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Strongyloides Stercoralis

Strongyloides stercoralis is a soil dwelling nematode capable of producing infection in humans and other mammals.

  • It is a parasite common in wet tropical areas and usually only seen in the UK in travellers who have returned from such areas.
  • Infection is most often acquired by walking barefoot on contaminated soil.
  • The infection caused by Strongyloides stercoralis (strongyloidiasis) can be either acute or chronic in nature. The chronic form of the infection is well documented in individuals who have been prisoners of war in the Far East.
  • Infection can be asymptomatic for many years. It is therefore very important to eradicate the parasite prior to starting immunosuppressive treatment or chemotherapy as failure to do so may result in a hyperinfection syndrome due to dissemination of the larvae to several organs, which is associated with a high mortality rate.1
Epidemiology
  • Incidence - Strongyloides stercoralis is thought to have infected 30-100 million people in 70 different countries.
  • Infection mainly occurs in tropical and subtropical areas but pockets of infection exist in the USA and several areas of Western Europe.
  • The prevalence of the infection is reported to be over 80% in some areas e.g. rural Argentina.
  • Infection is commonly associated with rural areas and unsanitary conditions.
Life cycle
  • This parasite has a complex life cycle involving both parasitic and free living stages.
  • The adult form can survive and reproduce either in the human small intestine or in the soil. In the small intestine of the adult, eggs hatch into rhabditiform larvae which are passed in the stool.
  • The larvae may either mature into filariform larvae that are capable of penetrating the skin, or develop into free living worms living in the soil independently of a human or mammalian host.
  • The infective filariform larvae, having penetrated the skin, travel via the blood stream to the lungs, then migrate up the airways to the oesophagus and are swallowed back into the intestine, where mating occurs to continue the cycle.
Presentation
  • Symptoms and signs Infection with Strongyloides has a variable effect on the host. Individuals may be asymptomatic for many years, or may develop a series of acute or chronic non-specific symptoms.
  • In other cases specific symptoms make the diagnosis more obvious, e.g. the migratory rash. Symptoms that may occur include:
Hyperinfection syndrome
  • In a massive hyperinfection, the larvae cause lung haemorrhage when passing from the capillaries to the alveoli.
  • The vast numbers of larvae also penetrate other organs which are not normally involved in the usual life cycle, e.g. urinary tract, central nervous system and liver.
  • Bacterial infection also occurs due to leakage of material through the damaged bowel. The bacteria then are carried on the surface of the larvae to produce meningitis, pneumonia and septicaemia, which are frequently the immediate cause of death in patients with hyperinfection syndrome.
  • Hyperinfection syndrome may occur due to immunosuppression of the host and particularly by treatment of the host with steroids.2
  • It is therefore particularly important to exclude and treat the infection in any person who has spent time in the tropics or subtropics prior to initiating treatment with immunosuppressive agents or steroids, as the mortality rate of hyperinfection syndrome is reported to be as high as 87%.1
Investigations
  • Definite diagnosis may be difficult unless larvae are seen in the stool. Often a high index of suspicion is needed together with one or more suggestive investigations.
  • Full blood count may show a mild eosinophilia.
  • Examination of stool samples may show the presence of larvae, although several samples be required as the larval output is minimal in the majority of cases.1
  • Culture of stool using agar tracking may be more successful, but is not routinely available in clinical practice.
  • An assay for immunoglobulins is currently being developed. Due to problems with specificity, it is likely to be only useful as a screening tool and not for diagnosis.
  • Chest x-ray: may show pulmonary infiltrates, consolidation or cavitations.
Management

All patients with Strongyloidiasis require treatment, whether or not they are symptomatic, due to the possibility of developing a hyperinfection syndrome at some stage in the future.

  • Albendazole 400 mg twice daily for 3 days, repeated after 3 weeks if necessary.
  • Ivermectin 200 micrograms/kg daily for 2 days may be the most effective drug for chronic Strongyloides infection.3
  • Symptomatic treatment includes antihistamines for pruritus.
  • Immunocompromised patients may require hospital admission and intensive care in disseminated infection.
Prognosis
  • Appropriate antihelminthic treatment results in a cure in the majority of patients, although re-infection is common in endemic areas.
  • Hyperinfection syndrome has a mortality rate of up to 87%.1
Prevention

Infection can be reduced by good sanitation and the wearing of footwear in endemic areas.


Document references
  1. Siddiqui AA, Berk SL; Diagnosis of Strongyloides stercoralis infection. Clin Infect Dis. 2001 Oct 1;33(7):1040-7. Epub 2001 Sep 5. [abstract]
  2. Keiser PB, Nutman TB; Strongyloides stercoralis in the Immunocompromised Population. Clin Microbiol Rev. 2004 Jan;17(1):208-17. [abstract]
  3. Zaha O, Hirata T, Kinjo F, et al; Strongyloidiasis--progress in diagnosis and treatment. Intern Med. 2000 Sep;39(9):695-700. [abstract]

Internet and further reading
  • DPDx; Strongyloidiasis - (No Authors Listed) Centers for Disease Control & Prevention, National Center for Infectious Diseases, Division of Parasitic Diseases
  • Carpenter Rose AE; Strongyloides stercoralis. eMedicine, March 2006.
Acknowledgements EMIS is grateful to Dr Colin Tidy for writing this article. The final copy has passed scrutiny by the independent Mentor GP reviewing team. ©EMIS 2008.
DocID: 2810
Document Version: 20
DocRef: bgp474
Last Updated: 9 Dec 2007
Review Date: 8 Dec 2009




















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