Strongyloidiasis: a long-lasting worm infection, risks and diagnosis in the UK

Strongyloidiasis is an infection with a roundworm, Strongyloides stercoralis. UKHSA lists it among the helminth (parasitic worm) infections, alongside schistosomiasis, soil-transmitted helminths such as roundworm, whipworm and hookworm, and filariasis. TravelHealthPro, the UK travel health service, explains that soil-transmitted helminths are parasitic worms that infect people who come into contact with worm eggs or larvae in soil, and are among the commonest infections worldwide, especially in hot, humid areas where sanitation and hygiene are poor.

What sets strongyloides apart, UKHSA explains, is that an infection can remain for life if not treated, and can become serious years later if the immune system is weakened. Someone who lived in or visited an affected area decades ago may therefore still be at risk.

It is not a condition acquired in the UK in the usual way. The people most at risk are those who have lived in, or had prolonged contact with soil or conditions in, parts of the world where it is common, including South and Southeast Asia and the Caribbean.

UKHSA says helminth infections are often asymptomatic but can cause significant illness and death if left untreated. For strongyloides specifically, infection is usually asymptomatic, but may cause characteristic skin rashes and non-specific gastrointestinal symptoms.

A raised eosinophil count, a type of white blood cell, may be the only clinical sign of a parasitic infection, according to UKHSA, which is why the possibility of helminths should be considered in people with unexplained symptoms, especially gastrointestinal, or an unexplained high eosinophil count after travel or living in the tropics. Because there may be no symptoms, the infection is often found by chance on a blood test.

The most important point for patients is what can happen if the immune system is suppressed. UKHSA says infection can become serious if steroids or other immunosuppressives are prescribed in later life, or if other immunosuppressive conditions co-exist, and that overwhelming infection can occur with a high mortality in people treated with corticosteroids or chemotherapy.

TravelHealthPro makes a similar point about travellers: those who are immunocompromised are at risk of overwhelming infection with Strongyloides stercoralis. If you have lived in an area where strongyloides is common and are about to begin steroids, chemotherapy, biologic medicines or a transplant, tell your doctor, as screening or preventive treatment may be considered beforehand.

UKHSA says diagnosis is by one of two methods: serology, a blood test that has high sensitivity in migrants, or stool microscopy, which has low sensitivity in migrants. A negative stool test therefore does not rule it out, which is why a blood test is preferred in people from endemic areas.

UKHSA recommends screening people with eosinophilia (above 0.4 x 10 to the power 9 per litre) according to where they were exposed: for exposure anywhere in the tropics, stool microscopy and strongyloides serology, and for sub-Saharan Africa, additional urine microscopy and schistosoma serology.

UKHSA says treatment with ivermectin is safe and effective, and notes that it is unlicensed for this use in the UK, which is why it is usually prescribed by or with advice from an infectious diseases or tropical medicine specialist. Because the infection can persist for life, treating it removes both the present risk and the future risk from immune-suppressing treatment.

Treatment of other worm infections is different. TravelHealthPro says soil-transmitted helminths such as hookworm, roundworm and whipworm are treated with mebendazole or albendazole, which are safe and generally effective, and UKHSA recommends praziquantel for schistosomiasis.

There is no vaccine or drug to prevent soil-transmitted helminth infection, according to TravelHealthPro. Prevention relies on good food, water and personal hygiene, and on travellers avoiding walking barefoot where hookworm is common, including beaches and areas that may be contaminated with human and animal waste.

For strongyloides the most useful steps are awareness and screening: anyone who has lived in an affected region, particularly if they are to be given steroids or other immunosuppressive treatment, should ask whether testing is appropriate.

Testing can be requested through a GP, a hospital team starting immunosuppressive treatment, or a migrant health or travel clinic. NHS infectious diseases and tropical medicine services manage confirmed infection.

Private travel clinics may offer post-travel screening bloods, which can be useful if you lived in an endemic area and have no symptoms. Share results and any treatment with your GP, so that the information is available if you need steroids in future.