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Strongyloides stercoralis is a worm that infects humans, estimated to affect at least 370 million people worldwide. Presentations range from an asymptomatic carrier state (detected on screening) to disseminated disease (hyperinfection) in the immunocompromised host. It is endemic in tropical and subtropical areas where sanitation standards are poor.1
Life cycle - see CDC. Human infection occurs when skin comes in contact with filariform larvae of Strongyloides, usually in soil contaminated by human faeces. The larvae penetrate the skin and migrate via the bloodstream to the lungs, where they are coughed up and swallowed, moving to the small bowel, where they develop into adult worms. They may also migrate directly to the intestine. The adult worms may live for up to 5 years in the host, laying eggs which develop into rhabditiform larvae that are excreted in the stool. These larvae contaminate soil where sanitation facilities are poor, developing into filariform larvae that can infect others. Strongyloides are also able to complete their entire lifecycle in the human host (auto-infection), meaning that infection can persist for several decades.2
A person with chronic asymptomatic Strongyloides infection may suddenly become acutely unwell with hyperinfection syndrome, if their T-cell immunity becomes depressed (e.g. due to steroids, biologic therapy, chemotherapy, HTLV-1, and to a lesser extent, HIV).3
Strongyloides stercoralis is endemic in tropical and subtropical areas, including the northern parts of Australia, and many source countries/transit countries for current Humanitarian entrants and asylum seekers in Australia. Rates of Strongyloides spp. infection are high in indigenous communities in Northern Australia.4,5 Strongyloidiasis is also a common infection among new arrivals to Australia, data from refugee health clinics suggest a positivity rate by serology of 20-40% in African and Karen groups.6-8
Many people with chronic Strongyloides infection are asymptomatic.
Stool examination is not sensitive for detecting Strongyloides infection.9 The rhabditiform larvae can sometimes be detected in stool using specialised laboratory techniques (e.g. Harada culture - NB not available at RCH). In cases of hyperinfection syndrome, filariform larvae may be found in respiratory or gastrointestinal specimens. Faecal PCR for Strongyloides is specific, but less sensitive.10
Immigrant health clinic protocols. Author: Vanessa Clifford and Georgie Paxton, January 2014. Updated June 2020. Contact email@example.com