The Unique Life Cycle of Strongyloides stercoralis and Implications for Public Health Action

Abstract

Strongyloides stercoralis has one of the most complex life cycles of the human-infecting nematodes. A common misconception in medical and public health professions is that S. stercoralis in its biology is akin to other intestinal nematodes, such as the hookworms. Despite original evidence provided by medical and veterinary research about this unique helminth, many assumptions have entered the scientific literature. This helminth is set apart from others that commonly affect humans by (a) the internal autoinfective cycle with autoinfective larvae randomly migrating through tissue, parthenogenesis, and the potential for lifelong infection in the host, the profound pathology occurring in hyperinfection and systemic manifestations of strongyloidiasis, and (b) a limited external cycle with a single generation of free-living adults. This paper aims to review and discuss original research on the unique life cycle of S. stercoralis that distinguishes it from other helminths and highlight areas where increased understanding of the parasite's biology might lead to improved public health prevention and control strategies.

Keywords: Strongyloides stercoralis; biology; control; life cycle; public health; strongyloidiasis.

Figure 1

The life cycle of Strongyloides stercoralis. Distinctive features include (a) random migration of autoinfective larvae, (b) embryonated egg rapidly hatches to rhabditiform larvae, and (c) single generation of free-living male and female adults. Source: CDC DPDx: (https://www.cdc.gov/dpdx/), with permission.

Figure 2

The life stages of Strongyloides stercoralis; (a) parasitic female with tapering anterior (arrow) and pointed caudal extremity (dart); (b) embryonated egg; (c) rhabditiform larva in faeces with short buccal cavity (arrow) and rhomboid genital primordium (dart); (d) filariform larva with oesophago-intestinal junction at mid-body (dart); (e) notched tail of the filariform larva (arrow); (f) free-living male with prominent spicule (dart); and (g) gravid free-living female with eggs in uterus (arrow). Note: Figure 2a,b are from faeces of a patient with hyperinfection; these life stages are not seen in patient faeces in the absence of severe hyperinfection. Figure attributions: (a,b,e): Dr Richard Bradbury, Central Queensland University; (d): Emeritus Professor John Goldsmid, University of Tasmania; (c,f,g): CDC DPDx web site (https://www.cdc.gov/dpdx/). Reproduced with permission.