Your Health A-Z


An intestinal infection caused by a parasite.


An intestinal infection caused by a parasite.

Alternative name

Threadworm infection

What is this?

Infection of the intestines by a parasite, of the type known as a nematode or helminth.

What causes this?

The parasite, strongyloides stercoralis, can survive for decades, living within the host person, without causing symptoms or problems, but when someone has a weakened immune system ( such as with HIV/Aids, or after a transplant ) it can spread and cause a disseminated and life-threatening illness.

Typically, one is infected when the larvae penetrate through the skin when in contact with infected soil, though you can also be infected if some of the larvae contaminate food. The larvae may thus directly reach the intestines, or may travel through the bloodstream to the lungs. Those in the lungs travel up the bronchi and get swallowed, thus reaching the intestines indirectly. Here they transform into parasitic female worms (curiously, parasitic male worms seem not to exist).

These females produce eggs without the need of males, and these grow into further larvae and are either passed out in the faeces, or may re-infect the host. There are two main forms of major illness associated with this infection. In hyper-infection, the life cycle is accelerated, leading to an excessive quantity of the larvae in lungs and gut. In disseminated strongyloidiasis, the larvae spread to other parts of the body not usually involved, including the central nervous system, heart, urinary tract, and other organs.

What are its symptoms?

In the mild form, soon after infection, there may be a mild rash at the site of entry of the larvae (usually the feet) , some coughing, wheezing and mild fever as they pass through the lungs; and perhaps some abdominal discomfort or diarrhoea when they reach the gut. In the severe form, there is marked abdominal pain, with nausea and vomiting, diarrhoea which may be bloody; coughing, wheezing and discomfort in breathing; fever and chills; and if there is spread to the central nervous system, headache and confusion. In the severe forms, germs usually confined to the interior of the gut may reach the bloodstream.

How is it diagnosed?

By identifying typical larvae in stool samples examined on consecutive days. Blood tests for antibodies can also be sensitive in identifying the presence of the larvae in someone with a normal immune system. Typical skin lesions may be seen, as the larvae migrate through the skin.

How is it treated?

With antihelminthic drugs, such as albendazole, or ivermectin, which are specifically effective in eliminating helminthic infections like this. Other antibiotics may be needed where the activity of the larvae have released gut-based germs into the bloodstream.

What is the prognosis?

The infestation may be free of symptoms or problems, but in the severe disseminated form, mortality can be as high as 80%.

When to call your doctor

When typical symptoms occur.

How can it be prevented?

Avoid walking barefoot in soil especially in areas where the organism is commonly found.

The information provided in this article was correct at the time of publishing. At Mediclinic we endeavour to provide our patients and readers with accurate and reliable information, which is why we continually review and update our content. However, due to the dynamic nature of clinical information and medicine, some information may from time to time become outdated prior to revision.

In the interest of our patients, in accordance with SA law and our commitment to expertise, Mediclinic cannot subscribe to the practice of online diagnosis. Please consult a medical professional for specific medical advice. If you have any major concerns, please see your doctor for an assessment. If you have any cause for concern, your GP will be able to direct you to the appropriate specialists.