Strongyloides stercoralis

Abstract

Strongyloidiasis has been estimated to affect over 600 million people worldwide. It is caused by Strongyloides stercoralis, a roundworm endemic to the tropics and subtropics, especially areas where sanitation is suboptimal Autochthonous transmission has been documented in rural areas of the USA and Europe. Humans are infected when larvae penetrate the skin or are ingested. Autoinfection, in which larvae generated in the host go on to re-infect the host, leads to a state of chronic asymptomatic infection often with eosinophilia. Hyperinfection syndrome may develop when patients develop immune suppression, due to medications such as corticosteroids or following solid-organ transplantation. Hyperinfection is characterized by exponential increase in parasitic burden, leading to tissue invasion and life-threatening disease and associated bloodstream infections due to enteric organisms. Cases following use of corticosteroids for COVID-19 pneumonia have been described. Strongyloidiasis can be diagnosed by direct visualization of larvae in stool or other body fluids, or by serology. Ivermectin is highly effective in treating the disease. Patients with exposure to endemic areas and those expected to become immune suppressed should be screened and treated before starting immune suppressive agents. Empiric treatment should be considered when timely testing is not readily available.

Keywords: Diagnosis; Hyperinfection; Immunosuppression; Ivermectin; Strongyloidiasis; Treatment.

Fig. 1

Lifecycle of S. stercoralis. (1) Filariform larvae penetrate the host’s skin and migrate to pulmonary parenchyma. (2) Filariform larvae are coughed up and swallowed. (3) Filariform larvae migrate to small intestine and lay eggs, which hatch into rhabditiform larvae. (4) Rhabditiform larvae are excreted in soil and give rise to infectious filariform larvae, which are able to penetrate skin and restart the cycle. S. stercoralis also has a free-living life cycle, independent of human hosts. (5) Rhabditiform larvae may give rise to infectious filariform larvae in the host itself, leading to invasion of intestinal mucosa and/or perianal skin, process known as autoinfection. In the right host, this may lead to hyperinfection syndrome. Figure created with Biorender