Strongyloides (Roundworm)

What Is Strongyloides/Strongyloidiasis?

Strongyloidiasis is a disease process which results from infection with Strongyloides (usually Strongyloides stercoralis), a nematode (roundworm) which occurs in many sub-tropical, tropical, and even temperate countries. Strongyloidiasis can affect people years after exposure, because the worm can reproduce itself inside the human body. Usually the immune system keeps parasite numbers relatively low, and there may be few or no symptoms. If the immune system is suppressed due to disease or medication, worms can multiply, leading to life-threatening Strongyloidiasis.

How Is It Transmitted?

It is acquired through contact with soil contaminated by faeces containing infective larval (immature) stages of the parasite. It is therefore more common in situations where hygiene and sanitation is poor. Strongyloides larvae penetrate the skin and migrate to the lungs, from where they are coughed up into the back of the mouth and swallowed; from here they pass through the gut to the lining of the small intestine. Here they mature into adult worms which can reproduce asexually (without male worms). New larvae migrate through the gut wall and to the lungs, are coughed up, swallowed… a cycle of 'autoinfection' is established. Person-to-person transmission has not been reported in the medical literature in uncomplicated strongyloidiasis.


Symptoms can occur intermittently over years, even decades, and may include rash, diarrhoea and/or abdominal pain, cough or other chest symptoms. There may be no symptoms at all.

Potentially fatal complicated strongyloidiasis can occur when the immune system is suppressed due to certain types of medication or serious illness.


As blood tests may remain positive after treatment, stool samples may be required for testing. Neither test is perfect, and false negatives do occur, so multiple specimens may be required.


Ivermectin (Stromectol) tablets are usually used to treat strongyloides infection. Side-effects from this medication can include mild nausea and dizziness, and short-lived diarrhoea.


Use footwear, avoid direct contact with soil, and maintain good personal hygiene.

Updated August 2021.

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