Strongyloidiasis

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Strongyloidiasis

 

A funny sounding name, for a funny sort of illness. Ellen Welch and Geoff Gill

explain how the consequences of this tropical disease can be far from funny

 

An example from recent history

 

Shortly after the second world war it became obvious that many of the men who

had been held captive in the Far East had contracted strongyloidiasis,

especially those prisoners who were forced to work on the infamous Thai-Burma

" death " railway. This 400 km railway line, engineered by the Japanese in an

attempt to win the war, stretched through mountainous jungle in northern

Thailand over to Burma (now Myanmar). A year of exhausting work with primitive

tools, in areas rife with tropical diseases, led to the deaths of 20 000 Allied

prisoners and 100 000 Asian labourers, and a railway that never fulfilled any

useful purpose. Among the host of tropical diseases contracted by the men,3

the tropical jungle environment of the Burma railway provided perfect conditions

for development of the filariform Strongyloides larvae, which infected the men

through the soles of their poorly shod feet as they worked.

Tropical medicine is a subject that is often neglected from medical student

timetables, so few junior doctors will be aware of the existence of the tiny

parasite Strongyloides stercoralis, the causal agent of strongyloidiasis. This

strange sounding disease is uncommon in the United Kingdom, but it's a big

problem around the world. Consequences can be fatal, and in countries where it

is rare, it is important to recognise it in patients returning from the tropics.

Globally, the prevalence of strongyloidiasis is estimated at 100 million cases.

What is strongyloidiasis? Strongyloides stercoralis is a soil dwelling

nematode worm (2 mm by 0.4 mm in size), common in the wet tropics of South

America, Africa, and South East Asia. The complex parasite has a dual life cycle

involving both parasitic and free living stages. Adult worms can survive and

reproduce both in the small intestine of man and in the soil, giving rise to a

variety of possible routes for infection. During

direct development, adult eggs hatch in the intestine into rhabditiform larvae,

which are passed in the stool. Under favourable conditions they mature in the

soil into filariform (infective) larvae that are capable of penetrating the skin

of humans. The rhabditiform larvae also have the ability to develop into free

living adult worms that exist in the soil independently of humans--this is known

as indirect development. Once the infective larvae have penetrated the skin,

they travel to the lungs via the circulatory system, where they migrate up the

airways, reach the oesophagus, and are swallowed back down to the intestine

where mating occurs, completing the cycle. Who gets it? Anyone in tropical

countries can get it. The usual mode of infection is via larval penetration

through the soles of the feet, when walking barefoot on contaminated soil.

Infection is associated with poverty and unsanitary conditions and is usually

found in rural areas, institutional settings, and

lower socio-economic groups. Since the larvae thrive in warm, wet soil,

exposure to the parasite in the United Kingdom is extremely rare.1 Dogs, cats,

and other mammals can also harbour the parasite.2 Clinical features Clinical

features of strongyloidiasis are variable and differ if the infection is acute

or chronic. In the acute stage of infection, diarrhoea (sometimes with dysentery

or steatorrhoea), and abdominal pain predominate, while the pathognomic larva

currens rash is the main feature in the chronic illness. This typical

serpiginous rash (follows a snake-like track) can appear and disappear, usually

around the trunk, in a few hours or days, which distinguishes it from the

similar, longer lasting cutaneous larva migrans rash of hookworms. Rarer

features of the infection relate to the passage of larvae through the lungs,

which can give rise to pulmonary infiltrates, pneumonitis, and asthma. Chronic

infection with Strongyloides stercoralis has been well

documented in ex Far East prisoners of war, 4 & shy;7 persisting asymptomatically

for over 30 years in some cases. Why does it last so long? In cases of

chronic strongyloidiasis, the lifecycle of the parasite is completed entirely

within the host. In the lower gastrointestinal tract, filariform larvae can

penetrate the bowel mucosa or perianal skin and then pass via the tissues to the

lungs. This " autoinfection " process means that Strongyloides can persist in

humans for decades, even after departure from endemic areas.5 Hyperinfection

Strongyloidiasis can persist for decades, with either vague symptoms or none at

all--but is still an extremely important disease to detect, since potentially

fatal hyperinfection may occur. During periods of immunosuppression, the worms

multiply and autoinfection is increased. The larvae migrate through the bowel

wall, taking with them Gram negative organisms that can lead to peritonitis and

multiorgan involvement.6 9 The hyperinfection

syndrome is difficult to treat and is nearly always fatal, making it important

to screen at risk patients embarking on immunosuppressive treatment. Diagnosis

and treatment Strongyloidiasis should be considered as a possible cause of

diarrhoea (with or without blood) in tropical countries. Rhabditiform larvae of

Strongyloides in the stool is diagnostic for the infection, but stool

examination is notorious for its lack of sensitivity.5 Hypereosinophilia is

suggestive of the infection, but lack of it does not exclude the diagnosis. In

the past, some patients were subjected to the duodenal string test, but this was

an unpleasant procedure that yielded poor results.10 Underdiagnosis of

strongyloidiasis was a major problem before the development of an enzyme linked

immunosorbent assay for Strongyloides (ELISA).

The antihelminth drug thiabendazole was the only treatment available for many

years,11 although it was occasionally ineffective and caused unpleasant side

effects in most patients.12 A dose of 400 mg of albendazole, however, taken

twice daily for three days, has shown a six month cure rate of 81%, with

negligible side effects, and has been the favoured drug since 1993.13

 

 

Ellen Welch, intercalating medical student, University of Westminster

Email: welchellen

 

Geoff Gill, consultant physician, diabetes and endocrinology, Aintree

Hospital, Liverpool

Email: g.gill

http://www.studentbmj.com/issues/03/08/education/280.php

 

 

" Respect means listening until everyone has been heard and understood, only

then is there a possibility of " Balance and Harmony " the goal of Indian

Spirituality. " Dave Chief, Grandfather of Red Dog

 

 

 

 

 

 

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