The susceptibility of adult schistosomes to immune attrition

Abstract

Mouse infection models are described that demonstrate reduction of egg production in Schistosoma haematobium infections and both worm loss and reduced fecundity in S. bovis infections. Neither phenomenon could be shown in S. mansoni infected mice. The immunological basis for these anti-adult responses was inferred by comparison with infections in T-cell deprived mice and by serum transfer of the ability to reduce a S. bovis worm burden into immunocompromised hosts. Vaccination with irradiation attenuated parasites was also shown to have consequences for the adults of a challenge infection of S. haematobium and S. bovis specifically. Prior vaccination resulted in an abrogation of the anti-fecundity and adult worm elimination that occurred in non-vaccinated similarly infected mice. These models are being used to define the targets and mechanisms involved in anti-adult attrition. A serological assay, quantitation of a circulating antigen (CAA) has been assessed for its ability to measure worm burdens of different species of schistosome in mice. This assay will be used to question whether anti-adult immunity contributes to the pattern of infection with S. mansoni and S. haematobium in man.

Protective immunity to Schistosoma haematobium infection is primarily an anti-fecundity response stimulated by the death of adult worms

“…The finding that protective immunity is likely to principally target fecundity is supported by the findings that lower levels of S. haematobium egg output were found relative to levels of circulating anodic antigen (a marker for worm burden) in adults than in children (25), and that S. haematobium fecundity is reduced by the immune response in mice (26). This analysis suggests that the most likely antigens to stimulate a protective response are ones that have their immune recognition boosted by treatment and that stimulate a primarily anti-fecundity response.…”

Immuno-epidemiology of human Schistosoma haematobiuminfection: preferential IgG3 antibody responsiveness to a recombinant antigen dependent on age and parasite burden

“…In experimental studies, adult S. haematobium worms have been shown to suffer immune mediated attrition and reduction of fecundity [ 4 - 6 ] and, as early as 1934, Fisher postulated that the epidemiology of human schistosome infections reflects these immunological processes [ 7 ]. More recently, Woolhouse used theoretical methods to predict the profiles which these immune responses would follow in a host population [ 8 , 9 ] and effectively set the framework for the immuno-epidemiology of helminth infections.…”

Sensitivity and specificity of human point-of-care circulating cathodic antigen (POC-CCA) test in African livestock for rapid diagnosis of schistosomiasis: a Bayesian latent class analysis

“…We are not aware of other studies in the literature reporting accuracy results for the detection of CCA in S. bovis or S. curassoni infections in livestock. However, CCA has been reported as being strongly associated with S. bovis worm and faecal egg counts in goats [54, 55] and CAA were detected in S. mattheei infected cows [56].…”