Strongyloidiasis

What is strongyloidiasis?

Strongyloidiasis is an intestinal infection caused by the parasitic roundworm (nematode) Strongyloides stercoralis. It differs from other parasitic nematode infections, e.g. filariasis, in both its clinical characteristics and its complex life cycle.

• Strongyloides parasites can persist and replicate inside human hosts for up to 30 years, causing minimal or no symptoms. However, in an immunocompromised host, they can cause a serious and life-threatening infection.
• The strongyloides parasitic life cycle is much more complicated than other parasitic nematodes as it can take place in two environments – a complete life cycle may take place within a human host or in a 'free-living' cycle that occurs out in the open environment.

Where is strongyloidiasis found?

Strongyloidiasis is predominantly a disease of tropical and sub-tropical countries, but cases also occur in temperate climates (including southeastern states of the United States). In countries such as West Africa, Southeast Asia and the Caribbean, infection rates are as high as 40%. It is most frequently found in rural areas, institutionalised-care settings, and in lower socio-economic groups. It is estimated to affect the lives of 70 million people worldwide.

The strongyloides life cycle

The most common way of contracting strongyloidiasis is penetration of the strongyloides larvae through the skin during contact with contaminated soil.

The larvae travel via the bloodstream to the lungs or directly to the small intestine. Infection via the lungs eventually reaches the pharynx (back of the mouth), where the larvae are swallowed, and enter the small intestine. Once in the small intestine, they moult twice to become parasitic adult female worms.

The adult worms live entwined in the lining of the small intestine and produce eggs that yield noninfective (rhabditiform) larvae. These larvae can be passed out of the host’s body in the stools where they moult, mate, and multiply through the free-living life cycle.

Alternatively, under certain conditions, autoinfection can occur. This is where the larvae become infective, carry out their life cycle and reinfect the body without even leaving the host.

What are the signs and symptoms of strongyloidiasis?

There are several clinical forms of strongyloidiasis.

Uncomplicated strongyloidiasis

In the acute phase directly after infection, patients may get a mildly itchy rash that often occurs at the site of larval skin penetration, usually on the feet. This may spread to the buttocks and waist areas. This rash has been referred to as ground itch. Gastrointestinal symptoms may include diarrhoea, abdominal pain and occasionally nausea and vomiting. Patients may also have a low-grade fever, coughing and wheezing, due to the migration of larvae through the lungs.

Strongyloidiasis can become chronic from persistent infection. Many patients with the chronic disease become entirely asymptomatic. Periodically they may experience vague abdominal discomfort, intermittent diarrhoea and constipation, and recurrent rashes.

Recurrent rashes are known as larva currens or creeping infection. It occurs from strongyloides autoinfection and appears as an eruption beginning in the perianal region that rapidly spreads and causes intense itching. Episodes usually last several hours before subsiding again for weeks or months. Because of autoinfection, recurrent larva currens may continue for many years, often decades.

Persistent strongyloidiasis infection can mimic peptic ulcer and gall bladder disease and often patients undergo treatment or surgery for either or both, only to fail to respond to these therapies.

Severe strongyloidiasis

There are two critical forms of strongyloidiasis, hyperinfection syndrome and disseminated strongyloidiasis.

• Hyperinfection syndrome occurs when there is excessive worm burden within the small intestine due to an acceleration of their normal life cycle.
• Disseminated strongyloidiasis occurs when the larvae spread to other organs (e.g. heart, urinary tract, central nervous system) that are generally not part of the parasitic life cycle. This may happen when patients with chronic strongyloidiasis become immunosuppressed.

Clinical signs and symptoms of severe strongyloidiasis can occur suddenly and involves severe abdominal pain, nausea and vomiting, bloody diarrhoea, coughing up blood, shortness of breath, stiff neck, headache, confusion, fever, chills and skin rash.

Skin rash may appear as petechiae and purpura over the trunk and extremities. The massive migration of larvae within the skin causes small blood vessels under the skin to break and bleed out.

How is strongyloidiasis diagnosed?

The diagnosis of strongyloidiasis is confirmed by strongyloides serology.

Some patients have eosinophilia. Faecal parasites may or may not be detected in the stool of infected individuals.

In areas where the disease is prevalent, screening for strongyloides is recommended before the introduction of immune suppressive medication and biologic agents.

How do you treat strongyloidiasis?

Treatment of strongyloidiasis is with anthelminthic therapy. Ivermectin at a dose of 200 mcg/kg daily as a single dose is the treatment of choice for uncomplicated strongyloidiasis. This drug does not kill the larvae form only the adult worms, so repeat dosing is necessary to eradicate the infection completely. Other effective drugs include albendazole and thiabendazole.

In addition to anthelmintic therapy for severe forms of strongyloidiasis, supportive treatment such as intravenous fluids for volume depletion, blood transfusion for GI bleeding, and mechanical ventilation for respiratory failure, may be required. Antibiotic treatment may be indicated if bacteremia or meningitis has also developed.