Previous or ongoing schistosome infections do not compromise the efficacy of the attenuated cercaria vaccine.
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.
Kariuki
Thomas M
TM
Department of Biology, P.O. Box 373, University of York, York YO10 5YW, United Kingdom.
Van Dam
Govert J
GJ
Deelder
André M
AM
Farah
Idle O
IO
Yole
Dorcas S
DS
Wilson
R Alan
RA
Coulson
Patricia S
PS
D000818:Animals; D000909:Antibodies, Helminth / Q000096:biosynthesis; D000947:Antigens, Helminth / Q000097:blood / Q000276:immunology / Q000528:radiation effects; D005243:Feces / Q000469:parasitology; D005260:Female; D005720:Gamma Rays; D006801:Humans; D007115:Immunization Schedule; D007814:Larva / Q000276:immunology / Q000528:radiation effects; D008297:Male; D010063:Ovum / Q000276:immunology; D048530:Papio anubis; D012008:Recurrence; D012550:Schistosoma mansoni / Q000276:immunology* / Q000528:radiation effects; D012555:Schistosomiasis mansoni / Q000276:immunology / Q000469:parasitology* / Q000517:prevention & control*; D014613:Vaccines, Attenuated / Q000008:administration & dosage / Q000276:immunology* / Q000627:therapeutic use*
D000909:Antibodies, Helminth; D000947:Antigens, Helminth; D014613:Vaccines, Attenuated