal–oral: swallowing embryonated eggs from soil, water or food contaminated with human faeces. There is no direct person-to-person spread, because eggs must mature in soil for about three weeks before they become infective.
The infection runs in two clinical phases – an early pulmonary phase as larvae migrate through the lungs, then an intestinal phase once adult worms settle in the gut.
| Phase | Timing after ingestion | Typical features |
|---|---|---|
| Pulmonary (larval migration) | ~1–2 weeks | Dry cough, wheeze, breathlessness, fever, eosinophilia and transient lung shadows – Löffler's syndrome (a temporary eosinophilic pneumonitis). Stool is negative at this stage. |
| Intestinal (adult worms) | From ~2–3 months | Often asymptomatic; vague abdominal pain, distension and nausea; heavy worm loads cause malnutrition and faltering growth, especially in children; worms may be passed in stool or vomit. |
Most infections are light and asymptomatic, and morbidity rises with worm burden. The two key primary-care skills are to recognise it in returning travellers and migrants – including the easily-missed pulmonary phase – and to never miss a complication such as bowel or biliary obstruction. Also consider it in any child with faltering growth or signs of malnutrition.
Source: WHO Soil-Transmitted Helminthiases
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