I N T R O D U C T I O N

The agent for Strongyloidiasis is the parasite Strongyloides, a common enteric helminth (roundworm, or intestinal nematode) also known as threadworm. Its taxonomy is as follows:

Phylm—Nematoda
Class—secernenta
Order—Rhabditida
Family—Strongyloididae
Genus—Strongyloides
Species—Strongyloides stercoralis

dogIt is generally found in many areas of the tropics and subtropics, but can also be found in temperate areas, including the South of the United States.
The most common form to infect humans is Strongyloides stercoralis. Dogs and cats have been known to be infected by this form, and there has been documentation of humans contracting the parasite from dogs as well (2). The parasite is transmitted through feces of infected individuals followed by direct penetration of the skin of a new host by its larvae.
Generally, infection is asymptomatic or includes mild gastrointestinal distress. However, in immunocompromised persons, an S. stercoralis infection can be devastating, causing multi-organ failure and having a mortality rate as high as 60-85% (4).
What is most unique about this nematode is that it has the ability to multiply within its host to cause an
autoinfection (see Life Cycle). Most nematodes must have their eggs or rhabditiorm larvae passed in the feces of the host to the external environment before they can develop into their infective stage, filariform larvae. This ability to produce infective larvae within the host contributes to Strongyloides’ ability to cause hyperinfection (see Clinical Presentation), especially in immunocompromised hosts.

 

C O N T A C T S

Emily Harnden, Class of 2006: eharnden@stanford.edu

Stanford University

Parasites and Pestilence: Infectious Public Health Challenges

Professor D. Scott Smith: ssmith@stanford.edu