Soil-transmitted helminths: worm infections and travel

The WHO identifies three main parasites that infect humans through soil: the roundworm Ascaris lumbricoides, the whipworm Trichuris trichiura and the hookworms Necator americanus and Ancylostoma duodenale. TravelHealthPro lists the same species. The WHO adds that a fourth, Strongyloides stercoralis, affects an estimated 600 million people globally and needs its own treatment.

The adult worms live in the intestine and eggs leave the body in faeces. In soil these eggs mature, so places without safe toilets and sewage disposal keep the cycle going.

TravelHealthPro describes these infections as among the commonest worldwide, especially in hot, humid areas where sanitation and hygiene are poor. Travellers catch roundworm or whipworm by eating fruit and vegetables that have not been carefully cooked, washed or peeled, and catch hookworm by walking barefoot on infected soil, including on beaches.

A weekend in a resort with good food hygiene carries a much lower risk than a long stay where children play on dirt floors or a volunteer placement involving fieldwork, which is why length of stay and the style of travel are relevant when a clinician decides whether to test.

The WHO states that light infections often cause no symptoms. Heavier infections cause intestinal problems, malnutrition, weakness and impaired growth, and severe cases may lead to bowel obstruction needing surgery. TravelHealthPro lists abdominal pain, loss of appetite, diarrhoea and general weakness, and explains that hookworm causes anaemia through intestinal blood loss while chronic infection can impair absorption of nutrients.

The NHS page on worms in humans adds that a worm-shaped rash, larger worms seen in stool, prolonged digestive symptoms or unexplained weight loss are reasons to see a GP, and that symptoms may take a long time to develop after exposure.

A GP can arrange stool tests for eggs and parasites and a blood count to look for anaemia or a raised eosinophil count, particularly in someone who has lived or worked in a high-risk region. Tell the clinician where you have been and for how long, because that guides which infections are considered. Some travel clinics and tropical medicine services offer screening for people returning after long stays.

TravelHealthPro states that drug treatment with mebendazole or albendazole is safe and effective, and the WHO recommends albendazole and mebendazole as safe, inexpensive medicines, with ivermectin used for Strongyloides. The NHS says treatment courses typically last between one and three days and that household members sometimes need treatment too. Choice of drug and dose is the prescriber decision.

TravelHealthPro advises avoiding barefoot walking in endemic areas, including on beaches, and following careful food and water hygiene. The NHS adds regular handwashing, drinking boiled water in high-risk areas and cooking meat thoroughly, and recommends regularly deworming pet dogs and cats.

Travellers with weakened immunity, for example from steroids or other immunosuppressants, need extra care because Strongyloides can cause severe disease in that setting, as TravelHealthPro notes. The WHO describes community strategies built on periodic deworming, hygiene education and better sanitation.

• Wear closed shoes or sandals on soil and wear footwear on beaches in endemic regions.

• Wash, peel or cook fruit and vegetables; avoid untreated water.

• Wash hands before eating and after using the toilet.

• Tell your GP about long stays in high-risk countries if you have unexplained anaemia or digestive symptoms.

This page is an overview. Individual worms are covered in separate guides, including ascariasis, trichuriasis, hookworm and strongyloidiasis, and the NHS also covers threadworm, which spreads by a different route within households and is not soil-transmitted.