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Strongyloidiasis

Widespread in tropical and subtropical regions, also endemic in Southern Europe.

An infection occurs when the larvae, living in the soil, are able to penetrate human skin. After this, they migrate to the lungs and are finally swallowed into the intestines where they develop into adult worms. Female worms settle in the small bowel produce eggs that hatch to more larvae. The larvae are excreted in faeces, or sometimes they re-enter the body of the same host through penetrating the bowel wall or the perianal skin.
Strongyloidiasis may be transmitted from person to person during close contact, which allows the larvae to penetrate intact skin.

The disease is estimated to affect 30-100 million people worldwide; the prevalence is likely to be underestimated.
In non-endemic regions, the disease may be encountered in visitors to and immigrants from endemic areas.
One of the most common causes of eosinophilia in individuals who have lived in endemic regions.
When immunosuppressive treatment is planned for patients who have resided in endemic regions, Strongyloides should always be screened for and eradicated.

Strongyloidiasis usually only causes a few symptoms, and one third of patients remain symptomless. However, it is possible that the patient develops a symptomatic disease decades after acquiring the infection.
Severe eosinophilia is typical, particularly during the lung migration phase of the larvae and in autoinfection.
The larval skin penetration may cause a pruritic papular rash following a hypersensitivity reaction to the parasite's antigens.
During the lung migration phase, asthmatic symptoms, lung infiltrates and eosinophilia may occur.
The intestinal infestation usually causes upper abdominal pain, mucous diarrhoea, vomiting, malabsorption and weight loss.
About 2 out of 3 people with chronic strongyloidiasis have eosinophilia.
Chronic infection may be associated with urticaria and pruritus of the skin. Sometimes cutaneous larva currens ("racing larva"), pathognomonic for strongyloidiasis, may occur, i.e. pruritic and rapidly progressing wheals which appear and disappear abruptly within a few hours.
In immunocompromised patients, strongyloidiasis may result in a life threatening hyperinfection syndrome where the high worm load will result in, for example, pain in the abdominal region, extensive lung infiltrates, recurrent bacterial sepsis or meningitis. If left untreated, disseminated strongyloidiasis in an immunocompromised patient carries a high mortality rate.

Detection of larvae in the faeces or in the duodenal fluid. Several faecal samples should be collected, since the excretion is not constant.
It may be difficult to identify larvae in mild disease forms, and Strongyloides culture from a fresh stool sample may assist the search. A negative result does not rule out the possibility of the disease.
Serum screening test for anti-helminth antibodies, which also detects Strongyloides antibodies, is available. It is applicable e.g. when looking for the cause of eosinophilia and in screening for chronic stronglyoidiasis in an asymptomatic patient; faecal sample tests are not sensitive enough for this purpose.

Must always be eradicated.
The most effective eradication treatment consists of ivermectin Ivermectin Versus Albendazole or Thiabendazole for Strongyloides Stercoralis Infection (200 µg/kg once daily for 2 days). If the patient was born in an endemic area of loiasis or has lived there for a long time (tropical West or Central Africa), a specialist in infectious diseases should be consulted before starting ivermectin. The drug should not be used during pregnancy and breastfeeding, and not for children weighing less than 15 kg.
Albendazole is an alternative (400 mg twice daily for 7 days). It may require a special licence in some countries. Albendazole must not be used during pregnancy, or at least during the first trimester, even though teratogenicity has not been established.
In immunosuppressed patients, the treatment is repeated after 2 weeks; do not hesitate to consult a specialist in infectious diseases about the treatment.
Successful eradication is confirmed by a stool sample after about 3 weeks.
If symptoms recur, readily consult a specialist in infectious diseases.
The treatment of hyperinfection syndrome has consisted of long courses of ivermectin, albendazole or thiabendazole either alone or in their combinations.
If strongyloidiasis is strongly suspected, a therapeutic trial is warranted.

Ross AG, Cripps AW. Enteropathogens and chronic illness in returning travelers. N Engl J Med 2013;369(8):784. [PubMed]