Parasitology

Research Article

The saga of schistosome migration and attrition

R. A. WILSONa1 c1

a1 Department of Biology, University of York, PO Box 373, York YO10 5YW

SUMMARY

Schistosomes infect the mammalian host by direct penetration of the skin and must then undergo a protracted migration to the site of parasitization, for Schistosoma mansoni the hepatic portal vasculature. This article reviews the work published roughly between 1976 and 1986 that clarified our understanding of the process in the laboratory mouse. A combination of histopathology, larval injection experiments and autoradiographic tracking revealed that migration involved one to several circuits of the pulmonary-systemic vasculature before chance delivery in cardiac output to splanchnic arteries that lead indirectly to the portal tract. The kinetics of migration through different capillary beds was established, with the lungs of naïve mice not the skin proving the greatest obstacle; a proportion of schistosomula entered the alveoli from where they did not recover. The ‘immunity’ displayed by mice with a chronic infection was shown to be an artefact of a ‘leaky’ hepatic portal system, generated as a result of egg-induced hepatic pathology. The blockade of pulmonary migration was exacerbated in mice vaccinated with irradiated cercariae by immune-mediated inflammatory foci that developed around lung schistosomula thus decreasing the proportion that matured, but parasite elimination was a prolonged process, not an acute cytolytic ‘hit.’

(Received January 08 2009)

(Revised January 16 2009)

(Accepted January 18 2009)

(Online publication March 06 2009)

Correspondence:

c1 Tel: 44 (0)1904 328600. Fax: 44 (0)1904 328505. E-mail: raw3@york.ac.uk

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