The contribution of host-related factors to low cure rates of praziquantelfor the treatment of Schistosoma mansoni in Senegal

Surprisingly low cure rates were repeatedly observed after treatment with a standard dosage of praziquantel in a recently established Schistosoma mans oni focus in northern Senegal. In 4 discrete cohorts from the same populati on, cure races were 18-36% and egg count reduction rates were 77-88%. Data and material of 920 compliant subjects from all 4 cohorts were further anal yzed to identify possible host-related factors associated with low cure rat es. The lowest cure rates were found in the highest egg count groups. Howev er, in low and moderate egg count groups, drug efficacy was also below norm al values. Cure rates were similar in males and females, showed no seasonal variation, and were independent of previous praziquantel treatment. They w ere significantly higher in adults than in children, also after allowing fo r intensify of infection. Individual water contact behavior and specific hu moral immune responses were examined in 2 extreme subgroups, either without significant egg count reduction or showing complete parasitologic cure. Th ere was no significant: difference in frequency and duration of water conta ct between those individuals with complete cure and those that showed littl e effect of praziquantel treatment. Levels of IgG, IgG1, IgG3, IgG4, IgM, a nd IgE against adult worm antigen were not different between the 2 subgroup s. Thus, the abnormally frequent failure of treatment observed in this focu s could not be associated with any host-related factor, other than age and pretreatment egg counts.