Strongyloides stercoralis is a nematode (roundworm) which lives in many tropical and sub-tropical areas of the world. Strongyloidiasis is the name given to the disease process, which results from infection with Strongyloides.
Strongyloidiasis can affect people years or even decades after the original 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. However, if the immune system is suppressed due to disease or medication, worms can multiply unchecked, leading to life-threatening disseminated Strongyloidiasis.
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 has a relatively complex life-cycle. The larvae penetrate the skin and migrate through the tissues to the lungs, from where they are coughed up into the back of the mouth, swallowed and pass through the gut to the lining of the small intestine. Here they mature into adults. The adult worms in the gut lining are all females. These have the unique capacity to reproduce asexually (without male worms). The new larvae so produced migrate through the gut wall, pass through the tissues to the lungs, and are coughed up, swallowed and pass to the small intestine to repeat the cycle. This cycle of auto (self) infection is what allows Strongyloides to persist in the body for long periods, even decades, without further exposure.
While this may be possible, Australian experts consider this unlikely. Person-to-person transmission has not been reported in the medical literature in uncomplicated strongyloidiasis.
Strongyloidiasis is known as the ‘most neglected of the neglected tropical diseases’. It is estimated that up to 370 million people are infected worldwide. Strongyloidiasis was first described in French soldiers returning from service in Indo-China, and to this day veterans who have seen active service in South-East Asia form a significant, and sometimes unrecognised, risk group. Returned World War Two prisoners of war, especially those that have worked on the Burma-Thailand railway, are at greatest risk. Studies of Australian veterans have shown up to 27% of ex-POWs and 11.6% of Vietnam veterans have tested positive to the parasite.
Other risk groups in Australia include migrants from tropical areas, as well
as rural Aboriginal communities from the Northern Territory and northern Queensland.
Uncomplicated chronic strongyloidiasis is the commonest presentation. Symptoms occur intermittently, often over years or even decades, and may include:
- Rash, either a characteristic itchy rapidly-moving curved linear rash on the buttocks called larva currens (from the Latin “to run”) or non-specific itchy urticaria (“hives”).
- Intermittent diarrhoea and/or abdominal pain.
- Chest symptoms including cough have been described much less frequently in the medical literature.
Commonly there are no symptoms at all.
Complicated, disseminated strongyloidiasis occurs when the immune system is suppressed, due to:
- Medication—most commonly steroids like prednisolone, but also anti-cancer chemotherapy and medication used to prevent graft rejection in transplant patients.
- Cancers like lymphoma and leukaemia.
This is a very serious, life-threatening medical condition. Parasites multiply unchecked. Large numbers may be found in lungs, bowel, and even in the central nervous system. Patients are very unwell, with severe pneumonia-like chest disease, a wide range of gut problems, and even possibly meningitis and/or brain abscesses. Bacteria carried by the parasites may cause local or generalised infection.
A blood test for Strongyloides is the usual method of detection. Stool tests may be used but they are technically challenging and unreliable.
It is relatively easy to diagnose disseminated Strongyloidiasis, as long as someone thinks about the possibility in the first place. This is because of the large numbers of larvae in the body in this condition.
Mostly however, doctors are trying to detect uncomplicated Strongyloidiasis in people who may have been exposed to the parasite. These people carry relatively small numbers of parasites, which may only intermittently pass out the faeces (bowel motions) and can therefore easily be missed in tests which look at larvae in faeces.
This is why blood tests are the preferred method of detection for ‘light’ infections.
Anyone who is concerned they have been exposed can speak with their GP about getting tested if they have not previously done so.
The following Veterans who may have been exposed in the tropics should ensure they are tested:
- Any Veteran that requires treatment with drugs that suppress immune function, including prednisolone and other corticosteroids, chemotherapy agents, and drugs used to prevent rejection in transplant patients.
- Any Veterans diagnosed with leukaemia or lymphoma.
- Veterans who have unusual itchy skin conditions, stomach pain or intermittent or chronic diarrhoea.
In Australia, standard treatment is with Ivermectin (Stromectol). It is given as a single dose, which depends upon body weight. The same dose should be repeated 1-2 weeks later. Stromectol is available on the RPBS for the treatment of strongyloidiasis. Side-effects are generally mild and may include nausea, dizziness, and diarrhoea, which usually only last for a short time.
Follow-up testing is important to ensure the blood test returns to negative signalling eradication of the parasite. Repeat testing should be undertaken 6-12 months after treatment. If the result remains positive another two doses of Stromectol should be taken 1-2 weeks apart and testing repeated after a further 6-12 months. If the test remains positive your GP may treat you again or possibly refer you to an Infectious Diseases Physician.
- Strongyloides can persist for decades after exposure.
- Veterans who have seen active service in South East Asia form a significant risk group.
- See your GP if you feel that you may have been exposed.