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Infection and Immunity, July 2006, p. 3979-3986, Vol. 74, No. 7
0019-9567/06/$08.00+0 doi:10.1128/IAI.01657-05
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
Institute of Primate Research, P.O. Box 24481, Karen, Nairobi, Kenya,1 Department of Parasitology, Leiden University Medical Centre, 2300 RC Leiden, The Netherlands,2 Department of Biology, University of York, York YO10 5YW, United Kingdom3
Received 11 October 2005/ Returned for modification 11 December 2005/ Accepted 5 April 2006
A current or previous schistosome infection might compromise the efficacy of a schistosome vaccine administered to humans. We have therefore investigated the influence of infection on vaccination, using the baboon as the model host and irradiated Schistosoma mansoni cercariae as the vaccine. Protection, determined from worm burdens in test and controls, was not diminished when vaccination was superimposed on a chronic infection, nor was it diminished when it followed a primary infection terminated by chemotherapy. Protection was also assessed indirectly based on fecal egg output and circulating antigen levels, as would be the case in human vaccine trials. In almost all instances, these methods overestimated protection, sometimes with discrepancies of >20%. The overwhelming immune response to egg deposition in infected animals made it difficult to discern a contribution from vaccination. Nevertheless, the well-documented immunomodulation of immune responses that follows egg deposition did not appear to impede the protective mechanisms elicited by vaccination with attenuated cercariae.
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