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Strongyloides is a type of threadworm that commonly infections humans and other mammals.

  • It is much less common in developed countries than another type of threadworm – pinworms. Colloquially, “threadworm” usually refers to pinworms.
  • The word “threadworm” derives from the appearance of worm – which often look like small white “threads” (of cotton)

The main human worm strongyloides stercoralis is widespread in tropical areas. It rare in countries where there is not faecal contamination of groundwater, and thus is rarely seen in the developed world. It in endemic in parts of the far east, (Vietnam, Cambodia, Laos – up to 10% of the population), commonly seen in South America, and also widespread in Africa (<1% of the population).

In Australia, it is commonly seen in rural and remote Aboriginal communities living in tropical areas.

It lives in the intestinal mucosa, and is transmitted via contaminated feral matter.Infection is lifelong without treatment. It causes abdominal pain and watery diarrhoea, although many patients may be asymptomatic for prolonged periods.

Avoiding use of unclean bedsheets when travelling to endemic areas, and also the use of plastic slippers whilst showering in endemic areas may help to reduce transmission.

In cases of disseminated strongyloidiasis, it can be life-threatening – and there are reports of patients with disseminated disease given corticosteroids that precipitated death (hyperinfective syndrome).

It causes an eosinophilia in the FBC – beware of giving steroids to anyone who has been to an endemic area and has an eosinophilia.

Treatment is with ivermectin or albendazole – but regimens can be complicated and it is advisable to seek specialist infectious diseases help.

Epidemiology and Aetiology

  • Worldwide, up to 370 million people are affected
  • In some rural and remote aboriginal communities in Australia, up to 60% of the population are infected
  • Immunosuppressed patients are at particular risk of potentially life threatening disseminated disease

Life cycle

  • Microscopic larvae (“filariform” larvae) penetrate the skin and enter the bloodstream
  • They travel to the heart, and into the pulmonary circulation
  • They then exit the circulation in the lung and climb up the trachea, to be swallowed into the gastrointestinal tract
  • In the intestine, mature adult females – approx 2-3mm long – penetrate the mucosa and lay up to 40 eggs per day
    • Females can reproduce without a male!
  • The larvae then penetrate the mucosal surface and enter the intestinal tract, where they are shed in the faeces
  • Many of these larvae then “auto infect” the original host by penetrating the colonic mucosa or perianal skin
  • Larvae can survive in soil for several weeks

Strongyloides is particularly difficult to treat due to its autoinfective nature. In severe cases, there are many millions of larvae in various parts of the lifecycle migrating through many internal organs.

Stages of infection can be divided into:

  • Acute
    • May cause acute onset gastrointestinal symptoms
  • Chronic
    • May be asymptomatic, or non-specific intermittent symptoms
  • Disseminated
    • High fatality rate
    • Can pre-dispose to sepsis and multiple end organ failure

Signs & Symptoms

  • Larva currens – visible tract marks on the skin – often seen on the abdomen and buttocks – represents the larvae migrating in the skin. Move at about 2-10cm per hour
  • Respiratory – pneumonia, lung abscess, haemoptysis, SOB
  • Abdominal – abdominal pain, diarrhoea, malnutrition, epigastric pain
  • Abscess of internal organs – e.g. renal, hepatic, brain
  • Eosinophilia
  • Sepsis – gram negative sepsis may occur due to bacteria carried by the larvae being introduced into the bloodstream


  • Strongyloides serology – highly sensitive and specific
    • May be falsely negative in acute cases which have not yet seroconverted
  • Faecal examination – may be negative in early or minor infection


  • All cases, even those discovered incidentally which are asymptomatic should be treated to avoid progression to potentially fatal disseminated disease
  • Difficult to treat – a single remaining parasite can cause re-infection
  • Ivermectin is the treatment of choice
  • Albendazole is second line – it is also less effective and although reduces severity of infection may not be curative
  • Follow-up is required to ensure eradication
    • At 6 months
    • Consider bloods for eosinophilia as well as serology and faecal examination
    • Eosinophilia may be the only sign of recurrence
    • Disease is considered eradicated if serology and faeces are negative and there are no ongoing symptoms


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Dr Tom Leach

Dr Tom Leach MBChB DCH EMCert(ACEM) FRACGP currently works as a GP and an Emergency Department CMO in Australia. He is also a Clinical Associate Lecturer at the Australian National University, and is studying for a Masters of Sports Medicine at the University of Queensland. After graduating from his medical degree at the University of Manchester in 2011, Tom completed his Foundation Training at Bolton Royal Hospital, before moving to Australia in 2013. He started almostadoctor whilst a third year medical student in 2009. Read full bio

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