Strongyloides stercoralis and Strongyloidosis
Strongyloidosis is a chronic, soil-transmitted, intestinal parasitic disease. Strongyloides stercoralis is a roundworm and the main causative agent of this disease. S. stercoralis has a unique life cycle, which consists of direct (homogonic) development a
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Strongyloides stercoralis and Strongyloidosis Masataka Korenaga and Fabrizio Bruschi
Abstract Strongyloidosis is a chronic, soil-transmitted, intestinal parasitic disease. Strongyloides stercoralis is a roundworm and the main causative agent of this disease. S. stercoralis has a unique life cycle, which consists of direct (homogonic) development and indirect (heterogonic) development. Parasitic adult females produce both sexes of the next generation parthenogenetically. Female larvae can choose the direct or indirect development depending on various environmental conditions. Autoinfection is one of the characteristic features of this parasite, which causes hyperinfection and disseminated infection. Strongyloidosis occurs mostly in humid tropics and subtropics of more than 70 countries, affecting people between 30 million and 100 million or higher. However, the precise number is not known up to the present, because of difficulties in diagnosis. Even in highly developed countries, like the USA, serious problems have been caused by transmission of S. stercoralis through organ transplantation. We describe the current status of strongyloidosis with special reference to biology, epidemiology, immunology, and vaccine development.
10.1
Introduction
Strongyloidosis is one of the chronic, soil-transmitted, intestinal helminth infections which affect the health of over one-third of the world population. 30–100 million people are estimated to be infected with Strongyloides spp. (CDC homepage). Strongyloides stercoralis is widespread, mainly in the tropics and subtropics and of species naturally infecting humans. Besides this species, M. Korenaga (*) Department of Parasitology, Kochi Medical School, Kochi University, Nankoku, Kochi 783-8505, Japan e-mail: [email protected] F. Bruschi Department of Translational Research, N.T.M.S., Universita` di Pisa, Pisa, Italy F. Bruschi (ed.), Helminth Infections and their Impact on Global Public Health, DOI 10.1007/978-3-7091-1782-8_10, © Springer-Verlag Wien 2014
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M. Korenaga and F. Bruschi
S. fuelleborni infection in humans has been reported but restricted in Africa and the Southeast Asian country of Papua New Guinea. The burden of strongyloidosis to humans has been underestimated in an aspect of global health. Strongyloidosis is one of the neglected tropical diseases and perhaps the most neglected (Olsen et al. 2009). In this chapter, we focused mainly on human strongyloidosis together with recent advances of experimental models relating to human strongyloidosis. The comprehensive review articles regarding strongyloidosis and Strongyloides spp. have been published elsewhere (Grove 1989a, b; Sato 2003; Montes et al. 2010; Krolewiecki et al. 2013).
10.2
The Agent
10.2.1 Life Cycle and Morphology The life cycle of S. stercoralis is unique. Infective third-stage larvae (L3i) penetrate the intact skin of hosts and migrate into the lungs via the bloodstream. The larvae pass the capillary walls and move to the alveoli, bronchus, and trachea and then go down the esophagu
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