Serum factors from infected baboons inhibit oviposition and cause unpairing of Schistosoma mansoni in vitro.

A reliable in vitro fecundity assay for Schistosoma mansoni was established. The main features that reduced variability in in vitro oviposition were pre-selection and randomization of worm pairs producing moderate numbers of eggs in initial 2-day culture, and short pre-incubation in serumless medium prior to addition of test sera to the cultures. In 4 of 6 total experiments testing the effects of serum from chronically infected baboons, significant (P less than or equal to 0.025) fecundity reduction ranging from 29 to 82% was found. Chronically infected baboon serum also caused consistently higher unpairing than normal serum. These results demonstrate the existence of serum factors which inhibit egg production and maintenance of the paired status of Schistosoma mansoni in vitro.